Polymers transition metal-catalyzed dehydrocoupling

None of the above described ring opening polymerization methods has, as yet, proved useful for the formation of polysilazane preceramic polymers. However, Si-N bond cleavage and reformation, as it occurs in reaction (13), is probably responsible in part for the curing or thermoset step in transition metal catalyzed dehydrocoupling polymerization of hydridosilazanes (31), as described below. 

CMS is a suitable reactant for the transition metal-catalyzed dehydrocoupling because of its multiple Si-H and N-H sites. The polymerization reaction catalyzed by Ru3(O0)i2 can be manipulated to form various types of polymers with different properties, as shown in Scheme 4. The elemental composition of each polymeric product are shown in Table 1 and the pyrolysis results in Table 2. 

Several comprehensive reviews on the preparation, structure, properties, photochemistry, and redistribution of polysilanes prepared by the Wurtz coupling method have been published.1516 31 33 There are also several excellent reviews on the transition-metal-complex-catalyzed dehydrocoupling of hydrosilanes to polysilanes.34 36 The present section reviews the more recent work on the dehydropolymerization of hydrosilanes to polysilanes, catalyzed by transition-metal complexes under homogeneous conditions. Extensions of the methodology to the dehydropolymerization of hydrogermanes, hydrostannanes, and hydrophosphanes to the corresponding polymers are also reviewed. The literature is covered up to early 1997. 

Borazine and its derivatives are also possible educts to synthesize precursors for Si-B-N-C ceramics. Sneddon and co-workers prepared Si-B-N-C preceramic precursors via the thermal dehydrocoupling of polysilazanes and borazines [7]. A further synthesis route is the hydroboration of borazines. The work group of Sneddon found that definite transition metal reagents catalyze hydroboration reactions with olefins and alkynes to give 5-substituted borazines [8]. Recently, Jeon et al. reported the synthesis of polymer-derived Si-B-N-C ceramics even by uncatalyzed hydroboration reactions from borazines and dimethyldivinylsilane [9]. 

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