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Highly Soluble Cyclic Organoalanes Based on Anionic Dicarbenes


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

The carbocyclic aluminium hydrides [(ADC)AlH2]2 are readily accessible as crystalline solids on the treatment of anionic dicarbenes Li(ADC) with LiAlH4. Hydroalumination of CO2 (and other organic substrates) with [(ADC)AlH2]2 has been shown to access [(ADC)Al(OCH(O))2]2 (and other products).

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Isolation of an Annulated 1,4-Distibabenzene Diradicaloid


H. Steffenfauseweh, D. Rottschäfer, Y. V. Vishnevskiy, B. Neumann, H.-G. Stammler, D. W. Szczepanik , R. S. Ghadwal*

The first 1,4-distibinine-1,4-diide compound [(ADC)Sb]2 (5) based on an anionic dicarbene (ADC) (ADC = PhC{N(Dipp)C}2, Dipp = 2,6-iPr2C6H3) is reported as a bordeaux-red solid. Compound 5, featuring a central six-membered C4Sb2 ring with formally Sb(I) atoms may be regarded as a base-stabilized cyclic bis-stibinidene in which each of the Sb atoms bears two lone-pairs of electrons. 5 undergoes 2e-oxidation with Ph3C[B(C6F5)4] to afford [(ADC)Sb]2­[B(C6F5)4]2 (6) as a brick-red solid. Each of the Sb atoms of 6 has an unpaired electron and a lone-pair. The broken-symmetry open-shell singlet diradical solution for (6)2+ is calculated to be 2.13 kcal/mol more stable than the closed-shell singlet. The diradical character of (6)2+ according to SS-CASSCF (state-specific complete active space self-consistent field) and UHF (unrestricted Hartree-Fock) methods amounts to 39% and 36%, respectively. Treatments of 6 with (PhE)2 yield [(ADC)Sb(EPh)]2[B(C6F5)4]2 (7-E) (E = S or Se). Reaction of 5 with (cod)Mo(CO)4 affords [(ADC)Sb]2­Mo(CO)4 (8).

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1,3-Imidazole Based Mesoionic Carbenes and Anionic Dicar­benes: Pushing the Limit of Classical N-Heterocyclic Carbenes


R. S. Ghadwal*

Mesoionic carbenes (iMICs) and anionic dicarbenes (ADCs) are readily accessible by the deprotonation of C2-arylated 1,3-imidazolium  salts,  which are prepared by the direct  C2-arylation  of classical  N-heterocyclic carbenes  (NHCs).  The implications of iMICs as potent σ-donor ligands for organometallic catalysis and ADCs as unique building blocks to access conceptually new main-group heterocycles with an annulated C4E2-ring have been showcased.


Crystalline Anions Based on Classical N-Heterocyclic Carbenes


A. Merschel, D. Rottschäfer, B. Neumann, H.-G. Stammler, M. Ringenberg, M. van Gastel, T. I. Demirer, D. M. Andrada, R. S. Ghadwal*

Herein, the first stable anions K[SIPrBp] (4a-K) and K[IPrBp] (4b-K) (SIPrBp = BpC{N(Dipp)CH2}2, IPrBp = BpC{N(Dipp)CH}2; Bp = 4-PhC6H4; Dipp = 2,6-iPr2C6H3) derived from classical N-heterocyclic carbenes (NHCs) (i.e. SIPr and IPr) have been isolated as violet crystalline solids. 4a-K and 4b-K are prepared by KC8 reduction of the neutral radicals [SIPrBp] (3a) and [IPrBp] (3b), respectively. The radicals 3a and 3b as well as [Me-IPrBp] 3c (Me-IPrBp = BpC{N(Dipp)CMe}2) are accessible as crystalline solids on treatment of the respective 1,3-imidazoli(ni)um bromides (SIPrBp)Br (2a), (IPrBp)Br (2b), and (Me-IPrBp)Br (2c) with KC8. The cyclic voltammograms (CVs) of 2a2c exhibit two one-electron reversible redox processes in –0.5 to –2.1 V region that correspond to the radicals 3a3b and the anions (4a4c)–. Computational calculations suggest a closed-shell singlet ground state for (4a4c)– with the singlet-triplet energy gap of 19-21 kcal/mol.

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