Functionalized N‑Heterocyclic Carbene Nonspectator Ligands upon Internal Alkyne Activation Reactions

Abstract

When studying the activation of 3-arylpropiolates by [TpRu(picolyl-RI)Cl]/NaBArF 4 (picolyl-MeI = 3-methyl-1-(2- picolyl)imidazol-2-ylidene (1); picolyl-MeBI = 3-methyl-1-(2- picolyl)benzoimidazol-2-ylidene (2)) a migratory insertion of the NHC into a ruthenium−carbon bond and an unprecedented C−N bond activation of the chelating picolyl-NHC ligand take place to give the new ruthenium metallacycles [TpRu(κ3-C,N,N′- =C(Ph) = C(CH2Py)(CO2Me)(MeI)][BArF 4] 3a and 4a and [TpRu(κ3-C,N,N′-=C(4-CF3Ph) = C(CH2Py)(CO2Me)(MeI)]- [BArF 4] 3b and 4b. X-ray crystal structures of 3a and 3b are reported, and a mechanistic pathway is proposed. In contrast, activation of internal alkynones by a mixture of [TpRu(picolyl-MeI)Cl] complex (1) and NaBArF 4 led to isolation and characterization of the corresponding disubstituted vinylidene complexes. Also, structures of [TpRu(picolyl-MeI)(= CC(COR)(Ph)][BArF 4] (R = Me (6a); Ph (6b)) are reported.