Solution structure investigations of olefin Pd(II) and Pt(II) complex ion pairs bearing α-diimine ligands by 19F, 1H-HOESY NMR

Complexes [M(η1,η2-C8H12OMe)((2,6-(R)2C6H3)NC(R′)C(R′)N((2,6-(R)2C6H3))]PF6 (where M=Pd, R=H and R′2=Me2 (1), M=Pd, R=Me and R′2=Me2 (2), M=Pd, R=Et and R′2=Me2 (3), M=Pd, R=iPr and R′2=Me2 (4), M=Pd, R=iPr and R′2=An (5), M=Pt, R=iPr and R′2=An (6)) were synthesized by the reaction of [M(η1,η2-C8H12OMe)Cl]2 with the appropriate α-diimine ligand in the presence of NH4PF6. Their ion pair structure in solution was investigated by detecting dipolar interactions between protons belonging to the cation and fluorine nuclei of the anion (interionic contacts) in the 19F, 1H-HOESY NMR spectra. In complexes 1–4, the anion in solution is located close to the peripheral protons of the α-diimine ligand and it interacts with the R′ protons and with the R protons that point toward the R′ groups. The steric protection of apical position exerted by the R substituents is clearly illustrated by the absence of interionic contacts between any protons of the cycloctenylmethoxy-moiety and the anion for R≥Me in 1–4. In complexes 5 and 6 the interactions between the anion and the peripheral N,N protons also predominate but other anion–cation orientations are significantly present and, consequently, the interionic structure is less specific.