Intermolecular Hydroamination of Methylenecyclopropane Catalyzed by Group IV Metal Complexes

The intermolecular hydroamination of methylenecyclopropane (MCP) and phenylmethylenecyclopropane (PhMCP) promoted by group IV metal complexes is presented. The reactivity and chemoselectivity of two titanium complexes having two different ancillary ligands, Ti(Ph2PNpy)2(NEt2)2 and Ti(NMe2)4, are presented and compared to those of the zirconium complexes Zr(Ph2PNpy)3NEt2 and Zr(NMe2)4. For the titanium complexes, the linear imine product A is always the predominant species, having E stereochemistry. For the zirconium complexes, the branched imine product B is obtained preferentially. Comparison of the activity of the complex Ti(Ph2PNpy)2(NEt2)2 with that of Ti(NMe2)4 reveals a strong relationship between the ancillary ligand at the catalytic complex and the suitability of the amine for the MCPs hydroamination reaction. A complex with a bulky ancillary ligand is suitable for the hydroamination of aliphatic amines and small aromatic amines, whereas a complex with a small ancillary ligand (steric hindrance) will allow the hydroamination of MCPs with bulky aromatic amines. Kinetic studies show that the hydroamination promoted by the homoleptic titanium complex exhibit a first-order dependence in complex and olefin and an inverse order dependence in amine. A plausible mechanism is presented on the basis of the obtained products, kinetic measurements, and syntheses of key intermediates.本文报道了IV族金属配合物催化亚甲基环丙烷（methylenecyclopropane, MCP）与苯基亚甲基环丙烷（phenylmethylenecyclopropane, PhMCP）的分子间氢胺化反应。研究了两种带有不同辅助配体的钛配合物——Ti(Ph₂PNpy)₂(NEt₂)₂与Ti(NMe₂)₄的反应活性与化学选择性，并将其与锆配合物Zr(Ph₂PNpy)₃NEt₂及Zr(NMe₂)₄进行对比。对于钛配合物体系，线性亚胺产物A始终为主要产物，且具有E型立体构型；而锆配合物体系则优先生成支链型亚胺产物B。对比Ti(Ph₂PNpy)₂(NEt₂)₂与Ti(NMe₂)₄的催化活性，可发现催化配合物的辅助配体与胺底物适配性之间存在显著关联：带有大位阻辅助配体的配合物适用于脂肪族胺与小型芳香族胺的氢胺化反应，而辅助配体空间位阻较小的配合物则可实现MCP与大位阻芳香族胺的氢胺化。动力学研究表明，均配型钛配合物催化的氢胺化反应对配合物与烯烃均为一级动力学依赖，而对胺底物则呈反级动力学依赖。基于产物分析、动力学测试及关键中间体的合成，本文提出了合理的反应机理。