Ferrocene-Based N-Heterocyclic Silylenes: Monomeric Silanechalcogenones, Silanimines, Silirenes, and Insertion Products with P.

The stable ferrocene-based N-heterocyclic silylenes fc[(N{B})Si] (A; fc=1,1'-ferrocenylene, {B}=(HCNDipp)B, Dipp=2,6-diisopropylphenyl) and fc[(NDipp)Si] (B) are compared in a study focussing on their reactivity towards a range of small to moderately sized molecular substrates, viz. P, S, Se, MesN (Mes=mesityl), RC≡CH, and RC≡CR (R=Ph, SiMe). The Dipp-substituted congener B exhibits a more pronounced ambiphilicity and is sterically less congested than its 1,3,2-diazaborolyl-substituted relative A, in line with the higher reactivity of the former. The difference in reactivity is obviously due more to electronic than to steric reasons, as is illustrated by the fact that both A and B react with the comparatively bulky substrate MesN under mild conditions to afford the corresponding silanimine fc[(N{B})Si=NMes] and fc[(NDipp)Si=NMes], respectively. The heavier ketone analogues fc[(N{B})Si=E] (E=S, Se, Te) are readily available from A and the corresponding chalcogen. In contrast, the reaction of the more reactive silylene B with elemental sulfur or selenium is unspecific, affording product mixtures. However, fc[(NDipp)Si=Se] is selectively prepared from B and (EtN)PSe; the Te analogue is also accessible, but crystallises as head-to-tail dimer.