Static and dynamic nuclear magnetic resonance studies of complexes of trimethylplatinum(IV) halides with olefinic thio- and seleno-ethers. X-Ray crystal structures of [PtXMe3(MeSeCHCHSeMe)](X = Cl or I)

Abstract

Complexes of general type [ PtXMe₃(MeECHCHEMe)](E = S or Se; X = Cl, Br, or I) have been isolated and their solution and solid-state structures established. Static structures in solution were characterised by ¹H, ¹³C, ⁷⁷Se, and ¹⁹⁵Pt n.m.r. parameters; the dynamic stereochemistry of these complexes, arising from low-temperature chalcogen inversion and high-temperature fluxional rearrangements, was studied quantitatively by variable-temperature ¹H n.m.r. spectroscopy. Correlations were found between ^l95Pt and ⁷⁷Se chemical shifts, and between ¹⁹⁵Pt shifts and ¹J(PtSe) values in these complexes. ¹J(CPt) values can be interpreted in terms of trans influence effects. The solution invertomer populations are very halogen- and temperature-dependent. In the case of selenium complexes, the predominant invertomer in solution corresponds to the single solid-state configuration as determined by X-ray crystallography. For the chloro-complex this is the meso-1 form and for the iodo-complex the meso-2 species. The effects of π-conjugation on the energies of the chalcogen inversion and platinum-methyl scrambling processes are discussed by comparing ΔG^‡(298.15 K) values with those for analogous complexes with aliphatic and aromatic chalcogen ligands.