Mechanistic studies of phosphorus-oxygen bond cleavages in group 7 dinuclear complexes of 2-pyridyl dimethylphosphinite

Abstract

Dinuclear chelates fac-L/sub 2/Re(CO)/sub 3/(M(CO)/sub 5/) (L/sub 2/ = 2-pyridyl dimethylphosphinite, 2, M = Re; 3, M = Mn) rearranged in benzene at 80/sup 0/C to provide the corresponding (CO)/sub 4/Re(..mu..OPYR)(..mu..-PMe/sub 2/)M(CO)/sub 4/ derivatives 5 (M = Re) and 6 (M = Mn) in 95 and 94% yield, respectively. The rearrangements exhibited first-order kinetics to > 3 half-lives and displayed the following kinetic parameters: M = Re, ..delta..H/sup + +/ = 24.2 +- 1.8 kcal/mol and ..delta..S/sup + +/ = -10 +- 5 eu; M = Mn, ..delta..H/sup + +/ = 22.2 +- 0.7 kcal/mol and ..delta..S/sup + +/ = -11 +- 2 eu. The reaction rates and the products formed were unaffected by added CO, methlating agents, or triphenylphospine. In the presence of carbon tetrachloride, the rearrangements afforded mixtures of the P-O cleavage products (5 or 6) and fac-(CO)/sub 6/L/sub 2/ReCl. Crossover studies showed the rearrangements of 2 and 3 to occur with statistically significant inter- and intramolecular components. The results are discussed in light of mechanisms involving CO dissociation, homo- and heterolytic metal-metal bond cleavage, and a novel dyotropic rearrangement.