Synthesis and Reactions of Dinuclear Palladium Complexes Containing Methyls and Hydride on Adjacent Palladium Centers: Reductive Elimination and Carbonylation Reactions

Article abstract of DOI:10.1021/ja00225a026

The transmetalation reaction of trimethylaluminum with the palladium chloride dimer Pd2Cl2(μ-dppm)2 (1) (dppm = bis(diphenylphosphino)methane) at -78 deg C gave an intermediate, Pd2ClMe(μ-dppm)2 (2), which disproportionated at ca. 10 deg C to yield the trans-face-to-face palladium dimer Pd2Cl2Me2(μ-dppm)2 (3) and a palladium dimer Pd2Cl2(μ-CH2)(μ-dppm)2 (5).The use of excess trimethylaluminum at -40 deg C gave the dimethyl complex, Pd2Me2(μ-dppm)2 (7).When 2 and 7 were protonated, a stable A-frame chloro-bridged dimer ⁺ (6) and a hydride-bidged dimer ⁺ (8) were obtained.Warming 6 in solution to ambient temperature caused the reductive elimination of methane; 8 lost methane and ethane at ambient temperatures.Both reductive eliminations were strictly intramolecular as determined by crossover experiments.The reaction of 6 with CO (1 atm) at -20 deg C first gave a carbonyl-bridged complex ⁺ (10) that rearranged to the acyl complex ⁺ (11) and then on warming eliminated acetaldehyde.The carbonylation of 8 (1 atm) proceeded stepwise to give first the mono- and then the diacyl complexes.The diacyl complex ⁺ (13) underwent the reductive elimination of acetaldehyde at ambient temperatures.