Ligand effects on CO bridging in binuclear manganese carbonyl complexes

Article abstract of DOI:10.1021/om00072a022

Reactions between Mn₂(CO)₁₀, (C₂H₆)₂PCH₂PPh₂(depm), and (c-C₆H₁₁)₂PCH₂PPh₂(dcpm) (depm = Et₂PCH₂PPh₂ and depm = (c-C₆H₁₁)₂PCH₂PPh₂) in refluxing decane gave binuclear complexes Mn₂-(CO)₆(depm)₂ and Mn₂(CO)₅(depm)₂, respectively. A solution of the depm complex could be decarbonylated to give Mn2(CO)5(depm)2 whose attempted isolation resulted in disproportionation to the starting hexacarbonyl and unidentified decomposition products. Carbonylation of Mn2(CO)6(dcpm)2 afforded Mn2(C0)g(dcpm)2 which slowly reverts to the starting pentacarbonyl in the absence of a CO partial pressure. Solutions of both pentacarbonyl complexes show a low frequency (1640 cm'1) CO stretch assigned to a four-electron bridging carbonyl (4EBC) ligand. Comparing diphosphine ligand electronic and steric characteristics, the steric demand of the ligand appears to dominate as the factor responsible for stabilization of the four-electron bridging carbonyl in dimanganese pentacarbonyl systems.