- Osmium-promoted dehydrogenation of amine-boranes and B-H bond activation of the resulting amino-boranes
-
The five-coordinate osmium complex OsH(SH)(CO)(PiPr 3)2, containing an electrophilic center bonded to the soft hydrogen sulfide ligand, promotes dehydrogenation of amine-boranes and captures the amino-borane products, form
- Esteruelas, Miguel A.,Fernandez, Israel,Lopez, Ana M.,Mora, Malka,Onate, Enrique
-
-
Read Online
- Borazine Thermal Decomposition in Unsaturated Vapor
-
The temperature dependence of vapor pressure over liquid and solid borazine has been measured by static tensiometry method with a membrane null-manometer at 200–259 K. Gas-phase heat-induced decomposition of borazine in its unsaturated vapor has been studied over the 373–473 K range.
- Zavgorodnii,Timoshkin, A. Yu.
-
-
Read Online
- Low-temperature synthesis of highly crystallized hexagonal boron nitride sheets with Li3N as additive agent
-
Highly crystallized hexagonal boron nitride (h-BN) sheets were obtained by a versatile method modifying the original synthesis by using an additive agent and, as a consequence, decreasing the temperature for the ceramization step (1200-1400 °C). This synthesis is based on the polymer-derived ceramics (PDCs) route using liquid-state polyborazylene (PBN) mixed with lithium nitride (Li3N) micropowders as additive agent. We have demonstrated that incorporation of Li3N as a crystallization promoter allows the onset of crystallization of h-BN at lower temperatures. Consequently, a high crystallization rate can be obtained from 1000 °C for bulk boron nitride, whereas the temperature has to be 1600-1800 °C under classical conditions. A series of samples incorporating Li3N (5 wt.-%) and annealed at various temperatures from 600 to 1400 °C was prepared and structurally characterized by Raman spectroscopy, XRD analyis, and TEM. Well-crystallized sheets with thicknesses of nanometers can be easily obtained by applying this method.
- Yuan, Sheng,Toury, Bérangère,Benayoun, Stéphane,Chiriac, Rodica,Gombault, Fran?ois,Journet, Catherine,Brioude, Arnaud
-
-
Read Online
- Preparation of h-BN nano-tubes, -bamboos, and -fibers from borazine oligomer with alumina porous template
-
h-BN nano-tubes, -bamboos, and -fibers were prepared separately from borazine oligomers using an alumina porous template at different wetting times of 20 h, 40 h and 2 weeks at room temperature, respectively. The borazine oligomer in the template was transformed to the h-BN nano-materials by two-step heat-treatment at 600 and 1200 °C in flowing N2. The FT-IR result confirmed the formation of BN. TEM and SEM images showed the formation of the nano-tubes in diameters 200-300 nm with thin walls about 10-20 nm thick, nano-bamboos 200-300 nm wide with knots at the separations of 0.5-1 μm, and the nano-fibers 15-20 μm long with fine crystallized BN particles. The mechanism for the formation of h-BN nano-tubes, -bamboos and -fibers is proposed.
- Wang, Yuting,Shimada, Shiro,Yamamoto, Yasunori,Miyaura, Norio
-
-
Read Online
- Efficient catalytic conversion of ammonia borane to borazine and its use for hexagonal boron nitride (white graphene)
-
Nickel nanoparticles (NiNPs) prepared in tetraglyme (TG) efficiently catalyzed the conversion of ammonia borane (AB, NH3BH3) to borazine (B3N3H6). Under the optimized conditions, 3 mol% of the NiNPs were introduced into a 1.5 M AB solution in TG and held at 80 °C for 6 h under a dynamic vacuum that was maintained at 30 torr. Borazine was isolated through a series of -45 °C, -78 °C, and -196 °C traps to give (-78 °C trap) pure borazine in 53% yield. The borazine produced was then utilized as a molecular precursor for high quality h-BN (white graphene) and large area h-BN sheets were prepared by applying low pressure chemical vapor deposition (LPCVD). Ultra-thin (single to few layers) h-BN was synthesized on Ni foil at the optimal ratio between borazine and NH3, and the number of layers was tuned by varying the NH3 partial pressure. The Royal Society of Chemistry 2013.
- Kim, Sung-Kwan,Cho, Hyunjin,Kim, Myung Jong,Lee, Hee-Jun,Park, Jin-Hyung,Lee, Young-Boo,Kim, Hwan Chul,Yoon, Chang Won,Nam, Suk Woo,Kang, Sang Ook
-
-
Read Online
- Dehydrocoupling of amine boranes via tin(IV) and tin(II) catalysts
-
Catalytic dehydrocoupling of primary and secondary amine boranes and ammonia borane using tin(IV) and tin(II) catalysts is presented. These tin compounds have been demonstrated to dehydrocouple phosphines where catalytic activity was dependent on metal oxidation state. In contrast, the mechanism of amine borane dehydrocoupling appears to be substrate dependent. The most sterically encumbered substrate, tBuNH2BH3, appears to engage in β-hydrogen elimination based on the observation of tBuN = BH2, whereas Me2NHBH3 appears to be involved in a chain-growth process as evidenced by linear diborazane and the absence of amino borane. Though these tin catalysts are moderately active in the spectrum of amine borane dehydrocoupling catalysts, the dependence of mechanism on substrate appears to be unique.
- Erickson, Karla A.,Wright, Dominic S.,Waterman, Rory
-
-
Read Online
- Thermolysis and solid state NMR studies of NaB3H8, NH3B3H7, and NH4B3H 8
-
In an effort to broaden the search for high-capacity hydrogen storage materials, three triborane compounds, NaB3H8, NH 3B3H7, and NH4B3H 8, were studied. In addition to hydrogen, thermal decomposition also releases volatile boranes, and the relative amounts and species depend on the cations (Na+, NH4+) and the Lewis base (NH 3). Static-sample hydrogen NMR is used to probe molecular motion in the three solids. In each case, the line width decreases from low temperatures to room temperature in accordance with a model of isotropic or nearly isotropic reorientations. Such motions also explain a deep minimum in the relaxation time T1. Translational diffusion never appears to be rapid on the 10 -5 s time scale of NMR.
- Huang, Zhenguo,Eagles, Mitch,Porter, Spencer,Sorte, Eric G.,Billet, Beau,Corey, Robert L.,Conradi, Mark S.,Zhao, Ji-Cheng
-
-
Read Online
- Thermal decomposition of cyclotriborazane
-
Cyclotriborazane (CTB), B3N3H12, is a crystalline white solid, which decomposes above 400 K to hydrogen and a few other products, depending on the reaction conditions. In this work we present investigations of the thermal decomposition of both the neat compound and CTB dissolved in diglyme and tetraglyme. Several thermophysical and analytical methods, such as differential scanning calorimetry (DSC), thermogravimetry (TG), mass spectroscopy (QMS), and 11B nuclear magnetic resonance spectroscopy (NMR) have been used for this investigation. The decomposition of the neat substance releases 3.1 mol H2/mol CTB and leads to a polymeric products and borazine. In open vessels, sublimation as a competing process also occurs. The enthalpy of the decomposition process (ΔRHs) has been determined as ΔRHs = -34.0 ± 2.9 kJ/mol. In contrast to the thermal decomposition of the pure substance, the decomposition in polyethers, such as diglyme and tetraglyme, leads above 370 K to borazine and small amounts of soluble oligomeric borazine species. Also BH3 group containing species are occurring as intermediates. In these systems no precipitation was detected. DSC measurements show for the decomposition in solution several strong exothermic effects. The overall decomposition enthalpy in diglyme is given by ΔRHd = -32.0 ± 2.8 kJ/mol and in tetraglyme by ΔRHt = -48.0 ± 4.7 kJ/mol. The enthalpy of solution of cyclotriborazane was determined in diglyme and in tetraglyme with the values ΔDHd = -2.1 ± 0.2 kJ/mol and ΔDHt = -4.6 ± 0.5 kJ/mol, respectively.
