Activation of Molecular Hydrogen by Arylcarbenes

Abstract

The hydrogenation reactions of diphenylcarbene 1, fluorenylidene 2, and dibenzocycloheptadienylidene 3 were investigated in solid H-2 and D-2 matrices and in H-2- and D-2-doped argon matrices at cryogenic temperatures. The reactivity of the carbenes towards H-2 increases in the order 1<3<2. Whereas 1 is stable in solid H-2, 2 and 3 react fast under the same conditions via quantum chemical tunneling. In D-2 both 1 and 3 are stable, whereas 2 slowly reacts. The different reactivity of the three carbenes is rationalized in terms of differing carbene stabilization energies.