Radiation enhancement of the catalytic properties of three-dimensional coordination polymers of Ru(II) with diisocyanide ligands

Coordination polymers are drawing increasing attention due to their versatility in structure and function, and their potential applications as catalysts. These polymers may be synthesized by using aryldiisocyanides, which when coordinated to a d6 metal such as Ru(II), act as bridges and give rise to two distinct types of three-dimensional polymeric networks. Polymer A, [Ru(1,4-diisocyanobenzene)_4/2²⁺(2Cl)^2-] _n has a tetragonal geometry, having, most likely, Ru-Ru stacking interactions in the z direction, while polymer B, [Ru(1,4-diisocyanobenzene)_6/2²⁺(2Cl)^2-] _n has a cubic geometry, having all the Ru atoms separated by the 1,4-diisocyanobenzene ligands. In the hydrogenation reaction of 1-hexene, polymer A is an efficient but a non-selective catalyst. The hydrogenation reaction is accompanied by isomerization, with trans 2-hexene as the leading isomer, which is hydrogenated as well after all the 1-hexene has been used up. The catalytic reaction proceeds with an induction period which suggests that polymer A in its original structure is not the actual catalyst. Irradiation of the reaction mixture with 350 nm UV light prior and during the catalytic reaction drastically reduces the induction period. This indicates that the energy of irradiation is sufficient to break the Ru-Ru stacking bonds, thus creating electron-deficient Ru sites prior to the addition of the olefin. An in-depth study of the influence of irradiation on the kinetics of the catalytic reaction is presented in this paper.