A cyclopentadienyl functionalized silylene – a flexible ligand for Si- and C-coordination

The synthesis of a 1,2,3,4-tetramethylcyclopentadienyl (Cp(4)) substituted four-membered N-heterocyclic silylene [{PhC(NtBu)(2)}Si(C(5)Me(4)H)] is reported first. Then, selected reactions with transition metal and a calcium precursor are shown. The proton of the Cp(4)-unit is labile. This results in two different reaction pathways: (1) deprotonation and (2) rearrangement reactions. Deprotonation was achieved by the reaction of [{PhC(NtBu)(2)}Si(C(5)Me(4)H)] with suitable zinc precursors. Rearrangement to [{PhC(NtBu)(2)}(C(5)Me(4))SiH], featuring a formally tetravalent silicon R(2)C[double bond, length as m-dash]Si(R′)–H unit, was observed when the proton of the Cp(4) ring was shifted from the Cp(4)-ring to the silylene in the presence of a Lewis acid. This allows for the coordination of the Cp(4)-ring to a calcium compound. Furthermore, upon reaction with transition metal dimers [MCl(cod)](2) (M = Rh, Ir; cod = 1,5-cyclooctadiene) the proton stays at the Cp(4)-ring and the silylene reacts as a sigma donor, which breaks the dimeric structure of the precursors.