Intermolecular vinylic carbon-hydrogen bond activation by a doubly-bonded organoditantalum complex

Abstract

Intermolecular C-H bond activation of hydrocarbons, in particular alkanes, by organotransition-metal species is a reaction of fundamental modeling importance for future efforts at hydrocarbon functionalization. Examples of hydrocarbon oxidative addition and of alkyl/hydrocarbon exchange have been reported with organometallic complexes of the late transition metals, metals from groups 6 and 7, and the lanthanides/actinides, but there are no examples of intermolecular alkane or vinylic C-H bond activation with metals from groups 4 and 5. Intermolecular vinylic C-H bond activation is an underrepresented area in hydrocarbon C-H bond activation by organometallics, with few mononuclear and dinuclear, as opposed to polynuclear, examples. The kinetic and thermodynamic differences between C-H activation involving the low-valent late metal and the high-valent lanthanide/actinide complexes suggest that intervening metal complexes, such as intermediate valent group 5 species, may exhibit optimal properties in C-H activation; the propensity for electronic unsaturation in complexes of these metals may lead to successful functionalization studies. Intramolecular ligand metalations and arene H/D exchange reactions with Nb and Ta complexes have been reported, and in principle intermolecular vinylic and alkane C-H bond reactivity should be feasible. They wish to report the first examples of isolable intermolecular vinylic C-H activation by an early transition-metal (groupsmore » 4 and 5) organometallic and by a metal-metal multiply bonded complex.« less