A nearly planar stannene with a reactive tin-carbon double bond

Bis(2,4,6-triisopropylphenyl)-2,7-di-tert-butylfluorenylidene starmane, TiP(2)Sn=CR(2), an isolable stannene that displays a deep-purple colour, was synthesized by dehydrofluorination of the corresponding fluorostarmane by tert-butyllithium. It exhibits the shortest Sn=C distance [2.003(5) angstrom] and the slightest twisting around this unsaturation (10 degrees) among the known stannenes. Its reaction with benzaldehyde according to a [2+2] cycloaddition and that with alpha-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. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008).