- Lewis acid-catalysed formation of two-dimensional phthalocyanine covalent organic frameworks
-
Covalent organic frameworks (COFs) offer a new strategy for assembling organic semiconductors into robust networks with atomic precision and long-range order. General methods for COF synthesis will allow complex building blocks to be incorporated into these emerging materials. Here we report a new Lewis acid-catalysed protocol to form boronate esters directly from protected catechols and arylboronic acids. This transformation also provides crystalline boronate ester-linked COFs from protected polyfunctional catechols and bis(boronic acids). Using this method, we prepared a new COF that features a square lattice composed of phthalocyanine macrocycles joined by phenylene bis(boronic acid) linkers. The phthalocyanines stack in an eclipsed fashion within the COF to form 2.3 n pores that run parallel to the stacked chromophores. The material's broad absorbance over the solar spectrum, potential for efficient charge transport through the stacked phthalocyanines, good thermal stability and the modular nature of COF synthesis, show strong promise for applications in organic photovoltaic devices.
- Spitler, Eric L.,Dichtel, William R.
-
-
Read Online
- Activation of Aryl Carboxylic Acids by Diboron Reagents towards Nickel-Catalyzed Direct Decarbonylative Borylation
-
The Ni-catalyzed decarbonylative borylation of (hetero)aryl carboxylic acids with B2cat2 has been achieved without recourse to any additives. This Ni-catalyzed method exhibits a broad substrate scope covering poorly reactive non-ortho-substituted (hetero)aryl carboxylic acids, and tolerates diverse functional groups including some of the groups active to Ni0 catalysts. The key to achieve this decarbonylative borylation reaction is the choice of B2cat2 as a coupling partner that not only acts as a borylating reagent, but also chemoselectively activates aryl carboxylic acids towards oxidative addition of their C(acyl)?O bond to Ni0 catalyst via the formation of acyloxyboron compounds. A combination of experimental and computational studies reveals a detailed plausible mechanism for this reaction system, which involves a hitherto unknown concerted decarbonylation and reductive elimination step that generates the aryl boronic ester product. This mode of boron-promoted carboxylic acid activation is also applicable to other types of reactions.
- Deng, Xi,Guo, Jiandong,Su, Weiping,Wang, Xiaotai,Zhang, Xiaofeng
-
supporting information
p. 24510 - 24518
(2021/08/12)
-
- Formation of a hydride containing amido-zincate using pinacolborane
-
Amido-zincates containing hydrides are underexplored yet potentially useful complexes. Attempts to access this type of zincate through combining amido-organo zincates and pinacolborane (HBPin)viaZn-C/H-BPin exchange led instead to preferential formation of amide-BPin and/or [amide-BPin(Y)]?(Y = Ph, amide, H), when the amide is hexamethyldisilazide or 2,2,6,6-tetramethylpiperidide and the hydrocarbyl group was phenyl or ethyl. In contrast, the use of a dipyridylamide (dpa) based arylzinc complex led to Zn-C/H-BPin metathesis being the major outcome. Independent synthesis and full characterisation of two LnLi[(dpa)ZnPh2] (L = THF,n= 3; L = PMDETA,n= 1) complexes,1and3, respectively, enabled reactivity studies that demonstrated that these species display zincate type reactivity (by comparison to the lower reactivity of the neutral complex (Me-dpa)ZnPh2,4, Me-dpa = 2,2′-dipyridyl-N-methylamine). This included1performing the rapid deprotonation of 4-ethynyltoluene and also phenyl transfer to α,α,α-trifluoroacetophenone in contrast to neutral complex4. Complex1reacted with one equivalent of HBPin to give predominantly PhBPin (ca.90%) and a lithium amidophenylzincate containing a hydride unit, complex7-A, as the major zinc containing product. Complex7-Atransfers hydride to an electrophile preferentially over phenyl, indicating it reacts as a hydridozincate. Attempts to react1with >1 equivalent of HBPin or with catecholborane led to more complex outcomes, which included significant borane and dpaZn substituent scrambling, two examples of which were crystallographically characterised. While this work provides proof of principle for Zn-C/H-BPin exchange as a route to form an amido-zincate containing a hydride, amido-organozincates that undergo more selective Zn-C/H-BPin exchange still are required.
