Alkylcobalt carbonyls. 8. (Chloromethyl)- and (chloroacetyl)cobalt carbonyls

Article abstract of DOI:10.1021/om00147a028

(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.