Cycloruthenation of N ‐(Naphthyl)salicylaldimine and Related Ligands: Utilization of the Ru–C Bond in Catalytic Transfer Hydrogenation

Abstract

Upon reaction with [Ru(PPh3)2(CO)2Cl2], N-(naphthyl)-4-R-salicylaldimines (R = OCH3, H, Cl; H2L1–H2L3) and 2-hydroxy-N-(naphthyl)naphthaldimine (H2L4) readily undergo cycloruthenation by C–H bond activation at the peri position to afford complexes of the type [Ru(PPh3)2(L)(CO)] (L = L1–L4). The crystal structures of the [Ru(PPh3)2(L)(CO)] (L = L1, L2, L4) complexes were determined and the structure of [Ru(PPh3)2(L3)(CO)] optimized by DFT calculations. The thermodynamics for the reaction of [Ru(PPh3)2(CO)2Cl2] with H2L2 to give [Ru(PPh3)2(L2)(CO)] were determined. All the complexes show intense absorptions in the visible and UV regions, which have been analyzed by TDDFT calculations. Cyclic voltammetry of the four cycloruthenated complexes showed two oxidations within the range 0.50–1.35 V versus SCE and a reduction at around –1.75 V versus SCE. The [Ru(PPh3)2(L)(CO)] (L = L1–L4) complexes were found to efficiently catalyze the transfer hydrogenation of carbonyl compounds.