A new aspect of the “pseudo water” concept of bis(trimethylsilyl)carbodiimide – “pseudohydrates” of aluminum

Abstract

Bis(trimethylsilyl)carbodiimide (BTSC), so-called “pseudo water” because of some analogies such as similar (group)electronegativities of Me3Si– vs. H– and –N=C=N– vs. –O–, may form two different kinds of “pseudo hydrates” of metals (M), i.e. M–N(SiMe3)=C=N(SiMe3) and M–N≡C–N(SiMe3)2, derived from its carbodiimide and cyanamide isomeric forms, respectively. With anhydrous AlCl3 in Me3SiCl solution BTSC was shown to be capable of forming both kinds of solvates, i.e. Cl3Al–N(SiMe3)–C≡N(SiMe3) (1) and ((Cl3Al)(Me3Si)NCN)3–Al–(N≡C–N(SiMe3)2)3 (2). Both compounds were isolated as crystalline solids, which undergo condensation reactions upon storage. By single-crystal X-ray diffraction analysis the constitution of 1 was confirmed unambiguously, and quantum chemical calculations (B3LYP/6-311++g(d,p)) confirmed that compound 1 is 6 kcal mol−1 more stable than its hypothetical N,N-bis(trimethylsilyl)cyanamide isomer Cl3Al–N≡C–N(SiMe3)2. Compound 1 represents the first crystallographically confirmed disilylcarbodiimide complex of a metal salt. The molecules of compound 2 are heavily disordered in the solid state (positional disorder of N≡C–N(SiMe3)2 vs. N≡C–N(SiMe3)(AlCl3) and positional disorder of SiMe3 vs. AlCl3 groups in the latter). Therefore, the identity of 2 was additionally confirmed by 13C, 15N, 27Al and 29Si CP/MAS NMR spectroscopy.

A Non-Hydrolytic Sol–Gel Route to Organic-Inorganic Hybrid Polymers: Linearly Expanded Silica and Silsesquioxanes

“…Silylcarbodiimides may also by viewed as “linearly expanded Si–O” compounds, since the oxygen atoms are replaced by NCN-units as alternative difunctional linkers of similar electronegativity [ 48 , 49 , 50 , 51 , 52 , 53 ]. This approach differs from the above oxides since Si–O bonds are replaced by Si–N bonds ( Figure 1 c).…”

“…Several attempts to extend this Sol–Gel system through replacing the chlorosilanes with other element halides were not successful. For example, analogous reactions with titanium chlorides, such as TiCl 4 or CpTiCl 3 , led to the formation of precipitates; the use of RAlCl 2 and gallium chlorides as starting materials gave soluble oligomers [ 52 ]. However, B-trichloroborazene (B 3 N 3 H 3 Cl 3 ) reacts similarly to the chlorosilanes with bis(trimethylsilyl)carbodiimide and forms B/C/N gels ( Scheme 3 b) that can be transformed into B/C/N and B 4 C ceramics [ 53 ].…”