Germacyclobutenes: generation by 1,1-carbalumination or 1,1-carbagallation and their photophysical properties

Marriage of heavy main group elements with π-conjugated materials for optoelectronic applications

This review article summarizes recent progress in the synthesis and optoelectronic properties of conjugated materials containing heavy main group elements from Group 13-16 as integral components. As will be discussed, the introduction of these elements can promote novel phosphorescent behavior and support desirable molecular and polymeric properties such as low optical band gaps and high charge mobilities for photovoltaic and thin film transistor applications.

Functionalized alkynyl-chlorogermanes: hydrometallation, Ge-Cl bond activation, Ge-H bond formation and chlorine-tert-butyl exchange via a transient germyl cation

Treatment of alkynyl-arylchlorogermanes ArylnGe(Cl)(C[triple bond, length as m-dash]C-(t)Bu)3-n (n = 1, 2) with HM(t)Bu2 (M = Al, Ga) yielded mixed Al or Ga alkenyl-alkynylchlorogermanes via hydrometallation reactions. Intramolecular interactions between the Lewis-basic Cl atoms and the Lewis-acidic Al or Ga atoms afforded MCGeCl heterocycles. The endocyclic M-Cl distances were significantly lengthened compared to the starting compounds and indicated Ge-Cl bond activation. Dual hydrometallation succeeded only with HGa(t)Bu2. One Ga atom of the product was involved in a Ga-Cl bond, while the second one had an interaction to a C-H bond of a phenyl group. In two cases treatment of chlorogermanes with two equivalents of HAl(t)Bu2 resulted in hydroalumination of one alkynyl group and formation of unprecedented Ge-H functionalized germanes, Aryl-Ge(H)(C[triple bond, length as m-dash]C-(t)Bu)[C(Al(t)Bu2)[double bond, length as m-dash]C(H)-(t)Bu] (Aryl = mesityl, triisopropylphenyl). The Al atoms of these compounds interacted with the α-C atoms of the alkynyl groups. Ph(Cl)Ge(C[triple bond, length as m-dash]C-(t)Bu)[C(Al(t)Bu2}[double bond, length as m-dash]C(H)-(t)Bu] reacted in an unusual Cl/(t)Bu exchange to yield the tert-butylgermane Ph((t)Bu)Ge(C[triple bond, length as m-dash]C-(t)Bu)[C{Al((t)Bu)(Cl)}[double bond, length as m-dash]C(H)-(t)Bu]. Quantum chemical calculations suggested the formation of a germyl cation as a transient intermediate.

Hydroalumination and hydrogallation of an aryl-chloro-dialkynylsilane: Si–Cl bond activation by intramolecular Al–Cl and Ga–Cl interactions

The chlorine functionalized dialkynylsilane (4- t Bu-C6H4)(Cl)Si(C≡C- t Bu)2 (3) reacted with equimolar quantities of H–Al t Bu2 or H–Ga t Bu2 by hydrometallation of a C≡C triple bond and formation of mixed alkenyl-alkynylsilanes (4 and 5) in which the Si and Lewis acidic metal atoms adopt geminal positions at the α-C atoms of the alkenyl groups. Intramolecular M···Cl interactions (M=Al, Ga) afforded four-membered SiCMCl heterocycles which in comparison with 3 had significantly lengthened Si–Cl bonds. Dual hydrometallation of 3 was only observed for H–Ga t Bu2. One Ga atom of the product (6) was coordinated by the silicon-bound Cl atom, while the second one showed an interaction with the aromatic ring of the tert-butyl-phenyl group. Treatment of the aluminium compound 4 with two equivalents of H–Ga t Bu2 afforded a Si–H bond by Cl-H exchange and release of Cl–Al t Bu2. The resulting silane (7) has the Si atom and two Ga atoms bridged by the α-C atoms of two vinyl groups. The specific functionality of 4 caused a remarkable reactivity. Phenyl isocyanate reacted by the formal insertion into the Al–C(vinyl) and the activated Si–Cl bonds and resulted in the formation of a C–C bond. The product (8) has a SiC2N heterocycle with an Si–N bond and exocyclic C=C and C=O double bonds. The keto group is coordinated to a Cl–Al t Bu2 molecule, which was formed by the shift of the Cl atom from silicon to aluminium.

Alkynyl functionalized Al/P-based frustrated Lewis pairs – aluminium alkynide elimination and evidence for the formation of 3H-phosphaallenes [R-PCC(H)-tBu]

Hydroalumination of dialkynylphosphines by H-Al[CH(SiMe₃)₂]₂afforded alkenyl–alkynyl phosphines which eliminate dialkylaluminium alkynides spontaneously to form phosphaallenes, aryl-PCC(H)-^tBu.