Kinetics, thermodynamics, and effect of BPh3 on competitive C-C and C-H bond activation reactions in the interconversion of allyl cyanide by [Ni(dippe)]
Kinetics, thermodynamics, and effect of BPh3 on competitive C-C and C-H bond activation reactions in the interconversion of allyl cyanide by [Ni(dippe)]
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DOI：
10.1021/ja037002e
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发表时间：
2004-03-24
影响因子：
15
通讯作者：
Jones, WD
中科院分区：
文献类型：
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作者：
Brunkan, NM;Brestensky, DM;Jones, WD
[(dippe)Ni(mu-H)](2)与烯丙氰在低温下定量反应生成eta(2)-烯烃配合物（dippe）Ni(CH2=CHCH2CN)(1)。在室温或更高温度下，烯烃配合物转化为C-CN裂解产物（dippe）Ni（eta(3) -烯丙基）（CN）(3)和烯烃异构化产物（dippe）Ni（eta(2) -丁腈）（顺式和反式-2）的混合物，它们通过C-H活化形成。后者是较长反应时间的唯一产物，表明C-CN的裂解是可逆的，并且丁腈配合物2比eta(3)-烯丙基物3具有更大的热力学稳定性。该反应的动力学是温度的函数，并通过模拟反应得到了速率常数。C-CN键形成的速率常数（与C-CN裂解相反）比C-CN和C-H活化的速率常数表现出更强的温度依赖性，使得观察到的C-H和C-CN裂解产物的分布强烈依赖于温度。C-CN形成步骤的活化参数与C-CN和C-H裂解步骤的活化参数也有很大不同（较大的δ δ（不相等）和正的δ δ（不相等））。Lewis酸BPh3在低温下与1加成，只生成C-CN活化产物（dippe）Ni（eta(3)-烯丙基）（CNBPh3）(4)。独立制备的（dippe）Ni(crotonon腈- bph3)（顺式-和反式-7）不与4相互转化，表明4是bph3介导反应的动力学产物。在室温下，4在溶液中缓慢分解为配合物5，结构为[(dippe)Ni（eta(3)-烯丙基）（NdropC-BPh3），而加入第二等量的BPh3立即产生[(dippe)Ni（eta(3)-烯丙基）](+)[Ph(3)BCdropNBPh(3)](-)(6)。比较所有的eta(3)-烯丙基配合物对pi-sigma烯丙基相互转化的障碍（通过动态H-1 NMR测定）表明，当烯丙基为a键时，轴向氰化物配体通过进入P2Ni方平面来促进eta-sigma相互转化。
Reaction of [(dippe)Ni(mu-H)](2) With allyl cyanide at low temperature quantitatively generates the eta(2)-olefin complex (dippe)Ni(CH2=CHCH2CN) (1). At ambient temperature or above, the olefin complex is converted to a mixture of C-CN cleavage product (dippe)Ni(eta(3) -allyl)(CN) (3) and the olefin-isomerization products (dippe)Ni(eta(2) -crotonitrile) (cis- and trans-2), which form via C-H activation. The latter are the exclusive products at longer reaction times, indicating that C-CN cleavage is reversible and the crotononitrile complexes 2 are more thermodynamically stable than eta(3)-allyl species 3. The kinetics of this reaction have been followed as a function of temperature, and rate constants have been extracted by modeling of the reaction. The rate constants for C-CN bond formation (the reverse of C-CN cleavage) show a stronger temperature dependence than those for C-CN and C-H activation, making the observed distribution of C-H versus C-CN cleavage products strongly temperature-dependent. The activation parameters for the C-CN formation step are also quite distinct from those of the C-CN and C-H cleavage steps (larger DeltaH(not equal) and positive DeltaS(not equal)). Addition of the Lewis acid BPh3 to 1 at low temperature yields exclusively the C-CN activation product (dippe)Ni(eta(3)-allyl)(CNBPh3) (4). Independently prepared (dippe)Ni(crotononitrile-BPh3) (cis- and trans-7) does not interconvert with 4, indicating that 4 is the kinetic product of the BPh3-mediated reaction. On standing in solution at ambient temperature, 4 decomposes slowly to complex 5, with structure [(dippe)Ni(eta(3) -allyl)(NdropC-BPh3) while addition of a second equivalent of BPh3 immediately produces [(dippe)Ni(eta(3)-allyl)](+)[Ph(3)BCdropNBPh(3)](-) (6). Comparison of the barriers to pi-sigma allyl interconversion (determined via dynamic H-1 NMR spectroscopy) for all of the eta(3)-allyl complexes reveals that axial cyanide ligands facilitate eta-sigma interconversion by moving into the P2Ni square plane when the allyl group is a-bound.