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2,4,6-Trimethylnitrosobenzene in CDCI3 exists as a mixture of monomer and Z- and E-azodioxy dimers. The dissociation kinetics of both dimers were measured by one-dimensional time-dependent NMR spectroscopy on non-equilibrium solutions, and by two-dimensional exchange spectroscopy (2D-EXSY) on equilibrium solutions. 2,4,6-Tri-t-butylnitrosobenzene is entirely monomeric in CDCl3 but forms mixed azodioxy dimers in the presence of nitrosobenzene. The dissociation kinetics of the mixed E-dimer were followed by NMR techniques. The activation energy parameters for these dissociation equilibria were compared with previous data on related nitrosobenzene and dimethylnitrosobenzene systems.

Trimethylplatinum(IV) iodide complexes with ditelluroether ligands, namely [PtlMe3(L–L)][L–L = MeTe(CH2)3TeMe, PhTe(CH2)3TePh or o-C6H4(TeMe)2] have been isolated as pure solids. 195Pt-{1H} and 125Te-{1H} NMR studies show that ambient-temperature solutions of the complexes with aliphatic ligand backbones consist predominantly of DL isomers. The complex [PtlMe3{MeTe(CH2)3TeMe}] also exists in significant amounts of both meso forms. In contrast, the meso-1 form is present in only very low abundance in [PtlMe3{PhTe(CH2)3TePh}] and [PtlMe3{o-C6H4(TeMe)2}]. Pyramidal tellurium inversion interconverts these isomeric species and precise rates of this process were measured at near-ambient temperatures by 195Pt-{1H} and 125Te-{1H} NMR two-dimensional exchange spectroscopy experiments, or by 1H one-dimensional NMR bandshape analysis at above-ambient temperatures in the case of [PtlMe3{o-C6H4(TeMe)2}]. Tellurium pyramidal inversion-energy barriers [ΔG‡(298.15 K)] were in the range 70–84 kJ mol–1, reflecting the nature of the the substituent at Te and the ligand backbone. Comparison of the tellurium inversion energy in [PtlMe3{MeTe(CH2)3TeMe}] with data for Se and S in analogous complexes of chalcogen ligands establishes the trend in inversion energies, namely Te > Se > S, on a firm quantitative basis.

N.m.r. studies of tungsten pentacarbonyl complexes of type [W(CO)5L] where L refers to open-chain ligands (PhCH2SSCH2Ph or MeSCH2SMe) and cyclic ligands (β-[graphic omitted]HMe, or [graphic omitted]H2) have revealed no evidence of carbonyl scrambling accompanying the tungsten–sulphur 1,2- or 1,3-metallotropic shifts. This implies stereochemical rigidity of the square-pyramidal W(CO)5 moiety, on the two-dimensional 13C n.m.r. time-scale, during these intersulphur–metal commutations, energy barriers (ΔGDagger;) for any carbonyl rearrangement being in excess of ca. 90 kJ mol–1. The results further indicate that the metallotropic shifts involve lateral movements of the rigid W(CO)5 moieties with no tendency to distort to seven-co-ordinate tungsten(0) species in the transition states.

Two-dimensional n.m.r. exchange spectroscopy has been used to measure the kinetics of four-site exchange associated with pyramidal sulphur inversion in the complex [PtIMe3(MeSCH2CH2SEt)]. Ethyl sulphur inversion occurs more readily than methyl sulphur inversion with ΔG‡ values for the processes differing by 3.3–7.2 kJ mol–1 depending on which pathways are considered. Application of the same n.m.r. method to the three-site exchange of the Pt-methyl groups has led to ΔG‡ values of 90.9 ± 0.5, 92.6 ± 0.4, and 97.7 ± 1.9 kJ mol–1. The first two values are attributed to ligand (180°)/PtMe3(120°) correlated rotations, the different values depending on which equatorial Pt-methyl group is interchanged. The third ΔG‡ value, arising from direct exchange of the two equatorial Pt-methyl environments, refers to independent ligand rotation and/or Pt-methyl scrambling.

Platinum(IV) complexes of general type [PtXMe3(RSCH2CH2SR′)](X = Cl, Br, or I; R = Me, R′= Et or But; R = R′= But) have been synthesised. Solid-state structures for two of the complexes (X = Cl, R = Me, R′= Et; X = I, R = Me, R′= But) have been established by X-ray crystallography. All the complexes have been extensively studied in solution by variable-temperature one- and two-dimensional n.m.r. spectroscopy. The thioalkyl dependence of the energy barriers for pyramidal sulphur inversion was found to be SMe > SEt SBut. At above-ambient temperatures ligand 180° rotations and PtMe3 120° rotations occur, these two fluxions showing high degrees of correlation.

N.m.r. studies of the complex [W(CO)5(PhCH2SSCH2Ph)] have revealed the absence of any carbonyl group scrambling accompanying the tungsten–sulphur 1,2-metallotropic shift; this implies stereochemical rigidity, on the two-dimensional 13C dynamic n.m.r. timescale, of the square pyramidel W(CO)5 unit during these intersulphur metal commutations.