- Ingleson, Michael J.,Nichol, Gary S.,Uzelac, Marina,Yuan, Kang
-
supporting information
p. 14018 - 14026
(2021/10/19)
-
- Synthesis of Boroxine and Dioxaborole Covalent Organic Frameworks via Transesterification and Metathesis of Pinacol Boronates
-
Boroxine and dioxaborole are the first and some of the most studied synthons of covalent organic frameworks (COFs). Despite their wide application in the design of functional COFs over the last 15 years, their synthesis still relies on the original Yaghi's condensation of boronic acids (with itself or with polyfunctional catechols), some of which are difficult to prepare, poorly soluble, or unstable in the presence of water. Here, we propose a new synthetic approach to boroxine COFs (on the basis of the transesterification of pinacol aryl boronates (aryl-Bpins) with methyl boronic acid (MBA) and dioxaborole COFs (through the metathesis of pinacol boronates with MBA-protected catechols). The aryl-Bpin and MBA-protected catechols are easy to purify, highly soluble, and bench-stable. Furthermore, the kinetic analysis of the two model reactions reveals high reversibility (Keq ~1) and facile control over the equilibrium. Unlike the conventional condensation, which forms water as a byproduct, the byproduct of the metathesis (MBA pinacolate) allows for easy kinetic measurements of the COF formation by conventional 1H NMR. We show the generality of this approach by the synthesis of seven known boroxine/dioxaborole COFs whose crystallinity is better or equal to those reported by conventional condensation. We also apply metathesis polymerization to obtain two new COFs, Py4THB and B2HHTP, whose synthesis was previously precluded by the insolubility and hydrolytic instability, respectively, of the boronic acid precursors.
- Hamzehpoor, Ehsan,Jonderian, Antranik,McCalla, Eric,Perepichka, Dmitrii F.
-
p. 13274 - 13280
(2021/09/07)
-
- Electronic Spectroscopy of 2-Phenyl-1,3,2-benzodioxaborole and Its Derivatives: Important Building Blocks of Covalent Organic Frameworks
-
Aryl boronate esters, such as 2-phenyl-1,3,2-benzodioxaborole (1), are important components in the formation of a variety of covalent organic frameworks. The addition of substituents on the aromatic rings of aryl boronate esters has the potential to modif
- Jimenez-Hoyos, Carlos A.,Knee, Joseph L.,Northrop, Brian H.,Ryan, Roberta P.,Savino, Cara
-
p. 529 - 537
(2020/02/25)
-
- Mechanism and Scope of Nickel-Catalyzed Decarbonylative Borylation of Carboxylic Acid Fluorides
-
This Article describes the development of a base-free, nickel-catalyzed decarbonylative coupling of carboxylic acid fluorides with diboron reagents to selectively afford aryl boronate ester products. Detailed studies were conducted to assess the relative rates of direct transmetalation between aryl boronate esters and diboron reagents and a bisphosphine nickel(aryl)(fluoride) intermediate. These investigations revealed that diboron reagents undergo transmetalation with this Ni(aryl)(fluoride) intermediate at rates significantly faster than their aryl boronate ester congeners. Furthermore, the reactivity of both boron reagents toward transmetalation is enhanced with increasing electrophilicity of the boron center. These mechanistic insights were leveraged to develop a catalytic decarbonylative borylation of acid fluorides that proved applicable to a variety of (hetero)aryl carboxylic acid fluorides as well as diverse diboron reagents. The acid fluorides can be generated in situ directly from carboxylic acids. Furthermore, the mechanistic studies directed the identification of various air-stable Ni pre-catalysts for this transformation.
- Malapit, Christian A.,Bour, James R.,Laursen, Simon R.,Sanford, Melanie S.
-
supporting information
p. 17322 - 17330
(2019/11/03)
-
- Isodesmic C-H Borylation: Perspectives and Proof of Concept of Transfer Borylation Catalysis
-
The potential advantages of using arylboronic esters as boron sources in C-H borylation are discussed. The concept is showcased using commercially available 2-mercaptopyridine as a metal-free catalyst for the transfer borylation of heteroarenes using arylboronates as borylation agents. The catalysis shows a unique functional group tolerance among C-H borylation reactions, tolerating notably terminal alkene and alkyne functional groups. The mechanistic investigation is also described.
