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(NEt 2)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.
|Number of pages||18|
|State||Published - 27 Aug 2007|