- Stable catalyst for intermolecular Pauson-Khand reaction
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The catalytic activity of previously formed Co2(CO) 6[P(Ph)3]2 (1) was compared with Co 2(CO)8 and the system formed by Co2(CO) 8 plus PPh3 in the intermole
- Arias, José Luis,Cabrera, Armando,Sharma, Pankaj,Rosas, Noe,Sampere, Rafael
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- Photochemical formation of a metal-metal bond following outer-sphere intervalence excitation in the ion pair [CoI(CO)3(PPh3)2][Co -I(CO)4]
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The absorption spectrum of the ion pair [CoI(CO)3(PPh3)2][Co -I(CO)4] in acetone displays a long-wavelength band at λmax = 386 nm that is assigned to an intervalence transfer (IT) transition from Co-I to Co+I. Upon IT excitation a photoreaction occurs according to the equation [CoI(CO)3(PPh3)2][Co -I(CO)4] → [(PPh3)-(CO)3Co0-Co0(CO) 3PPh3] + CO with a quantum yield of Φ = 0.012. It is suggested that in the primary photochemical step the radicals [Co(CO)3(PPh3)2] and [Co(CO)4] are generated. These radicals are labile and undergo dissociation and substitution reactions and finally dimerize to yield the stable photoproduct.
- Vogler, Arnd,Kunkely, Horst
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- Structural studies of derivatives of methinyltricobalt enneacarbonyls. III. Crystal structure and reaction studies of bis(methinyltricobalt enneacarbonyl)acetylene (Co6(CO)18C4)
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The compound Co6(CO)18C4 is one product of the reaction of ClCCo3(CO)9 with mesitylene. Its crystal and molecular structure has been determined by three-dimensional X-ray analysis. Crystals are triclinic, space group P1 with one centrosymmetric molecule in a cell of dimensions a = 8.87 (1), b = 12.61 (2), c = 7.97 (1) ?; α = 106.9 (2), β = 111.7 (1), γ = 70.1 (1)°. X-Ray data were collected by conventional film techniques using Co Kα radiation and the intensities of 1088 reflections above background were measured photometrically. The structure was refined anisotropically by full-matrix least-squares procedures to a conventional R factor of 0.047. The structure is composed of discrete molecules formed by the insertion of a carbon-carbon triple bond between two identical -CCo3(CO)9 units. In the linear carbon chain, C-C≡C-C, at the center of the molecule, the C-C and C≡C bond lengths are 1.37 (1) and 1.24 (2) ?, respectively. The mean Co-Co bond length is 2.47 (1) ?. The optimum experimental conditions for formation of Co6(CO)18C4 and related compounds from arenes and YCo3(CO)9 compounds are given and a number of reactions of Co6(CO)18C4 and derivatives are reported and discussed.
- Dellaca,Penfold,Robinson,Robinson, Ward T.,Spencer
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- SYNTHESIS AND FRAGMENTATION KINETICS OF TETRAKIS(TRIPHENYLPHOSPHINE)OCTACARBONYLTETRACOBALT
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Reaction of Co4(CO)12 with triphenylphosphine is shown to proceed at room temperature in n-heptane or 1,2-dichloroethane (DCE) to form Co4(CO)8(PPh3)4 which has been isolated and characterized by analysis and IR spectroscopy.The complex is rather unstable to air and light, especially in solution.Its IR spectra show that Co4(CO)8(PPh3)4 probably exists as an equilibrium mixture of forms containing symmetrically bridging and semibridging CO groups, the form with semibridging carbonyls being favored by steric effects and by DCE as a solvent as compared to n-heptane.The kinetics of fragmentation in DCE to form Co2(CO)6(PPh3)2 have been studied and shown to proceed by three paths that involve, in order of decreasing ease, rate-determining PPh3 dissociation, CO dissociation, and spontaneous activation without loss or gain of ligands in forming the transition state.The activation parameters for spontaneous fragmentation suggest that the degree of weakening of the bonding within the Co4 cluster is quite high in the transition state and that the Co4 cluster is weaker than the Ru3 cluster in Ru3(CO)9(PPh3)3.The complexes Co4(CO)84, Co4(CO)8(dppm)2 (dppm = Ph2PCH2PPh2), and probably Co4(CO)8(P-n-Bu3)4 are shown to be much more stable to fragmentation than Co4(CO)8(PPh3)4 and the instability of the latter is ascribed to the steric effect of its large substituents.
