Coordination-Mode Control of Bound Nitrile Radical Complex Reactivity: Intercepting End-on Nitrile-Mo(III) Radicals at Low Temperature

被引：11

作者：

Germain, Meaghan E. ^{[1
]}

Temprado, Manuel ^{[2
,3
]}

Castonguay, Annie ^{[1
]}

Kryatova, Olga P. ^{[1
]}

Rybak-Akimova, Elena V. ^{[1
]}

Curley, John J. ^{[2
]}

Mendiratta, Arjun ^{[2
]}

Tsai, Yi-Chou ^{[2
]}

Cummins, Christopher C. ^{[2
]}

Prabhakar, Rajeev ^{[3
]}

McDonough, James E. ^{[3
]}

Hoff, Carl D. ^{[3
]}

机构：

[1] Tufts Univ, Dept Chem, Medford, MA 02155 USA

[2] MIT, Dept Chem, Cambridge, MA 02139 USA

[3] Univ Miami, Dept Chem, Coral Gables, FL 33146 USA

来源：

JOURNAL OF THE AMERICAN CHEMICAL SOCIETY | 2009年 / 131卷 / 42期

基金：

美国国家科学基金会;

关键词：

HYDROGEN-BOND ACCEPTOR; MOLYBDAZIRIDINE-HYDRIDE; ATOM-TRANSFER; DINITROGEN; NITROGEN; BENZONITRILE; DERIVATIVES; ACTIVATION; BIS(ACETYLACETONATE); ELIMINATION;

D O I：

10.1021/ja905849a

中图分类号：

O6 [化学];

学科分类号：

0703 ;

摘要：

Variable temperature equilibrium studies were used to derive thermodynamic data for formation of eta(1) nitrile complexes with Mo(N['Bu]Ar)(3), 1. (1-AdamantylCN = AdCN: Delta H degrees = -6 +/- 2 kcal mol(-1), Delta S degrees = -20 +/- 7 cal mol(-1) K-1. C6H5CN = PhCN: Delta H degrees = -14.5 +/- 1.5 kcal mol(-1), Delta S degrees = -40 +/- 5 Cal mol(-1) K-1. 2,4,6-(H3C)(3)C6H2CN = MesCN: Delta H degrees = -15.4 +/- 1.5 kcal mol(-1), Delta S degrees = -52 +/- 5 cal mol(-1) K-1.) Solution calorimetric studies show that the enthalpy of formation of 1-[eta(2)-NCNMe2] is more exothermic (Delta H 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: Delta H-on double dagger = 5 +/- 1 kcal mol(-1), Delta S-on double dagger = -28 +/- 5 cal mol(-1) K-1; PhCN: Delta H-on double dagger = 5.2 +/- 0.2 kcal mol(-1), Delta S-on double dagger = -24 +/- 1 cal mol(-1) K-1; MesCN: Delta H-on double dagger = 5.0 +/- 0.3 kcal mol(-1), Delta S-on double dagger = -26 +/- 1 cal mol(-1) K-1). Binding of Me2NCN was observed to proceed by reversible formation of an intermediate complex 1 -[eta(1)-NCNMe2] which subsequently forms 1-[eta(2)-NCNMe2]: Delta H double dagger(k1) = 6.4 +/- 0.4 kcal mol(-1), Delta S double dagger(k1) = -18 +/- 2 cal mol(-1) K-1, and Delta H double dagger(k2) = 11.1 +/- 0.2 kcal mol(-1), Delta S double dagger(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: Delta H double dagger = 6.7 +/- 0.6 kcal mol(-1), Delta S double dagger = -27 +/- 4 cal mol(-1) K-1. The oxidative addition of PhSSPh to 1-[eta(2)-NCNMe2] also followed a second-order rate law but was much slower: Delta H double dagger = 12.2 +/- 1.5 kcal mol(-1) and Delta S double dagger = -25.4 +/- 5.0 cal mol(-1) K-1. The crystal structure of 1-[eta(1)-NC(SPh)NMe2] is reported. Trapping of in situ generated 1-[eta(1)-NCNMe2] by PhSSPh was successful at low temperatures (-80 to -40 degrees C) as studied by stopped flow methods. If 1-[eta(1)-NCNMe2] is not intercepted before isomerization to 1-[eta(2)-NCNMe2] 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.

引用

页码：15412 / 15423

页数：12

共 42 条

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