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Although tetrameric Al(I) compounds have been known for a long time, the monomeric Al(I) compounds that are analogous to carbenes are very recent entrants in Al(I) chemistry. They possess novel structural features and exhibit distinct reactivity. This has resulted in the isolation and characterization of various unusual aluminum(III) compounds such as the aluminatetrazoles and aluminacyclopropenes. In comparison to the recent emergence of monomeric aluminum(I) compounds, stable silylenes and germylenes (carbene analogues of silicon and germanium) were recognized much earlier. This led to the evolution of the Si(II) and Ge(II) chemistry that at times surpasses the sophistication achieved in divalent carbon chemistry. Thus, while carbon lacks an example of a stable chlorocarbene (LCCl), for silicon there is one example of LSiCl, and for germanium there are a fair number of LGeCl compounds. While reactivity studies on LSiCl are anticipated, the utility of RGeCl as a synthon is well documented. Exotic compounds such as a germanethioacid chloride, a germanium(II) hydride, and a germanium(II) hydroxide are some of the examples that were derived from LGeCl. Recent results from our laboratory at Göttingen have helped in the development of these interesting areas of research, and the present account summarizes our contributions to the chemistry of Al(I), Si(II), and Ge(II).

This article reports the reduction of the chloride [PhC(NtBu) 2 ]GeCl with potassium in THF to afford the reddish crystals of [PhC(NtBu) 2 ] 2 Ge 2 (2). The molecule of 2 contains a Ge-Ge bond. The X-ray structure and DFT calculation indicate that the Ge-Ge bond possesses an unusual gauche-bent geometry. The Ge-Ge bond length in 2 is 2.570 Å, which is very close to the single Ge-Ge interaction (2.61 Å) but significantly longer than that for typical digermenes, R 2 GeGeR 2 (2.21-2.51 Å) and the two structurally characterized digermynes (2.2850 Å and 2.2060 Å), which proves that there is no multiple bond character in 2.

Based on reactions known in organotin chemistry, the robust hexaferrocene assembly [{BuSn(O)OC(O)Fc}6] is obtained in quantitative yield by the reaction of two commercially available reactants. The X‐ray crystal structure (see picture) shows a symmetric giant wheel arrangement of the ferrocene units attached in a cyclic manner to a central drumlike stannoxane core. Cyclic voltammetric studies show a single quasireversible oxidation peak.