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首页> 美国卫生研究院文献>other >The Influence of the Oxygen Atom Acceptor on the Reaction Coordinate and Mechanism of Oxygen Atom Transfer From the Dioxo-Mo(VI) Complex TpiPrMoO2(OPh) to Tertiary Phosphines
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The Influence of the Oxygen Atom Acceptor on the Reaction Coordinate and Mechanism of Oxygen Atom Transfer From the Dioxo-Mo(VI) Complex TpiPrMoO2(OPh) to Tertiary Phosphines

机译：协调和氧原子转移从二氧钼（VI）复合物TpiprmoO2（OpH）的机制对反应的氧原子受体的影响对叔膦

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The oxygen atom transfer reactivity of the dioxo-Mo(VI) complex, TpiPrMoO2(OPh) (TpiPr = hydrotris(3-isopropylpyrazol-1-yl)borate), with a range of tertiary phosphines (PMe3, PMe2Ph, PEt3, PBun3, PEt2Ph, PEtPh2 and PMePh2) has been investigated. The first step in all the reactions follows a second-order rate law indicative of an associative transition state, consistent with nucleophilic attack by the phosphine on an oxo ligand, viz. TpiPrMoO2(OPh) + PR3 → TpiPrMoO(OPh)(OPR3). The calculated free energy of activation for the formation of the OPMe3 intermediate (Chem. Eur. J. 2006, 12, 7501) is in excellent agreement with the experimental ΔG‡ value reported here. The second step of the reaction, i.e., the exchange of the coordinated phosphine oxide by acetonitrile, TpiPrMoO(OPh)(OPR3) + MeCN → TpiPrMoO(OPh)(MeCN) + OPR3, is first-order in starting complex in acetonitrile. The reaction occurs via a dissociative interchange (Id) or associative interchange (Ia) mechanism, depending on the nature of the phosphine oxide. The activation parameters for the solvolysis of TpiPrMoO(OPh)(OPMe3) (ΔH‡ = 56.3 kJ mol−1; ΔS‡ = −125.9 J mol−1 K−1; ΔG‡ = 93.8 kJ mol−1) and TpiPrMoO(OPh)(OPEtPh2) (ΔH‡ = 66.5 kJ mol−1; ΔS‡ = −67.6 J mol−1 K−1; ΔG‡ = 86.7 kJ mol−1) by acetonitrile are indicative of Ia mechanisms. In contrast, the corresponding parameters for the solvolysis reaction of TpiPrMoO(OPh)(OPEt3) (ΔH‡ = 95.8 kJ mol−1; ΔS‡ = 26.0 J mol−1 K−1; ΔG‡ = 88.1 kJ mol−1) and the remaining complexes by the same solvent are indicative of an Id mechanism. The equilibrium constant for the solvolysis of the oxo-Mo(V) phosphoryl complex, [TpiPrMoO(OPh)(OPMe3)]+, by acetonitrile was calculated to be 1.9 × 10−6. The oxo-Mo(V) phosphoryl complex is more stable than the acetonitrile analogue, whereas the oxo-Mo(IV) acetonitrile complex is more stable than the phosphoryl analogue. The higher stability of the Mo(V) phosphoryl complex may explain the phosphate inhibition of sulfite oxidase.

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