Germacyclobutenes: Generation by 1,1‐Carbalumination or 1,1‐Carbagallation and Their Photophysical Properties |
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| Authors: | Prof?Dr Werner Uhl Stefan Pelties Jens Tannert Prof?Dr Bart Jan Ravoo Prof?Dr Ernst‐Ulrich Würthwein |
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| Affiliation: | 1. Institut für Anorganische und Analytische Chemie der Universit?t Münster, Corrensstra?e 30, 48149 Münster (Germany), Fax: (+49)?251‐8336660;2. Organisch‐chemisches Institut der Universit?t Münster, Corrensstra?e 40, 48149 Münster (Germany) |
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| Abstract: | Aluminium‐ and gallium‐functionalised alkenylalkynylgermanes, R12Ge(C?C?R2)C{E(CMe3)2}?C(H)?R2] (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. |
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| Keywords: | carbagallation carbalumination germanium heterocycles photoluminescence |
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