Synthesis and NMR study of intramolecular silacyclobutane complexes: 8-aza-5,11-dioxa-4-silaspiro[3,7]undecane and 8-methyl-8-aza-5,11-dioxa-4-silaspiro[3,7]undecane

The intramolecular silacyclobutane complexes with pentaacoordination at silicon, 8-aza-5,11- dioxa-4-silaspiro(3,7)undecane and 8-methyl-8-aza-5,11-dioxa-4-silaspiro(3,7)undecane, were synthesized by reacting 1,1-dimethoxy- or 1,1-bis(diethylamino)silacyclobutanes with the corresponding diethanolamines. The existence of (Si N) pentaacoordination at silicon was deduced from the pronounced upfield 29 Si and downfield 13 C NMR shifts as well as from the low temperature 13 C NMR study of their dynamic behavior in solution that proved complexes to appear as two isomers with coalescence barriers of 11.5 kcal/mol and 12.9 kcal/mol for 1 and 2, respectively.