Synthesis and activity of ruthenium carbene complexes as reusable catalyst for olefin metathesis (Part I). Carbamoylsilane synthesis: Their reactivity and mechanism in the addition of electrophilically substituted alkenes

In the past decade, olefin metathesis catalysts based on transition metal alkylidene complexes have become a very powerful tool for carbon-carbon bond forming reactions. Olefin Metathesis allows for the catalytic cleavage and formation of C-C multiple bonds under mild conditions in the presence of various functional groups. Olefin metathesis can be mediated by a number of transition metals, but one of the most widely used catalysts is the Grubbs ruthenium alkylidenes. They are highly efficient catalyst precursors, moderately sensitive to moisture and air, and very tolerant of many different organic functional groups. However, these catalysts are prepared by using expensive ruthenium alkylidene complexes, which are rarely reusable after their first use, and often possess serious problems during purification. Given the growing importance of olefin metathesis in organic synthesis, it is very important to find an effective method to recycle these catalysts and obtain highly pure products.;A variety of homogeneous and heterogeneous polymer-supported ruthenium carbene catalysts (PCy3)2Ru(=CHPh)Cl2, and (PCy3)Ru(SIMes)(=CHPh)Cl2 have been prepared and found to be very effective for olefin metathesis. They show comparable reactivity to their homogeneous counterparts. These catalysts are reusable, recovered inexpensively and without significant waste generation, yielding highly pure products.;The second part of this dissertation reports reactivity and mechanism studies of the reaction between carbamoylsilanes and electrophilically functionalized olefins. The Si-C bond of N,N-dimethylcarbamoyl (trimethyl)silanes added regiospecifically to the C=C bond of electrophilically functionalized alkenes to afford beta-silyl-beta-functionalized amides. In contrast, carbonyl addition products were formed when hindered alkenic esters were used. Increased reactivity was observed when more crowded (at Si or N) carbamoylsilanes were used. Variations in carbamoylsilane structures were used to probe possible factors influencing the reaction rate.