- Rochette, étienne,Desrosiers, Vincent,Soltani, Yashar,Fontaine, Frédéric-Georges
-
supporting information
p. 12305 - 12311
(2019/08/20)
-
- Metal-Free Radical Borylation of Alkyl and Aryl Iodides
-
A metal-free radical borylation of alkyl and aryl iodides with bis(catecholato)diboron (B2cat2) as the boron source under mild conditions is introduced. The borylation reaction is operationally easy to conduct and shows high functional group tolerance and broad substrate scope. Radical clock experiments and density functional theory calculations provide insights into the mechanism and rate constants for C-radical borylation with B2cat2 are disclosed.
- Cheng, Ying,Mück-Lichtenfeld, Christian,Studer, Armido
-
p. 16832 - 16836
(2018/11/23)
-
- Bench-Stable Sulfoxide-Based Boronates: Preparation and Application in a Tandem Suzuki Reaction
-
A set of novel aromatic and heteroaromatic bench-stable sulfoxide-based boronates was prepared. The structure of the boronates was established by means of X-ray crystallography, and the prepared boronates were successively used in Suzuki cross-coupling reactions under different conditions. We also developed a tandem Suzuki reaction so that a base is generated during the nucleophilic addition of Grignard reagents to 4-bromobenzaldehyde. The formed intermediates were smoothly coupled with the prepared boronates and the boronic acids under external base-free conditions. (Figure presented.).
- ?ubiňák, Marek,Eigner, Václav,Tobrman, Tomá?
-
supporting information
p. 4604 - 4614
(2018/10/31)
-
- An efficient method for the hydrolysis of potassium organotrifluoroborates promoted by montmorillonite K10
-
An efficient and non-expensive method for conversion of diverse potassium organotrifluoroborates to their corresponding boronic acids promoted by montmorillonite K10 using water as the reaction solvent is described. Further interconversion of potassium organotrifluoroborates to their corresponding boronic esters, via boronic acid intermediates was also successfully accomplished. The products were obtained in good yields, being the rate of hydrolysis influenced by the type of substituent present in the boronic acid.
- Silva, Renato L.,Santos, Cosme S.,Santos, Jonh A. M.,Oliveira, Roberta A.,Menezes, Paulo H.,Freitas, Juliano C. R.
-
p. 1777 - 1785
(2018/09/04)
-
- Self-Assembly of Fluorinated Boronic Esters and 4,4′-Bipyridine into 2:1 N→B Adducts and Inclusion of Aromatic Guest Molecules in the Solid State: Application for the Separation of o, m, p -Xylene
-
A series of 2:1 fluorinated arylboronic ester adducts with 4,4′-bipyridine sustained by N→B dative bonds have been synthesized. The degree of fluorination in the arylboronic esters derived from catechol is shown to modulate the molecular conformation of t
- Campillo-Alvarado, Gonzalo,Vargas-Olvera, Eva C.,H?pfl, Herbert,Herrera-Espa?a, Angel D.,Sánchez-Guadarrama, Obdulia,Morales-Rojas, Hugo,Macgillivray, Leonard R.,Rodríguez-Molina, Braulio,Farfán, Norberto
-
p. 2726 - 2743
(2018/05/09)
-
- Boron trifluoride facilitated transesterification of dioxaborolanes
-
The direct transesterification of dioxaborolanes (alkane-1,2-diol based boronate esters) was explored. Using BF3·OEt2, alkane-1,2-diol based mono- and bis-boronate esters (i.e., pinacol and ethylene glycol) have been converted quantitatively to either benzene-1,2-diol or alkane-1,3-diol based boronate esters. In the case of pinacol esters, esterification is facilitated by the accompanying pinacol rearrangement, thus shifting the reaction equilibrium.
- Kombala, Chathuri J.,Ekanayake, Dulamini I.,Gross, Dustin E.
-
p. 3782 - 3786
(2017/09/09)
-
- Enhanced Reactivity of Aerobic Diimide Olefin Hydrogenation with Arylboronic Compounds: An Efficient One-Pot Reduction/Oxidation Protocol
-
A catalyst-free and efficient method for simultaneous olefin hydrogenation and oxidation of arylboronate esters to phenols with hydrazine hydrate and molecular oxygen is presented. The process is based on the utilization of a readily available Lewis acidic arylboron compound, which evades common problems associated with the catalyst-free aerobic hydrogenation of olefins with diimide. Using an operationally simple procedure, the protocol smoothly delivers phenol derivatives and various alkanes in excellent yields with remarkable functional group compatibility. The method allows the reaction to be scaled up to 1 g of the starting materials.