- Huq, Rokeya,Poee, Anthony
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- An NMR study of cobalt-catalyzed hydroformylation using para-hydrogen induced polarisation
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The syntheses of Co(η3-C3H5)(CO) 2PR2R′ (R, R′ = Ph, Me; R, R′ = Me, Ph; R = R′ = Ph, Cy, CH2Ph) and Co(η3-C 3H5)(CO)(L) (L = dmpe and dppe) are described,
- Godard, Cyril,Duckett, Simon B.,Polas, Stacey,Tooze, Robert,Whitwood, Adrian C.
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p. 2496 - 2509
(2009/12/02)
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- The application of polymer-bound carbonylcobalt(0) species in linker chemistry and catalysis
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Carbonylcobalt(0) species have been used as linkers between alkynes and a polymer support for the first time. The alkynes may be loaded indirectly onto a phosphine functionalised polymer via their hexacarbonyldicobalt(0) complex, or directly onto a cobalt
- Comely, Alex C.,Gibson, Susan E.,Hales, Neil J.,Johnstone, Craig,Stevenazzi, Andrea
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p. 1959 - 1968
(2007/10/03)
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- Solution Homolytic Bond Dissociation Energies of Organotransition-Metal Hydrides
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The homolytic bond dissociation energies (BDEs) of the mononuclear metal carbonyl hydride complexes (η5-C5H5)M(CO)3H (M = Cr, Mo, W), (η5-C5Me5)Mo(CO)3H, (η5-C5H5)W(CO)2(PMe3)H, (η5-C5H5)M(CO)2H (M = Fe, Ru), H2Fe(CO)4, Mn(CO)4PPh3H, Mn(CO)5H, Re(CO)5H, and Co(CO)3LH (L = CO, PPh3, P(OPh)3) have been estimated in acetonitrile solution by the use of a thermochemical cycle that reguires knowledge of the metal hydride pKa and the oxidation potential of its conjugate base (anion).The BDE values obtained by this method fall in the range 50-67 kcal/mol.In mostcases, these results agree well with literature data.Our data provide strong support for the common assumption that the M-H bond energies are greater for third-row and for second-row metals than for first-row metals, the difference being 5-11 kcal/mol.Effects of neither phosphine or phosphite substitution nor permethylation of the cyclopentadienyl ring on the M-H bond energies could be detected within the error limits of the method.The results are discussed in relation to previous M-H BDE estimates and metal hydride reactivity patterns.
- Tilset, Mats,Parker, Vernon D.
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p. 6711 - 6717
(2007/10/02)
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- Oxidation-reduction of carbonylcobalt cation-anion pairs in coupling to dimeric cobalt carbonyls
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The carbonylcobalt cation Co(CO)3(PPh3)2+ reacts with the anionic Co(CO)3PPh3- upon mixing to afford quantitative yields of the dimeric Co2(CO)6(PPh3)2. The same coupling occurs with the analogous Bu3P-substituted cation-anion pair to produce Co2(CO)6(PBu3)2, but at a significantly attenuated rate. Cross couplings of the substitution-inert Co(CO)3P2+ and Co(CO)3P′-, as well as the reverse phosphine combination, afford mixtures of Co2(CO)6P2, Co2(CO)6PP′ and Co2(CO)6P′2 diagnostic of extensive ligand (P,P′) scramblings. Facile ligand exchange of reactive intermediates is also indicated by the production of only Co2-(CO)6(PBu3)2 from Co(CO)3(PPh3)2+ and Co(CO)3PPh3- when carried out in the presence of added PBu3-without materially affecting the coupling rate. The marked solvent and salt effects together with the observation of characteristic charge-transfer absorption bands point to the contact ion pairs [Co(CO)3P2+] [Co(CO)3P′-] as critically involved in the rate-limiting activation process. A general mechanistic formulation is presented in Scheme II, in which the contact ion pair evolves into the radical pair consisting of the 19-electron Co(CO)3P2? and the 17-electroh Co(CO)3P′?. The behavior of these carbonylcobalt radicals is independently established in the preparative and transient electrochemistry of their precursors Co(CO)3P2+ and Co(CO)3P′- in reduction (Ec) and oxidation (Ea), respectively. Indeed the reactivity patterns in ion-pair, annihilation parallel the differences in the redox potentials J(Ec - Ea) as a direct measure of the driving force for electron transfer. Cyclic voltammetry is shown to be a particularly useful probe to demonstrate (i) the rapid dimerization rates of the 17-electron radicals to afford dicobalt carbonyls and (ii) the facile exchange of phosphine ligands between Co(CO)3P? and Co(CO)3P′? via the highly labile 19-electron intermediates Co(CO)3PP′?. Although the electron-transfer mechanism in Scheme II accounts for all the experimental observations relating to ion-pair annihilation, the possibility of alternative nonradical pathways previously proposed is also discussed.
