Synthesis, Characterisation, and Catalytic Evaluation of Ru-ONO Complexes Featuring N- and P-Based Ligands

Nine new ruthenium complexes featuring nitrogen and phosphorus donor ligands were synthesised from a Ru precursor featuring a rigid ONO-pincer ligand. The choice of nitrogen- and phosphorous-based ancillary ligands was guided by a careful evaluation of their different electronic and steric properties. This evaluation aimed to understand how these ligands, once coordinated, could influence the structural, electronic, and catalytic activity of the corresponding complexes. The range of complexes showed moderate catalytic activity in the transfer hydrogenation of alcohols, with the best performing catalyst achieving 96 % conversion in 1 hour (TON=96, TOF=96 h⁻¹). All complexes were characterised using ¹H, ¹³C, ³¹P (where applicable) NMR spectroscopy, CHN (microanalysis) and HR-MS analyses. Single crystal structures were obtained for all nine new complexes, as well two new polymorphs of the precursor complex. Complimentary electrochemical (cyclic voltammetry) and density functional theory (DFT) studies provided additional insights into the structural and electronic properties of the different complexes.