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Germacyclobutenes: Generation by 1,1‐Carbalumination or 1,1‐Carbagallation and Their Photophysical Properties
Author(s) -
Uhl Werner,
Pelties Stefan,
Tannert Jens,
Ravoo Bart Jan,
Würthwein ErnstUlrich
Publication year - 2015
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201405739
Subject(s) - excited state , chemistry , atomic orbital , atom (system on chip) , crystallography , gallium , photochemistry , metal , photoluminescence , electron , materials science , atomic physics , organic chemistry , physics , optoelectronics , quantum mechanics , computer science , embedded system
Aluminium‐ and gallium‐functionalised alkenylalkynylgermanes, R 1 2 Ge(CCR 2 )[C{E(CMe 3 ) 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 GeC(alkynyl) bonds and favour the thermally induced insertion of these C atoms into the EC(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 GeC 3 heterocycle and endo‐ and exocyclic CC bonds resulted from concomitant GeC 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.