Porphyrins fused to N-heterocyclic carbene palladium complexes as tunable precatalysts in Mizoroki-Heck reactions: How the porphyrin can modulate the apparent catalytic activity?

摘要

Porphyrins fused to N-heterocyclic carbenes (NHCs) 1M, with inner metal M = Ni, Cu, Zn and H2, were used to synthesize palladium(II) complexes. These complexes behaved as precatalysts for high-temperature Mizoroki-Heck reactions between iodobenzene and styrene. Despite similar electronic properties between 1M ligands, catalytic activity was found to significantly depend on the presence, or not, of a central metal incorporated in the porphyrin core: a conversion of iodobenzene between 80-90% was observed with metalloporphyrins (M = Ni, Cu and Zn), whereas only 30% was observed with free-base porphyrins (M = H2) after 10 h. Palladium leaching and subsequent trapping of free palladium in the inner core of the free-base porphyrin modified the concentration of Pd(0) active species and may explain the lower catalytic activity observed. (C) 2015 Academie des sciences. Published by Elsevier Masson SAS. This is an open access article under the CC BY-NC-ND license.