Variation on the π‐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 π ‐acceptor ligands are reported. Cationic species [Rh( η 4 ‐cod)(IPr)(NCCH 3 )] + and [Rh(CO)(IPr)(L) 2 ] + (L=pyridine, CH 3 CN) were obtained by chlorido abstraction in suitable complexes, whereas the cod‐CO derivative [Rh( η 4 ‐cod)(IPr)(CO)] + was formed by the carbonylation of [Rh( η 4 ‐cod)(IPr)(NCCH 3 )] + . Alternatively, neutral derivatives of type RhCl(IPr)(L) 2 {L= t BuNC or P(OMe) 3 } can be accessed from [Rh( μ ‐Cl)( η 2 ‐coe)(IPr)] 2 . In addition, the mononuclear species Rh(CN)( η 4 ‐cod)(IPr) was prepared by cyanide‐chlorido anion exchange, which after carbonylation afforded the unusual trinuclear compound [Rh{1κ C ,2κ 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 π‐acceptor ligand on the catalyst.