Alkenyl-functionalized NHC iridium-based catalysts for hydrosilylation

A family of alkenyl-functionalized N-heterocyclic-carbene-iridium(I) complexes has been synthesized, providing a series of mono-coordinated, bis-chelate and pincer alkenyl-NHC species. Olefin coordination is highly influenced by the nature of the substituents on the NHC ring, and on the length of the alkenyl branch. A fluxional process involving coordination/decoordination of the olefin in bis-allyl-NHC complexes has been studied, and the activation parameters have been determined by means of VT-NMR spectroscopy. The mono-coordinated complexes are highly active in the hydrosilylation of terminal alkynes, showing high selectivity for the Z-isomers, with no alpha-isomers or dehydrogenative silylation processes being observed. The molecular structures reported that are representative of the species have been determined by means of X-ray crystallography.