Tri-tert-butylsilylsilylenes with Alkali Metal Substituents ( t Bu3Si)SiM (M = Li, K):  Electronically and Sterically Accessible Triplet Ground States

Lithium-, sodium-, and potassium-substituted silirenes 2a−c have been prepared by the reaction of bis(tri-tert-butylsilyl)silirene 1 with the corresponding alkali metals and characterized by NMR spectroscopy and chemical trapping (2a and 2b). Lithio- and potassiosilylenes, Li( t Bu3Si)2Si: (4a) and K( t Bu3Si)2Si: (4b), were generated by low-temperature irradiation of 2a and 2b, respectively, and their EPR spectra revealed the characteristic broad EPR signals at 790 mT for 4a and 780 mT for 4b. The Curie law dependence observed for 4a was in accord with a triplet ground state, also assigned to 4b. Computations on model lithiosilylenes support these assignments.