Heavier congeners of CO and CO(2) as ligands: from zero-valent germanium (‘germylone’) to isolable monomeric GeX and GeX(2) complexes (X = S, Se, Te)

In contrast to molecular CO and CO(2), their heavier mono- and dichalcogenide homologues, EX and EX(2) (E = Si, Ge, Sn, Pb; X = O, S, Se, Te), are important support materials (e.g., SiO(2)) and/or semiconductors (e.g., SiS(2)) and exist typically as insoluble crystalline or amorphous polymers under normal conditions. Herein, we report the first successful synthesis and characterisation of an extraordinary series of isolable monomeric GeX and GeX(2) complexes (X = S, Se, Te), representing novel classes of compounds and heavier congeners of CO and CO(2). This could be achieved by solvent-dependent oxidation reactions of the new zero-valent germanium (‘germylone’)–GaCl(3) precursor adduct (bis-NHC)Ge(0)→GaCl(3)1 (bis-NHC = H(2)C[{NC(H)[double bond, length as m-dash]C(H)N(Dipp)}C:](2), Dipp = 2,6-iPr(2)C(6)H(3)) with elemental chalcogens, affording the donor–acceptor stabilised monomeric germanium(iv) dichalcogenide (bis-NHC)Ge(IV)([double bond, length as m-dash]X)[double bond, length as m-dash]X→GaCl(3) (X = S, 2; X = Se, 3) and germanium(ii) monochalcogenide complexes (bis-NHC)Ge(II)[double bond, length as m-dash]X→GaCl(3) (X = Se, 4; X = Te, 5), respectively. Moreover, the reactivity of 4 and 5 towards elemental sulphur, selenium, and tellurium has been investigated. In THF, the germanium(ii) monoselenide complex 4 reacts with activated elemental selenium to afford the desired germanium(iv) diselenide complex 3. Unexpectedly, both reactions of 4 and 5 with elemental sulphur, however, lead to the formation of germanium(iv) disulfide complex 2 under liberation of elemental Se and Te as a result of further oxidation of the germanium centre and replacement of the Se and Te atoms by sulphur atoms. All novel compounds 1–5 have been fully characterised, including single-crystal X-ray diffraction analyses, and studied by DFT calculations.