Trimethylsilylnitrene and Its Surprising Rearrangement to N-(Dimethylsilyl)methanimine via Silaziridine and Silaazomethine Ylide

Photolysis of trimethylsilyl azide at 254nm in Ar matrix at 15K generates the triplet ground state trimethylsilylnitrene 2aT, observed by ESR spectroscopy (|D/hc| = 1.540cm(-1); |E/hc| = 0.0002cm(-1)). Calculations at the CASPT2(14,13) level reveal the open-shell singlet nitrene 2aS((1)A) is a discrete intermediate lying approximate to 38kcal mol(-1) above the triplet. The normally expected rearrangement of the nitrene 2aS to dimethylsilanimine 3a has a high calculated barrier (33kcal mol(-1)), which explains why this product has never been observed. Instead, the singlet nitrene 2aS inserts into a methyl C-H bond to yield silaziridine 12 via an activation barrier of only 6kcal mol(-1). Ring opening of 12 generates a 1-silaazomethine ylide 13, in which a facile 1,2-H shift yields N-(dimethylsilyl)methanimine 5, all with barriers well below the energy of the singlet nitrene.