Methyl transfers. 15. CoIPc- as a nucleophile and leaving group

Article abstract of DOI:10.1021/ja00072a020

Many complexes of cobalt in the +1 oxidation state are excellent nucleophiles. The complex with phthalocyanine, Pc^2-, is an example; the rates of reaction of complex (Co^IPc)^-, 1^-, with MeI and other alkylating agents in dimethylacetamide (DMA) solution are reported. In contrast to previous studies with other Co(I) complexes, the rate of reaction of the methylated product, (MeCo^IIIPc, 3) with I^- is also readily measured, allowing a kinetic evaluation of the equilibrium constant K = [1^-][MeI]/[3][I^-] = 0.004 in DMA at 25 °C. Similarly, Br^- also reacts with 3 reversibly, and the rate and equilibrium constants are reported. Thus 1^- is also a good leaving group. With CN, 3 gives complex MeCo^IIIPcCN^- reversibly and slowly gives MeCN in a reaction zero order in CN^-. The fast identity rate constants for I^- attack on MeI as well as that for Br^- attack on MeI are given. Two different paths to the identity methyl transfer rate constant, k_CoCo, for the 1^- + 3 reaction with use of the Marcus equation gave k_CoCo = 4.4 M^-1 s^-1 from the 3 + I^- data but k_CoCo = 0.088 M^-1 s^-1 from the 3 + Br^- data. This discrepancy, which is outside of experimental error, constitutes a deviation from the Marcus treatment; it is discussed.