METHYL TRANSFERS .15. COIPC- AS A NUCLEOPHILE AND LEAVING GROUP

Many complexes of cobalt in the +1 oxidation state are excellent nucleophiles. The complex with phthalocyanine, Pc2-, is an example; the rates of reaction of complex (Co(I)Pc)-, 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(III)Pc, 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-degrees-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(III)PcCN-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.