21407-17-0Relevant academic research and scientific papers
Crystal structures of the dimeric cobalt compounds [Co(PPhMe2)(CO)3]2 and [Co2(PPhMe2)3(CO)5]
Llewellyn, Simon A.,Green, Malcolm L.H.,Cowley, Andrew R.
, p. 3785 - 3789 (2006)
The molecular structures of the dimeric cobalt compounds [Co(PPhMe2)(CO)3]2 and [Co2(PPhMe2)3(CO)5] have been characterised by X-ray crystallography. The compound [Co2
Oxidation-reduction of carbonylcobalt cation-anion pairs in coupling to dimeric cobalt carbonyls
Lee,Kochi
, p. 567 - 578 (2008/10/08)
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.
Charge-Transfer Ion Pairs. Structure and Photoinduced Electron Transfer of Carbonylmetalate Salts
Bockman, T. M.,Kochi, J. K.
, p. 4669 - 4683 (2007/10/02)
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.
