Theoretical analysis of concerted and stepwise mechanisms of Diels-Alder reactions of butadiene with silaethylene and disilene.
Theoretical analysis of concerted and stepwise mechanisms of Diels-Alder reactions of butadiene with silaethylene and disilene.
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DOI：
10.1021/jp074391g
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发表时间：
2007-12
期刊：
影响因子：
--
通讯作者：
H. Wakayama;S. Sakai
中科院分区：
文献类型：
--
作者：
H. Wakayama;S. Sakai
用从头算分子轨道方法研究了丁二烯与硅乙烯和二硅烯的Diels-Alder反应的协同和分步反应机理。对于丁二烯和硅乙烯的反应，存在一个几乎是分步的非对称协同过程和两个分步过程。对于分步过程的第一步，C-Si键的形成比C-C键的形成更有利。在CASPT2计算水平下，协同过渡态的活化能垒仅比C-Si键形成的第一步过渡态的活化能垒低0.89千卡/摩尔。对于丁二烯和二硅烯的反应，用CASSCF方法计算得到Cs对称性约束的协调型过渡态的活化势垒比阶跃过渡态的活化能垒高约9kcal/mol。在CASPT2/6-311++G(d，p)计算水平下，包括非动力学关联能在内，第一步反应的势垒消失，但丁二烯与二硅烯的反应是通过阶梯过程进行的。
The concerted and the stepwise mechanisms of the Diels-Alder reactions of butadiene with silaethylene and disilene were studied by ab initio MO methods. For the reaction of butadiene and silaethylene, an asymmetric concerted process that is almost stepwise and two stepwise processes were located. For the first step of the stepwise process, the C-Si bond formation is more favorable than the C-C bond formation. The activation energy barrier of the concerted transition state is only 0.89 kcal/mol lower than that of the first-step transition state of the C-Si bond formation for the stepwise process by the CASPT2 calculation level. For the reaction of butadiene and disilene, the activation energy barrier of the concerted-type transition state constrained with Cs symmetry is about 9 kcal/mol higher than that of the stepwise transition state by the CASSCF method. The energy barrier of the first step of the stepwise reaction disappears at the CASPT2/6-311++G(d,p) calculation level including the nondynamical correlation energy, although the reaction of the butadiene with disilene occurs through the stepwise-like process.