Methyl transfer to nucleophilic metal carbonylate anions in catalytic methanol homologation

The kinetics of the stoichiometric reaction of methyltrialkylammonium cations with nucleophilic metal carbonylate anions was investigated in terms of its relationship to a new catalytic methanol homologation method. At high temperatures and pressures of H/sub 2/ and CO, a methyl group from each cation is incorporated into methane or ethanol. In the ionizing solvent, N-methylpyrrolidinone, the reaction using iron tetracarbonyl hydride anion is first order in both the methylammonium cation and iron carbonylate anion concentrations and zero order with respect to the partial pressures of hydrogen or carbon monoxide. The enthalpy and entropy of activation, in the temperature range of 180-210/sup 0/C, are 44 kcal/mol and +17 eu, respectively. The second-order rate constants exhibit a primary kinetic salt effect, increasing with decreasing salt concentration. The rate constants also increased with decreasing dielectric constant of the solvent. The data are consistent with methyl group transfers (S/sub N/2) between ions as the rate-limiting step. At 200/sup 0/C and 245 atm (3:1 CO/H/sub 2/) the second-order rate constants, 2.0 x 10/sup -4/ M/sup -1/ s/sup -1/ for Mn(CO)/sub 5//sup -/, are a measure of the nucleophilicities of these carbonylates toward tetramethylammonium ion. In the case of the manganate system, the product selectivity (ethanol vs. methane) was found to be independent of H/sub 2/ or CO partial pressure between 61 and 184 atm but slightly dependent on the concentration of Mn(CO)/sub 5//sup -/. These factors are discussed in terms of reaction mechanism. 31 references, 6 figures, 3 tables.