1-Isothiocyanato-3,7,10-trimethyl-5-aza-2,8,9-trioxa-1-silabicyclo[126.96.36.199]undecane 3, containing transannular N → Si bond, has been synthesized by transesterification reaction of trisisopropanolamine and triethoxyisothiocyanato silane. To study the reactivity of exocyclic NCS group, 3 was treated with methyliodide, triethylsilane and aniline. All synthetic compounds have been characterized by spectroscopic methods and elemental analysis and by an X-ray crystal structure determination in the case of 3. Single crystal X-ray studies have shown that the asymmetric unit contains two crystallographically independent molecules. It has depicted the distorted trigonal bipyramidal coordination at the silicon atom with N → Siav. bond distance of 2.0385 å. The structural investigations were complemented by quantum chemical studies of the structure.