Exchange reactions of bis(trimethylsilyl)carbodiimide (BTSC) with diorganodichlorosilanes were investigated with the aim to synthesize substitution products of the types R 2 SiCl(NCNSiMe 3 ), R 2 Si(NCNSiMe 3 ) 2 , and [R 2 Si(NCN)] n (R = Me, Ph, PhCH 2 , and Vin), which can be used as precursors for Si/C/N materials with tuned pore structures. Extensive 29 Si NMR spectroscopic investigations indicated that complex product mixtures containing several of the mentioned compounds are formed, independent of the starting materials and reaction conditions. The relative stabilities of the cyclic silylcarbodiimides of ring sizes 4n with n = 2-6 were calculated with DFT methods and compared, also considering the respective isomeric cyanamides with rings containing 2n atoms. According to these quantum chemical studies, the cyclic tetramer [Ph 2 Si(NCN)] 4 was predicted to be the most stable among the phenyl-substituted rings. It was experimentally synthesized via pyridine-catalyzed reactions of Ph 2 SiCl 2 with BTSC, isolated as [Ph 2 Si(NCN)] 4 3 (dioxane) 2 and structurally analyzed. In the course of attempts to selectively prepare oligosilylcarbodiimides from cyclosilazanes, high-quality crystals of hexaphenylcyclotrisilazane [Ph 2 Si-NH] 3 were obtained and characterized by X-ray single crystal structure analysis.

Reactions of various organochlorosilanes with the salphen-like tetradentate (ONN′O′) ligand o-HO-p-MeO-C6H3C(Ph)N(o-C6H4)NCHC6H4-o-OH, bearing two chemically and sterically different imine moieties, provided insights into the regio- and diastereoselectivity of various rearrangement reactions. Whereas thermally driven allyl- and UV-induced phenyl-shift reactions from the Si to an imine carbon atom yield one diastereomer, hydride-shift reactions were found to be less diastereoselective; however, only the sterically less demanding salicylaldimine site was attacked in all these rearrangement reactions.

No abstract

No abstract