- Rational Synthesis of Metallo-Cations Toward Redox- A nd Alkaline-Stable Metallo-Polyelectrolytes
-
Cations are crucial components in emerging functional polyelectrolytes for a myriad of applications. Rapid development in this area necessitates the exploration of new cations with advanced properties. Herein we describe a combination of computational and experimental design of cobaltocene metallo-cations that have distinct electronic and redox properties. One of the direct outcomes on the first synthesis of a complete set of cation derivatives is to discover highly stable cations, which are further integrated to construct metallo-polyelectrolytes as anion-exchange membranes in solid-state alkaline fuel cells. The device performance of these polyelectrolytes under highly basic and oxidative environments is competitive with many organo-polyelectrolytes.
- Zhu, Tianyu,Sha, Ye,Firouzjaie, Horie Adabi,Peng, Xiong,Cha, Yujin,Dissanayake, D. M. M. Mevan,Smith, Mark D.,Vannucci, Aaron K.,Mustain, William E.,Tang, Chuanbing
-
-
Read Online
- Mobile metal-metal bonds: Studies on mixed valence Ir3 and Ir4 clusters
-
The dicationic clusters [(C5Me5)4Ir4S4] 2+ ([1]2+) and [(C5Me5)3Ir3S2] 2+ ([2]2+) were prepared by treatment of [(C5Me5)IrCl2]2 with (Me3Si)2S followed by ion exchange chromatography. Crystallographic characterization of the tetrairidium cluster [1]2+ reveals a cubane motif consisting of interpenetrated Ir4 and S4 tetrahedra. The Ir4 core is distorted from idealized tetrahedral symmetry by virtue of a single IrIV-IrIV bonding contact of 2.764(1) ?. The four IrIV-IrIII contacts are nearly equivalent at 3.5 ?, while the IrIII?IrIII distance is 3.683(1) ?. Variable-temperature 1H NMR studies indicate that [I]2+ is fluxional with a coalescence temperature of 13 °C (400 MHz), corresponding to ΔG? = 57 kJ/mol. This dynamic process is attributed to migration of the metal-metal bond arising from internal IrIV/IrIII self-exchange. Cyclic voltammetry studies of [1]2+ reveal a pair of reversible one-electron reductions at -218 and -487 mV vs Ag/AgCl. Chemical reduction of [1]2+ was effected with cobaltocene while the neutral cluster could be reoxidized with HC1/O2. In the solid state [1]2+ features a trigonal-bipyramidal Ir3S2 core with average Ir-Ir contacts of 2.82 ? and Ir-S distances of 2.28 ?. Cyclic voltammetry studies indicate that this closo dication undergoes two single electron reductions at -712 and -993 mV. Cobaltocene reduction of [2]2+ afforded dark blue crystals of neutral [2]0. Variable-temperature 1H NMR spectra of [2]0 reveal dynamic behavior, with coalescence at 60 °C (400 MHz), corresponding to ΔG? = 64 kJ/mol. These structural dynamics suggest migration of the nonbonding Ir?Ir interaction among the three edges of the Ir3 triangle.
- Venturelli, Anne,Rauchfuss, Thomas B.
-
-
Read Online
- Unprecedented tris-phosphido-bridged triangular clusters with 42 valence electrons. chemical, electrochemical and computational studies of their formation and stability
-
This paper presents the synthesis and structural characterization of the unprecedented tris-phosphido-bridged compounds Pt3(μ-PBu t2)3X3 (X = Cl, Br, I), having only 42 valence electrons, while up to now analogous clusters typically have 44e -. The new species were obtained by an apparent bielectronic oxidation of the 44e- monohalides Pt3(μ-PBu t2)3(CO)2X with the corresponding dihalogen X2. Their X-ray structures are close to the D3h symmetry, similarly to the 44e- analogues with three terminal carbonyl ligands. The products were also obtained by electrochemical oxidation of the same monohalides in the presence of the corresponding halide. In a detailed study on the formation of Pt3(μ-PBut 2)3I3, the redox potentials indicated that I2 can only perform the first monoelectronic oxidation but is unsuited for the second one. Accordingly, the 43e- intermediate [Pt3(μ-PBut2)3(CO) 2I]+ was ascertained to play a key role. Another piece of information is that, together with the fully oxidized product Pt 3(μ-PBut2)3I3, the transient 44e- species [Pt3(μ-PBut 2)3(CO)3]+ is formed in the early steps of the reaction. In order to extract detailed information on the formation pathway, involving both terminal ligand substitutions and electron transfer processes, a DFT investigation has been performed and all the possible intermediates have been defined together with their associated energy costs. The profile highlights many important aspects, such as the formation of an appropriate couple of 43e- intermediates having different sets of terminal coligands, and suitable redox potentials for the transfer of one electron. Optimizations of 45e- associative intermediates in the ligand substitution reactions indicate their possible involvement in the redox process with reduction of the overall energy cost. Finally, according to MO arguments, the unique stability of the 42e- phosphido-bridged Pt 3 clusters can be attributed to the simultaneous presence of three terminal halides.