- Schellenberg,Kriehme,Wolf
-
-
Read Online
- Dehydrogenation of ammonia-borane by Shvo's catalyst
-
Shvo's cyclopentadienone-ligated ruthenium complex is an efficient catalyst for the liberation of exactly two molar equivalents of hydrogen from ammonia-borane, a prospective hydrogen storage medium. The mechanism for the dehydrogenation features a ruthenium hydride resting state from which dihydrogen loss is the rate-determining step.
- Conley, Brian L.,Williams, Travis J.
-
-
Read Online
- The mechanism of borane-amine dehydrocoupling with bifunctional ruthenium catalysts
-
Borane-amine adducts have received considerable attention, both as vectors for chemical hydrogen storage and as precursors for the synthesis of inorganic materials. Transition metal-catalyzed ammonia-borane (H3N-BH 3, AB) dehydrocoupling offers, in principle, the possibility of large gravimetric hydrogen release at high rates and the formation of B-N polymers with well-defined microstructure. Several different homogeneous catalysts were reported in the literature. The current mechanistic picture implies that the release of aminoborane (e.g., Ni carbenes and Shvo's catalyst) results in formation of borazine and 2 equiv of H2, while 1 equiv of H 2 and polyaminoborane are obtained with catalysts that also couple the dehydroproducts (e.g., Ir and Rh diphosphine and pincer catalysts). However, in comparison with the rapidly growing number of catalysts, the amount of experimental studies that deal with mechanistic details is still limited. Here, we present a comprehensive experimental and theoretical study about the mechanism of AB dehydrocoupling to polyaminoborane with ruthenium amine/amido catalysts, which exhibit particularly high activity. On the basis of kinetics, trapping experiments, polymer characterization by 11B MQMAS solid-state NMR, spectroscopic experiments with model substrates, and density functional theory (DFT) calculations, we propose for the amine catalyst [Ru(H)2PMe3{HN(CH2CH2PtBu 2)2}] two mechanistically connected catalytic cycles that account for both metal-mediated substrate dehydrogenation to aminoborane and catalyzed polymer enchainment by formal aminoborane insertion into a H-NH 2BH3 bond. Kinetic results and polymer characterization also indicate that amido catalyst [Ru(H)PMe3{N(CH2CH 2PtBu2)2}] does not undergo the same mechanism as was previously proposed in a theoretical study.
- Marziale, Alexander N.,Friedrich, Anja,Klopsch, Isabel,Drees, Markus,Celinski, Vinicius R.,Schmedt Auf Der Guenne, Joern,Schneider, Sven
-
-
Read Online
- Bismuthanylstibanes
-
Thermally-robust bismuthanylstibanes are prepared in a one-step, high yield reaction, providing the first examples of neutral Bi-Sb σ-bonds in the solid state. DFT calculations indicate that the bis(silylamino)naphthalene scaffold is well-suited for supporting otherwise labile bonds. The reaction chemistry of the Bi-Sb bond is debuted by showing fission using NH3BH3 and insertion of a sulfur atom, the latter providing the first example of a Bi-S-Sb motif. This journal is
- Chitnis, Saurabh S.,Marczenko, Katherine M.
-
-
Read Online
- Trends in the Series of Ammine Rare-Earth-Metal Borohydrides: Relating Structural and Thermal Properties
-
Ammine metal borohydrides display extreme structural and compositional diversity and show potential applications for solid-state hydrogen and ammonia storage and as solid-state electrolytes. Thirty-two new compounds are reported in this work, and trends in the full series of ammine rare-earth-metal borohydrides are discussed. The majority of the rare-earth metals (RE) form trivalent RE(BH4)3·xNH3 (x = 7-1) compounds, which possess an intriguing crystal chemistry changing with the number of ammonia ligands, varying from structures built from complex ions (x = 5-7), to molecular structures (x = 3, 4), one-dimensional chains (x = 2), and structures built from two-dimensional layers (x = 1). Divalent RE(BH4)2·xNH3 (x = 4, 2, 1) compounds are observed for RE2+ = Sm, Eu, Yb, with structures varying from molecular structures (x = 4) to two-dimensional layered (x = 2, 1) and three-dimensional structures (Yb(BH4)2·NH3). The crystal structure and composition of the compounds depend on the volume of the rare-earth ion. In all structures, NH3 coordinates to the metal, while BH4- has a more flexible coordination and is observed as a bridging and terminal ligand and as a counterion. RE(BH4)3·xNH3 (x = 7-5, 4) releases NH3 stepwise during thermal treatment, while mainly H2 is released for x ≤ 3. In contrast, only NH3 is released from RE(BH4)2·xNH3 due to the lower charge density on the RE2+ ion and higher stability of RE(BH4)2. The thermal stability of RE(BH4)3·xNH3 increase with increasing cation charge density for x = 5, 7, while it decreases for x = 4, 6. For x = 3, the thermal stability decreases with increasing charge density, due to the destabilization of the BH4- group, making it more reactive toward NH3. This research provides a large number of novel compounds and new insight into trends in the crystal chemistry of ammine metal borohydrides and reveals a correlation between the local metal coordination and the thermal stability.
- Grinderslev, Jakob B.,Jensen, Torben R.
-
supporting information
p. 2573 - 2589
(2021/02/16)
-
- Amine-Borane Dehydrogenation and Transfer Hydrogenation Catalyzed by α-Diimine Cobaltates
-
Anionic α-diimine cobalt complexes, such as [K(thf)1.5{(DippBIAN)Co(η4-cod)}] (1; Dipp=2,6-diisopropylphenyl, cod=1,5-cyclooctadiene), catalyze the dehydrogenation of several amine-boranes. Based on the excellent catalytic properties, an especially effective transfer hydrogenation protocol for challenging olefins, imines, and N-heteroarenes was developed. NH3BH3 was used as a dihydrogen surrogate, which transferred up to two equivalents of H2 per NH3BH3. Detailed spectroscopic and mechanistic studies are presented, which document the rate determination by acidic protons in the amine-borane.
