H/D exchange at sp3 carbons in the coordination sphere of platinum(ii)

Abstract

The [PtCl(η¹-CH₂CH₂OR)(Me₂phen)], Me₂phen = 2,9-dimethyl-1,10-phenanthroline, complex is indefinitely stable in the solid state; however, when dissolved in protic deuterated solvents at basic pH, it undergoes H–D exchange at the Me₂phen Me's. An analogous H–D exchange process takes place in the related [PtCl₂(Me₂phen)] complex which is sterically strained and very easily can detach one nitrogen of Me₂phen yielding a T-shaped species. In contrast, the H–D exchange is considerably slower in the [Pt(OR)₂(Me₂phen)] complex characterized by smaller size and lower trans-labilizing effect of the oxygen donor ligands. It is suggested that the formation of a T-shaped intermediate could foster the C–H activation via oxidative addition to the metal centre. In accord with this hypothesis, the H/D exchange was found to be considerably slower in analogous complexes with 6,6′-dimethyl-2,2′-bipyridyl (Me₂bpy), where the greater flexibility of Me₂bpy, as compared to Me₂phen, reduces the strain in the four coordinate substrate and hence the propensity to dissociate one end of the bidentate ligand.