- Funaioli, Tiziana,Leoni, Piero,Marchetti, Lorella,Albinati, Alberto,Rizzato, Silvia,Fabrizi De Biani, Fabrizia,Ienco, Andrea,Manca, Gabriele,Mealli, Carlo
-
-
Read Online
- Biolabeling with cobaltocinium tags
-
A label for amino and thiol functionalities of peptides and proteins based on the activated cobaltocinium hexafluorophosphate succinimide ester (CoS) is presented. Despite the known selectivity of a succinimide ester towards amines, CoS also modifies cysteine residues under the same reaction conditions. The derivatized biomolecules were investigated using liquid chromatography with subsequent electrospray-mass spectrometric detection (LC/ESI-MS). In combination with their remarkable stability under physiological conditions, easy handling and good spectroscopic properties, cobaltocinium ions provide all requirements for a powerful labeling reagent. Furthermore, in direct comparison to the isoelectronic well-established ferrocene reagents, the higher redox potential and the chemical stability of the cobaltocinium moiety add to the benefits as a derivatizing agent for bioanalysis.
- Müller-Bomke, Susanne,Sperling, Michael,Hayen, Heiko,Karst, Uwe
-
-
Read Online
- Synthesis and solution self-assembly of side-chain cobaltocenium-containing block copolymers
-
The synthesis of side-chain cobaltocenium-containing block copolymers and their self-assembly in solution was studied. Highly pure monocarboxycobaltocenium was prepared and subsequently attached to side chains of poly(tert-butyl acrylate)-block-poly(2-hyd
- Ren, Lixia,Hardy, Christopher G.,Tang, Chuanbing
-
-
Read Online
- Crystal forms of hexafluorophosphate organometallic salts and the importance of charge-assisted C-H - F hydrogen bonds
-
Architecture, stability, and behavior with temperature of the hexafluorophosphate salts [(C5H5)2Co][PF6] (1), [(C5H5)2Fe][PF6] (2), [(C6H6)2Cr][PF6] (3), and [(C6H5Me)2Cr][PF6] (4) have been investigated. Crystals 1 and 2 have been measured by variable-temperature X-ray diffraction and differential scanning calorimetry. The phase-transitional behavior of [(C5H5)2Co][PF6], which undergoes two fully reversible crystal-to-crystal phase transitions, has been compared with the known behavior of [(C5H5)2Fe][PF6]. The room- and low-temperature phases (form I and form II) of [(C5H5)2Fe][PF6] and [(C5H5)2Co][PF6] are isostructural and isomorphous. The basic packing features of crystalline 1 and 2 are maintained on substituting the metallocene system with the bisbenzenechromium cation in 3. The architecture common to the three salts is otherwise disrupted by substituting toluene for benzene in 4. It has been shown that, when assisted by the difference in charge between anions and cations, the C-H - F interactions play a significant role. The structural parameters obtained for C-H - F interactions in 1-4 have been compared with data retrieved from the Cambridge Crystallographic Database on interactions of the X-H - F(δ-) type (X - C, N, O) in organometallic salts of the PF6- anion.
