A Distorted Trigonal Antiprismatic Cationic Silicon Complex with Ureato Ligands: Syntheses, Crystal Structures and Solid State 29 Si NMR Properties

Insertion of phenyl isocyanate into the Si–N bond of N ‐(trimethylsilyl)diethylamine yields the N′ ‐silylated N , N ‐diethyl‐ N′ ‐phenylurea 1 , which undergoes transsilylation with SiCl 4 to yield the C 3 ‐symmetric cationic hexacoordinate silicon complex 3s + [tris‐κ‐ O , N′ ‐( N , N ‐diethyl‐ N′ ‐phenylureato)siliconium] as chloride salt, which was characterized crystallographically. The cationic complex 3s + exhibits a distorted trigonal antiprismatic coordination sphere about the silicon atom with fac arrangement of the three N‐atoms (and the three O‐atoms) relative to one another. This C 3 ‐symmetric complex undergoes isomerization into its asymmetric isomer 3a + ( mer arrangement of NNN or OOO relative to one another) in CDCl 3 solution. Hence, two 29 Si NMR signals appear and four sets of signals emerge in the 1 H and 13 C NMR spectra. Despite its pronounced axial symmetry, the 29 Si NMR shielding tensor of the cation 3s + in its chloride salt exhibits an unusually small span (less than 20 ppm), which was analyzed CP/MAS NMR spectroscopically and by computational methods.