Photolysis of alkyloxy vanadium(V) chelates. A possible general route to alkyloxy radicals

Abstract

We have studied the photochemical reactions (λ= 365 nm) of nineteen vanadium(V) chelates of structure VOQ2OR where Q is the 8-quinolyloxo ligand and R is an alkyl group. In all cases photolysis proceeds in a first-order fashion to yield the vanadium(IV) chelate VOQ2 identified by u.v.-visible and e.s.r. spectroscopy. The VV chelates photoinitiate free-radical polymerization and the quantum yields of photoinitiation with methyl methacrylate as monomer have been determined and compared with the quantum yields of chelate photodecomposition. Each molecule of chelate decomposing gives rise to one initiating radical.

The dependence of the quantum yield of photodecomposition ϕd on the nature of R is discussed. The inductive effect of R, which influences the natures of the V[double bond, length as m-dash]O and V—OR bonds, also affects ϕd and a correlation between the stretching frequency of V[double bond, length as m-dash]O and ϕd has been found.

The photolytic products in benzene solution have been examined by spin-trapping and g.l.c. techniques; results are consistent with the primary formation, isomerization and β-scission of alkyloxy radicals.