由钨烯丙基配合物引发的碳氢化合物C-H键的热活化

Ng Stephen H K, Adams Craig S, Hayton Trevor W, Legzdins Peter, Patrick Brian O

Department of Chemistry, University of British Columbia, Vancouver, British Columbia, Canada V6T 1Z1.

J Am Chem Soc. 2003 Dec 10;125(49):15210-23. doi: 10.1021/ja037076q.

Gentle thermolysis of the allyl complex, CpW(NO)(CH(2)CMe(3))(eta(3)-H(2)CCHCMe(2)) (1), at 50 degrees C in neat hydrocarbon solutions results in the loss of neopentane and the generation of transient intermediates that subsequently activate solvent C-H bonds. Thus, thermal reactions of 1 with tetramethylsilane, mesitylene, and benzene effect single C-H activations and lead to the exclusive formation of CpW(NO)(CH(2)SiMe(3))(eta(3)-H(2)CCHCMe(2)) (2), CpW(NO)(CH(2)C(6)H(3)-3,5-Me(2))(eta(3)-H(2)CCHCMe(2)) (3), and CpW(NO)(C(6)H(5))(eta(3)-H(2)CCHCMe(2)) (4), respectively. The products of reactions of 1 with other methyl-substituted arenes indicate an inherent preference of the system for the activation of stronger arene sp(2) C-H bonds. For example, C-H bond activation of p-xylene leads to the formation of CpW(NO)(CH(2)C(6)H(4)-4-Me)(eta(3)-H(2)CCHCMe(2)) (5) (26%) and CpW(NO)(C(6)H(3)-2,5-Me(2))(eta(3)-H(2)CCHCMe(2)) (6) (74%). Mechanistic and labeling studies indicate that the transient C-H-activating intermediates are the allene complex, CpW(NO)(eta(2)-H(2)C=C=CMe(2)) (A), and the eta(2)-diene complex, CpW(NO)(eta(2)-H(2)C=CHC(Me)=CH(2)) (B). Intermediates A and B react with cyclohexene to form CpW(NO)(eta(3)-CH(2)C(2-cyclohexenyl)CMe(2))(H) (18) and CpW(NO)(eta(3)-CH(2)CHC)(Me)CH(2)C(beta)H(C(4)H(8))C(alpha)H (19), respectively, and intermediate A can be isolated as its PMe(3) adduct, CpW(NO)(PMe(3))(eta(2)-H(2)C=C=CMe(2)) (20). Interestingly, thermal reaction of 1 with 2,3-dimethylbut-2-ene results in the formation of a species that undergoes eta(3) --> eta(1) isomerization of the dimethylallyl ligand following the initial C-H bond-activating step to yield CpW(NO)(eta(3)-CMe(2)CMeCH(2))(eta(1)-CH(2)CHCMe(2)) (21). Thermolyses of 1 in alkane solvents afford allyl hydride complexes resulting from three successive C-H bond-activation reactions. For instance, 1 in cyclohexane converts to CpW(NO)(eta(3)-C(6)H(9))(H) (22) with dimethylpropylcyclohexane being formed as a byproduct, and in methylcyclohexane it forms the two isomeric complexes, CpW(NO)(eta(3)-C(7)H(11))(H) (23a,b). All new complexes have been characterized by conventional spectroscopic methods, and the solid-state molecular structures of 2, 3, 4, 18, 19, 20, and 21 have been established by X-ray crystallographic analyses.

在纯净烃类溶液中，将烯丙基配合物CpW(NO)(CH₂CMe₃)(η³-H₂CCHCMe₂) (1)于50℃进行温和热解，会导致新戊烷的损失，并生成随后能活化溶剂C-H键的瞬态中间体。因此，1与四甲基硅烷、均三甲苯和苯的热反应实现了单一的C-H活化，并分别专一性地生成了CpW(NO)(CH₂SiMe₃)(η³-H₂CCHCMe₂) (2)、CpW(NO)(CH₂C₆H₃-3,5-Me₂)(η³-H₂CCHCMe₂) (3)和CpW(NO)(C₆H₅)(η³-H₂CCHCMe₂) (4)。1与其他甲基取代芳烃的反应产物表明，该体系内在地倾向于活化更强的芳烃sp² C-H键。例如，对二甲苯的C-H键活化生成了CpW(NO)(CH₂C₆H₄-4-Me)(η³-H₂CCHCMe₂) (5) (26%)和CpW(NO)(C₆H₃-2,5-Me₂)(η³-H₂CCHCMe₂) (6) (74%)。机理和标记研究表明，瞬态C-H活化中间体是丙二烯配合物CpW(NO)(η²-H₂C=C=CMe₂) (A)和η²-二烯配合物CpW(NO)(η²-H₂C=CHC(Me)=CH₂) (B)。中间体A和B与环己烯反应，分别生成CpW(NO)(η³-CH₂C(2-环己烯基)CMe₂)(H) (18)和CpW(NO)(η³-CH₂CHC)(Me)CH₂C(β)H(C₄H₈)C(α)H (19)，中间体A可以以其PMe₃加合物CpW(NO)(PMe₃)(η²-H₂C=C=CMe₂) (20)的形式分离出来。有趣的是，1与2,3-二甲基-2-丁烯的热反应生成了一种物种，该物种在初始C-H键活化步骤后，会发生二甲基烯丙基配体的η³→η¹异构化，生成CpW(NO)(η³-CMe₂CMeCH₂)(η¹-CH₂CHCMe₂) (21)。在烷烃溶剂中对1进行热解，会得到由三个连续C-H键活化反应产生的烯丙基氢化物配合物。例如，1在环己烷中转化为CpW(NO)(η³-C₆H₉)(H) (22)，同时生成二甲基丙基环己烷作为副产物，而在甲基环己烷中它会形成两种异构配合物，CpW(NO)(η³-C₇H₁₁)(H) (23a,b)。所有新配合物均通过传统光谱方法进行了表征，并通过X射线晶体学分析确定了2、3、4、18、19、20和21的固态分子结构。