Experimental and computational studies of the stability and reactivity of a half-sandwich 16-electron spin triplet MoII complex containing a terminal hydroxide ligand - Archive ouverte HAL Accéder directement au contenu
Article Dans Une Revue New Journal of Chemistry Année : 1998

Experimental and computational studies of the stability and reactivity of a half-sandwich 16-electron spin triplet MoII complex containing a terminal hydroxide ligand

Résumé

Compound CpMo(OH)(PMe3)2, 1, a stable monomeric 16-electron organometallic complex with a spin triplet ground state and a terminal hydroxide ligand, is obtained from the reaction of CpMoCl(PMe3)3 with KOH. Density functional (B3LYP) geometry optimizations for a CpMo(OH)(PH3)2 model system afford a spin triplet ground state with a bent endo hydroxide ligand. An excited singlet state with a bent exo OH ligand is found 2.27 kcal mol-1 higher in energy. Analogous calculations on other related CpMoX(PH3)2 systems provide a spin triplet ground state for X=Cl and H, whereas the compound with X=PH2 has a singlet ground state. Addition of PH3 leads to a calculated bond energy of 20.9, 14.3, 7.2 and 6.8 kcal mol-1 relative to the 16-electron singlet state for H, Cl, PH2 and OH, respectively. These values are consistent with qualitative expectations based on the strength of the Mo–X π interaction and steric strain in the CpMo(PH3)3 and CpMo(PH3)2 fragments. Crude estimates of the thermodynamic strength of the Mo–X π interactions have been derived. The calculations also show that an α-H elimination from the hydroxide ligand to afford CpMoH(O)(PH3) plus PH3 should be thermodynamically favored but suggest that it is kinetically difficult. Compound 1 slowly decomposes in C6D6 in the presence of PMe3 by a process that is initiated by the activation of a solvent C–D bond. This process produces a mixture of CpMoH(PMe3)3, 4, CpMo(η2-CH2PMe2)(PMe3)2, 5, C6D5OH and PMe3-dn (n=1–9) molecules. The relative isotopic distribution of the free PMe3-dn molecules can be satisfactorily simulated. The analogous decomposition of CpMo(OD)(PMe3)2 (1-OD) revealed a rapid exchange of the deuteroxide D atom and a PMe3 ligand H atom. The decomposition of 1 in the presence of PMe3 in C6D6 is catalyzed by water or methanol. The molecules are believed to engage in hydrogen bonding interactions with the OH lone pairs, thereby modifying the electronic structure of compound 1 and enhancing the reactivity toward the oxidative addition of the solvent C–D bonds.
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Dates et versions

hal-03312506 , version 1 (06-10-2021)

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Rinaldo Poli, Elsje Alessandra Quadrelli. Experimental and computational studies of the stability and reactivity of a half-sandwich 16-electron spin triplet MoII complex containing a terminal hydroxide ligand. New Journal of Chemistry, 1998, 22 (5), pp.435-450. ⟨10.1039/A709187G⟩. ⟨hal-03312506⟩
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