A Nearly Planar Stannene with a Reactive Tin–Carbon Double Bond

Abstract Bis(2,4,6‐triisopropylphenyl)‐2,7‐di‐ tert ‐butylfluorenylidenestannane, Tip 2 Sn=CR 2 , 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)