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 reaction of 1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2a]pyrimidinyl potassium, [hpp]−K+ (1), with dimethyldichlorosilane, diphenyldichlorosilane or cyclotetramethylenedichlorosilane (1,1-dichloro silolane) in THF resulted in the formation of the in solid-state unexpected diionic dimer λ4Si-[Me2SiCl(hpp)]2 (2) (76%), as well as λ5Si-Ph2SiCl(hpp) (3) (87%) and λ5Si-(CH2)4SiCl(hpp) (4) (28%). Compounds 3 and 4 are the first synthesised examples of four ring (–λ5Si–N–Cdouble bond; length as m-dashN–) guanidine structures. 1H and 13C NMR show the compounds to have a symmetric guanidine unit in solution. 29Si NMR analysis shows the structures, in selected solvents, to be of λ5Si-type for 3 and to the major part for 2. Compound 4, on the other hand, is of ionic λ4Si-type. The syntheses and molecular structures of the compounds are discussed.