Theoretical study of C-H and N-H sigma-bond activation reactions by titinium(IV)-imido complex. Good understanding based on orbital interaction and theoretical proposal for N-H sigma-bond activation of ammonia.
Theoretical study of C-H and N-H sigma-bond activation reactions by titinium(IV)-imido complex. Good understanding based on orbital interaction and theoretical proposal for N-H sigma-bond activation of ammonia.
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DOI：
10.1021/ja071825c
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发表时间：
2007-06
影响因子：
15
通讯作者：
Noriaki Ochi;Y. Nakao;Hirofumi Sato;S. Sakaki
中科院分区：
文献类型：
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作者：
Noriaki Ochi;Y. Nakao;Hirofumi Sato;S. Sakaki
采用密度泛函理论（DFT）、MP2 to MP4（SDQ）和CCSD（T）方法研究了（Me 3SiO）2 Ti（= NSiMe 3）1对甲烷C-H σ键和氨N-H σ键的活化.甲烷的C-H σ键活化以14.6（21.5）kcal/mol的活化势垒（Ea）和-22.7（-16.5）kcal/mol的反应能（Δ E）发生，得到（Me 3SiO）2 Ti（Me）[NH（SiMe 3）]，其中DFT-和MP4（SDQ）-计算值在下文中分别不带括号和在括号中给出。CH 3基团的电子布居增加，但H原子布居减少，从前体络合物进入过渡态，这表明C-H σ键活化以异裂方式发生，与氧化加成不同。Ti原子数在从前体络合物进入过渡态时显著增加，这表明发生了从甲烷到Ti的电荷转移（CT）。这些布居变化是由Ti= NSiMe 3的d（pi）-p（pi）成键轨道、Ti的d（z2）轨道和甲烷的C-H σ-成键和σ *-反键轨道之间的轨道相互作用引起的。C-H σ键的反向区域选择性活化导致（Me_3SiO）_2Ti（H）[NMe（SiMe_3）]的形成，其Ea值较大，结晶度较小。从Ti-H、Ti-CH_3、Ti-NH_3、N-H和N-CH_3的键能和过渡态轨道相互作用等方面讨论了其原因。氨的N-H σ键活化是以异裂方式进行的，其Ea值为19.0（27.9）kcal/mol，热膨胀系数为-45.0（-39.4）kcal/mol，明显大于C-H σ键活化。本文还研究了钛-次烷基配合物[（PNP）Ti（CSiMe 3）] 3（PNP = N-[2-（PH 2）2-苯基]2-]）对氨的N-H σ键活化作用。该反应在较小的E（a）值为7.5（15.3）kcal/mol和较大的热焓为-60.2（-56.1）kcal/mol的情况下发生。这些结果使我们预测，N-H σ键活化氨可以实现这些配合物。
The C-H sigma-bond activation of methane and the N-H sigma-bond activation of ammonia by (Me3SiO)2Ti(=NSiMe3) 1 were theoretically investigated with DFT, MP2 to MP4(SDQ), and CCSD(T) methods. The C-H sigma-bond activation of methane takes place with an activation barrier (Ea) of 14.6 (21.5) kcal/mol and a reaction energy (DeltaE) of -22.7 (-16.5) kcal/mol to afford (Me3SiO)2Ti(Me)[NH(SiMe3)], where DFT- and MP4(SDQ)-calculated values are given without and in parentheses, respectively, hereafter. The electron population of the CH3 group increases, but the H atomic population decreases upon going to the transition state from the precursor complex, which indicates that the C-H sigma-bond activation occurs in heterolytic manner unlike the oxidative addition. The Ti atomic population considerably increases upon going to the transition state from the precursor complex, which indicates that the charge transfer (CT) occurs from methane to Ti. These population changes are induced by the orbital interactions among the d(pi)-p(pi) bonding orbital of the Ti=NSiMe3 moiety, the Ti d(z2) orbital and the C-H sigma-bonding and sigma*-antibonding orbitals of methane. The reverse regioselective C-H sigma-bond activation which leads to formation of (Me3SiO)2Ti(H)[NMe(SiMe3)] takes place with a larger Ea value and smaller exothermicity. The reasons are discussed in terms of Ti-H, Ti-CH3, Ti-NH3, N-H, and N-CH3 bond energies and orbital interactions in the transition state. The N-H sigma-bond activation of ammonia takes place in a heterolytic manner with a larger Ea value of 19.0 (27.9) kcal/mol and considerably larger exothermicity of -45.0 (-39.4) kcal/mol than those of the C-H sigma-bond activation. The N-H sigma-bond activation of ammonia by a Ti-alkylidyne complex, [(PNP)Ti(CSiMe3)] 3 (PNP = N-[2-(PH2)2-phenyl]2-]) ,was also investigated. This reaction takes place with a smaller E(a) value of 7.5 (15.3) kcal/mol and larger exothermicity of -60.2 (-56.1) kcal/mol. These results lead us to predict that the N-H sigma-bond activation of ammonia can be achieved by these complexes.