Department of Chemistry, Tufts University, 62 Talbot Avenue, Medford, Massachusetts 02155, USA.
J Am Chem Soc. 2009 Oct 28;131(42):15412-23. doi: 10.1021/ja905849a.
Variable temperature equilibrium studies were used to derive thermodynamic data for formation of eta(1) nitrile complexes with Mo(N[(t)Bu]Ar)(3), 1. (1-AdamantylCN = AdCN: DeltaH(degrees) = -6 +/- 2 kcal mol(-1), DeltaS(degrees) = -20 +/- 7 cal mol(-1) K(-1). C(6)H(5)CN = PhCN: DeltaH(degrees) = -14.5 +/- 1.5 kcal mol(-1), DeltaS(degrees) = -40 +/- 5 cal mol(-1) K(-1). 2,4,6-(H(3)C)(3)C(6)H(2)CN = MesCN: DeltaH(degrees) = -15.4 +/- 1.5 kcal mol(-1), DeltaS(degrees) = -52 +/- 5 cal mol(-1) K(-1).) Solution calorimetric studies show that the enthalpy of formation of 1-[eta(2)-NCNMe(2)] is more exothermic (DeltaH(degrees) = -22.0 +/- 1.0 kcal mol(-1)). Rate and activation parameters for eta(1) binding of nitriles were measured by stopped flow kinetic studies (AdCN: DeltaH(on)(++) = 5 +/- 1 kcal mol(-1), DeltaS(on)(++) = -28 +/- 5 cal mol(-1) K(-1); PhCN: DeltaH(on)(++) = 5.2 +/- 0.2 kcal mol(-1), DeltaS(on)(++) = -24 +/- 1 cal mol(-1) K(-1); MesCN: DeltaH(on)(++) = 5.0 +/- 0.3 kcal mol(-1), DeltaS(on)(++) = -26 +/- 1 cal mol(-1) K(-1)). Binding of Me(2)NCN was observed to proceed by reversible formation of an intermediate complex 1-[eta(1)-NCNMe(2)] which subsequently forms 1-[eta(2)-NCNMe(2)]: DeltaH(++)(k1) = 6.4 +/- 0.4 kcal mol(-1), DeltaS(++)(k1) = -18 +/- 2 cal mol(-1) K(-1), and DeltaH(++)(k2) = 11.1 +/- 0.2 kcal mol(-1), DeltaS(++)(k2) = -7.5 +/- 0.8 cal mol(-1) K(-1). The oxidative addition of PhSSPh to 1-[eta(1)-NCPh] is a rapid second-order process with activation parameters: DeltaH(++) = 6.7 +/- 0.6 kcal mol(-1), DeltaS(++) = -27 +/- 4 cal mol(-1) K(-1). The oxidative addition of PhSSPh to 1-[eta(2)-NCNMe(2)] also followed a second-order rate law but was much slower: DeltaH(++) = 12.2 +/- 1.5 kcal mol(-1) and DeltaS(++) = -25.4 +/- 5.0 cal mol(-1) K(-1). The crystal structure of 1-[eta(1)-NC(SPh)NMe(2)] is reported. Trapping of in situ generated 1-[eta(1)-NCNMe(2)] by PhSSPh was successful at low temperatures (-80 to -40 degrees C) as studied by stopped flow methods. If 1-[eta(1)-NCNMe(2)] is not intercepted before isomerization to 1-[eta(2)-NCNMe(2)] no oxidative addition occurs at low temperatures. The structures of key intermediates have been studied by density functional theory, confirming partial radical character of the carbon atom in eta(1)-bound nitriles. A complete reaction profile for reversible ligand binding, eta(1) to eta(2) isomerization, and oxidative addition of PhSSPh has been assembled and gives a clear picture of ligand reactivity as a function of hapticity in this system.
采用变温平衡研究，推导了 η(1)腈配合物与 Mo(N[(t)Bu]Ar)(3) 1 的热力学数据。（1-金刚烷腈，ΔH(degrees)=-6±2 kcal mol(-1)，ΔS(degrees)=-20±7 cal mol(-1) K(-1)。苯腈，ΔH(degrees)=-14.5±1.5 kcal mol(-1)，ΔS(degrees)=-40±5 cal mol(-1) K(-1)。2,4,6-(H(3)C)(3)C(6)H(2)腈，ΔH(degrees)=-15.4±1.5 kcal mol(-1)，ΔS(degrees)=-52±5 cal mol(-1) K(-1)。）溶液量热研究表明，1-[η(2)-NCNMe(2)]的生成焓更具放热性（ΔH(degrees)=-22.0±1.0 kcal mol(-1)）。通过停流动力学研究测量了 η(1)腈配体的结合反应速率和活化参数（AdCN：ΔH(on)(++)=5±1 kcal mol(-1)，ΔS(on)(++)=-28±5 cal mol(-1) K(-1)；PhCN：ΔH(on)(++)=5.2±0.2 kcal mol(-1)，ΔS(on)(++)=-24±1 cal mol(-1) K(-1)；MesCN：ΔH(on)(++)=5.0±0.3 kcal mol(-1)，ΔS(on)(++)=-26±1 cal mol(-1) K(-1)）。观察到 Me(2)NCN 的结合是通过可逆形成中间体 1-[η(1)-NCNMe(2)]，随后形成 1-[η(2)-NCNMe(2)]来进行的：ΔH(++)(k1)=6.4±0.4 kcal mol(-1)，ΔS(++)(k1)=-18±2 cal mol(-1) K(-1)，和 ΔH(++)(k2)=11.1±0.2 kcal mol(-1)，ΔS(++)(k2)=-7.5±0.8 cal mol(-1) K(-1)。PhSSPh 对 1-[η(1)-NCPh]的氧化加成是一个快速的二级过程，其活化参数为：ΔH(++)=6.7±0.6 kcal mol(-1)，ΔS(++)=-27±4 cal mol(-1) K(-1)。PhSSPh 对 1-[η(2)-NCNMe(2)]的氧化加成也遵循二级速率定律，但速度要慢得多：ΔH(++)=12.2±1.5 kcal mol(-1)，ΔS(++)=-25.4±5.0 cal mol(-1) K(-1)。报道了 1-[η(1)-NC(SPh)NMe(2)]的晶体结构。通过停流方法研究发现，PhSSPh 可以在低温（-80 至-40°C）下成功捕获原位生成的 1-[η(1)-NCNMe(2)]。如果在异构化为 1-[η(2)-NCNMe(2)]之前不拦截 1-[η(1)-NCNMe(2)]，则在低温下不会发生氧化加成。通过密度泛函理论研究了关键中间体的结构，证实了 η(1)-键合腈中碳原子的部分自由基性质。组装了一个完整的可逆配体结合、η(1)到 η(2)异构化和 PhSSPh 氧化加成的反应剖面，清晰地描绘了该体系中配体反应性随配位体亲核性的变化。
