Abstract
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.