From Unsymmetrically Substituted Benzamidinato and Guanidinato Dichlorohydridosilanes to Novel Hydrido N‑Heterocyclic Silylene Iron Complexes

Starting
from the unsymmetric N,N′-substituted thiourea
compounds (R)­N­(H)­C­(S)­N­(H)­(tBu)
(1, R = Dipp: 2,6-iPr2-C6H3; 2, R = 1-adamantyl),
the corresponding asymmetric carbodiimines (R)­NCN­(tBu) (3, R = Dipp; 4, R = 1-adamantyl) are readily accessible in high yields upon reduction
with LiHMDS (Li­[N­(SiMe3)2]). The reaction of
compound 3 with PhLi followed by SiCl4 afforded,
in a one-pot reaction, the asymmetric benzamidinato-stabilized trichlorosilane
[PhC­{(NtBu)­(NDipp)}]­SiCl3 (5). Similarly, silanes [PhC­{(NtBu)­(NDipp)}]­SiHCl2 (6), [(NMe2)­C­{(NtBu)­(NDipp)}]­SiHCl2 (7), and [PhC­{(NtBu)­(NAd)}]­SiHCl2 (8) could also be
isolated. All novel trichloro- or dichlorohydridosilanes were fully
spectroscopically characterized and studied by single-crystal X-ray
diffraction analyses, the latter revealing in all cases a distorted-trigonal
bipyramidal five-coordinate silicon center. The reactions of silanes 5–8 with K2[Fe­(CO)4] were also explored: In the case of the reaction of silane 5 with K2[Fe­(CO)4], no reaction was
observed even after prolonged heating. However, in the case of the
silanes 6–8, the selective formation
of the corresponding hydrido SiII:→Fe0 complexes [[R1C­{(NtBu)­(NR2)}]­(H)­Si:→Fe­(CO)4] (9, R1 = Ph, R2 = Dipp; 10, R1 = NMe2, R2 = Dipp; 11, R1 = Ph, R2 = 1-adamantyl) could be achieved. Complexes 9–11 represent unprecedented hydrido-N-heterocyclic
silylene complexes, bearing asymmetric ligand backbones. Complexes 9–11 were fully spectroscopically characterized,
and in addition the single-crystal X-ray structure analysis of compound 10 is reported.