Synthesis of an N-Heterocylic Boryl-Stabilized Disilyne and Its Application to the Activation of Dihydrogen and C-H Bonds.

The synthesis of low-valent silicon compounds that enable the activation of small molecules has been of great current interest. Reduction of N-heterocyclic boryltribromosilane (NHB)SiBr 3 (2, NHB=[ArN(CMe) 2 NAr]B, Ar=2,6-iPr 2 C 6 H 3 ) with three equiv. of lithium in diethyl ether yielded the NHB-stabilized disilyne (NHB)Si≡Si(NHB) (3). Disilyne 3 slowly reacted with toluene, leading to the activation of one benzylic C-H bond and one C=C double bond with the formation of 4. Treatment of 3 with dihydrogen under 1 atm at room temperature resulted in the exclusive formation of the first boryl-stabilized 1,2-dihydrodisilene. Compounds 3-5 have been characterized by single-crystal X-ray diffraction studies, which indicated the co-planarity of the B-Si-Si-B plane with the NHB rings in compounds 3 and 5. DFT calculations indicated the significant π electron delocalization of the Si-Si multiple bonds to the B-N bonds in NHB rings.