Nuclear magnetic resonance investigations of configurational nonrigidity in dinuclear platinum(IV) complexes. Part 3. Novel fluxional rearrangements in [(PtXMe3)2(SCHRSCHRECHR)](X = Cl, Br, or I; R = H or Me; E = S or CH2) complexes

Abstract

The title complexes have been synthesised for the first time. For the complex with R = H and E = S, X-ray and n.m.r. data indicate that the six-membered trithian ring adopts a boat conformation. Novel fluxional rearrangements in this complex have been studied by dynamic n.m.r. methods. One of these processes involves a series of 60° pivots of the cyclic ligand about individual S → Pt bonds which average the ligand-methylene and equatorial Pt–Me environments. The energy (ΔG^‡) of this process has been computed to be 58.6 kJ mol^–1 and is halogen independent. A higher-energy process associated with ligand dissociation–recombination involves a scrambling of the Pt–Me groups. For the complex with R = H and E = CH₂, where the sulphur-pivot process cannot take place, only Pt–Me scrambling occurs. For the complex with R = Me and E = S, where the ligand ring adopts the usual chair conformation, the ligand-methyl groups prevent the pivot process from occurring at a measurable rate.