Phosphonium coupling reaction mechanism

Hillhouse and co-workers discovered a new route to carbyne complexes which is based on the reverse of carbyne-carbonyl coupling (J72). Reaction of complex 200 with carbon suboxide affords the ketenyl complex 201 [Eq. (159)]. Formation of the ketenyl ligand in 201 was postulated to arise from attack of phosphine on an intermediate ketenylidene complex. Warming of complex 201 results in cleavage of the ketenyl ligand and formation of the phosphonium carbyne complex 202. This mechanism was put to work in a more direct fashion by reaction of complex 200 with PhjPCCO [Eq.(160)]. 

A more detailed study into the mechanism of ruthenium bimetallic melt catalysis for alcohol/ester production has been undertaken for the ruthenium-cobalt combination. Specifically, for the triruthenium dodecacarbonyl-dicobalt octacarbonyl couple, dispersed in tetrabutyl-phosphonium bromide, we have defined the experimental limits of this catalysis, demonstrated multiple catalyst recycle (7) and most importantly, identified some of the relationships linking catalyst productivity, alcohol-ester carbon distributions, and certain key operating parameters with the catalytically active metal carbonyl species present in these reaction media. 

---