Beiträge zur chemie der halogensilan-addukte

Dimethyl-, diphenyl- and cyclotetramethylene silylchloride derivatives of guanidine, their synthesis and structure. Formation of pentacoordinated silicon compounds and an unexpected diionic disila-diguanidinium dichloride

“…The in solid-state pentacoordinate compound 4, on the other hand, showed one peak at 26.1 ppm in tetrachloroethane (decomposed in CDCl 3 ), which should be explained as an ionic k 4 Si-compound [32]. The 13 C NMR of 4 in THF-d 8 also showed only 4 signals from the guanidine unit, leading to the conclusion of a symmetric molecule with respect to the two rings in the structure.…”

“…This shift value is in the area between the border values for an ionic k 4 Si-and a k 5 Si-coordination state [32]. If we assume a similar level for the border value for a k 5 Si-coordinated 2 as for very similar structures in C 6 D 6 (À57 ppm, referred by Kummer et al [32]), the shift value of À52.2 ppm for compound 2 will indicate that the major part is in a k 5 Si-coordination state and a minor part in an ionic k 4 Si-coordination state. In the 13 C NMR (C 6 D 6 ), only 5 types of carbons are shown in the molecule.…”

“…We therefore looked at 4-ring k 5 Si-amidines as well as 5-ring k 5 Si and 4-ring k 6 Si-guanidine systems. The examples we found were a guanidine (5) by Kummer [32] together with a k 6 Si-bis-amidine (6) and k 5 Si-amidine (7) by Karsch [33][34][35] (Scheme 3).…”

“…The in solid-state pentacoordinate compound 3 shows one signal in C 2 D 2 -Cl 4 at À77.3 ppm and in CDCl 3 at À77.2 ppm. Compound 3 thus keeps its k 5 Si-coordination from solid state in both solvents [32]. The 13 C NMR spectra of 3 in CDCl 3 reveal only 4 signals originating from the [hpp] À unit, indicating a symmetric structure, where the two rings are equal on the timescale of the NMR experiment.…”

“…Selected bond lengths (Å ) of 3 and 4 in comparison to k 5 Si-chloro-dimethyl-(3,4,7,8-tetrahydro-2H,6H-pyrimido[1,2-a]pyrimidin-1-yl-methyl-C 0 1 0 ,N 0 9 0 )-silicon (5)[32], cis-dichlorosilicon (bis)methyl-isopropyl amidinate (6) and k 5 Si-1,3-diaza-1-tert-butyl-4-phenyl-3-(bistrifluoromethylmethylene)-2,2-dichloro-2-fluoro-2-silacyclobute-3-ene(7).…”