NEW BASIC LIGANDS FOR HOMOGENEOUSLY CATALYTIC METHANOL CARBONYLATION .30. (DIOXANYLMETHYL)PHOSPHANERHODIUM COMPLEXES AS MODEL COMPOUNDS IN METHANOL CARBONYLATION

The cationic complex [Rh(COD)(P ∼ O)2][PF6] (3) is obtained from [μ-ClRh(COD)]2 (1), NaPF6/acetone and the ligand Me3Si(CH2)3P(Ph)CH2C4H7O2 (2). In 3 COD is displaced by CO to form [trans-(P ∼ O)2Rh(CO)3][PF6] (4). 4 readily eliminates carbon monoxide to form the complex [trans-(P ∼ O)(P O)Rh (CO)][PF6] (6). The reaction is reversible. With rapid methyl migration oxidative addition of CH3I to 6 affords the acyl complex [cis-(P O)2Rh(I)(COCH3)][PF6] (5) containing two RhO bonds. Heating of 5 in the presence of CO results in the reductive elimination of CH3C(O)I, which upon hydrolysis is transformed to CH3CO2H. With cleavage of both RhO bonds back reaction occurs to give 4. The "opening and closing mechanism" of the dioxanylmethyl phosphane promotes the formation of the complexes within the reaction cycle. © 1990.