A new hexakis(isocyanato)silicate(IV) and the first neutral Lewis-base adducts of silicon tetraisocyanate.

The new silicates K2Si(NCE)6, E = O, S (1a,b) were synthesised directly by reaction of silicon tetrachloride with potassium cyanate or thiocyanate. 1a,b can be converted to the salts (PPN)2[Si(NCE)6] (2a,b) with bulky cations (PPN+ = N(PPh3)2+), which contain isolated silicate dianions. Reaction of 1a with diimines affords the hexacoordinate complexes Si(NCO)4L, L = bpy (3), phen (4), which are the first isolated neutral adducts to Si(NCO)4. The compounds were characterised by a combination of IR and NMR spectroscopies, MS, TGA, DSC and X-ray diffraction.