Photo-Redox Mechanism for the Reaction of “Cation-like” Zirconocene Silyl Complexes with Silanes

A kinetic study of the photochemical reaction of [Cp 2 Zr(μ-SiH 2 Ph)] 2 2+ 2[BBu n (C 6 F 5 ) 4 - n ] - ( 1 ) with PhCH 2 SiH 3 to give the analogous PhCH 2 SiH 2 complex 2 was carried out using a combination of NMR and EPR spectroscopy to follow the rates of disappearance of reactants and the appearance of intermediates and products. The paramagnetic intermediate [Cp 2 Zr III ] + [BBu n (C 6 F 5 ) 4 - n ] - ( 3 ) is produced with a quantum efficiency of 0.96 ± 0.16 on irradiation of 1 with light having λ < 450 nm. The rate law and analysis of intermediates supports a Zr(IV)/Zr(III) redox mechanism in which the rate-determining step is photodecomposition of 1 to generate 3 and silyl radicals by homolytic dissociation. In the presence of excess PhCH 2 SiH 3 3 reacts rapidly to give products.