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N-Heterocyclic Carbene Analogues of Wittig Hydrocarbon


H. Steffenfauseweh, Y. V. Vishnevskiy, B. Neumann, H.-G. Stammler, B. de Bruin, R.  S. Ghadwal*

N-Heterocyclic carbene (NHC) analogues of Wittig hydrocarbon, i.e. [(NHC)2(Stil)] have been reported as crystalline solids. One-electron oxidations of[(NHC)2(Stil)] afford radical cations [(NHC)2(Stil)]●+, which can be further oxidized into the dications [(NHC)2(Stil)]2+. The CVs of [(NHC)2(Stil)]2+ are consistent with the synthetic viability of [(NHC)2(Stil)] and the radical cations [(NHC)2(Stil)]●+.


Access to a peri-Annulated Aluminium Compound via C–H Bond Activation by a Cyclic Bis-Aluminylene


A. Merschel, Y. V. Vishnevskiy, B. Neumann, H.-G. Stammler, R. S. Ghadwal*

KC8 reduction of 2-I with a catalytic amount the NHC (IMe4) has been shown to afford the peri-annulated compound 4 as a colorless crystalline solid. The formation of 4 suggests intramolecular insertion of the putative bis-aluminylene 3 into the C–H bonds of HCMe2 groups. Calculations predict singlet ground state for 3 while the conversion of 3 into 4 is thermodynamically favored by 61 kcal/mol.


Divergent Reactivity of a Cyclic Bis-Hydridostannylene: A Masked Sn(I) Diradicaloid


F. Ebeler, B. Neumann, H.-G. Stammler, R. S. Ghadwal*

Reactivity (including catalytic activity) of the hydridostannylene (1-H2) with a variety of unsaturated (alkyne, carbonyl, azo) substrates has been reported. 1-H2 (e.g.) undergoes dehydrogenative [2+2]-cycloaddition with Ph2CO to form the 1,4-distannabarrelene 1-OCPh2, which readily liberates Ph2CO on exposure to H2 and regenerates 1-H2. Thus, 1-H2 behaves as a masked Sn-diradicaloid 1 that also affords 1-OCPh2on treatment with Ph2CO.


Isolation of an Anionic Dicarbene Embedded Sn2P2 Cluster and Reversible CO2 Uptake


F. Ebeler, Y. V. Vishnevskiy, B. Neumann, H.-G. Stammler, R. S. Ghadwal*

Decarbonylation of a cyclic bis-phosphaethynolatostannylene [(ADC)Sn(PCO)]2 based on an anionic dicarbene framework (ADC = PhC{N(Dipp)C}2; Dipp = 2,6-iPr2C6H3) under UV light results in the formation of a Sn2P2 cluster compound [(ADC)SnP]2 as a green crystalline solid. The electronic structure of [(ADC)SnP]2 has been analyzed by quantum-chemical calculations. At room temperature, [(ADC)SnP]2 reversibly binds with CO2 and forms [(ADC)2{SnOC(O)P}SnP]. [(ADC)SnP]2 enables catalytic hydroboration of CO2 and reacts with elemental selenium and Fe2(CO)9 to afford [(ADC)2{Sn(Se)P}SnSe] and [(ADC)Sn{Fe(CO)4}P]2, respectively. All compounds have been characterized by multinuclear NMR spectroscopy and their solid-state molecular structures have been determined by single-crystal X-ray diffraction.

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Boosting the π-Acceptor Property of Mesoionic Carbenes by Carbonylation with Carbon Monoxide


A. Merschel, Y. V. Vishnevskiy, B. Neumann, H.-G. Stammler, R. S. Ghadwal*

Direct room temperature dimerization of carbon monoxide by anionic dicarbenes Li(ADC) has been reported to quantitatively yield (E)-ethene-1,2-bis(olate) bridged mesoionic carbene (iMIC) lithium compounds COen-[(iMIC)Li]2. They undergo 2e-oxidation to afford 1,2-dione bridged bis iMIC, COon-(iMIC)2 containing compounds while redox neutral salt metatheses yield COen-[(iMIC)E]2 compounds E = main group element).


Ring-Opening of 1,3-Imidazole Based Mesoionic Carbenes (iMICs) and Ring-Closing Clicks: Facile Access to iMIC-Compounds


A. Merschel, Y. V. Vishnevskiy, B. Neumann, H.-G. Stammler, R. S. Ghadwal*

Herein, ring-opening of mesoionic carbenes (iMICs) (iMIC = [ArC{N(Dipp)}2C(SiMe3)C:) (Dipp = 2,6-iPr2C6H3, Ar = Ph, 4-Me2NC6H4 or 4-PhC6H4) based on an 1,3-imidazole scaffold to yield N-ethynylformimidamide (eFIM) derivatives as crystalline solids (eFIM = {(Dipp)N=C(Ar)N(Dipp)}C≡CSiMe3) is reported. eFIMs are thermally stable under inert gas atmosphere and show moderate air stability (t1/2 = 3h for Ar = Ph). eFIMs are excellent surrogates of iMICs, which generally have a limited shelf-life, and readily undergo ring-closing click reactions with a variety of main-group as well as transition metal Lewis acids to form hitherto challenging iMIC-compounds in good to excellent yields. In addition to the relevance of eFIMs in the synthesis of iMIC-compounds, quantification of the stereoelectronic properties of a representative iMIC (Ar = Ph) by experimental and theoretical methods suggests remarkably σ-donor property and steric profile of these new ligand sets.

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