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  1. Here, the molecular structures of CpMo(PMe 3)(CO) 2H and CpMo(PMe 3) 2(CO)H have been determined by X-ray diffraction, thereby revealing four-legged piano-stool structures in which the hydride ligand is trans to CO. However, in view of the different nature of the four basal ligands, the geometries of CpMo(PMe 3)(CO) 2H and CpMo(PMe 3) 2(CO)H deviate from that of an idealized four-legged piano stool, such that the two ligands that are orthogonal to the trans H–Mo–CO moiety are displaced towards the hydride ligand. While CpRMo(PMe 3) 3–x(CO) xH (Cp R = Cp, Cp*; x = 1, 2, 3) are catalysts formore » the release of H 2 from formic acid, the carbonyl derivatives, CpRMo(CO)3H, are also observed to form dinuclear formate compounds, namely, [Cp RMo(μ-O)(μ-O 2CH)] 2. The nature of the Mo···Mo interactions in [CpMo(μ-O)(μ-O 2CH)] 2 and [Cp*Mo(μ-O)(μ-O 2CH)] 2 have been addressed computationally. In this regard, the two highest occupied molecular orbitals of [CpMo(μ-O)(μ-O 2CH)] 2 correspond to metal-based δ* (HOMO) and σ (HOMO–1) orbitals. The σ 2δ *2 configuration thus corresponds to a formal direct Mo–Mo bond order of zero. The preferential occupation of the δ* orbital rather than the δ orbital is a consequence of the interaction of the latter orbital with p orbitals of the bridging oxo ligands. In essence, lone-pair donation from oxygen increases the electron count so that the molybdenum centers can achieve an 18-electron configuration without the existence of a Mo–Mo bond, whereas a Mo=Mo double bond is required in the absence of lone-pair donation.« less
  2. A series of cadmium thiolate compounds that feature a sulfur-rich coordination environment, namely [Tm But]CdSAr, have been synthesized by the reactions of [Tm But]CdMe with ArSH (Ar = C 6H 4-4-F, C 6H 4-4-Bu t, C 6H 4-4-OMe, and C 6H 4-3-OMe). In addition, the pyridine-2-thiolate and pyridine-2-selenolate derivatives, [Tm But]CdSPy and [Tm But]CdSePy have been obtained via the respective reactions of [Tm But]CdMe with pyridine-2-thione and pyridine-2-selone. The molecular structures of [Tm But]CdSAr and [Tm But]CdEPy (E = S or Se) have been determined by X-ray diffraction and demonstrate that, in each case, the [CdS 4] motif is distortedmore » tetrahedral and approaches a trigonal monopyramidal geometry in which the thiolate ligand adopts an equatorial position; [Tm But]CdSPy and [Tm But]CdSePy, however, exhibit an additional long-range interaction with the pyridyl nitrogen atoms. The ability of the thiolate ligands to participate in exchange was probed by 1H and 19F nuclear magnetic resonance (NMR) spectroscopic studies of the reactions of [Tm But]CdSC 6H 4-4-F with ArSH (Ar = C 6H 4-4-Bu t or C 6H 4-4-OMe), which demonstrate that (i) exchange is facile and (ii) coordination of thiolate to cadmium is most favored for the p-fluorophenyl derivative. Furthermore, a two-dimensional EXSY experiment involving [Tm But]CdSC 6H 4-4-F and 4-fluorothiophenol demonstrates that degenerate thiolate ligand exchange is also facile on the NMR time scale.« less

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