Variation On The Pi-Acceptor Ligand Within A Rh-I-N-Heterocyclic Carbene Framework: Divergent Catalytic Outcomes For Phenylacetylene-Methanol Transformations

A series of neutral and cationic rhodium complexes bearing IPr {IPr=1,3-bis-(2,6-diisopropylphenyl)imidazolin-2-carbene} and pi-acceptor ligands are reported. Cationic species [Rh(eta(4)-cod)(IPr)(NCCH3)](+) and [Rh(CO)(IPr)(L)(2)](+) (L=pyridine, CH3CN) were obtained by chlorido abstraction in suitable complexes, whereas the cod-CO derivative [Rh(eta(4)-cod)(IPr)(CO)](+) was formed by the carbonylation of [Rh(eta(4)-cod)(IPr)(NCCH3)](+). Alternatively, neutral derivatives of type RhCl(IPr)(L)(2) {L=(BuNC)-Bu-t or P(OMe)(3)} can be accessed from [Rh(mu-Cl)(eta(2)-coe)(IPr)](2). In addition, the mononuclear species Rh(CN)(eta(4)-cod)(IPr) was prepared by cyanide-chlorido anion exchange, which after carbonylation afforded the unusual trinuclear compound [Rh{1 kappa C,2 kappa N-(CN)}(CO)(IPr)](3). Divergent catalytic outcomes in the phenylacetylene-methanol transformations have been observed. Thus, enol ethers, arisen from hydroalkoxylation of the alkyne, were obtained with neutral Rh-CO catalyst precursors whereas dienol ethers were formed with cationic catalysts. Variable amounts of alkyne dimerization, cyclotrimerization or polymerization products were obtained in the absence of a strong pi-acceptor ligand on the catalyst.