Conformational studies in palladium(IV) and platinum(IV) chemistry. Crystal structure of the l,l-bis(pyrazol-l-ethane complex fac-PtIMe3((pz)2CHMe-N,N'}

Abstract

The reaction of iodomethane with the l,l-bis(pyrazol-1-yl)ethane complex PtMe2{(pz)2CHMe-N,N’) gives the platinum(IV) complex fac-PtIMe3((pz)2CHMe-N,N’), which has been fully characterized, by, among other means, an X-ray structural study. The analogous palladium(IV) complex has also been prepared by a similar reaction in (CD3)2C0 at - 30°C and the two complexes exhibit similar 1H NMR spectra. For the palladium(IV) species, however, reductive elimination of ethane occurs above -30°C to give PdIMe((pz)2CHMe-N,N’). The 1H NMR spectra of the platinum(IV) and palladium(IV) complexes show that they are present in one configuration in solution, and large downfield shifts of the methine CHCH3 resonance, compared with the same proton in MMe2((pz)2CHMe-N,N’), are consistent with a conformation of the six-membered chelate ring that places the methine proton adjacent to the iodine attm. The octahedral platinum(IV) complex adopts this configuration in the solid state, with I...H = 3.1 A. The 1H NMR and structural studies support earlier assignments of solution behaviour for platinum(IV) and palladium(IV) complexes of related ligands, e.g. (pz)(py)CH, and (py)2CHMe (py = pyridin-2-yl), and confirm the influence of hydrogen...halogen interactions on 1H NMR spectra of octahedral complexes of this type.