Annulated 1,4-Disilabenzene-1,4-diide and Dihydrogen Splitting.

The isolation of silicon analogues of phenyl anions such as (CH) and (CH) is challenging owing to their extremely high reactivity associated with their silylene character and weak C-Si π-interaction. Herein, we report the first annulated 1,4-disilabenzene-1,4-diide compound [(ADC)Si] () based on anionic dicarbene (ADC) scaffolds (ADC = PhC{N(Dipp)C}; Dipp = 2,6-PrCH) as a green-yellow crystalline solid. Compound is prepared by KC reduction of the Si(IV) chloride [(ADC)SiCl] () or the cyclic bis-chlorosilylene [(ADC)SiCl] (), which are also prepared for the first time.

Non-Kekulé meta-Quinodimethane Singlet Diradicals Based on Classical N-Heterocyclic Carbenes.

Diradicals based on a meta-quinodimethane (m-QDM) scaffold generally have a triplet ground state and are rather scarce. Herein, m-QDM-based non-Kekulé diradicals [3,3'-(NHC)BP] (3-NHC) (NHC = SIPr = C{N(Dipp)CH}; IPr = C{N(Dipp)CH}, Me-IPr = C{N(Dipp)CMe}; Dipp = 2,6-iPrCH; BP = 1,1'-CHCH) featuring N-heterocyclic carbene (NHC) pendants are reported as crystalline solids. The EPR spectra of 3-NHC show both allowed (Δm = 1) and forbidden (Δm = 2; 'half-field') transitions characteristic for triplet diradicals.

N-Heterocyclic Carbene Analogues of Wittig Hydrocarbon.

N-Heterocyclic carbene (NHC) analogues of Wittig hydrocarbon, [(NHC)(Stil)(NHC)] (3a-c) (NHC = SIPr (1a) = C[N(Dipp)CH], Dipp = 2,6-iPrCH; IPr (1b) = C[N(Dipp)CH]; Me-IPr (1c) = C[N(Dipp)CMe] and Stil = CHCHCHCH) have been reported as crystalline solids. 3a-c are prepared by two-electron reductions of the corresponding bis-1,3-imidazoli(ni)um bromides [(NHC)(Stil)NHC)](Br) (2a-c) with KC in >94 % yields. 2a-c are accessible by the nickel catalyzed direct C-C coupling of NHCs (1a-c) with (E)-4,4'-dibromostilbene.

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

Carbocyclic aluminium halides [(ADC)AlX] (2-X) (X=F, Cl, and I) based on an anionic dicarbene (ADC=PhC{N(Dipp)C}, Dipp = 2,6-iPrCH) framework are prepared as crystalline solids by dehydrohalogenations of the alane [(ADC)AlH] (1). KC reduction of 2-I affords the peri-annulated Al(III) compound [(ADC)AlH] (4) (ADCPhC{N(Dipp)C(Dipp)N}, Dipp=2-iPr,6-(MeC)CH)) as a colorless crystalline solid in 76 % yield. The formation of 4 suggests intramolecular insertion of the putative bis-aluminylene species [(ADC)Al] (3) into the methine C-H bond of HCMe group.

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

Herein, reactivity studies of a cyclic bis-hydridostannylene [(ADC)SnH] (1-H) (ADC=PhC{(NDipp)C}; Dipp=2,6-iPrCH) with various unsaturated organic substrates are reported. Reactions of terminal alkynes (RC≡CH) with 1-H afford mixed acetylide-vinyl-functionalized bis-stannylenes via dehydrogenation and hydrostannylation. Treatment of 1-H with PhC≡CCH gives a unique distannabarrelene via dehydrogenative C-H stannylation and hydrostannylation of the C≡CCH moiety.

