Trimethylpalladium(IV) chemistry. Conformational and fluxional effects in related palladium(IV) and platinum(IV) complexes of flexible bidentate nitrogen donor ligands

Iodomethane reacts with palladium(II) complexes PdMe2(L2), where L2 is a flexible nitrogen donor ligand such as l,l-bis(pyridin-2-yl)ethane [(py)2CHMe], to form unstable trimethylpalladium(IV) complexes characterized as fac-PdIMe3(L2) by comparison of their variable temperature 1H NMR spectra with those of stable trimethylplatinum(IV) analogues. The complexes fac-MIMe3{(py)2CHMe} occur as mixtures of isomers, with the chelate ring having the CH group adjacent to iodine in one isomer and adjacent to the methyl group trans to iodine in the other isomer. Complexes containing pyrazol-l-y1 (pz) or N-methylimidazol-l-y1 (mim) donors, fac-MIMe3(L2) [L2 = (pz)2CH2, (pz)(mim)CH2, and (py)(pz)CH2] undergo fluxional behaviour involving inversion of the six-membered chelate rings.