Richard M. Laine

Catalytic synthesis of oligosilazanes part 2

Abstract Preliminary studies on transition metal-catalyzed dehydrocoupling of Si-H bonds with H-N bonds to form Si-N bonds, silazanes and H 2 are described. A number of transition metal complexes have been tested as catalyst precursors for the dehydrocoupling reaction. Of these, Ru 2 (CO) 8 -(Et 3 Si) 2 proved to be the most active homogeneous catalyst, and Pd particles produced by the in situ reduction of Pd(OAc) 2 were the most active heterogeneous catalysts. Kinetic studies of the ruthenium-catalyzed reaction of Et 3 SiH with primary amines, RNH 2 (R = n-Pr, n-Bu, s-Bu and t-Bu) were run at 70 °C in THF. The effects of changes in Et 3 SiH, amine and catalyst concentrations on rates of reaction were examined. The data indicate that the dehydrocoupling catalytic cycle involves an extremely complex set of equilibria wherein the rate-determining step is dependant on the steric requirements of the amine and fragmentation of the starting Ru 3 (CO) 12 cluster.

New Catalytic Routes to Preceramic Polymers: Ceramic Precursors to Silicon Nitride and Silicon-Carbide Nitride

Abstract : Pyrolysis of a set of silicon and nitrogen substituted polysilazanes are conducted under a set of standard conditions (5 degrees C/min to 900 degrees C in a nitrogen atmosphere). The apparent ceramic compositions and ceramic yields for pyrolyzed samples of the polysilazanes (Ph(H)SiNH)x, (C6H13(H)SiNH)x, (Me(H)SiNH)x, and (H2SiNMe)x are determined. Preliminary conclusions concerning structure/reactivity relationships are discussed based on the pyrolysis results. Keywords: Polysilazanes, Structure/reactivity relationships, Catalysis, Synthesis, Pyrolysis, New catalytic reactions. Reprints.

Transition Metal Catalyzed Synthesis of Organometallic Polymers

Transition metal catalysts have recently been used to synthesize organo- metallic oligomers and polymers containing boron or silicon in the polymer backbone. Three types of transition metal catalyzed reactions have proven useful for organometallic polymer synthesis: (1) dehydrocoupling by self- reaction (2E-H —> H2 + E-E) or by reaction with an acidic hydrogen (E-H + X-H —> H2 + E-X); (2) redistribution of Si-H bonds with Si-O bonds, -[MeHSiO]x —> MeSiH3 + -[Me(O)1.5]x- and, (3) ring opening polymerization. In this review, we examine the potential utility of these catalytic methods for the synthesis of organometallic polymers. In each instance, an effort is made to illustrate the generality or lack thereof for reaction types. Relevant literature and proposed reaction mechanisms for each reaction are discussed.

Chemical processing of glasses

The development of chemical processing methods for the fabrication of glass and ceramic shapes for photonic applications is frequently Edisonian in nature. In part, this is because the numerous variables that must be optimized to obtain a given material with a specific shape and particular properties cannot be readily defined based on fundamental principles. In part, the problems arise because the basic chemistry of common chemical processing systems has not been fully delineated. The prupose of this paper is to provide an overview of the basic chemical problems associated with chemical processing. The emphasis will be on sol-gel processing, a major subset pf chemical processing. Two alternate approaches to chemical processing of glasses are also briefly discussed. One approach concerns the use of bimetallic alkoxide oligomers and polymers as potential precursors to mulimetallic glasses. The second approach describes the utility of metal carboxylate precursors to multimetallic glasses.