M⋯H–C interaction – Agostic or not: A comparison of phenyl- versus pyridyl-bridged transition metal dimers

•Helicate pincer complexes were structurally characterized.•Close M⋯H–C distances indicated possible agostic interactions in one complex.•Theoretical studies indicated weak hydrogen bonds – not agostic interactions.

Two transition metal complexes of 2,6-bis[N-(8-quinolyl)carbamoyl]pyridine (L1) and one of 2,6-bis[N-(8-quinolyl)carbamoyl]benzene (L2) were synthesized and structurally characterized. Nickel(II) and copper(II) complexes with L1 gave bifurcated-pyridine dimeric complexes (1 and 2). A copper(II) complex of L2 gave the dimeric complex, 3, in which the isophthaloyl C–H moieties of both ligands have short contacts with the pair of copper centers. Density functional theory calculations at the B3LYP/6-31G∗ and B97-D/6-31G∗ levels of theory offer strong supporting evidence that the Cu(II)⋯H–C interactions in 3 are best described as weak hydrogen bonds rather than agostic interactions.

Graphical abstractStructural results for three quinoline-appended amide-based pincers indicate helicate formation around Ni(II) and Cu(II) dimeric complexes. In the Cu(II) complex with the isophthalamide pincer a possible agostic C–H⋯M was observed and is the focus of this study.Figure optionsDownload full-size imageDownload as PowerPoint slide