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

We report the room temperature dimerization of carbon monoxide mediated by C4/C5-vicinal anionic dicarbenes Li(ADC) (ADC = ArC{(Dipp)NC} ; Dipp = 2,6-iPr C H ; Ar = Ph, DMP (4-Me NC H ), Bp (4-PhC H )) to yield (E)-ethene-1,2-bis(olate) (i.e. O-C=C-O = CO ) bridged mesoionic carbene (iMIC) lithium compounds CO -[(iMIC)Li] (CO -[iMIC] = [ArC{(Dipp)NC} (CO)] ) in quantitative yields.

Isolation of an Anionic Dicarbene Embedded Sn P Cluster and Reversible CO Uptake.

Decarbonylation of a cyclic bis-phosphaethynolatostannylene [(ADC)Sn(PCO)] based on an anionic dicarbene framework (ADC = PhC{N(Dipp)C} ; Dipp = 2,6-iPr C H ) under UV light results in the formation of a Sn P cluster compound [(ADC)SnP] as a green crystalline solid. The electronic structure of [(ADC)SnP] is analyzed by quantum-chemical calculations. At room temperature, [(ADC)SnP] reversibly binds with CO and forms [(ADC) {SnOC(O)P}SnP].

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

Herein, ring-opening of mesoionic carbenes (iMICs) (iMIC=[ArC{N(Dipp)} C(SiMe )C:) (Dipp=2,6-iPr C H , Ar=Ph, 4-Me NC H or 4-PhC H ) based on an 1,3-imidazole scaffold to yield N-ethynylformimidamide (eFIM) derivatives as crystalline solids (eFIM={(Dipp)N=C(Ar)N(Dipp)}C≡CSiMe ) is reported. eFIMs are thermally stable under inert gas atmosphere and show moderate air stability (t 3 h 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.

Highly Soluble Cyclic Organoalanes Based on Anionic Dicarbenes.

Cyclic organoalane compounds [(ADC )AlH ] (ADC = ArC{(DippN)C} ; Dipp = 2,6-iPr C H ; Ar = Ph or 4-PhC H (Bp)) based on anionic dicarbene (ADC) frameworks have been reported as crystalline solids. Treatments of Li(ADC ) with LiAlH at room temperature afford [(ADC )AlH ] with the concomitant release of LiH. Compounds [(ADC )AlH ] are stable crystalline solids and are freely soluble in common organic solvents.

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

Classical N-heterocyclic carbenes (NHCs) featuring the carbene center at the C2-position of 1,3-imidazole framework (i.e. C2-carbenes) are well acknowledged as very versatile neutral ligands in molecular as well as in materials sciences.

Isolation of an Annulated 1,4-Distibabenzene Diradicaloid.

The first 1,4-distibabenzene-1,4-diide compound [(ADC)Sb] (5) based on an anionic dicarbene (ADC) (ADC=PhC{N(Dipp)C} , Dipp=2,6-iPr C H ) is reported as a bordeaux-red solid. Compound 5, featuring a central six-membered C Sb ring with formally Sb 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 2 e-oxidation with Ph C[B(C F ) ] to afford [(ADC)Sb] [B(C F ) ] (6) as a brick-red solid.

Crystalline Anions Based on Classical N-Heterocyclic Carbenes.

Herein, the first stable anions K[SIPr ] (4 a-K) and K[IPr ] (4 b-K) (SIPr =BpC{N(Dipp)CH } , IPr =BpC{N(Dipp)CH} ; Bp=4-PhC H ; Dipp=2,6-iPr C H ) derived from classical N-heterocyclic carbenes (NHCs) (i.e. SIPr and IPr) have been isolated as violet crystalline solids.

Isolation of an Arsenic Diradicaloid with a Cyclic C As -Core.

Herein, we report on the synthesis, characterization, and reactivity studies of the first cyclic C As -diradicaloid {(IPr)CAs} (6) (IPr = C{N(Dipp)CH} ; Dipp = 2,6-iPr C H ). Treatment of (IPr)CH (1) with AsCl affords the Lewis adduct {(IPr)CH }AsCl (2). Compound 2 undergoes stepwise dehydrochlorination to yield {(IPr)CH}AsCl (3) and {(IPr)CAsCl} (5 a) or [{(IPr)CAs} Cl]OTf (5 b).