- Maier, Thomas M.,Sandl, Sebastian,Shenderovich, Ilya G.,Jacobi von Wangelin, Axel,Weigand, Jan J.,Wolf, Robert
-
p. 238 - 245
(2019/01/04)
-
- Inorganic Triphenylphosphine
-
A completely inorganic version of one of the most famous organophosphorus compounds, triphenylphosphine, has been prepared. A comparison of the crystal structures of inorganic triphenylphosphine, PBaz3 (where Baz=B3H2N3H3) and PPh3 shows that they have superficial similarities and furthermore, the Lewis basicities of the two compounds are remarkably similar. However, their oxygenation and hydrolysis reactions are starkly different. PBaz3 reacts quantitatively with water to give PH3 and with the oxidizing agent ONMe3 to give the triply-O-inserted product P(OBaz)3, an inorganic version of triphenyl phosphite; a corresponding transformation with PPh3 is inconceivable. Thermodynamically, what drives these striking differences in the chemistry of PBaz3 and PPh3 is the great strength of the B?O bond.
- Gorman, Adam D.,Bailey, Jonathan A.,Fey, Natalie,Young, Tom A.,Sparkes, Hazel A.,Pringle, Paul G.
-
supporting information
p. 15802 - 15806
(2018/11/23)
-
- Iron(II) Complexes of a Hemilabile SNS Amido Ligand: Synthesis, Characterization, and Reactivity
-
We report an easily prepared bis(thioether) amine ligand, SMeNHSMe, along with the synthesis, characterization, and reactivity of the paramagnetic iron(II) bis(amido) complex, [Fe(κ3-SMeNSMe)2] (1). Binding of the two different thioethers to Fe generates both five- and six-membered rings with Fe-S bonds in the five-membered rings (av 2.54 ?) being significantly shorter than those in the six-membered rings (av 2.71 ?), suggesting hemilability of the latter thioethers. Consistent with this hypothesis, magnetic circular dichroism (MCD) and computational (TD-DFT) studies indicate that 1 in solution contains a five-coordinate component [Fe(κ3-SMeNSMe)(κ2-SMeNSMe)] (2). This ligand hemilability was demonstrated further by reactivity studies of 1 with 2,2′-bipyridine, 1,2-bis(dimethylphosphino)ethane, and 2,6-dimethylphenyl isonitrile to afford iron(II) complexes [L2Fe(κ2-SMeNSMe)2] (3-5). Addition of a Br?nsted acid, HNTf2, to 1 produces the paramagnetic, iron(II) amine-amido cation, [Fe(κ3-SMeNSMe)(κ3-SMeNHSMe)](NTf2) (6; Tf = SO2CF3). Cation 6 readily undergoes amine ligand substitution by triphos, affording the 16e- complex [Fe(κ2-SMeNSMe)(κ3-triphos)](NTf2) (7; triphos = bis(2-diphenylphosphinoethyl)phenylphosphine). These complexes are characterized by elemental analysis; 1H NMR, M?ssbauer, IR, and UV-vis spectroscopy; and single-crystal X-ray diffraction. Preliminary results of amine-borane dehydrogenation catalysis show complex 7 to be a selective and particularly robust precatalyst.
- Das, Uttam K.,Daifuku, Stephanie L.,Iannuzzi, Theresa E.,Gorelsky, Serge I.,Korobkov, Ilia,Gabidullin, Bulat,Neidig, Michael L.,Tom Baker
-
supporting information
p. 13766 - 13776
(2017/11/24)
-
- Visible Light Photocatalysis Using a Commercially Available Iron Compound
-
[CpFe(CO)2]2 (1) (Cp = η5-C5H5) is an effective precatalyst for the hydrophosphination of alkenes with Ph2PH under visible light irradiation, which appears to be a unique way to promote metal-catalyzed hydrophosphination. Additionally, 1 is a photocatalyst for the dehydrogenation of amine boranes and formation of siloxanes from tertiary silanes. These reactions have similar, if not improved, reactivity over the same transformations using 1 or related CpFeMe(CO)2 under UV irradiation, consistent with the notion that hydrophosphination with 1 proceeds via formation of CpFe(CO)2?. These results demonstrate that catalyst selection can avail the use of commercially available LED bulbs as photon sources, potentially replacing mercury arc lamps or other energy intensive processes in known or new catalytic reactions.
- Pagano, Justin K.,Bange, Christine A.,Farmiloe, Sarah E.,Waterman, Rory
-
p. 3891 - 3895
(2017/10/30)
-
- Formation of high-molecular weight polyaminoborane by Fe hydride catalysed dehydrocoupling of methylamine borane
-
The complex [(PNHP)Fe(H)(CO)(HBH3)] (PNHP = HN(CH2CH2Pi-Pr2)2) serves as a catalyst precursor for the selective dehydrocoupling of methylamine borane at room temperature, tentatively via an off-metal polymerisation pathway.
- Anke,Han,Klahn,Spannenberg,Beweries
-
supporting information
p. 6843 - 6847
(2017/07/10)
-
- Dehydrogenation of ammonia borane through the third equivalent of hydrogen
-
Ammonia borane (AB) has high hydrogen density (19.6 wt%), and can, in principle, release up to 3 equivalents of H2 under mild catalytic conditions. A limited number of catalysts are capable of non-hydrolytic dehydrogenation of AB beyond 2 equivalents of H2 under mild conditions, but none of these is shown directly to derivatise borazine, the product formed after 2 equivalents of H2 are released. We present here a high productivity ruthenium-based catalyst for non-hydrolytic AB dehydrogenation that is capable of borazine dehydrogenation, and thus exhibits among the highest H2 productivity reported to date for anhydrous AB dehydrogenation. At 1 mol% loading, (phen)Ru(OAc)2(CO)2 (1) effects AB dehydrogenation through 2.7 equivalents of H2 at 70 °C, is robust through multiple charges of AB, and is water and air stable. We further demonstrate that catalyst 1 has the ability both to dehydrogenate borazine in isolation and dehydrogenate AB itself. This is important, both because borazine derivatisation is productivity-limiting in AB dehydrogenation and because borazine is a fuel cell poison that is commonly released in H2 production from this medium.
- Zhang, Xingyue,Kam, Lisa,Williams, Travis J.
-
p. 7672 - 7677
(2016/05/24)
-
- The role of ammonia in promoting ammonia borane synthesis
-
Ammonia promotes the synthesis of pure ammonia borane (AB) in excellent yields from sodium borohydride and ammonium sulfate in tetrahydrofuran under ambient conditions. An examination of the influence of added ammonia reveals that it is incorporated into the product AB, contrary to its perceived function as a catalyst or a co-solvent. Mechanistic studies point to a nucleophilic attack by ammonia on ammonium borohydride with concurrent dehydrogenation to yield AB.
- Ramachandran, P. Veeraraghavan,Kulkarni, Ameya S.
