Strukturuntersuchungen an Verbindungen mit höher koordiniertem Silicium: Modelle zum Studium der nucleophilen Substitution an Silicium-Zentren

Abstract

Silicon compounds substituted by 2-(dimethylaminomethyl)phenyl groups [C 6H 4CH 2N(CH 3) 2] n SiX 4- n (X  Cl, H, organo group, n = 1–4) are available by the reaction of the appropriate chlorosilanes with 2-(dimethylaminomethyl)phenyllithium. A comparison of the 29Si NMR spectroscopic shifts δ with the values obtained for corresponding phenyl silanes shows that there is higher coordination of the silicon atom by N → Si contacts, except for the silanes 11 (X  Cl; n = 3) and 12 ( n = 4). X-ray crystal structure analysis confirms pentacoordination of the silicon atom in the dichlorosilanes 4 (X  Cl; n = 2) and 5. For [C 6H 4CH 2N(CH 3) 2] 3SiH ( 10) heptacoordination of the silicon atom is found in the crystalline state [ d(N → Si) ≈ 301 pm]. The tetrasubstituted derivative [C 6H 4CH 2N(CH 3) 2] 4Si ( 12) has no N → Si contacts in solution and in the solid state: st eric congestion does not allow higher coordination. 10: colourless prisms, monoclinic, space group P 2 1/ n; lattice constants: a = 889.0(3), b = 1677.5(8), c = 3471(1) pm; β = 90.35(3)°. 12: colourless prisms, pseudo tetragonal, space group I4 1/ a; lattice constants: a = b = 1699.7(4), c = 3398.9(17) pm.