Coordination properties of unsymmetrical Schiff base ligands containing N3 donor sets when restricted to bidentate chelate bonding modes. Crystal structures of fac-[PtIMe3(PMAMP)] (PMAMP=2-{(2′-pyridylmethylene)aminomethyl}pyridine) and fac-[PtIMe3(PMAQ)]

The N3 ligands 2-{(2′-pyridylmethylene)aminomethyl}pyridine, (PMAMP), 8-{(2′-pyridylmethylene)amino}quinoline, (PMAQ) and 2-[{(6′-methyl-2′-pyridyl)methylene}aminomethyl]pyridine (MPMAMP) are analogous to 2,2′:6′,2″-terpyridine in respect of their spatial arrangement of N donor atoms. When acting as bidentate chelates PMAMP and PMAQ bind exclusively to the PtIV moiety PtIMe3 such that the five-membered chelate rings incorporate the imine bond. This was deduced by detailed solution NMR studies and X-ray crystal structures. In contrast, the ligand MPMAMP, with 6-methyl substitution of the pyridyl ring attached to the carbon of the imine bond, preferentially, but not exclusively, coordinates to the nitrogen of the other pyridyl ring. The population ratio of the two complexes formed was 6:1 (303 K, CDCl3 solution), but there was no NMR evidence of exchange between these species, in the temperature range 303–413 K, resulting from 1,4-metallotropic shifts, as occurs in analogous complexes such as fac-[PtIMe3(2,2′:6′,2″-terpyridine)].