Mechanism for thermal generation of transient rhenium(0) radicals. Reaction of a (triphenylmethyl)rhenium complex with two-electron ligands

Article abstract of DOI:10.1021/om00118a017

Reaction of (η³-CPh₃)Re(CO)₄ (1) with 2 equiv of the cage phosphite 1-methyl-4-phospha-3,5,8-trioxabicyclo[2.2.2]octane (MPTB) results in formation of mer-trans-Re(CO)₃(MPTB) ₂(4-(diphenylmethylene)cyclohexa-2,5-diene) (2a). In solution at 233 K, 2a isomerizes to the facial-cis isomer 2b. At higher temperatures, 2a and 2b decompose via metal-alkyl bond homolysis to give Ph₃C radicals and the transient Re(0) radicals Re(C0)₃(MPTB)₂, which decompose. The reactivity of (η³-CPh³)Re(CO)₄ toward other neutral two-electron phosphorus donor ligands is similar, but the corresponding rhenium-alkyl products Re(CO)₃P₂(4-(diphenylmethylene)cyclohexa-2,5-diene) could not be isolated from solution. Instead, they were derivatized with use of Ph₃SnH or CCl₄ to the corresponding hydrides or chlorides. Several mechanisms that could account for the observed reactivity of 1 with phosphines and phosphites to generate transient Re(0) radicals are discussed.