-
p. 16433 - 16440
(2016/10/31)
-
- Zirconium-Catalyzed Amine Borane Dehydrocoupling and Transfer Hydrogenation
-
κ5-(Me3SiNCH2CH2)2N(CH2CH2NSiMe2CH2)Zr (1) has been found to dehydrocouple amine borane substrates, RR′NHBH3 (R = R′ = Me; R = tBu, R′ = H; R = R′ = H), at low to moderate catalyst loadings (0.5-5 mol %) and good to excellent conversions, forming mainly borazine and borazane products. Other zirconium catalysts, (N3N)ZrX [(N3N) = N(CH2CH2NSiMe2CH2)3, X = NMe2 (2), Cl (3), and OtBu (4)], were found to exhibit comparable activities to that of 1. Compound 1 reacts with Me2NHBH3 to give (N3N)Zr(NMe2BH3) (5), which was structurally characterized and features an η2 B-H σ-bond amido borane ligand. Because 5 is unstable with respect to borane loss to form 2, rather than β-hydrogen elimination, and 2-4 do not exhibit X ligand loss during catalysis, dehydrogenation is hypothesized to proceed via an outer-sphere-type mechanism. This proposal is supported by the catalytic hydrogenation of alkenes by 2 using amine boranes as the sacrificial source of hydrogen.
- Erickson, Karla A.,Stelmach, John P. W.,Mucha, Neil T.,Waterman, Rory
-
p. 4693 - 4699
(2015/10/28)
-
- Nitrogen-Based Ligands Accelerate Ammonia Borane Dehydrogenation with the Shvo Catalyst
-
(Chemical Equation Presented) We previously reported that quantitative poisoning, a test for homogeneous catalysis, behaves oddly in the dehydrogenation of ammonia borane (AB) by Shvo's catalyst, whereas the "poison" 1,10-phenanthroline (phen) accelerates catalysis and apparently prevents catalyst deactivation. Thus, we proposed a protective role for phen in the catalysis. Herein we account for the mechanistic origin of this accelerated AB dehydrogenation in the presence of phen and define the relevance boundaries of our prior proposal. In so doing, we present syntheses for novel amine- and pyridine-ligated homologues of the Shvo catalyst and show their catalytic efficacy in AB dehydrogenation. These catalysts are synthetically easy to access, air stable, and rapidly release over 2 equiv of H2. The mechanisms of these reactions are also discussed.
- Zhang, Xingyue,Lu, Zhiyao,Foellmer, Lena K.,Williams, Travis J.
-
p. 3732 - 3738
(2015/08/19)
-
- Probing the second dehydrogenation step in ammonia-borane dehydrocoupling: Characterization and reactivity of the key intermediate, B-(cyclotriborazanyl)amine-borane
-
While thermolysis of ammonia-borane (AB) affords a mixture of aminoborane- and iminoborane oligomers, the most selective metal-based catalysts afford exclusively cyclic iminoborane trimer (borazine) and its B-N cross-linked oligomers (polyborazylene). This catalysed dehydrogenation sequence proceeds through a branched cyclic aminoborane oligomer assigned previously as trimeric B-(cyclodiborazanyl)amine-borane (BCDB). Herein we utilize multinuclear NMR spectroscopy and X-ray crystallography to show instead that this key intermediate is actually tetrameric B-(cyclotriborazanyl)amine-borane (BCTB) and a method is presented for its selective synthesis from AB. The reactivity of BCTB upon thermal treatment as well as catalytic dehydrogenation is studied and discussed with regard to facilitating the second dehydrogenation step in AB dehydrocoupling. This journal is
- Kalviri, Hassan A.,G?rtner, Felix,Ye, Gang,Korobkov, Ilia,Baker, R. Tom
-
p. 618 - 624
(2015/02/19)
-
- Boron nitride coated rhodium black for stable production of syngas
-
A blanket of hexagonal boron nitride (h-BN) was grown on rhodium black by atmospheric pressure chemical vapor deposition. During methane oxidation at 650 °C the as-synthesized material showed steady syngas production shortly after oxygen interruption, whereas the activity of uncovered rhodium black degraded. The improved activity of the catalyst was attributed to the boron nitride coating, which serves to stabilize rhodium metal and avoid particle agglomeration by carbon deposition. These results present a compelling technique for metal catalyst modification with boron nitride in cases where coking is a problem.
- Chien, Andrew C.,Van Bokhoven, Jeroen A.
-
p. 3518 - 3524
(2015/07/02)
-
- Cobalt-catalyzed ammonia borane dehydrocoupling and transfer hydrogenation under aerobic conditions
-
Two cobalt compounds, Cp?Co(CO)I2 (1) and CpCo(CO)I2 (2) (Cp? = η5-C5Me5, Cp = η5-C5H5), catalyze the dehydrogenation of ammonia borane under either anaerobic or aerobic conditions and are also effective hydrogenation catalysts for alkenes and alkynes using ammonia borane as a hydrogen source, also in the presence of air.
- Pagano, Justin K.,Stelmach, John P. W.,Waterman, Rory
-
supporting information
p. 12074 - 12077
(2016/01/15)
-
- Mechanistic studies of ammonia borane dehydrogenation catalyzed by iron pincer complexes
-
A series of iron bis(phosphinite) pincer complexes with the formula of [2,6-(iPr2PO)2C6H 3]Fe(PMe2R)2H (R = Me, 1; R = Ph, 2) or [2,6-(iPr2PO)2-4-(MeO)C6H 2]Fe(PMe2Ph)2H (3) have been tested for catalytic dehydrogenation of ammonia borane (AB). At 60 °C, complexes 1-3 release 2.3-2.5 equiv of H2 per AB in 24 h. Among the three iron catalysts, 3 exhibits the highest activity in terms of both the rate and the extent of H2 release. The initial rate for the dehydrogenation of AB catalyzed by 3 is first order in 3 and zero order in AB. The kinetic isotope effect (KIE) observed for doubly labeled AB (kNH3BH3/k ND3BD3 = 3.7) is the product of individual KIEs (k NH3BH3/kND3BH3 = 2.0 and kNH3BH3/k NH3BD3 = 1.7), suggesting that B-H and N-H bonds are simultaneously broken during the rate-determining step. NMR studies support that the catalytically active species is an AB-bound iron complex formed by displacing trans PMe3 or PMe2Ph (relative to the hydride) by AB. Loss of NH3 from the AB-bound iron species as well as catalyst degradation contributes to the decreased rate of H2 release at the late stage of the dehydrogenation reaction.
