The cationic hydride alkylidene complexes [TpMe2Ir(═CH−CH3)(H)(PMe3)]+ and [Cp*Ir(═CH−CH3)(H)(PMe3)]+ (TpMe2 = hydrotris(3,5-dimethyl-1-pyrazolyl)borate; Cp* = pentamethylcyclopentadienyl) are experimentally known to tautomerize to the corresponding hydride alkene species. Our computational study on the mechanism shows that the reaction takes place through formation of the corresponding alkyl intermediates, with participation of species involving α- and β-CH agostic interactions. Computed energy barriers reproduce the available experimental kinetic data and agree with a much faster process in the Cp* system. The highest stabilization of the hydride alkylidene complex (the reactant) in the TpMe2 system appears as the main reason for the higher barrier found. The difference between the two complexes is due to the steric effects of the spectator ligands.

We thank the ICIQ Foundation, the Spanish Ministerio de Ciencia e Innovacion (Consolider Ingenio 2010 CSD2006-0003 and CSD2007-000006; projects CTQ2007-62814, CTQ2008-06866-CO2-01/BQU, CTQ2008-06866-CO2-02/BQU, and CTQ2008-03077/BQU, FEDER support), Generalitat de Catalunya (grants 2009SGR0259 and XRQTC), and Junta de Andalucia (project numbers FQM-315 and FQM-67). M.B. thanks the Spanish Ministerio de Ciencia e Innovacion for a “Juan de la Cierva” grant.

6 páginas, 3 figuras, 5 esquemas.

Peer reviewed