- Grepioni, Fabrizia,Cojazzi, Gianna,Draper, Sylvia M.,Scully, Noelle,Braga, Dario
-
-
Read Online
- Synthesis, crystal structure and comparative electrochemistry of metallocenyldiphenylphosphines of ruthenocene, osmocene, ferrocene and cobaltocenium hexafluorophosphate
-
The metallocenyldiphenylphosphines [M(C5H5)(C 5H4PPh2)] with M = Fe(II) (ferrocenyl = Fc), 1, Ru(II) (ruthenocenyl = Rc), 2, Os(II) (osmocenyl = Oc), 3, and Co(III) +PF6- (cobaltocenium hexafluorophosphate = [Cc][PF6]), 4, were synthesized and the crystal structure of RcPPh2, 2, (Z = 4, monoclinic, space group P21/c) was determined. The differences in reactivity of each metallocenyl derivative were such that 1 could be obtained from a Friedel Crafts reaction between ferrocene and PPh2Cl in the presence of AlCl3 as catalyst. Both the ruthenocene and osmocene derivatives 2 and 3 were obtained by reacting the monolithiated metallocene precursor with PPh2Cl. However, monolithiation of ruthenocene had to be achieved via a stoichiometric amount of tBuLi. For osmocene, monolithiation was achieved by a 20% excess of nBuLi. This was evidenced by the failure to isolate any bisphosphine, Oc(PPh2)2, during workup. Complex 4 could not be obtained via phosphination of free cobaltocenium hexafluorophosphate. Phosphine derivatisation of free cyclopentadiene prior to complexation with Co III was required to form [CcPPh2][PF6], 4. The electrochemistry of all phosphines was studied by voltammetric techniques in CH2Cl2/0.1 mol dm-3 [N(nBu) 4][B(C6F5)4]. A reversible one-electron transfer process for the ferrocenyl group of 1 was observed at 0.078 V vs. FcH/FcH+. The osmocenyl and ruthenocenyl derivatives exhibited irreversible metallocenyl oxidations at 0.355 and 0.476 V respectively. The cobaltocenium complex, 4, exhibited two reversible one-electron transfer reductions to liberate first a neutral CoII cobaltocene species at -1.062 V and then an anionic CoI cobaltocene species at -2.122 V. A single electrochemical irreversible, one-electron oxidation at the phosphorus centre which forms a quickly-decomposing phosphorus radical cation, Mc+Ph2P+, was also observed at Epa > 0.754 V. The newly-formed Mc+Ph2P + species or its chemical decomposition products can be oxidized at Epa > 1.090 V vs. FcH/FcH+.
- Fourie, Eleanor,Van Rensburg, J. Marthinus Janse,Swarts, Jannie C.
-
-
- Synthesis, electrochemistry, and reactivity of half-sandwich ruthenium complexes bearing metallocene-based bisphosphines
-
The bimetallic complexes CpRu(P-P)X [Cp = n5-C5H 5; X = Cl, H; P-P = dppf (1,1′-bis(diphenylphosphino)ferrocene) , dppr (1,1′-bis(diphenylphosphino)ruthenocene), dppo (1,1′- bis(diphenylphosphino)-osmocene), dippf (1,1′-bi
- Shaw, Anthony P.,Norton, Jack R.,Buccella, Daniela,Sites, Lauren A.,Kleinbach, Shannon S.,Jarem, Daniel A.,Bocage, Katherine M.,Nataro, Chip
-
p. 3804 - 3814
(2009/12/04)
-
- Molecular and electronic structure of square planar complexes [Pd II(tbpy)(LN,OIP)]0, [PdII(tbpy)(LN,OISQ](PF 6), and [PdII(tbpy)(LN,O IBQ](PF6)(BF4)·2CH2Cl 2
-
Three PdII complexes which are members of the same electron-transfer series have been synthesized. Refluxing of the reaction mixture containing equimolar amounts of PdCl2, 2-(2-trifluoromethyl) anilino-4,6-di-tert-butylphenol (H2LN,O), 4,4′-di-tert-butyl-2,2′-dipyridyl (tbpy), and 3 equiv of triethylamine in MeOH under an argon atmosphere followed by exposure to air and addition of KPF6 after cooling to room temperature yields reddish brown crystals of paramagnetic (S = 1/2) [Pd(LISQN,O)(tbpy)](PF 6) (2). Reaction of 2 with one equiv of [CoCp2] in dry and degassed CH2Cl2 using anaerobic conditions gives diamagnetic [Pd(LIPN,O)(tbpy)] (1), which is the one-electron reduced form of 2. One-electron oxidation of 2 in CH2Cl2 under argon with one equiv of NOBF4 affords diamagnetic [Pd(LIBQN,O)( tbpy)](PF6)(BF4)·2CH2Cl 2 (3). Complexes 1, 2, and 3 constitute three members of the same electron-transfer series. They are ideally suited to distinctly distinguish the geometrical and spectroscopic features of the N,O-coordinated, closed-shell, diamagnetic o-iminophenolate (LIPN,O)2-, the corresponding open-shell π-radical o-iminobenzosemiquinonate (LISQN,O)1- (Srad = 1/2), and the closed-shell o-iminobenzoquinone (LIBQN,O)0 forms. All complexes were characterized by X-ray crystallography (100 K), cyclic voltammetry, EPR, and UV-vis spectroscopy. Complex 2 exhibits three reversible electron transfer waves in the cyclic voltammogram. Structural characterization of complex 3 reveals an interesting strong ion pairing between the BF 4 anion and the complex dication with a short C-F distance of 2.7 A. The Royal Society of Chemistry.
