Novel stereoelectronic properties of 5-coordinate ruthenium(0) complexes

Abstract

We report the synthesis and analysis of five-coordinate 18-electron (formally) PNP–Ru(0) halido nitrosyl complexes (PNP)RuX(NO) (X = I, Br, Cl). These compounds show substantial geometric deviation from literature-reported isoelectronic analogs. Instead of the typical trigonal bipyramidal or square pyramidal structures, they adopt a Y-shaped distorted trigonal bipyramidal geometry, which is unprecedented for formal d⁸ complexes. Demonstrating further non-classical behavior, in the distorted trigonal plane, the π-donating halido ligand (X) and the PNP amine form the acute bond angle, while the π-accepting NO resides in the obtuse coordination site, and it is evident from SC-XRD, IR, and multinuclear NMR spectroscopy that the nature of the X ligand influences the degree of distortion. In addition to the spectroscopic and crystallographic analyses, the nature of the rare and, for 5-coordinate species, unprecedented X–Ru(0) bond is assessed by means of natural population analysis and orbital interactions. The computational and spectroscopic results show a clear dependence on the π-donating capability and the electronegativity of the X ligand. Finally, DFT analysis of the hypothetical structures (PNP)RuF(NO) and (PNP)Ru(OMe)(NO) at the PBE0 and TPSSh levels of theory corroborated our experimental findings.