Mechanism of Re2(CO)10 Substitution Reactions: Crossover Experiments with 185Re2(CO)10 and 187Re2(CO)10

Article abstract of DOI:10.1021/ja00342a029

185Re2(CO)10 and 187Re2(CO)10 were prepared separately and then utilized in combination in crossover experiments to probe for fragmentation to mononuclear rhenium species in thermal and photochemically initiated substitution reactions.For the CO-Re2(CO)10 exchange reaction, a reaction separately analyzed for 13CO-12CO interchange, no crossover was observed at 150 deg C after 14 half-lives of reaction (14 h).Similarily, the thermal reaction sequences of Re2(CO)10 + P(C6H5)3 = Re2(CO)9P(C6H5)3 + CO and Re2(CO)9P(C6H5)3 + P(C6H5)3 = Re2(CO)82 + CO were examined at 150 deg C (maintaining a CO pressure of ca. 560-640 mm).No crossover was detectable in either Re2(CO)10 or Re2(CO)9P(C6H5)3 (relative to blank experiments).Hence, phosphine substitution reactions proceed without a detectable formation of mononuclear rhenium species.These observations support a CO dissociative mechanism.A model based upon this mechanism can accurately reproduce the mass spectra observed during 13CO-12CO interchange.In the absence of a CO atmosphere, 185Re2(CO)10 and 187Re2(CO)10 formed 185Re187Re(CO)10 and this interchange was nearly complete at 150 deg C within 14-16 half-lives.All photochemically initiated reactions with the two labeled decacarbonyls led to complete crossover within short reaction times.It appears then that the primary mode of reaction for Re2(CO)10 under photolysis conditions involves Re-Re bond scission as an early elementary step.Also, the reversible steps leading to the precursor(s) to Re2(CO)10 decomposition include scission of the rhenium-rhenium bond.