A Masked Boryl-Substituted Oxo-Bridged Bis-Silylene: Synthesis and Reductive-Elimination and Synergistic Oxidative-Addition Reactivity.

Controlled oxidation of NHB-stabilized disilyne (NHB)Si ≡ Si(NHB) (, NHB = [ArN(CMe)NAr]B, Ar = 2,6-PrCH) with one equivalent of trimethylamine N-oxide (MeN─O) in dry -hexane gave oxo-bridged bis-silepin in high yields. DFT calculations disclosed that silepin is only more stable by 13.4 kcal/mol than the corresponding oxo-bridged bis-silylene intermediate (NHB)Si(μ-O)Si(NHB), and was very likely to be formed by the insertion of the two divalent Si atoms into the pendant aryl rings in bis-silylene intermediate . The two silicon atoms in bis-silepin could undergo formal reductive-elimination of the aryl rings and sequential oxidative-insertion reactions with small molecules and organic substrates. Treatment of with HO, S, and P at 60 °C yielded compounds - via reductive-elimination of the aryl rings, followed by the sequential oxidative-addition of these molecules at the two Si(II) centers. Similarly, reactions of with PhSiH, a diphenylalkyne, pyridines, 1,3,4,5-tetramethylimidazolin-2-ylidene (IMe), PhCO, and thiophene yielded the corresponding polycyclic bis-silanes - via reductive-elimination and oxidative-addition of C-H, Si-H, C≡C, and aromatic C═C, C-S, and C═N bonds at the two Si atoms. These novel reactions indicated the pronounced bis-silylene reactivity of bis-silepin , consistent with the low-energy barrier for the interconversion between and , as disclosed by DFT calculations.