CONFORMATIONAL STUDIES IN PALLADIUM(IV) AND PLATINUM(IV) CHEMISTRY - CRYSTAL-STRUCTURE OF THE 1,1-BIS(PYRAZOL-1-YL)-ETHANE COMPLEX FAC-PTIME3((PZ)2CHME-N,N')

The reaction of iodomethane with the 1,1-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)2CO at - 30-degrees-C, and the two complexes exhibit similar 1 H NMR spectra. For the palladium(IV) species, however, reductive elimination of ethane occurs above - 30-degrees-C to give PdIMe[(pz)2CHMe-N,N'). The H-1 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 atom. The octahedral platinum(IV) complex adopts this configuration in the solid state, with I...H = 3.1 angstrom. The H-1 NMR and structural studies support earlier assignments of solution behaviour for platinum(IV) and palladium(IV) complexes of related ligands, e.g. (pz)(py)CH2 and (py)2CHMe (py = pyridin-2-yl), and confirm the influence of hydrogen ... halogen interactions on H-1 NMR spectra of octahedral complexes of this type.