The Structure of the Carbene Stabilized Si<sub>2</sub>H<sub>2</sub> May Be Equally Well Described with Coordinate Bonds as with Classical Double Bonds

The cyclic alkyl­(amino) carbene stabilized Si<sub>2</sub>H<sub>2</sub> has been isolated in the molecular form of composition (Me-cAAC:)<sub>2</sub>Si<sub>2</sub>H<sub>2</sub> (<b>1</b>) and (Cy-cAAC:)<sub>2</sub>Si<sub>2</sub>H<sub>2</sub> (<b>2</b>) at room temperature. Compounds <b>1</b> and <b>2</b> were synthesized from the reduction of HSiCl<sub>3</sub> using 3 equiv of KC<sub>8</sub> in the presence of 1 equiv of Me-cAAC: and Cy-cAAC:, respectively. These are the first molecular examples of Si<sub>2</sub>H<sub>2</sub> characterized by single crystal X-ray structural analysis. Moreover, electrospray ionization mass spectrometry and <sup>1</sup>H as well as <sup>29</sup>Si NMR data are reported. Furthermore, the structure of compound <b>1</b> has been investigated by theoretical methods. The theoretical analysis of <b>1</b> explains equally well its structure with coordinate bonds as with classical double bonds of a 2,3-disila-1,3-butadiene.