Molecular conformations and pi-hydrogen bonds in anti- and syn- binuclear Rh(I) complexes of as-indacene-diide: a computational study

Ab initio calculations are employed to interpret the different conformations in mono- and bi-nuclear Rh(I) derivatives of as-indacene, observed by X-ray crystallography. In particular, we discuss the quite unusual COD (1,5-cyclooctadiene) group orientation in the homo-bimetallic complex anti-{2,7-dimethyl-as-indacene-diide-[Rh(COD)]2}, which is related to the metal hapticity and is stabilised by the presence of π-hydrogen bonds between olefin protons of COD and the π-electron cloud of the six-membered ring of the bridging ligand. Finally, the structure of syn-{2,7-dimethyl-as-indacene-diide-[Rh(COD)]2} is treated where mainly steric constraints appear to control the spatial disposition of the ancillary ligands. Second-order perturbative natural bond orbital (NBO) analysis provides a meaningful picture of non-covalent intramolecular C–H⋯C(π) interactions.