- Santra, Surojit,Guin, Joyram
-
supporting information
p. 7253 - 7257
(2015/11/25)
-
- Vibrational properties of boroxine anhydride and boronate ester materials: Model systems for the diagnostic characterization of covalent organic frameworks
-
The vibrational characteristics of 28 different boronic acid, boroxine anhydride, and boronate ester species have been systematically investigated using a combination of experimental infrared (IR) spectroscopy and computational modeling. IR bands characteristic to each boron-containing functionality have been categorized and assigned in conjunction with density functional theory (B3LYP/6-31G(d)), with the aim of better understanding and distinguishing the vibrational characteristics of covalent organic frameworks (COFs) built from boronic acids. In several cases, vibrational assignments differ from those previously reported in the literature on boronic acid-based COFs. Vibrations commonly regarded as diagnostic for one functionality are found in regions of the IR spectrum where other functionalities also show characteristic peaks. The collective experimental and computational results reveal that several alternative bands in the IR region can be used to more diagnostically distinguish between boronic acid, boroxine anhydride, and boronate ester species. The results presented herein provide the tools for straightforward characterization of boroxine anhydride and boronate ester species using IR spectroscopy. The results can be applied to additional theoretical studies of larger COF-like assemblies as well as the analysis of other boronic-acid-based materials.
- Smith, Merry K.,Northrop, Brian H.
-
p. 3781 - 3795
(2014/07/08)
-
- Intramolecular interactions in ortho-methoxyalkylphenylboronic acids and their catechol esters
-
(Graph Presented) Catechol esters of ortho-methoxyalkylphenylboronic acids have been synthesized and characterized by 17O NMR spectroscopy. The results were compared with the data for the parent acids. The influence of intramolecular and intermolecular hydrogen bonds on the properties of the boronic acids has been discussed. The 17O NMR data for the boronic esters proved that there are no O → B interactions in the investigated compounds. This fact is connected with weak Lewis acidity of the parent acids and their low sugars' receptors activity. Crystal structure of ortho -methoxyphenylboronic acid catechol ester was determined.
- Adamczyk-Wozniak, Agnieszka,Borys, Krzysztof M.,Czerwinska, Karolina,Gierczyk, Blazej,Jakubczyk, Michal,Madura, Izabela D.,Sporzynski, Andrzej,Tomecka, Ewelina
-
p. 616 - 621
(2013/10/08)
-
- Solid-state 11B and 13C NMR, IR, and X-ray crystallographic characterization of selected arylboronic acids and their catechol cyclic esters
-
Nine arylboronic acids, seven arylboronic catechol cyclic esters, and two trimeric arylboronic anhydrides (boroxines) are investigated using 11B solid-state NMR spectroscopy at three different magnetic field strengths (9.4, 11.7, and 21.1T). Through the analysis of spectra of static and magic-angle spinning samples, the 11B electric field gradient and chemical shift tensors are determined. The effects of relaxation anisotropy and nutation field strength on the 11B NMR line shapes are investigated. Infrared spectroscopy was also used to help identify peaks in the NMR spectra as being due to the anhydride form in some of the arylboronic acid samples. Seven new X-ray crystallographic structures are reported. Calculations of the 11B NMR parameters are performed using cluster model and periodic gauge-including projector-augmented wave (GIPAW) density functional theory (DFT) approaches, and the results are compared with the experimental values. Carbon-13 solid-state NMR experiments and spectral simulations are applied to determine the chemical shifts of the ipso carbons of the samples. One bond indirect 13C-11B spin-spin (J) coupling constants are also measured experimentally and compared with calculated values. The 11B/10B isotope effect on the 13C chemical shift of the ipso carbons of arylboronic acids and their catechol esters, as well as residual dipolar coupling, is discussed. Overall, this combined X-ray, NMR, IR, and computational study provides valuable new insights into the relationship between NMR parameters and the structure of boronic acids and esters. Copyright
- Oh, Se-Woung,Weiss, Joseph W. E.,Kerneghan, Phillip A.,Korobkov, Ilia,Maly, Kenneth E.,Bryce, David L.
