Iron(II), Cobalt(II), Nickel(II), and Zinc(II) Silylene Complexes: Reaction of the Silylene [iPrNC(NiPr2)NiPr]2Si with FeBr2, CoBr2, NiBr2⋅MeOCH2CH2OMe, ZnCl2, and ZnBr2

Reaction of the donor-stabilized silylene [iPrNC(NiPr2)NiPr]2Si (1) with FeBr2, CoBr2, NiBr2⋅MeOCH2CH2OMe, ZnCl2, and ZnBr2 afforded the respective transition-metal silylene complexes 4–8, the formation of which can be described in terms of a Lewis acid/base reaction (4, 5, 7, 8) or a nucleophilic substitution reaction (6). However, the reactivity profile of silylene 1 is not only based on its strong Lewis base character; the different coordination modes of the two guanidinato ligands (4–6 vs. 7 and 8) add an additional reactivity facet. The paramagnetic compounds 4 and 5 and the diamagnetic compounds 6⋅THF, 7, and 8⋅0.5 Et2O were structurally characterized by single-crystal X-ray diffraction. In addition, compound 6⋅THF was studied by 15N and 29Si solid-state NMR spectroscopy, and 7 and 8 were characterized by NMR spectroscopic studies in the solid state (15N, 29Si) and in solution (1H, 13C, 29Si). Compounds 4–8 represent very rare examples of FeII, CoII, NiII, and ZnII silylene complexes. Four-coordinate silicon(II) compounds with an SiN3M skeleton (M=Fe, Co, Ni) and M in the formal oxidation state +2 (4–6) have not yet been reported, and five-coordinate silicon(II) compounds with an SiN4Zn skeleton (7, 8) are also unprecedented.