- Lee,Kochi
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p. 567 - 578
(2008/10/08)
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- Charge-Transfer Ion Pairs. Structure and Photoinduced Electron Transfer of Carbonylmetalate Salts
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Brightly colored crystals, readily isolated from such colorless carbonylmetalates as Co(CO)4(1-), Mn(CO)5(1-), and V(CO)6(1-) in conjunction with various metallocenium and pyridinium cations, are identified as charge-transfer (CT) salts by their unambiguous absorption and diffuse reflectance spectra.X-ray crystallography of such CT salts establishes the relevant interionic separations, the spatial cation/anion orientations, as well as the deviations from tetrahedral Co(CO)4(1-) configuration that are all inherent to the charge-transfer interaction of intimate ion pairs.The Co(CO)4(1-) distortions, as observed in the crystal structures, are also revealed by their characteristic carbonyl IR spectra.The persistence of the unique carbonyl IR and charge-transfer absorption bands in nonpolar solvents thus leads to contact ion pairs (CIP) that are closely related or structurally the same as those elucidated by X-ray crystallography.Accordingly, the charge-transfer excitation of contact ion pairs can be examined directly in solution by time-resolved spectroscopy.The spectral observation of the radical pair .> from the 532-nm excitation of the charge-transfer salt with a 10-ns laser pulse represents the experimental verification of Mulliken theory.As such, the efficient scavenging of such labile 17-electron carbonylmetal radicals as Co(CO)4. and Mn(CO)5. affords a rich menu of productive photochemistry attendant upon the charge-transfer excitation of contact ion pairs.
- Bockman, T. M.,Kochi, J. K.
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p. 4669 - 4683
(2007/10/02)
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- Synthesis and reactivity of titanium/cobalt complexes with Ti-O-C-Co bridges
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Reactions between titanium metallocene dicarbonyls and dicobalt octacarbonyl were investigated and found to give a variety of Ti/Co complexes depending on the reaction conditions. Reaction between Cp2Ti(CO)2 and Co2(CO)8 in nondonor solvents led to the formation of the known Cp2Ti[OCCo3(CO)9]2 via a novel redox/cluster-building process. However, reaction between Cp2Ti(CO)2 and Co2(CO)8 in tetrahydrofuran led to the formation of the ionic compound [Cp2Ti(THF)2][Co(CO)4]. A mechanism in which isocarbonyl bridge formation is required to build the cluster compounds is proposed. Reaction between Cp*2Ti(CO)2 (Cp* = pentamethylcyclppentadienyl) and Co2(CO)8 yields the Ti(IV) isocarbonyl-bridged complex Cp*2Ti[OCCo(CO)3]2 from toluene but gives the paramagnetic Ti(III) dinier [Cp*2TiOCCo(CO)3]2 from hexane solution. Reactions of the above Ti/Co complexes with triphenylphosphine induce inner-sphere electron transfer from Co to Ti to take place via the isocarbonyl bridge.
- Merola, Joseph S.,Campo, Kathryn S.,Gentile, Robert A.
