Metal-proton interactions in benzylamine complexes of palladium(II): The effect of methyl substitution at nitrogen and the role of the interaction during cyclopalladation. X-ray crystal structure of tetrabenzylaminepalladium(II) acetate chloride

Abstract

Reaction of Pd(O₂CMe)₂ with PhCH₂NH₂ leads to either Pd(NH₂CH₂Ph)₂(O₂CMe)₂ or [Pd(NH₂CH₂Ph)₄] [O₂CMe]₂. The X-ray crystal structure of [Pd(NH₂CH₂Ph)₄] [Cl] [O₂CMe] shows pairs of [Pd(NH₂CH₂Ph)₄]²⁺ ions held together by hydrogen bonds from the NH proton to chlorine and oxygen atoms of the anions, and the absence of interactions between phenyl ring ortho protons and the metal. PhCH₂NHMe reacts with Pd(O₂CMe)₂ giving Pd(NHMeCH₂Ph)₂(O₂CMe) and PhCH₂NMe₂ gives the cyclometallate [Pd(NMe₂CH₂Ph-C,N)(µ-O₂CMe)]₂. ¹H N.M.R. spectra indicate that the complexes Pd(NMe₂CH₂Ph)(L)(O₂CMe)₂ (L = PhNH₂, o-MeC₆H₄NH₂) prepared from [Pd(L)(O₂CMe)(µ-O₂CMe)]₂, contain an interaction of the benzylamine ortho aromatic protons with the metal whereas Pd(NHMeCH₂Ph)(L)(O₂CMe)₂ (L = o-MeC₆H₄NH₂) does not. ¹H n.m.r. analysis of PdCl₄²- and PhCH₂NMe₂ in (²H_l)methanol at 400 MHz indicates a 1 : 1 reaction stoichiometry and metal-proton interactions in intermediates containing above-plane and in-plane geometry of the aromatic ring, before metallation takes place. A 400-MHz spectral analysis of Pd(O₂CMe), and PhCH₂NMe₂ in CDCl, suggests similarly orientated species arise in the reaction giving [Pd(NMe₂CH₂Ph-C,N)(µ-O₂CMe)]₂.