- Bhattacharya, Papri,Krause, Jeanette A.,Guan, Hairong
-
supporting information
p. 11153 - 11161
(2014/08/18)
-
- Thermally induced dehydrogenation of amine-borane adducts and ammonia-borane by group 6 cyclopentadienyl complexes having single and triple metal-metal bonds
-
Treatment of solutions of ammonia-borane (NH3·BH 3, AB) with catalytic amounts (5 mol-%) of the singly bonded dimers [M2Cp2(CO)6] [M = Cr (1a), Mo (1b), W (1c); Cp = cyclopentadienyl] under mild thermal activation (333 K) led to the progressive dehydrogenation of the adduct and quantitative conversions were achieved after 12, 24, and >34 h, respectively. At the initial stages of these reactions (low conversions), the major products were cyclic and branched oligomers of aminoborane (NH2=BH2). However, at longer reaction times (high conversions), the major products were, in all cases, borazine, [HNBH] 3, and polyborazylene, [NBHx] (x 3] [M = Cr (2a), Mo (2b), W (2c)], which are supposed to be the catalytically active species in these processes, as also supported by similar catalytic activity exhibited by pure samples of the dihydride [Mo2Cp2(H)2(μ-Ph 2PCH2PPh2)(CO)2] (2b′). Under similar conditions, 1a-c were also active catalysts for the dehydrogenation of adducts derived from substituted amines (tBuH2N·BH3 and Me2HN·BH3), although the rate of dehydrogenation was significantly lower than that of AB. This lower activity follows from deprotonation of hydrides 2 by the free amines, which are in turn generated through B-N bond-cleavage processes. The dehydrogenation products of tBuH2N·BH3 are also derived from oligomerization processes of the corresponding aminoborane (tBuHN=BH2), which in this case was identified in the reaction mixtures, but even at long reaction times, the formation of the borazine-like product was not complete, and the reaction mixture contained significant amounts of (poorly defined) soluble polymeric materials. For Me2HN·BH3, the major product obtained in all of the reactions was cyclic dimer [Me2N=BH 2]2. Similar studies were performed with triply bonded complexes [Mo2Cp2(CO)4] (3b) and [Mo 2Cp2(μ-Ph2PCH2PPh 2)(CO)2] (3b′), which displayed similar catalytic activity while remaining essentially unperturbed along the reactions, and these complexes yielded product distributions that were similar to those observed for singly bonded dimers 1a-c. Readily accessible group 6 binuclear cyclopentadienyl complexes having single and triple M-M bonds are efficient catalysts for the dehydrogenation of a range of amine-borane adducts, including ammonia-borane, under mild thermal activation (333 K). Copyright
- Garcia-Vivo, Daniel,Huergo, Estefania,Ruiz, Miguel A.,Travieso-Puente, Raquel
-
p. 4998 - 5008
(2013/10/21)
-
- Synthetic and mechanistic studies of metal-free transfer hydrogenations applying polarized olefins as hydrogen acceptors and amine borane adducts as hydrogen donors
-
Metal-free transfer hydrogenation of polarized olefins (RR′ CCEE′: R, R′ = H or organyl, E, E′ = CN or CO2Me) using amine borane adducts RR′NH-BH3 (R = R′ = H, AB; R = Me, R′ = H, MAB; R = tBu, R′ = H, tBAB; R = R′ = Me, DMAB) as hydrogen donors, were studied by means of in situ NMR spectroscopy. Deuterium kinetic isotope effects and the traced hydroboration intermediate revealed that the double H transfer process occurred regio-specifically in two steps with hydride before proton transfer characteristics. Studies on substituent effects and Hammett correlation indicated that the rate determining step of the HN transfer is in agreement with a concerted transition state. The very reactive intermediate [NH2BH2] generated from AB was trapped by addition of cyclohexene into the reaction mixture forming Cy2BNH2. The final product borazine (BHNH)3 is assumed to be formed by dehydrocoupling of [NH2BH2] or its solvent stabilized derivative [NH2BH2]-(solvent), rather than by dehydrogenation of cyclotriborazane (BH2NH 2)3 which is the trimerization product of [NH 2BH2].
- Yang, Xianghua,Fox, Thomas,Berke, Heinz
-
p. 852 - 860
(2012/02/05)
-
- Donor-acceptor complexation and dehydrogenation chemistry of aminoboranes
-
A series of formal donor-acceptor adducts of aminoborane (H 2BNH2) and its N-substituted analogues (H 2BNRR′) were prepared: LB-H2BNRR′2- BH3 (LB = DMAP, IPr, IPrCH2 and PCy3; R and R′ = H, Me or tBu; IPr = [(HCNDipp)2C:] and Dipp = 2,6-iPr 2C6H3). To potentially access complexes of molecular boron nitride, LB-BN-LA (LA = Lewis acid), preliminary dehydrogenation chemistry involving the parent aminoborane adducts LB-H2BNH 2-BH3 was investigated using [Rh(COD)Cl]2, CuBr, and NiBr2 as dehydrogenation catalysts. In place of isolating the intended dehydrogenated BN donor-acceptor complexes, the formation of borazine was noted as a major product. Attempts to prepare the fluoroarylborane-capped aminoborane complexes, LB-H2BNH 2-B(C6F5)3, are also described.
- Malcolm, Adam C.,Sabourin, Kyle J.,McDonald, Robert,Ferguson, Michael J.,Rivard, Eric
-
p. 12905 - 12916
(2013/02/22)
-
- A self-contained regeneration scheme for spent ammonia borane based on the catalytic hydrodechlorination of BCl3
-
Recycling: A self-contained procedure for the recycling of BNH-waste, based on the three major steps: polymer break-up, amine supported catalytic hydrodehalogenation of boron halogens, and the base exchange in borane amine adducts, is developed (see picture). Beyond the original task of recycling spent ammonia borane, the process provides a new means to produce borohydride species efficiently, by the direct use of molecular hydrogen. Copyright
- Reller, Christian,Mertens, Florian O.R.L.
-
supporting information
p. 11731 - 11735
(2013/01/15)
-
- Iron complex-catalyzed ammonia-borane dehydrogenation. A potential route toward B-N-containing polymer motifs using earth-abundant metal catalysts
-
Ammonia-borane (NH3BH3, AB) has garnered interest as a hydrogen storage material due to its high weight percent hydrogen content and ease of H2 release relative to metal hydrides. As a consequence of dehydrogenation, B-N-containing oligomeric/polymeric materials are formed. The ability to control this process and dictate the identity of the generated polymer opens up the possibility of the targeted synthesis of new materials. While precious metals have been used in this regard, the ability to construct such materials using earth-abundant metals such as Fe presents a more economical approach. Four Fe complexes containing amido and phosphine supporting ligands were synthesized, and their reactivity with AB was examined. Three-coordinate Fe(PCy3)[N(SiMe3)2]2 (1) and four-coordinate Fe(DEPE)[N(SiMe3)2]2 (2) yield a mixture of (NH2BH2)n and (NHBH)n products with up to 1.7 equiv of H2 released per AB but cannot be recycled (DEPE = 1,2-bis(diethylphosphino)ethane). In contrast, Fe supported by a bidentate P-N ligand (4) can be used in a second cycle to afford a similar product mixture. Intriguingly, the symmetric analogue of 4 (Fe(N-N)(P-P), 3), only generates (NH2BH2)n and does so in minutes at room temperature. This marked difference in reactivity may be the result of the chemistry of Fe(II) vs Fe(0).
- Baker, R. Tom,Gordon, John C.,Hamilton, Charles W.,Henson, Neil J.,Lin, Po-Heng,Maguire, Steven,Murugesu, Muralee,Scott, Brian L.,Smythe, Nathan C.