-
experimental part
p. 388 - 401
(2012/08/13)
-
- COVALENT ORGANIC FRAMEWORKS AND METHODS OF MAKING SAME
-
Crystalline COFs comprising a phthalocyanine moiety and a boron-containing multifunctional linking group joined by boronate ester bonds. A method for making crystalline COFs comprising Lewis acid catalyzed formation of boronate ester bonds between protected catechol subunits and multifunctional linkers comprising boronic acid groups. The COFs can be used in applications such as, for example, electronic devices.
- -
-
Page/Page column 17
(2011/10/31)
-
- Chelate restrained boron cations for intermolecular electrophilic arene borylation
-
Highly electrophilic boron species that borylate arenes are generated by halide abstraction from CatBX (Cat = catecholato, C6H 4O22-, X = Cl or Br) by [Et3Si] [CbBr6] (CbBr6 = [closo-1-H-CB11H 5Br6]-). A transient [CatB][CbBr6] related species reacts as a synthetic equivalent of [CatB]+ in intermolecular electrophilic borylation, with reactions proceeding rapidly at 25 °C. The [CatB]+ moiety was shown to be strongly Lewis acidic on the basis of 1H and 31P{1H} NMR spectroscopy of the crotonaldehyde and triethylphosphine oxide adducts, respectively. Catalytic quantities of [Et3Si][CbBr6] and CatBX were effective for the high-yielding borylation of arenes by CatBH in a highly atom efficient cycle with H2 the only byproduct. Successful catalysis was dependent on the robust [CbBr6]- anion and the use of electrophile-resistant borane sources
- Del Grosso, Alessandro,Pritchard, Robin G.,Muryn, Chris A.,Ingleson, Michael J.
-
body text
p. 241 - 249
(2010/04/04)
-
- Pronounced effects of substituents on the iridium-catalyzed borylation of aryl C-H bonds
-
Iridium trisboryl complexes containing bisphosphine and bipyridine ligands and pinacolate and catecholate substituents on boron are reported. A large difference in reactivity towards the borylation of C-H bonds is observed for this series of trisboryl complexes, and this difference is attributed to the electron-donating properties of the pinacolate vs. catecholate groups, and the steric and electronic properties of bipyridine vs. bisphosphine ligands.
- Liskey, Carl W.,Wei, Carolyn S.,Pahls, Dale R.,Hartwig, John F.
-
p. 5603 - 5605
(2010/01/31)
-
- Sequential C-F activation and borylation of fluoropyridines via intermediate Rh(i) fluoropyridyl complexes: A multinuclear NMR investigation
-
The C-F bond activation of fluoropyridines by [Rh(SiPh3) (PMe3)3] afforded Rh(i) fluoropyridyl complexes of the type [Rh(ArF)(PMe3)3] with concomitant formation of fluorotriphenylsilane; subsequent treatment with bis-catecholatodiboron yielded fac-[Rh(Bcat)3(PMe3) 3] and the free fluoropyridyl boronate esters (ArFBcat). The Royal Society of Chemistry.
- Lindup, Richard J.,Marder, Todd B.,Perutz, Robin N.,Whitwood, Adrian C.
-
p. 3664 - 3666
(2008/03/14)
-
- Structural elucidation of a nickel boryl complex. A recyclable borylation Ni(II) reagent of bromobenzene
-
The first nickel complex bearing a boryl moiety, (PNP)Ni[B(catechol)] (PNP = N[2-P(CHMe2)2-4-methylphenyl]2-), has been prepared, structurally characterized, and analyzed by DFT; this rare species is shown to be a recyclable reagent for the borylation of bromobenzene, via an unusual cycle, by applying the ingredients catecholborane and NaBH 4. The Royal Society of Chemistry.
- Adhikari, Debashis,Huffman, John C.,Mindiola, Daniel J.
