| Although organic synthetic methods have advanced rapidly in the past several decades, practical separation technology has been somewhat slower to develop. While heterogeneous catalysts are easily recovered after reaction, they often suffer from serious deficiencies, namely low selectivity and activity and metal leaching. Homogeneous catalysts are generally more reactive, selective, stable, and more readily characterized and modified than heterogeneous catalysts. However, soluble catalysts are not readily recoverable from solution. In addition, present recovery methods often lead to catalyst degradation. Therefore, there exists a need to develop efficient catalyst separation strategies that combine the desirable features of both heterogeneous and homogeneous catalysis, as well as a need to develop robust homogeneous catalysts that can be incorporated into these strategies.; The primary goal of the research described in this dissertation was to explore and develop new, efficient catalyst separation schemes based on the use of soluble polymers as supports for transition metal catalysts. Success was achieved in the development of a novel biphasic catalyst recovery scheme that involves the use of a biphasic solvent system that reversibly becomes monophasic with mild heating in combination with a soluble polymer support that displays a strong phase preference under biphasic conditions. Catalyst recovery can thus be effected by a simple phase separation at room temperature. This approach was tested by using soluble polymer supports such as poly( N-isopropylacrylamide) and poly(ethylene glycol) modified with either a dye probe to study the polymer's phase distribution behavior and then successfully applied to the same polymers modified with suitable transition metal catalysts.; The second goal of the research described in this dissertation was the synthesis and testing of novel palladacycle catalysts. New tridentate sulfur-carbon-sulfur (SCS) catalysts were synthesized and shown to by highly stable, air-insensitive, active palladium(II) catalysts for carbon-carbon bond forming reactions. Once incorporated into a soluble polymer support, these catalysts could be readily recovered by solvent precipitation or through the use of a thermomorphic system. The initial success of this project led to the study of modified SCS palladacycles as well as the development of a novel class of palladacycles generated by the cyclometallation of azobenzene derivatives. |