-
p. 5598 - 5609
(2012/05/20)
-
- Concentration-dependent dehydrogenation of ammonia-borane/triglyme mixtures
-
The dehydrogenation reaction of the hydrogen-storage compound ammonia-borane (AB) dissolved in triglyme (TG) reveals an unexpected but favourable concentration dependence of its dehydrogenation behaviour. Formal reaction-order considerations and 11B NMR spectroscopic analytics point towards a complex AB decomposition and hydrogen-release scheme that in highly concentrated solutions partly begins to resemble that of the solid-state case. The analysis of the gas-release characteristics identified two hydrogen desorption events that display an increasing peak overlap with increasing initial AB concentration. 11B NMR spectroscopic studies indicate that the concentration-dependent stability of the intermediate diammoniate of diborane, the presence of which appears to influence the rates of several dehydrogenation steps by interacting with various other intermediates, is one of the key factors for the overall hydrogen release.
- Kostka, Johannes F.,Schellenberg, Rene,Baitalow, Felix,Smolinka, Tom,Mertens, Florian
-
-
- A three-stage mechanistic model for ammonia-borane dehydrogenation by Shvo's catalyst
-
We propose a mechanistic model for three-stage dehydrogenation of ammonia-borane (AB) catalyzed by Shvo's cyclopentadienone-ligated ruthenium complex. We provide evidence for a plausible mechanism for catalyst deactivation and the transition from fast catalysis to slow catalysis and relate those findings to the invention of a second-generation catalyst that does not suffer from the same deactivation chemistry. The primary mechanism of catalyst deactivation is borazine-mediated hydroboration of the ruthenium species that is the active oxidant in the fast catalysis case. This transition is characterized by a change in the rate law for the reaction and changes in the apparent resting state of the catalyst. Also, in this slow catalysis situation, we see an additional intermediate in the sequence of boron, nitrogen species, aminodiborane. This occurs with concurrent generation of NH3, which itself does not strongly affect the rate of AB dehydrogenation.
- Lu, Zhiyao,Conley, Brian L.,Williams, Travis J.
-
p. 6705 - 6714
(2012/11/14)
-
- Promoted hydrogen release from ammonia borane with mannitol via a solid-state reaction route
-
Promoted hydrogen release from ammonia borane (NH3BH 3, AB) with mannitol (C6H8(OH)6, MA) additive is reported. It is found that for the MA/2AB sample, the dehydrogenation temperature is lowered by ~25 °C compared to that of neat AB, the liberation of undesired byproduct borazine is suppressed, and the released ammonia can be removed by using anhydrous MgCl2 as absorber. The analyses of Raman, Fourier transform infrared spectroscopy and 11B nuclear magnetic resonance spectroscopy demonstrate the breaking of B-N, B-H and O-H bonds and the formation of B-O bonds for the dehydrogenation process of MA/2AB. These results suggest a solid-state dehydrogenation reaction between AB and MA: the B-Hδ- bonds in AB and the O-H δ+ bonds in MA combine with each other to release H 2. Furthermore, the use of the perfect -OH carrier MA as additive leads to a straightforward understanding of the improved dehydrogenation of AB under the effect of hydroxyl groups in the solid state.
- Pan, Yuede,Wang, Yan,Liang, Yanliang,Tao, Zhanliang,Chen, Jun
-
p. 871 - 875
(2012/03/07)
-
- Catalytic redistribution and polymerization of diborazanes: Unexpected observation of metal-free hydrogen transfer between aminoboranes and amine-boranes
-
Ir-catalyzed (20 °C) or thermal (70 °C) dehydrocoupling of the linear diborazane MeNH2-BH2-NHMe-BH3 led to the formation of poly- or oligoaminoboranes [MeNH-BH2]x (x = 3 to >1000) via an initial redistribution process that forms MeNH 2?BH3 and also transient MeNH=BH2, which exists in the predominantly metal-bound and free forms, respectively. Studies of analogous chemistry led to the discovery of metal-free hydrogenation of the B=N bond in the "model" aminoborane iPr2N=BH2 to give iPr2NH?BH3 upon treatment with the diborazane Me3N-BH2-NHMe-BH3 or amine-boranes RR′NH?BH3 (R, R′ = H or Me).
- Robertson, Alasdair P. M.,Leitao, Erin M.,Manners, Ian
-
p. 19322 - 19325
(2012/01/13)
-
- Dehydrogenation performance of NH3BH3 with Mg 2NiH4 addition
-
The dehydrogenation performance of NH3BH3 destabilized by Mg2NiH4 was investigated. It was found that the onset dehydrogenation temperature was reduced, and no gaseous by-products were released during the whole decomposition process. This enhanced dehydrogenation performance could be attributed to the destabilization effect of Mg2NiH4. In comparison with the 2NH3BH 3/MgH2 sample, the dehydrogenation behavior and destabilization mechanism are different. 4NH3BH3/Mg 2NiH4 composite exhibits a three-step decomposition feature. NH3BH3 and Mg2NiH4 decomposed separately. The destabilization effect of Mg2NiH 4 on the chemical bonds of NH3BH3 plays a crucial role in the enhanced dehydrogenation performance. Our results provide a new insight on destabilized dehydrogenation behavior of NH3BH 3 after metal hydrides addition.
- Weng, Baicheng,Wu, Zhu,Li, Zhilin,Leng, Haiyan
-
-
- A robust, air-stable, reusable ruthenium catalyst for dehydrogenation of ammonia borane
-
We describe an efficient homogeneous ruthenium catalyst for the dehydrogenation of ammonia borane (AB). This catalyst liberates more than 2 equiv of H2 and up to 4.6 system wt % H2 from concentrated AB suspensions under air. Importantly, this catalyst is robust, delivering several cycles of dehydrogenation at high [AB] without loss of catalytic activity, even with exposure to air and water.
- Conley, Brian L.,Guess, Denver,Williams, Travis J.
-
p. 14212 - 14215
(2011/10/18)
-
- Frustrated Lewis pairs beyond the main group: Cationic zirconocene- phosphinoaryloxide complexes and their application in catalytic dehydrogenation of amine boranes
-
The cationic zirconocene-phosphinoaryloxide complexes [Cp 2ZrOC6H4P(t-Bu)2][B(C 6F5)4] (3) and [Cp*2ZrOC 6H4P(t-Bu)2][B(C6F5) 4] (4) were synthesized by the reaction of Cp2ZrMe 2 or Cp*2ZrMe2 with 2-(diphenylphosphino) phenol followed by protonation with [2,6-di-tert-butylpyridinium][B(C 6F5)4]. Compound 3 exhibits a Zr-P bond, whereas the bulkier Cp* derivative 4 was isolated as a chlorobenzene adduct without this Zr-P interaction. These compounds can be described as transition-metal-containing versions of linked frustrated Lewis pairs (FLPs), and treatment of 4 with H2 under mild conditions cleaved H 2 in a fashion analogous to that for main-group FLPs. Their reactivity in amine borane dehydrogenation also mimics that of main-group FLPs, and they dehydrogenate a range of amine borane adducts. However, in contrast to main-group FLPs, 3 and 4 achieve this transformation in a catalytic rather than stoichiometric sense, with rates superior to those for previous high-valent catalysts.
- Chapman, Andy M.,Haddow, Mairi F.,Wass, Duncan F.
