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

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