C—H activation by organometallics: The role of matrix isolation studies

Abstract

Advances are reported in the application of matrix isolation in combination with solution techniques to the study of C-H activation reactions of organometallics. Laser-induced fluorescence proves applicable to all the open-shell metallocenes studied, (75-CsHs) M (M = Mo, W, Re) and (75-C5Me5),Re. Studies with pulsed dye-lasers allow the determination of excitation spectra and the emission lifetimes. Three types of situation are encountered when the behaviour of photoproducts in matrices is compared with that in solution. In the type 1 situation, a coordinatively unsaturated intermediate is stabilised by the matrix. It may be observed in solution using time-resolved spectroscopy if the matrix and solution studies share a common spectroscopic technique (e.g. Ru(Me,PCH,CH,PMe,),). In type 2 reactions, photolysis leads to an unstable isomer of the precursor. Such species may often be observed by NMR following photolysis of solutions or frozen solutions at low temperature. The cage formed by the matrix or viscous solvent may play a significant role in this type of reaction as, for instance, in the isomerisation of some metal-ethene complexes. Type 3 reactions involve intermolecular reaction in the matrix (e.g. (75.-C5H )Rh(CO), with methane), but the products of reaction may be very labile. ?he corresponding reactions with alkanes may be observed by laser flash photolysis with the aid of a common spectroscopic method. © 1990 IUPAC