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p. 2950 - 2954
(2008/10/08)
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- Alkylcobalt carbonyls. 8. (Chloromethyl)- and (chloroacetyl)cobalt carbonyls
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(Chloroacetyl)cobalt tetracarbonyl, ClCH2C(O)Co(CO)4 (1), was prepared by the reaction of ClCH2C(O)Cl with Na[Co(CO)4]. 1 readily decarbonylates to (chloromethyl)cobalt tetracarbonyl (2). 1 is formed from 2 at ~5 bar of CO pressure and room temperature or at 1 bar of CO by cooling to ~-10°C in a reversible reaction. 2 gives with PPh3 the CO-substituted acyl derivative ClCH2C(O)Co(CO)3PPh3 (3) that can be decarbonylated at 50°C to the corresponding alkyl complex ClCH2Co(CO)3PPh3 (4). 4 takes up CO even under 1 bar of pressure at room temperature. The 3 ? 4 equilibrium is reversible. 1 was characterized by IR spectra, 2-4 could be isolated, and the structures of 3 and 4 were determined by X-ray diffraction. 2 reacts with the methoxide ion to yield CH2(COOMe)2. These results represent the first examples of (a) the carbonylation/decarbonylation reaction couple of an XCH2M vs. XCH2C(O)M (X = Cl, Br, I; M = transition metal) pair, (b) a ligand substitution reaction of a chloromethyl complex with a tertiary phosphine, and (c) the structure determination of a chloromethyl complex as well as (d) the structural study of an alkyl-/acylcobalt carbonyl pair with the same organic group. 3 crystallizes with monoclinic symmetry in the space group P21/c with Z = 4 and cell dimensions of a = 1212.3 (2) pm, b = 928.9 (3) pm, c = 2029.9 (4) pm, and β = 104.15 (2)°. Structure solution by Patterson methods and refinement with 3305 unique observed reflections led to a final R value of 0.057. The crystals of 4 are tetragonal of space group P43, with Z = 4 in a unit cell of dimensions a = b = 1086.3 (1) pm and c = 1815.5 (4) pm. The structure was determined by direct methods and refined with 4358 unique observed reflections to a final R value of 0.033.
- Galamb, Vilmos,Pályi, Gyula,Boese, Roland,Schmid, Günter
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p. 861 - 867
(2008/10/08)
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- Cobalt hydroformylation catalyst supported on a phosphinated polyphosphazene. Identification of phosphorus-carbon bond cleavage as mode of catalyst deactivation
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The interaction of Co2(CO)8 with [NP(OPh)1.7(OC6H4PPh2) 0.3]n (1), N3P3(OPh)5(OC6H4PPh 2) (2), PPh2-linked polystyrene (3), or triarylphosphine [PPh3, P(p-CH3C6H4)3] yielded species of the type Co2(CO)7PR3, [Co(CO)3PR3]2, and [Co(CO)3(PR3)2]+Co(CO) 4- as identified by infrared spectroscopy and 31P NMR. Catalysts derived from 1 were expected to have higher thermal stability based on the inherent thermal stability of 1 vs. 3. A study of the catalyst system 1/Co2(CO)8 for 1-hexene hydroformylation revealed an initial activity equal to its homogeneous analogue. This has been rationalized as due to cleavage of cross-linking P-Co-P sites during reaction with CO/H2 to give soluble hydride HCo(CO)3PR3 type species. All of the catalysts also revealed a time-dependent decrease in catalytic activity, due to a cobalt-mediated phosphorus-carbon bond cleavage. Benzene, toluene, benzyl alcohol, and P-MeC6H4CH2OH were detected as primary cleavage products. When olefin was omitted from these reactions, R2PH was observed.
- Dubois, Robert A.,Garrou, Philip E.,Lavin, Karen D.,Allcock, Harry R.
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p. 460 - 466
(2008/10/08)
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- Organometallic compounds with metal-metal bonds. II. The insertion of tin(II) and germanium (II) halides into metal-metal bonds
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New examples of insertion reactions into metal-metal bonds are described. Tin(II) chloride reacts smoothly with dicobalt octacarbonyl, [(C6H5)3PCo(CO)3]2, or dimeric π-cyclopentadienylnickel carbonyl
- Patmore,Graham
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p. 1405 - 1407
(2007/12/18)
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