Herein, we wish to describe the efficient three-step synthesis of a novel highly hindered, but flexible, N-heterocyclic carbene and its coordination chemistry to Ag(i) and Rh(i).

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New C2-symmetric bicyclo[2.2.1]hepta-2,5-dienes bearing methyl and phenyl substituents at the 2 and 5 positions were prepared enantiomerically pure through a two-step sequence starting from the readily available bicyclo[2.2.1]hepta-2,5-dione. Due to the instability or volatility of these dienes, their isolation was achieved through the formation of the corresponding stable [RhCl(diene)]2 complexes. These chiral rhodium complexes displayed high activity and enantioselectivity (up to 99% ee) in the rhodium-catalyzed 1,4-addition and 1,2-addition of phenylboronic acid to cyclic enones and N-sulfonylimines, respectively.

The hydrosilylation of terminal alkynes by silanes catalyzed by N-heterocyclic carbene platinum(0) complexes has been investigated. The alkynes included 1-octyne and phenylacetylene. The silanes investigated were bis(trimethylsilyloxy)methylsilane, (trimethylsilyloxy)dimethylsilane, tert-butyldimethylsilane, triphenylsilane, phenyldimethylsilane, triethylsilane, and triethoxysilane. X-ray crystal structures for [Pt(N,N‘-dicyclohexylimidazol-2-ylidene)(η2-dimethylacetylenedicarboxylate)2] (8) and [Pt{C(E)C(E)−C(E)C(E)}(N,N‘-dimethylbenzimidazol-2-ylidene)(σ-NCCH3)] (10) (E = CO2Me) have been obtained. A selectivity model, based on structural parameters of the N-heterocyclic carbene, has been devised in order to rationalize the observed regioselectivity obtained. By a judicious choice of catalyst, alkyne, and silane, the regioselectivity of the addition can be controlled.