|Ph.D Thesis||Department of Chemistry|
|Supervisor:||Prof. Eisen Moris|
|Full Thesis text|
This research is focused on two chemical transformations, the hydroamination and hydrosilylation reactions. Both transformations are addition reactions that would not proceed without the presence of a catalyst. We have focused on applying Group IV metal complexes as catalysts since these complexes have several advantages. First, titanium is the 2nd most abundant transition element in the earth’s crust and is quite inexpensive relatively to many of the later metals. Second, titanium is readily removed from the products by flushing through an alumina or silica plug. Third, on hydrolysis the metal containing product is TiO2, a nontoxic compound found in many consumption products (e.g toothpastes). Additionally, human tissues can easily tolerate zirconium metal complexes, which make them suitable for biocompatible implants.
The field of hydroamination reaction promoted by Group IV metal complexes has remained limited to allene and alkyne substrates. In this research we introduce a new group of substrates suitable for this transformation, the methylenecyclopropanes (MCP). The intermolecular hydroamination of methylenecyclopropane (MCP) and phenylmethylenecyclopropane (PhMCP) promoted by group IV complexes is presented. The reactivity and chemoselectivity of two titanium complexes having two different ancillary ligands, Ti(Ph2PNpy)2(NEt2)2, Ti(NMe2)4, are presented and compared to the zirconium complexes Zr(Ph2PNpy)3NEt2, Zr(NMe2)4. For the titanium complexes, the linear imine product A is always the predominant with the E stereochemistry. For the zirconium complexes, the branched imine product B is obtained preferentially.
Comparison of the activities of complex Ti(Ph2PNpy)2(NEt2)2 with Ti(NMe2)4 reveals strong relationship between the ancillary ligand at the catalytic complex and the suitability of the amine for the MCPs hydroamination reaction. A plausible mechanism is presented based on the obtained products, kinetic measurement, and synthesis of key intermediates.
The field of hydrosilylation reaction promoted by Group IV metal complexes has focused mainly on applying metallocene metal complexes as catalysts for the hydrosilylation of alkenes. In this research we have studied the hydrosilylation of alkenes promoted by readily available, Group IV, homoleptic complexes. Those complexes have been found to be efficient catalysts for the hydrosilylation reaction of alkenes. The scope of alkenes and silanes suitable for this transformation was studied. Product analysis reveals that for all tested alkenes two hydrosilylation products and one hydrogenation product were obtained. However, no olefinic products were obtained. The use of bulkier ligands on the metal center allows us to control and to increase the chemoselectivity of the reaction, as shown in the hydrosilylation of PhMCP.