Crystalline phosphino-functionalized mesoionic olefins (p-MIOs).

Phosphino-functionalized mesoionic olefins (p-MIOs), (iMIC)CHR (iMIC = PhC{N(Dipp)}C(PPh)C, Dipp = 2,6-iPrCH; R = H 4a or Ph 4b), derived from a 1,3-imidazole-based mesoionic carbene (iMIC) are reported. The p-MIOs 4a (blue) and 4b (green) are crystalline solids and have been characterized by NMR spectroscopy and X-ray diffraction as well as DFT calculations. The calculated proton affinities of 4a (291.

Mesoionic Dithiolates (MIDts) Derived from 1,3-Imidazole-Based Anionic Dicarbenes (ADCs).

Mesoionic dithiolates [(MIDt )Li(LiBr) (THF) ] (MIDt ={SC(NDipp)} CAr; Dipp=2,6-iPr C H ; Ar=Ph 3 a, 3-MeC H (3-Tol) 3 b, 4-Me NC H (DMP) 3 c) and [(MIDt )Li(THF) ] (4) are readily accessible (in≥90 % yields) as crystalline solids on treatments of anionic dicarbenes Li(ADC ) (2 a-c) (ADC ={C(NDipp) } CAr) with elemental sulfur. 3 a-c and 4 are monoanionic ditopic ligands with both the sulfur atoms formally negatively charged, while the 1,3-imidazole unit bears a formal positive charge. Treatment of 4 with (L)GeCl (L=1,4-dioxane) affords the germylene (MIDt )GeCl (5) featuring a three-coordinated Ge atom.

Tuning the Electronic Properties of Main-Group Species by N-Heterocyclic Vinyl (NHV) Scaffolds.

ConspectusMolecules and materials with easily tunable electronic structures and properties are at the forefront of contemporary research. π-Conjugation is fundamental in organic chemistry and plays a key role in the design of molecular materials. In this Account, we showcase the applicability of N-heterocyclic vinyl (NHV) substituents based on classical N-heterocyclic carbenes (NHCs) for tuning the structure, properties, and stability of main-group species (E) via π-conjugation and/or π-donation.

Isolation of 1,4-Diarsinine-1,4-diide and 1,4-Diarsinine Derivatives.

1,4-Diarsinine-1,4-diide compound [(ADC )As] (5) (ADC ={C(DippN)} CPh, Dipp=2,6-iPr C H ) with a planar C As ring fused between two 1,3-imidazole scaffolds has been isolated as a red crystalline solid. Compound 5, formally comprising an 8π-electron C As ring, is antiaromatic and undergoes 2e-oxidation with AgOTf to form the 6π-electron aromatic system [(ADC )As] (OTf) (6).

Metalloradical Cations and Dications Based on Divinyldiphosphene and Divinyldiarsene Ligands.

Metalloradicals are key species in synthesis, catalysis, and bioinorganic chemistry. Herein, two iron radical cation complexes (3-E)GaCl [(3-E) = [{(IPr)C(Ph)E} Fe(CO) ] , E = P or As; IPr = C{(NDipp)CH} , Dipp = 2,6-iPr C H ] are reported as crystalline solids. Treatment of the divinyldipnictenes {(IPr)C(Ph)E} (1-E) with Fe (CO) affords [{(IPr)C(Ph)E} Fe(CO) ] (2-E), in which 1-E binds to the Fe atom in an allylic (η -EEC ) fashion and functions as a 4e donor ligand.

An Open-Shell Singlet Sn Diradical and H Splitting.

