Activation of CO Using a 1,2-Disilylene: Facile Synthesis of an Abnormal N-Heterocyclic Silylene.

Reaction of the 1,2-disilylene, [{ArC(NDip) 2 }Si] 2 1 (Dip=2,6-diisopropylphenyl, Ar=4-C 6 H 4 Bu t ), with CO proceeds via insertion of CO into one Si-N bond, and Si-Si bond cleavage, to cleanly give the bis(silylene), {ArC(NDip) 2 }Si(:)O C S i ( : ) ( N D i p )​ 2 C ‾ Ar 2, under ambient conditions. The reaction can be partially reversed when solutions of 2 are subjected to UV irradiation. The five-membered heterocyclic fragment of 2 represents the first silicon analogue of an "abnormal" N-heterocyclic carbene (aNHC), a view which is substantiated by a computational analysis of the compound. Reaction of 2 with [Mo(CO) 6 ] under UV light affords the chelate complex, [Mo(CO) 4 (κ 2 -Si,Si-2)] 3, while reaction with [Fe(CO) 5 ] gives the unusual silyleneyl bridged complex, [{Fe 2 (CO) 6 }{μ-Si[(NDip) 2 CAr]} 2 ] 4. The same coordination complexes can be accessed by reaction of 1 with [Mo(CO) 6 ] or [Fe(CO) 5 ] under UV light. As is the case for aNHCs, d-block metal complexes of bis(silylene) 2 could prove useful as bespoke catalysts for organic transformations.