- Kokatam, Swarna-Latha,Chaudhuri, Phalguni,Weyhermueller, Thomas,Wieghardt, Karl
-
p. 373 - 378
(2008/02/06)
-
- Synthesis and characterization of a bimetallic boratabenzene cobalt complex
-
Reaction of 1,4-(BBr2)2C6H4 with cobaltocene gives a bimetallic cobalt complex with cyclopentadienyl and boratabenzene ligands. Oxidation allows the dicationic dicobalt(III) complex to be isolated; the bis(hexafluorophosphate) salt has been structurally characterized. Variable-temperature magnetic susceptibility measurements on the neutral dicobalt(II) complex showed substantial deviation from the Curie -Weiss law; a fit to the Bleaney-Bowers equation for a singlet ground state and a triplet excited state gave an exchange interaction of J = ca. -28 cm -1. Electrochemical studies, as well as near-infrared data on the mixed-valence species, suggest that the interaction between the metal centers is weak.
- Hascall, Tony,Beck, Victoria,Barlow, Stephen,Cowley, Andrew R.,O'Hare, Dermot
-
p. 3808 - 3813
(2008/10/09)
-
- Synthesis, structures, and redox properties of mixed-sandwich complexes of cyclopentadienyl and hydrotris(pyrazolyl)borate ligands with first-row transition metals
-
The synthesis, structures and redox properties of mixed-sandwich complexes of cyclopentadienyl and hydrotris(pyrazolyl)borate ligands with first-row transition metals were studied. Crystal structure determinations were performed for various complexes. Ana
- Brunker, Tim J.,Cowley, Andrew R.,O'Hare, Dermot
-
p. 3123 - 3138
(2008/10/08)
-
- Molecular and electronic structures of bis(pyridine-2,6-diimine)metal complexes [ML2](PF6)(n) (n = 0, 1, 2, 3; M = Mn, Fe, Co, Ni, Cu, Zn)
-
A series of mononuclear, octahedral first-row transition metal ion complexes mer-[M(II)L02](PF6)2 containing the tridentate neutral ligand 2,6-bis[1-(4-methoxyphenylimino)ethyl]pyridine (L0) and a Mn(II), Fe(II), Co(II), Ni(II), Cu(II), or Zn(II) ion have been synthesized and characterized by X-ray crystallography. Cyclic voltammetry and controlled potential coulometry show that each dication (except those of Cu(II) and Zn(II)) can be reversibly one-electron-oxidized, yielding the respective trications [M(III)L02]3+, and in addition, they can be reversibly reduced to the corresponding monocations [ML2]+ and the neutral species [ML2]0 by two successive one-electron processes. [MnL2]PF6 and [CoL2]PF6 have been isolated and characterized by X-ray crystallography; their electronic structures are described as [Mn(III)L12]PF6 and [Co(I)L02]PF6 where (L1)1- represents the one-electron-reduced radical form of L0. The electronic structures of the tri-, di-, and monocations and of the neutral species have been elucidated in detail by a combination of spectroscopies: UV-vis, NMR, X-band EPR, Mossbauer, temperature-dependent magnetochemistry. It is shown that pyridine-2,6-diimine ligands are noninnocent ligands that can be coordinated to transition metal ions as neutral L0 or, alternatively, as monoanionic radical (L1)1-. All trications are of the type [M(III)L02]3+, and the dications are [M(II)L02]2+. The monocations are described as [Mn(III)L12]+ (S = 0), [Fe(II)L0L1]+ (S = 1/2 ), [Co(I)L02]+ (S = 1), [Ni(I)L02]+ (S = 1/2 ), [Cu(I)L02]+ (S = 0), [Zn(II)L1L0]+ (S = 1/2 ) where the Mn(III) and Fe(II) ions are low-spin-configurated. The neutral species are described as [Mn(II)L12]0, [Fe(II)L12]0, [Co(I)L0L1]0, [Ni(I)L0L1]0, and [Zn(II)L12]0; their electronic ground states have not been determined.
