Stabilization of cyclic and acyclic carbon(0) compounds by differential coordination of heterocyclic carbenes: a theoretical assessment.

Recently, donor stabilized divalent carbon(0) compounds have undergone intense experimental and theoretical investigation due to their strong electron rich character. In this Article, some new cyclic and acyclic carbon(0) compounds stabilized by differential coordination modes (such as abnormal, remote and a mixture of both) of N-heterocyclic carbenes are studied theoretically. The cyclic carbon(0) compounds proposed in this study are unusual in the sense that they contain a five membered ring consisting of only carbon atoms with a central carbon atom in the formal oxidation state of zero. All these compounds are found to be very strong nucleophiles which might have wide implications in catalysis. Calculation of first proton affinities of these molecules reveal that they are better σ donors than the carbon(0) compound supported by normal N-heterocyclic carbenes. Quantum chemical calculations indicate that these molecules possess very high donor-acceptor L → C bond strengths and are thermodynamically stable. Calculation of the bond dissociation energies for the complexation of one and two molecules of AuCl indicates the possible isolation of their gem dimetalated derivatives.