Synthesis of New Silylated and N−Si−N bridged Urea Derivatives from Aminosilanes and Diisocyanates

Urea derivatives of the general motifs R¹(N(SiMe₃)C(O)NR²R³)₂ and [R¹(NC(O)NR²R³)₂SiMe₂]_n (R¹=difunctional organic linker, i. e., core of diisocyanate used; R²,R³= H,ⁿPr; H,Ph; Et,Et) were synthesized by insertion of four different diisocyanates (1,6-HMDI, 2,4-TDI, 1,3-TMXDI and 4,4'-MDI) into aminotrimethylsilanes Me₃SiNR²R³ and diaminodimethylsilanes Me₂Si(NR²R³)₂. The products obtained were analyzed by NMR and IR spectroscopy. Insertion into aliphatic aminosilanes was found to be favored for primary over secondary amino groups. For insertion into 4,4'-methylenebis(phenylisocyanate) (4,4'-MDI), good results were obtained for silanes derived from secondary amines as well. Insertion into aminosilanes with aromatic N-bound substituents turned out to be kinetically inhibited. Elucidation of molecular structures of the products by crystallography and NMR spectroscopy revealed interesting differences in N-Si connectivity, caused by steric and electronic effects of the reactants and migration of -SiMe₃ and -(SiMe₂)- moieties.