Reactivity of N-Heterocyclic Carbenes with [Ru3(CO)12] and [Os3(CO)12]. Influence of Ligand Volume and Electronic Effects

• Published in: Organometallics 2008-01, Vol.27 (2), p.211-217
• Main Authors: Cabeza, Javier A, del Río, Ignacio, Miguel, Daniel, Pérez-Carreño, Enrique, Sánchez-Vega, M. Gabriela
• Format: Article
• Language: English
• ISSN: 0276-7333; 1520-6041
• DOI: 10.1021/om7009655

The room-temperature reactions of [Ru3(CO)12] and [Os3(CO)12] with a variety of N-heterocyclic carbenes (NHCs) have been studied. [Ru3(CO)12] reacts easily with N,N′-dimethylimidazol-2-ylidene (Me2Im), more slowly with N-methyloxazol-2-ylidene (MeOx), and very slowly with N,N′-dimesitylimidazol-2-ylidene (Mes2Im) to give the corresponding CO substitution products [Ru3(NHC)(CO)11], but it does not react with the very bulky N,N′-bis(2,6-diisopropylphenyl)imidazol-2-ylidene (Dipph2Im). DFT calculations have shown that [Ru3(Dipph2Im)(CO)11] is a minimum in the corresponding potential energy surface; therefore, the absence of reaction between [Ru3(CO)12] and Dipph2Im has a kinetic origin associated with the large volume of this NHC. [Os3(CO)12] reacts with Me2Im to give [Os3(Me2Im)(CO)11]. However, MeOx is not basic enough and Mes2Im and Dipph2Im are too bulky to react with [Os3(CO)12], which is less reactive than [Ru3(CO)12]. Therefore, the reactions of [Ru3(CO)12] and [Os3(CO)12] with NHCs are strongly influenced by the electronic properties and steric demands of the NHCs and also by the intrinsic reactivity of the metal–carbonyls.