-
p. 8826 - 8829
(2011/08/04)
-
- An investigation on the synthesis of borazine
-
Borazine is a promising precursor for boron nitride. A detailed investigation on the reaction of sodium borohydride and ammonium sulfate from 40 °C to 120 °C for synthesis of borazine was performed. The reaction was monitored by means of 11B nuclear magnetic resonance (11B NMR) and Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), mass spectroscopy (MS). The reaction produces mainly ammonia borane (AB), but not borazine at temperatures below 60 °C. Increases of temperature promote yield of borazine, which reaches the maximum around 110 °C. Whereas further increased temperature causes severe polymerization of borazine, and hence holds back yields of borazine.
- Li, Jun-Sheng,Zhang, Chang-Rui,Li, Bin,Cao, Feng,Wang, Si-Qing
-
p. 173 - 176
(2011/03/21)
-
- Facile metal free regioselective transfer hydrogenation of polarized olefins with ammonia borane
-
Transfer hydrogenation of polarized olefins bearing strongly electron-withdrawing groups on one side of the double bond was achieved with ammonia borane under mild conditions without using a catalyst. Mechanistic studies proved the character of the direct H transfers proceeding stepwise with a unique hydroboration intermediate and hydride before proton transfer.
- Yang, Xianghua,Fox, Thomas,Berke, Heinz
-
p. 2053 - 2055
(2011/03/22)
-
- Potassium(I) amidotrihydroborate: Structure and hydrogen release
-
Potassium(I) amidotrihydroborate (KNH2BH3) is a newly developed potential hydrogen storage material representing a completely different structural motif within the alkali metal amidotrihydroborate group. Evolution of 6.5 wt % hydrogen starting at temperatures as low as 80 °C is observed and shows a significant change in the hydrogen release profile, as compared to the corresponding lithium and sodium compounds. Here we describe the synthesis, structure, and hydrogen release characteristics of KNH 2BH3.
- Diyabalanage, Himashinie V. K.,Nakagawa, Tessui,Shrestha, Roshan P.,Semelsberger, Troy A.,Davis, Benjamin L.,Scott, Brian L.,Burrell, Anthony K.,David, William I. F.,Ryan, Kate R.,Jones, Martin Owen,Edwards, Peter P.
-
p. 11836 - 11837
(2010/10/04)
-
- Metal chloride-doped ammonia borane thermolysis: Positive effect on induction period as well as hydrogen and borazine release
-
In this work we studied the effect of metal chlorides (CoCl2, FeCl3 and AlCl3) on thermal decomposition of ammonia borane NH3BH3 (AB). The chlorides were chosen because they are simple and cost-effective. They showed promising performances as the onset temperature of AB decomposition decreased. Temperatures of 52, 65 and 85 °C were determined for CoCl2-, FeCl3- and AlCl 3-doped AB whereas it was 99 °C for AB. The induction period of AB dehydrogenation has been reduced. The relative mass losses were found as being 11.9, 12.3 and 10.4 wt% at about 110 °C but at 85 °C they were 4.5, 4.5 and 1.6 wt%, respectively. The gaseous side-products were analyzed and traces of borazine B3N3H6 were detected. It was found that the CoCl2 presence has a positive effect on the B 3N3H6 evolution. The solid by-products were characterized by XRD and IR: [NH2BH2]x forms after the first decomposition of AB and [BNHx]z forms after the second decomposition. The IR-print of [BNHx]z resembles that of BN, what suggests high dehydrogenation extent. These results are analyzed and discussed in the present paper.
- Benzouaa,Demirci,Chiriac,Toche,Miele
-
-
- An improved synthesis of borazine with aluminum chloride as catalyst
-
Borazine is an excellent precursor for boron nitride. However the existing synthetic methods for the preparation of borazine have drawbacks such as relatively high reaction temperatures, side reactions, long reaction times, and low yields. An improved synthesis procedure was disclosed, which involved the use of aluminum chloride as a catalyst in the reaction of sodium borohydride with ammonium sulfate. The aluminum chloride catalyst: brought the reaction temperature down from 120-140 °C to 45 °C. Improved yields of borazine were obtained in comparison to the reaction without a catalyst. In addition, the reaction process was investigated in detail by 11B NMR spectroscopy and Fourier transform, infrared spectroscopy (FTIR). It was found that aluminum, borohydride formed in very small quantity when aluminum chloride was introduced, which plays an important role in the reaction.
- Li, Jun-Sheng,Zhang, Chang-Rui,Li, Bin,Cao, Feng,Wang, Si-Qing
-
p. 1763 - 1766
(2010/08/13)
-
- Acid-catalyzed dehydrogenation of amine-boranes
-
A method of dehydrogenating an amine-borane using an acid-catalyzed reaction. The method generates hydrogen and produces a solid polymeric [R1R2B—NR3R4]n product. The method of dehydrogenating amine-boranes may be used to generate H2 for portable power sources.
- -
-
Page/Page column 5
(2010/02/16)
-
- Base-promoted ammonia borane hydrogen-release
-
The strong non-nucleophilic base bis(dimethylamino)naphthalene (Proton Sponge, PS) has been found to promote the rate and extent of H 2-release from ammonia borane (AB) either in the solid state or in ionic-liquid and tetraglyme solutions. For
- Himmelberger, Daniel W.,Chang, Won Yoon,Bluhm, Martin E.,Carroll, Patrick J.,Sneddon, Larry G.
-
p. 14101 - 14110
(2010/01/31)
-
- Development of rhenium catalysts for amine borane dehydrocoupling and transfer hydrogenation of olefins
-
Five-coordinated rhenium(I) hydride complexes of the type [Re(Br)(H)(NO)(PR3)2] (R = Cy 2a, iPr 2b) were prepared from [Re(Br)2(NO)(PR3)2(η2- H2)] (R = Cy la,. iPr lb) via deprotonation of the η2-H2 ligands with various bases. Filling the vacant site of 2a or 2b by various less bulky two-electron donors produced the 18-electron complexes [Re(Br)(H)(NO)(PR3)2(L)] (L = O 2 3, CH2=CH2 4, acetylene 5, H2 6, CO 7, CH3CN 8). The influence of the trans-coordinated ligand on the Re-H bond was examined. The 1H NMR chemical shift of the hydride depends on L in the order O2 > acetylene > CH 2=CH2 > H2 > CO > CH3CN. The reactions of 2a or 2b with the IMes or SIMes ligands afforded the five-coordinated complex [Re(Br)(H)(NO)(PR3)(NHC)] (NHC = IMes 9 (IMes = 1,3bis(2,4,6-trimethylphenyl)imidazol-2-ylidene), SIMes 10 (SIMes = l,3-bis(2,4,6-trimethylphenyl)4,5-dihydroimidazol-2-ylidene)) via replacement of one phosphine. The reaction of 2a or 2b with n-BuLi leads to the formation of the n-butene-coordinated dihydride complexes [Re(H)2(NO)(PR 3)2(η2-n-CH2=CHC 2H5)] (R = Cy 12a, iPr 12b). Species 1a and 1b reacted also with NaNMe2BH3, affording the tetrahydride complexes [Re(H)4(NO)(PR3)2] (R = Cy 14a, iPr 14b) via the intermediacy of 2a and 2b. The molecular structures of complexes 8b, 10a, and 10b were established by single-crystal X-ray diffraction studies. The five-coordinated rhenium(I) hydride complexes 2a, 2b, 9a, and 9b catalyzed the dehydrocoupling of Me2NHBH3 and the transfer hydrogenation of olefins using Me2NHBH3 as a hydrogen donor, which showed high activities. Mechanistic studies were carried out indicating that these rhenium(I) hydride catalyses allowed formation of dihydrogen hydride complexes. A plausible catalytic cycle for both dehydrocoupling and transfer hydrogenation was proposed, which implies the ability of rhenium(I) complexes to activate B-H and N-H bonds by the facile redox interplay of Re(I) and Re(III) species.