-
p. 4489 - 4491
(2008/09/16)
-
- Stability of boronic esters - Structural effects on the relative rates of transesterification of 2-(phenyl)-1,3,2-dioxaborolane
-
Relative rates of reaction of the achiral cyclic phenylboronic ester 2-(phenyl)-1,3,2-dioxaborolane with a wide variety of structurally modified diols, have been studied to understand the factors influencing the relative stabilities of boronic esters. It is found that the alkyl substituents on the α-carbons of diols slow down the transesterification, but produce thermodynamically more stable boronic ester. Six-membered boronic esters are thermodynamically more stable than their corresponding five-membered analogs. Amongst cyclic 1,2-diols, cis-1,2-cyclopentanediol displaces ethylene glycol instantaneously whereas trans-1,2-cyclopentanediol is totally unreactive, which suggests that the cis-stereochemistry of the 1,2-diol is a prerequisite for transesterification. Among the 1,5-diols, diethanolamine displaces ethylene glycol quite rapidly forming a more stable bicyclic chelate in which nitrogen is attached to boron by a coordinating bond (as evident by 11B NMR spectroscopy). The oxygen atom of di(ethylene glycol) and the sulfur atom of 2,2′-thiodiethanol do not assist in displacing the ethylene glycol from their boronic esters.
- Roy, Chandra D.,Brown, Herbert C.
-
p. 784 - 790
(2007/10/03)
-
- Synthesis and reactivity of cobalt boryl complexes
-
The synthesis and reactivity of phosphine-cobalt boryls, were investigated. The reactivity studies have shown that alkyne diboration takes place and borylation of aryl bromides is possible with low selectivity. Boryl transfer was investigated initially by
- Adams, Christopher J.,Baber, R. Angharad,Batsanov, Andrei S.,Bramham, George,Charmant, Jonathan P.H.,Haddow, Mairi F.,Howard, Judith A.K.,Lam, Wai Han,Lin, Zhenyang,Marder, Todd B.,Norman, Nicholas C.,Orpen, A. Guy
-
p. 1370 - 1373
(2007/10/03)
-
- Waste-free and facile solid-state protection of diamines, anthranilic acid, diols, and polyols with phenylboronic acid
-
Phenylboronic acid (2) reacts quantitatively by ball-milling in the solid state with o-phenylendiamine, 1,8-diaminonaphthalene, anthranilic acid, pyrocatechol, pyrogallol, pinacol, bicyclic cis-diols, mannitol, and inositol to form the five- or six-membered cyclic phenyl-boronic amides or esters. Catalysts or other auxiliaries are strictly excluded as they are not required and would have to be removed after the reactions. These varied model reactions provide pure protected products without the necessity of further purifying workup and the potential for protection chemistry is demonstrated. Some of the reactions can also be quantitatively performed if stoichiometric mixtures of the reactants are co-ground or co-milled and heated to appropriate temperatures either below the eutectics or above the melting points. The temperatures are much higher in the latter case. Similar reactions in solution suffer from less than 100% yield of the mostly sensitive compounds that are difficult to purify and thus create much waste. The hydrolysis (de-protection) conditions of the products are rather mild in most cases. Therefore, this particularly easy access to heteroboroles, heteroborolanes, heteroborinones, heteroborines, and heteroborinines is highly valuable for their more frequent use in protective syntheses.
- Kaupp, Gerd,Naimi-Jamal, M. Reza,Stepanenko, Vladimir
-
p. 4156 - 4160
(2007/10/03)
-
- Copper promoted C-N and C-O bond cross-coupling with phenyl and pyridylboronates
-
Acyclic and cyclic esters, as well as anhydride (boroxine) of phenylboronic acids are efficient phenylating agents in copper promoted C-N and C-O bond cross-coupling reactions. The first successful C-N cross-coupling of a heterocyclic boronate with heteroarenes, such as indazole, has been demonstrated.
- Chan, Dominic M. T.,Monaco, Kevin L.,Li, Renhua,Bonne, Damien,Clark, Charles G.,Lam, Patrick Y. S.
