Silicon becomes colored: Stable biradicals were prepared from an N-heterocyclic carbene stabilized SiCl2 and a cyclic alkyl(amino)carbene, and characterized as two polymorphs. The deep-blue crystals of one polymorph are stable upon exposure to air for about a week, while the solution in THF decomposes rapidly when exposed to air. In a side reaction, the different carbene species react with each other under C-H activation and C-C bond formation in the presence of the biradical. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.