- De Bruin, Bas,Bill, Eckhard,Bothe, Eberhard,Weyhermueller, Thomas,Wieghardt, Karl
-
p. 2936 - 2947
(2008/10/08)
-
- Metallocene complexes of iron and cobalt derived from the 4,4′-bis(η5-cyclopentadienyl)octafluorobiphenyl ligand
-
The reaction of decafluorobiphenyl with 10 equiv of sodium cyclopentadienide (NaCp) in THF (65°C, 2 h) afforded 4,4′-bis(cyclopentadienyl)octafluorobiphenyl (1) as a mixture of double-bond isomers in 72percent yield after workup and purification. Subsequent treatment with sodium hydride in THF (25°C, 6 h) afforded disodium 4,4′-bis(cyclopentadienyl)octafluorobiphenyl (2). Reaction of NaCp, ligand 2, and FeBr2 (21:1:10 mol ratio) in THF afforded mostly ferrocene as well as the diiron complex CpFe(η5-C5H4-4,4′-C6F 4C6F4-η5-C5H 4)FeCp (3), the linear triiron complex Cp[Fe(η5-C5H4-4,4′-C 6F4C6-F4-η5C 5H4)]2FeCp (4), and the linear tetrairon complex Cp[Fe(η5-C5H4-4,4′-C 5F4C6F4-η5-C 5H4)]3FeCp (5), which were isolated by liquid chromatography. Solution voltammetric analysis of 3 showed a single, reversible two-electron oxidation at +200 mV, 4 showed two reversible oxidations (2:1 ratio) at +180 and +372 mV, respectively, and 5 snowed two reversible oxidations (2:2 ratio) at +192 and +382 mV, respectively (all vs Cp2Fe|Cp2Fe+). A similar reaction of NaCp, ligand 2, and CoBr2 in THF was worked up with air and dilute aqueous HCl followed by aqueous KPF6 to afford a mixture of cobaltocenium hexafluorophosphates, from which [Cp2Co]+PF6- and the dicobalt complex [CpCo(η5-C5H4-4,4′-C 6F4C6F4-η5-C 5H4)CoCp]2+[PF6-] 2 (6) were isolated by liquid chromatography. CV analysis of 6 showed a single, reversible CoII|CoIII wave at +232 mV relative to Cp2Co|Cp2Co+. These voltammetric data suggest that no significant electronic communication exists between two metals bridged by this conjugated dibasic ligand (2). A crystal structure of diiron complex 3 demonstrated the conformational preferences of the CpC6F4C6F4Cp ligand in the solid state with respective torsional angles of 37.5°, 50.1°, and 32.1°.
- Hollandsworth, Carl B.,Gary Hollis Jr.,Slebodnick, Carla,Deck, Paul A.
