Nuclear magnetic resonance investigations of configurational non-rigidity in dinuclear platinum(IV) complexes. Part 5. Intra-molecular rearrangements in the dinuclear platinum(IV) complexes of 1,3,5,7=tetrathiocane. X-Ray Crystal Structure of [(PtClMe3)2-(SCH2SCH2SCH2SCH2)]

Abstract

The complexes [(PtXMe3)2(bCH2SCH2SCH2SkH2)] (X = CI, Br, or I) have been prepared by direct reaction of 183,5,7-tetrathiocane with the appropriate halogenotrimethylplatinum(iv) tetramer, [ (PtXMe,),] (X = CI, Br, or I). The X-ray crystal diffraction structure of [(PtCIMe3)2(SCH2SCH2SCH2SCH2)] shows the dimeric platinum moiety to be 1,3-co-ordinated to the ligand which has a chair-boat conformation. Low-temperature H n.m.r. spectroscopy confirms such a structure to be retained in solution for all three complexes. Lineshape changes observed in variable-temperature 1 H n.m.r. investigations are consistent with the complexes undergoing metal-pivot and platinum-methyl intramolecular rearrangements. Alternative mechanisms are discussed for both processes. It is concluded that the former comprises a series of 90" 1,5-metal pivots, and the latter, 120" rotations of methyl groups on the commuting Pt atom. Full bandshape analyses have been undertaken for both motions. Evidence is presented in support of the two fluxions being different manifestations of one transition state rather than independent rearrangements.