33570-17-1Relevant academic research and scientific papers
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.
Alkylcobalt carbonyls. 8. (Chloromethyl)- and (chloroacetyl)cobalt carbonyls
Galamb, Vilmos,Pályi, Gyula,Boese, Roland,Schmid, Günter
, p. 861 - 867 (2008/10/08)
(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.