-
p. 3863 - 3865
(2007/10/03)
-
- 14-Electron four-coordinate Ru(II) carbyl complexes and their five-coordinate precursors: Synthesis, double agostic interactions, and reactivity
-
The structure of five-coordinate Ru(II) complexes RuHCl(CO)(PiPr3)2,1, RuCl2(CO)(PiPr3)2, 2, and Ru(Ph)Cl(CO)(PtBu2Me)2, 12, are reported. All three of these complexes have square-based pyramid geometry with the strongest σ-donor ligand trans to the vacant site. These 16-electron complexes do not show bona fide agostic interactions. This is attributed to the strong trans influence ligand (H, CO, and Ph) and π-donation of the Cl, which is further supported by the fact that two agostic interactions are present in the Cl- removal product of 12, i.e., the four-coordinate [RuPh(CO)L2]BAr′4 (L = PtBu2Me, Ar′ = 3,5-C6H3(CF3)2), 16. Structural comparison of 16 and 12 reveals that removal of Cl- does not change the remaining ligand arrangements but creates two low-lying LUMOs for agostic interactions, which persist in solution as evidenced by IR spectroscopy. Reactions of 16 with E-H (E = B, C(sp)) bonds cleave the Ru-Ph bond and form Ru-E/H bonds by different mechanisms. The reaction with catecholborane gives [RuH(CO)L2]BAr′4, which further reacts with catecholborane to give [Ru(BR2)(CO)L2]BAr′4. However, the reaction with Me3SiCCH undergoes a multistep transformation to give a PhCCSiMe3- and Me3SiCCH-coupled product, the mechanism of which is discussed. Reaction of RuCl2(CO)L2 with 1 equiv MeLi affords RuMeCl(CO)L2, 5, which further reacts with MeLi forming RuMe2(CO)L2, 7. Variable-temperature 13C{1H} NMR spectra reveal the two methyls in 7 are inequivalent and exchange by overcoming an energy barrier of 6.8 kcal/mol at -30 °C. The chloride of 5 can be removed to give [RuMe(CO)L2]BAr′4.
- Huang, Dejian,Streib, William E.,Bollinger, John C.,Caulton, Kenneth G.,Winter, Rainer F.,Scheiring, Thomas
-
p. 8087 - 8097
(2007/10/03)
-
- C-H Activation and Functionalization of Unsaturated Hydrocarbons by Transition-Metal Boryl Complexes
-
Transition-metal boryl complexes of the form Cp′Fe(CO)LBcat and (CO)5MBcat, where Cp′ = C5H5, C5Me5, M = Mn, Re, L = CO, PMe3, and cat = 1,2-O2C6H4, were synthesized by reaction of ClBcat with [Cp′Fe(CO)L]- or [M(CO)5]-. X-ray crystal structures of CpFe-(CO)2Bcat, Cp*Fe(CO)2Bcat, and (CO)5MnBcat were obtained. Upon irradiation, these metal boryl complexes reacted with arenes and alkenes to form aryl- and vinylboronate ester products in moderate to high yields. Monosubstituted arenes with methyl, chloro, trifluoromethyl, methoxy, and dimethylamino substituents were used as substrates, and the resulting ratios of ortho- to meta- to para-substituted arene products were measured. No significant electronic effects were observed, indicating that the chemistry is not occurring through a typical electrophilic aromatic substitution pathway. Competition experiments between toluene and other substituted arenes were conducted. Reactivity differences were small, but anisole was found to have the fastest rate of reaction. Kinetic isotope effects were measured for the reaction of CpFe(CO)2Bcat, (CO)5MnBcat, or (CO)5ReBcat with benzene/ benzene-d6 mixtures and were found to be 3.3 ± 0.4, 2.1 ± 0.1, and 5.4 ± 0.4, respectively. This difference in isotope effect along with differences in selectivities with substituted arsenic reagents rules out a mechanism by which a common free Beat radical attacks free substrate. Several experiments were also conducted to probe for CO loss. A 13CO-labeling experiment, CO inhibition experiment, and PMe3 trapping experiment indicate that the mechanism most likely proceeds through irreversible CO loss to form a 16-electron intermediate. Functionalization of alkenes to form vinylboronate esters was also observed, and mechanistic studies showed the absence of a measurable kinetic isotope effect for reaction of CpFe(CO)2Bcat or (CO)5ReBcat with ethylene/ethylene-d4 mixtures or for reaction with ethylene-d2.
- Waltz, Karen M.,Muhoro, Clare N.,Hartwig, John F.
-
p. 3383 - 3393
(2008/10/08)
-
- Derivatization and Mass Spectrometric Investigation of Substituted Benzeneboronic Acids. The Use of Linked Scanning During Gas Chromatography Mass Spectrometry
-
Substituted benzeneboronic acids are important intermediates in the synthesis of support matrices for affinity chromatography but their analysis by mass spectrometry is hindered by thermal reactions in the ion source.A simple derivatization with 1,2- or 1
- Longstaff, Colin,Rose, Malcolm Edward
-
p. 508 - 518
(2007/10/02)
-