Gstrein, Fabian: Silicon Compounds in Low Oxidation States Supported by a Cyclic (Alkyl)(Amino)Carbene : Synthesis, Structure and Reactivity. - Bonn, 2023. - Dissertation, Rheinische Friedrich-Wilhelms-Universität Bonn.
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author = {{Fabian Gstrein}},
title = {Silicon Compounds in Low Oxidation States Supported by a Cyclic (Alkyl)(Amino)Carbene : Synthesis, Structure and Reactivity},
school = {Rheinische Friedrich-Wilhelms-Universität Bonn},
year = 2023,
month = mar,

note = {Abstract: Silicon compounds in low oxidation states, especially dihalosilylenes (SiX2), are highly unstable molecules, which are involved as fleeting intermediates in the industrial production of chlorosilanes and semiconductor grade silicon. Their high reactivity, which ultimately lead to either disproportionation or polymerization, could be tamed by the use of strong σ-donating N-heterocyclic carbene (NHC) ligands, which sequestered their electrophilicity through the reversed polarized ylidic Siδ−−NHCδ+ bond. This concept enabled the isolation of dihalosilylenes (SiX2) as bottleable SiX2(NHC) adducts, which had in recent years a major impact on the development of molecular silicon chemistry. It was anticipated that the ylidic character could be tuned by using a strong σ-donor and strong π-acceptor cyclic (alkyl)(amino)carbene (CAAC) ligand leading to an unique reactivity pattern of the resulting adduct SiX2(CAAC). For this sake, the CAAC stabilized dibromosilylene SiBr2(CAAC) (1) was prepared and a detailed synthetic and physiochemical study was planned.
Highlights: In this work the high synthetic potential of compound 1 could be shown in a plethora of novel unsaturated compounds with intriguing synthetic potential. Among them CAAC-supported silicon(II) bromides SiBr(R)(CAAC) (R = SiTMS3 (2-Si), PMes2 (2-P), Mes (2-Mes), NTMS2 (2-N), OMes* (2-O)) (Mes* = C6H2-2,4,6-tBu3), neutral two-coordinated silicon(I) radicals Si(R')(CAAC) (R' = SiTMS3 (3-Si), NTMS2 (3-N), OMes* (3-O)), 1,4-diamino-2,3-disila-butadienes Si2(R'')2(CAAC)2 (R'' = Br (9-Br), Cp'(9-Cp'), Mes (9-Mes), C≡CTMS (9-C2TMS), C≡CMes (9-C2Mes)), potassium silenides SiK(R''')(CAAC) (R''' = SiTMS3 (4-Si), C≡CTMS (10-C2TMS)) and CAAC-supported heavier tetrelavinylidenes (CAAC)E=SiBr(Tbb)    (E = Si (14), Ge (14-Ge)) (Tbb = C6H2-2,6-Dsi2-4-tBu, Dsi = CH(SiMe3)2) are particularly instructive allowing to probe the electronic structure via a combination of structural, spectroscopic and theoretical studies. Detailed kinetic studies revealed an irreversible E→Z isomerization of the Si=CCAAC double bond in SiBr(Eind)(CAAC) (2-Eind) and an irreversible (Z,Z)(E,E) isomerization of the two Si=CCAAC bonds in disilabutadiene Si2(Mes)2(CAAC)2 (9-Mes), as well as a reversible E→Z isomerization of the Si=CCAAC bond in the silenyl-germylene (ArMes)Ge–Si(C2TMS)(CAAC) (12) (ArMes = C6H3-2,6-Mes2).},

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