Bis(2,4,6‐triisopropylphenyl)‐2,7‐di‐tert‐butylfluorenylidenestannane, Tip2Sn=CR2, an isolable stannene that displays a deep‐purple colour, was synthesized by dehydrofluorination of the corresponding fluorostannane by tert‐butyllithium. It exhibits the shortest Sn=C distance [2.003(5) Å] and the slightest twisting around this unsaturation (10°) among the known stannenes. Its reaction with benzaldehyde according to a [2+2] cycloaddition and that with α‐ethylenic aldehydes and ketones such as crotonaldehyde and methyl vinyl ketone by a [2+4] cycloaddition proceeded in near‐quantitative yield. With acetone, an ene reaction occurred. The four‐membered ring 1,2‐oxastannacyclobutane obtained with benzaldehyde underwent a ring expansion with a second molecule of benzaldehyde to afford the six‐membered ring dioxastannacyclohexane.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

The stannene Tip 2 SnCR 2 (1; Tip = 2,4,6-triisopropylphenyl, CR 2 = 2,7-di-tert-butylfluorenylidene) gives [2 + 2] cycloadditions with phenyl isocyanate and diphenylketene (by the CO bond) and phenyl isothiocyanate (by the CS bond) to afford the corresponding four-membered heterocycles. [2 + 3] cycloadditions are observed between 1 and N-tert-butyl α-phenyl nitrone and methyl (benzylideneamino)acetate. Very different reactions occur with nitriles: an insertion of a C−H bond of acetonitrile across the SnC double bond and a [2 + 2] cycloaddition between SnC double bond and CN unsaturation of pivalonitrile.