title: Germacyclobutenes: generation by 1,1-carbalumination or 1,1-carbagallation and their photophysical properties.
abstract: Aluminium- and gallium-functionalised alkenylalkynylgermanes, R(1) 2 Ge(C≡C-R(2) )[C{E(CMe3 )2 }=C(H)-R(2) ] (E=Al, Ga), exhibit a close contact between the coordinatively unsaturated Al or Ga atoms and the α-C atoms of the intact ethynyl groups. These interactions activate the Ge-C(alkynyl) bonds and favour the thermally induced insertion of these C atoms into the E-C(vinyl) bonds by means of 1,1-carbalumination or 1,1-carbagallation reactions. For the first time the latter method was shown to be a powerful alternative to known metallation processes. Germacyclobutenes with an unsaturated GeC3 heterocycle and endo- and exocyclic C=C bonds resulted from concomitant Ge-C bond formation to the β-C atoms of the alkynyl groups. These heterocyclic compounds show an interesting photoluminescence behaviour with Stokes shifts of >110 nm. The fascinating properties are based on extended π-delocalisation including σ*-orbitals localised at Ge and Al. High-level quantum chemical DFT and TD-DFT calculations for an Al compound were applied to elucidate their absorption and emission properties. They revealed a biradical excited state with the transfer of a π-electron into the empty p-orbital at Al and a pyramidalisation of the metal atom.
authors.affiliation: Institut für Anorganische und Analytische Chemie der Universität Münster, Corrensstraße 30, 48149 Münster (Germany), Fax: (+49) 251-8336660. uhlw@uni-muenster.de.
authors.forename: Werner
authors.initials: W
authors.lastname: Uhl
authors.forename: Stefan
authors.initials: S
authors.lastname: Pelties
authors.forename: Jens
authors.initials: J
authors.lastname: Tannert
authors.forename: Bart Jan
authors.initials: BJ
authors.lastname: Ravoo
authors.forename: Ernst-Ulrich
authors.initials: EU
authors.lastname: Würthwein
keywords: carbagallation; carbalumination; germanium; heterocycles; photoluminescence