Chasing the agostic interaction in ligand assisted cyclometallation reactions of palladium(ii)

• Published in: Dalton transactions : an international journal of inorganic chemistry 2017, Vol.46 (46), p.16126-16138
• Main Authors: Sajjad, M Arif, Christensen, Kirsten E, Rees, Nicholas H, Schwerdtfeger, Peter, Harrison, John A, Nielson, Alastair J
• Format: Article
• Language: English
• Subjects: Acetophenone; Crystallography; Density functional theory; Electron density; Electrons; Imines; Mathematical analysis; NMR; Nuclear magnetic resonance; Palladium
• ISSN: 1477-9226; 1477-9234
• DOI: 10.1039/c7dt03525j

A 500 MHz NMR study of the reaction between 1-tetralone oxime and PdCl in CD OD shows resonances attributable to a potential agostic intermediate prior to the formation of the insoluble cyclopalladated product which itself was characterised by X-ray crystallography. Calculated structural, spectroscopic, QTAIM, NBO and NCI analysis results obtained from density functional theory (DFT) calculations give a full description of the putative agostic intermediate [PdCl (1-tetralone oxime)] (1) which is shown to include a previously unrecognised π-electron density donation from the aromatic ring to the metal in close proximity to the agostic carbon atom. Changing the (N)-OH donor to (N)-OMe does not effect the magnitude of these interactions. (N)-OH and (N)-OMe acetophenone imines in which the aromatic ring has the potential to rotate show similar agostic and π-electron donation to the alicyclic ring counterparts. 1-Tetralone which coordinates to the metal by a Pd-O bond that is much weaker than the Pd-N complexes has a slightly stronger agostic component and slightly weaker π-electron donation than the oxime counterpart.