-
p. 3610 - 3614
(2008/10/08)
-
- Spectroscopic comparisons of MoW(porphyrin)2 heterodimers with homologous Mo2 and W2 quadruple bonds: A dynamic NMR and resonance raman study
-
The rotational barrier for MoW(meso-monotolyl octaethylporphyrin)2 ([(TOEP)MoW(TOEP)]) has been determined (ΔG((+))(rot) = 10.6 ± 0.1 kcal/mol) by variable-temperature NMR and complete band shape analysis and is compared with values previously obtained for the analogous homodimers. The overall quadruple bond strengths of these isostructural dimolybdenum, ditungsten, and molybdenum - tungsten porphyrin dimers have also been compared by calculation of the force constants corresponding to each metal - metal bond stretching frequency as observed by resonance Raman spectroscopy. The Raman results are as follows: [Mo(OEP)]2, ν(MoMo) = 310 cm-1, k = 2.72 mdyn/A?; [(OEP)MoW(OEP)], ν(MoW) = 279 cm-1, k = 2.89 mdyn/A?; [Mo(TOEP)]2, ν(MoMo) = 310 cm-1, k = 2.72 ν(MoMo) [W(TOEP)]2 ν(WW) = 275 cm-1, k = 4.08 mdyn/A?; and [(TOEP)-MoW(TOEP)], ν(MoW) = 278 cm-1, k = 2.89 mdyn/A?: [MoMoW(TOEP)]. Both the 1H NMR and Raman specta are consistent with a [(Por)MoW(Por)] structure wherein the Mo(Por) congener experiences a more drastic 'bending-back' distortion of the porphyrin macrocycle.
- Collman, James P.,Harford,Franzen, Stefan,Eberspacher,Shoemaker, Richard K.,Woodruff, William H.
-
p. 1456 - 1465
(2007/10/03)
-
- Improvements in the preparation of cyclopentadienyl thallium and methylcyclopentadienylthallium and in their use in organometallic chemistry
-
Improved preparation methods of cyclopentadienylthallium and methylcyclopentadienylthallium, giving quantitative yields and incorporating ultrasound techniques, are described. Their use as starting materials for a wide range of organometallic syntheses is discussed and demonstrated.
- Neto, Alberto Federman,Borges, Aurea Donizete Lanchote,Miller, Joseph,Darin, Vitor Andre
-
p. 1299 - 1314
(2008/10/09)
-
- PENTAMETHYLCYCLOPENTADIENYL TRANSITION-METAL COMPLEXES. ELECTROCHEMISTRY OF TRANSITION-METAL pi -COMPLEXES. 7. CYCLOPENTADIENYL(ARENE)COBALT CATIONS: PREPARATION, ELECTROCHEMICAL REDUCTION, AND SPECTROSCOPIC INVESTIGATION OF THE PARAMAGNETIC D7 MONOCATIONS.
-
A novel halogen/arene exchange reaction starting from left bracket Co(pmco)X//2 right bracket //2 (pmcp equals eta **5-1,2,3,4,5-pentamethylcyclopentadienyl, X equals Cl, Br) makes accessible the Co(pmcp)(arene)**2** plus dications. A series of these sandwich cations substituted to a varying degree by methyl groups in either ligand ring was prepared. Electrochemical (cyclic voltammetry and polarography at the DME) reduction of Co(cp)(arene)**2** plus and Co(pmcp)(arene)**2**30 (cp equals eta **5-cyclopentadienyl, pmcp equals eta **5-pentamethylcyclopentadienyl; arene: bz equals eta **6-benzene, mes equals eta **6-mesitylene, pmbz equals eta **5-cyclopentadienyl, and hmbz equals // eta **6-hexamethylbenzene) salts (BF//4** minus , PF//6** minus ) in propylene carbonate revealed two reversible one-electron reduction steps of nearly constant separation for each compound ( plus 0. 4 to minus 0. 12 v and minus 0. 56 to minus 1. 1 vs. SCE respectively). These results are compared to the reduction potentials determined for the two-step reduction of Co(hmbz)//2**2** plus in the same solvent and to potentials for related sandwich systems in the literature. A regular displacement of both reduction potentials with the number and the position of the methyl substituents at either ring on comparison with the results of an INDO-SCF calculation yields a relation between the electrochemical substituent effect and the bonding of the ligand.
- Koelle,Fuss,Rajasekharan,Ramakrishna,Ammeter,Boehm
-
p. 4152 - 4160
(2007/10/02)
-
