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](2)Si (1) with FeBr2, CoBr2, NiBr2 center dot 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 center dot HF, 7, and 8 center dot 0.5 Et2O were structurally characterized by single-crystal X-ray diffraction. In addition, compound 6 center dot THF was studied by N-15 and Si-29 solid-state NMR spectroscopy, and 7 and 8 were characterized by NMR spectroscopic studies in the solid state (N-15, Si-29) and in solution (H-1, C-13, Si-29). Compounds 4-8 represent very rare examples of Fe-II, Co-II, Ni-II, and Zn-II 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.