Variation on the π‐Acceptor Ligand within a RhI−N‐Heterocyclic Carbene Framework: Divergent Catalytic Outcomes for Phenylacetylene‐Methanol Transformations

Abstract

AbstractA 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(η4‐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(η4‐cod)(IPr)(CO)]+ was formed by the carbonylation of [Rh(η4‐cod)(IPr)(NCCH3)]+. Alternatively, neutral derivatives of type RhCl(IPr)(L)2 {L=tBuNC or P(OMe)3} can be accessed from [Rh(μ‐Cl)(η2‐coe)(IPr)]2. In addition, the mononuclear species Rh(CN)(η4‐cod)(IPr) was prepared by cyanide‐chlorido anion exchange, which after carbonylation afforded the unusual trinuclear compound [Rh{1κC,2κN‐(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.