- Jiang, Yanfeng,Blacque, Olivier,Fox, Thomas,Frech, Christian M.,Berke, Heinz
-
p. 5493 - 5504
(2009/12/25)
-
- Homogeneous catalytic dehydrogenation/dehydrocoupling of amine-borane adducts by the Rh(I) Wilkinson's complex analogue RhCl(PHCy2) 3 (Cy ) cyclohexyl)
-
The Rh(l) complex RhCI(PHCy2)3 (1) (Cy = cyclohexyl, C6H11) has been investigated as a catalyst for the dehydrogenation/dehydrocoupling of dimethylamine-borane adduct Me 2NH·BH3 (3) at 20 °C to afford the cyclic dimer [Me2N-BH2]2 (4). Unlike previously studied neutral and Cationic Rh(l) precatalysts such as [{Rh(μ-CI)(1,5-cod)} 2] and [Rh(1,5-cod)2]OTf (1,5-cod = 1,5-cyclooctadiene, C8H12, OTf = OSO2CF3) with weakly electron-donating ligands at the metal center, which are reduced to catalytically active Rh(0) species, catalytic dehydrogenation of 3 using 1 was found to occur in a homogeneous manner according to nanofiltration experiments, Hg(0) poisoning and kinetic studies. Moreover, the presence of the sterically bulky ligand PHCy2 in complex 1 has been found to significantly increase the rate of reaction previously reported for Wilkinson's catalyst RhCI(PPh3)3. The catalytic activity of 1 toward a range of other amine-borane adducts RR'NH · BH3 (e.g., RR' = 'Pr 2, MeBz, MeH) at 20 °C was also investigated. The third row transition metal analogue of 1, the lr(l) complex lrCI(PHCy2) 3 (2), was also explored as a catalyst for the dehydrocoupling of 3 and was found to exhibit much reduced catalytic activity compared to 1 but proved significantly more active for sterically encumbered substrates. Addition of the strong Lewis acid B(C6F5)3 as a co-catalyst to both 1 and 2 has been found to significantly increase the rate of the dehydrocoupling reactions in all cases. The Rh(l) complex 1 (but not the lr(l) analogue 2) was also found to be active for the catalytic dehydrocoupling of the phosphine-borane adduct Ph2PH·BH3 (14) at 60-90 °C to afford linear dimer Ph2PH-BH2-PPh 2-BH3 (15).
- Sloan, Matthew E.,Clark, Timothy J.,Manners, Ian
-
p. 2429 - 2435
(2009/08/08)
-
- Coordination of aminoborane, NH2BH2, dictates selectivity and extent of H2 release in metal-catalysed ammonia borane dehydrogenation
-
In situ 11B NMR monitoring, computational modeling, and external trapping studies show that selectivity and extent of H2 release in metal-catalysed dehydrogenation of ammonia borane, NH3BH3, are determined by co
- Pons, Vincent,Baker, R. Tom,Szymczak, Nathaniel K.,Heldebrant, David J.,Linehan, John C.,Matus, Myrna H.,Grant, Daniel J.,Dixon, David A.
-
p. 6597 - 6599
(2009/04/20)
-
- Interaction of lithium hydride and ammonia borane in THF
-
The two-step reaction between LiH and NH3BH3 in THF leads to the production of more than 14 wt% of hydrogen at 40 °C. The Royal Society of Chemistry.
- Xiong, Zhitao,Chua, Yong Shen,Wu, Guotao,Xu, Weiliang,Chen, Ping,Shaw, Wendy,Karkamkar, Abhi,Linehan, John,Smurthwaite, Tricia,Autrey, Thomas
-
p. 5595 - 5597
(2009/04/13)
-
- Dehydrocoupling of dimethylamine-borane catalysed by rhenium complexes and its application in olefin transfer-hydrogenations
-
Re(I) complexes are applied as catalysts for the dehydrocoupling of Me 2NH·BH3 and the transfer-hydrogenation of olefins. The Royal Society of Chemistry.
- Jiang, Yanfeng,Berke, Heinz
-
p. 3571 - 3573
(2008/03/12)
-
- Synthesis and chemical transformations of ionic octahydrotriborates: Cleavage of the B3H8- anion
-
New octahydrotriborates LiB3H8·4Dn (Dn is dioxane), LiB3H8·2Dn, NaB3H 8·Dn, KB3H8·2.5Dn, [Mg(NH 3)6](B3H8)2, [Mg(Dg) 2](B3H8)2 (Dg is diglyme), [Mg(Dg)2](BH4)(B3H8), [Ca(Dg) 2](BH4)(B3H8), [Sr(Dg) 2](B3H8)2, and [C(NH 2)3]B3H8 were synthesized, and solvated salts with the B3H8- anion were prepared. It was shown that LiB3H8 forms hydrazinates of variable composition containing one to four hydrazine moles and the ammoniates LiB3H8·4NH3 and LiB3H 8·3NH3. The properties of the resulting salts and their solvates were studied. The temperature limits of the partial or complete desolvation of the solvates were established. The solubility of NaB 3H8·3Dn and tetraalkylammonium octahydrotriborates in organic solvents was studied over a wide temperature range. The heats of combustion in an oxygen atmosphere were measured, and the enthalpies of formation were calculated: ΔfH0(Me 4NB3H8) = -157.4 kJ/mol, Δy fH0(Et4NB3H8) = -262.5 kJ/mol, and ΔfH0(Bu4NB3H 8) = -443.8 kJ/mol. The destruction of the B3H 8- anion to give the BH4- ion and unstable borane B2H4 was found and confirmed experimentally for the first time. The destruction was studied in reactions of octahydrotriborates with Lewis bases (hydrazine and triphenylphosphine) and Lewis acids (AlCl3 and Al(BH4)3) and also in heat treatment. The B2H4 borane was isolated as the B 2H4·2PPh3 adduct. The reaction NaB 3H8·Dn → NaBH4 + B 5H9 + (H2 + Dn) can be conveniently used to prepare pentaborane(9) under laboratory conditions. The reaction of octahydrotriborate with aluminum chloride Bu4NB3H 8 + AlCl3 → Bu4N[Cl3Al(BH 4)] + B4H10 allows one to prepare tetraborane(10) with a fairly high yield and with a satisfactory degree of purity.
- Titov
-
p. 1471 - 1479
(2008/10/09)
-