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    Dimerization of a marginally stable disilenyl germylene to tricyclic systems: evidence for reversible NHC-coordination
    (Royal Soc Chemistry, 2016) Nieder, David; Yıldız, Cem Burak; Jana, Anukul; Zimmer, Michael; Huch, Volker; Scheschkewitz, David
    Tetrasiladigermatricyclohexanes in two isomeric forms (chair and doubly-bridged tetrahedron) are obtained by the reaction of MeLi with an alpha-chlorosilyl functionalized NHC-stabilized silagermenylidene. Si-29 NMR at low temperature proves the initial formation of a monomeric NHC-adduct of a disilenyl germylene followed by cyclisation to the isomeric heavy cyclopropene. Addition of an excess of NHC stabilizes the both intermediates and demonstrates the reversibility of rate-determining initial equilibria involving NHC dissociation. Finally, a mixture of two isomeric tricyclic Si4Ge2 species is obtained: at elevated temperature the chair isomer converts to the doubly edge-bridged tetrahedron.
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    Diverse reactivity of an electrophilic phosphasilene towards anionic nucleophiles: Substitution or metal-amino exchange
    (WILEY-V C H Verlag Gmbh, 2016) Willmes, Philipp; Junk, Lukas; Huch, Volker; Yıldız, Cem Burak; Scheschkewitz, David
    The reaction of MesLi (Mes=2,4,6-trimethylphenyl) with the electrophilic phosphasilene R-2(NMe2)Si-RSi=PNMe2 (2, R=Tip=2,4,6-triisopropylphenyl) cleanly affords R-2(NMe2)Si-RSi=PMes and thus provides the first example of a substitution reaction at an unperturbed Si=P bond. In toluene, the reaction of 2 with lithium disilenide, R2Si=Si(R)Li (1), apparently proceeds via an initial nucleophilic substitution step as well (as suggested by DFT calculations), but affords a saturated bicyclo[1.1.0]butane analogue as the final product, which was further characterized as its Fe(CO)(4) complex. In contrast, in 1,2-dimethoxyethane the reaction of 1 with 2 results in an unprecedented metal-amino exchange reaction.
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    Reactivity enhancement of a diphosphene by reversible N-heterocyclic carbene coordination
    (Royal Society of Chemistry, 2018) Dhara, Debabrata; Kalita, Pankaj; Mondal, Subhadip; Narayanan, Ramakirushnan Suriya; Mote, Kaustubh R.; Huch, Volker; Zimmer, Michael; Yıldız, Cem Burak; Scheschkewitz, David; Chandrasekhar, Vadapalli; Jana, Ankul
    Diphosphene TerMesP = PTerMes (1; TerMes = 2,6-Mes2C6H3; Mes = 2,4,6-Me3C6H2) and NHCMe42 (NHCMe4 = 1,3,4,5-tetramethylimidazol-2-ylidene) exist in an equilibrium mixture with the NHCMe4-coordinated diphosphene 3. While uncoordinated 1 is inert to hydrolysis, the NHC adduct 3 readily undergoes hydrolysis to afford a phosphino-substituted phosphine oxide with the liberation of NHCMe4. On this basis, conditions suitable for the catalytic use of NHCMe4 were identified. Similarly, while the hydrogenation of free diphosphene 1 with H3N·BH3 is very slow, 3 reacts instantaneously with H3N·BH3 at room temperature to afford a dihydrodiphosphane. © 2018 The Royal Society of Chemistry.
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    Regiodiscriminating reactivity of isolable NHC-coordinated disilenyl germylene and Its cyclic isomer
    (American Chemical Society, 2016) Nieder, David; Huch, Volker; Yıldız, Cem Burak; Scheschkewitz, David
    An isolable NHC-coordinated disilenyl germylene R2Si-SiR-GePh center dot NHCiPr2Me2 (5b: R = 2,4,6-triisopropylphenyl, NHCiPr2Me2 = 1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene) is obtained from the reaction of the a-chloro silyl functionalized heavier vinylidene analogue R2(Cl)Si-RSi-Ge center dot NHCiPr2Me2 with phenyllithium. The disilenyl germylene 5b isomerizes at 40 degrees C to the NHC-adduct of the corresponding heavier cyclopropylidene analogue 6b. Both 5b and 6b display near perfect regiodiscrimination in their reactions with phenylacetylene and xylyl isocyanide, affording in the case of each reagent two different regioisomers of NHC-coordinated cyclic germylenes. DFT calculations reveal that the Si-Si bond accounts for the high reactivity of 5b even at low temperature while in the case of cyclic 6b the low-valent germanium center requires a considerable thermal activation