The mechanism and stereochemistry of the reaction of pentacarbonyl-methylmanganese with phosphites

Abstract

Pentacarbonylmethylmanganese reacts under kinetically controlled conditions with 4-methyl(or ethyl)-2,6,7-trioxa-1-phosphabicyclo[2,2,2]octane to afford cis-CH₃COMn(CO)₄P(OCH₂)₃CR (R = CH₃ or C₂H₅). The rate of reaction is dependent on ligand concentration in the solvents chloroform and benzene but independent of ligand concentration in acetonitrile and acetone. In tetrahydrofuran as solvent, reaction proceeds through competing unimolecular and bimolecular reactions. The rates of reaction are strongly solvent-dependent, and the reactivity sequence MeCN Me₂CO > THF > CHCl₃ > C₆H₆ is observed. Decarbonylation of the cis-acyl complexes affords cis-CH₃Mn(CO)₄P(OCH₂)₃CR (R = CH₃ or C₂H₅), which reacts with P(OCH₂)₃CR₂(R = CH₃ to afford cis-CH₃COMn(CO)₃[P(OCH₂)₃CR]₂(R = CH₃), in which the phosphite ligands are mutually cis. The mechanism of these reactions is discussed.