Preparation of Diphenyl(tricyclohexylphosphine)manganese(II) and Its Reactions with Carbon Dioxide and Organic Carbonyl Compounds

Treatment of Mn(acac)3 (acac=acetylacetonato ligand) with AlPh3·Et2O in the presence of PCy3 (Cy=cyclo-C6H11) gave a new diphenylmanganese(II) complex, Ph2MnPCy3 (1). Complex 1 reacted with allylic compounds, CH2=CHCH2X (X=Br, OPh, OCH2CH=CH2, and OCOCH3), to give allylbenzene. Carbon dioxide was found to be inserted into the phenyl-manganese σ-bond of 1 to give bis(benzoato)manganese complex, (PhCOO)2MnPCy3, 2, which on successive treatment with HCl and diazomethane produced methyl benzoate. Complex 1 reacted with aldehydes, ketones, and esters having no active α-hydrogen atom to give alkoxomanganese species in solution, indicating that the insertion of C=O double bond into the phenyl-manganese σ-bond occurred. On the other hand, acetone and acetophenone reacted with Ph2MnPCy3 to give benzene and 2-oxoalkyl complexes, (RCOCH2)2Mn(PCy3)m (R=Me, Ph), 3. Reaction of alcohols with 1 afforded alkoxomanganese compounds which catalyze the Tishchenko type and Meerwein-Pondorf type reactions as well as transesterification reactions at room temperature.