The first Sn diradical [(ADC )Sn] (4) based on an anionic dicarbene (ADC ={CN(Dipp)} CPh; Dipp=2,6-iPr C H ) scaffold has been isolated as a green crystalline solid by KC reduction of the corresponding bis-chlorostannylene [(ADC )SnCl] (3). The six-membered C Sn -ring of 4 containing six π-electrons shows a diatropic ring current, thus 4 may also be regarded as the first 1,4-distannabenzene derivative. DFT calculations suggest an open-shell singlet (OS) ground state of 4 with a remarkably small singlet-triplet energy gap (ΔE =4.

Isolation of a Ge(I) Diradicaloid and Dihydrogen Splitting.

The cyclic Ge(I) compound [(ADC)Ge] () (ADC = {CN(Dipp)}CPh, Dipp = 2,6-PrCH) containing a 6π-electron CGe framework has been isolated as a red crystalline solid. CASSCF calculations reveal a closed-shell singlet ground state for with a considerable diradical character ( = 34%). Thus, the diradicaloid readily splits dihydrogen at room temperature to yield the elusive bis-hydridogermylene [(ADC)GeH] ().

Nickel-Catalyzed Intramolecular 1,2-Aryl Migration of Mesoionic Carbenes (iMICs).

Intramolecular 1,2-Dipp migration of seven mesoionic carbenes (iMIC ) 2 a-g (iMIC =ArC{N(Dipp)} CHC; Ar=aryl; Dipp=2,6-iPr C H ) under nickel catalysis to give 1,3-imidazoles (IMD ) 3 a-g (IMD =ArC{N(Dipp)CHC(Dipp)N}) has been reported. The formation of 3 indicates the cleavage of an N-C bond and the subsequent formation of a C-C bond in 2, which is unprecedented in NHC chemistry. The use of 3 in accessing super-iMICs (5) (S-iMIC=ArC{N(Dipp)N(Me)C(Dipp)}C) has been shown with selenium (6), gold (7), and palladium (8) compounds.

Isolation of a 16π-Electrons 1,4-Diphosphinine-1,4-diide with a Planar C P Ring.

Herein, we report the first 1,4-diphosphinine-1,4-diide compound [(ADC )P] (5-Ph) (ADC =PhC{(NDipp)C} ; Dipp=2,6-iPr C H ) derived from an anionic dicarbene (ADC ) as a red crystalline solid. Compound 5-Ph containing a 16π-electron planar fused-tricyclic ring system was obtained by the 4e reduction of [(ADC )PCl ] (4-Ph) with Mg (or KC ) in a quantitative yield. Experimental and computational results imply that the central 8π-electrons C P ring of 5-Ph, which is fused between two 6π-electrons C N aromatic rings, is antiaromatic.

Isolation of Elusive Electrophilic Phosphinidene Complexes with π-Donor N-Heterocyclic Vinyl Substituents.

Phosphinidene complexes of the general formula RPM(CO) (R = an alkyl or aryl group; M = a transition metal) are electrophilic and thermally unstable. Thus, the isolation of these elusive species for structural elucidations remains a challenge. Herein, we report the first terminal phosphinidene complexes [{(NHC)C(Ph)}P]Fe(CO) [NHC = IPr = C{(NDipp)CH} for ; Me-IPr = C{(NDipp)CMe} for ; Dipp = 2,6-PrCH; NHC = N-heterocyclic carbene] as red crystalline solids containing a π-donor N-heterocyclic vinyl (NHV) substituent at the phosphorus atom.

Distannabarrelenes with Three Coordinated Sn Atoms.

Crystalline 1,4-distannabarrelene compounds [(ADC ) Sn ]SnCl (3-Ar) (ADC ={ArC(NDipp) CC}; Dipp=2,6-iPr C H , Ar=Ph or DMP; DMP=4-Me NC H ) derived from anionic dicarbenes Li(ADC ) (2-Ar) (Ar=Ph or DMP) have been reported. The cationic moiety of 3-Ar features a barrelene framework with three coordinated Sn atoms at the 1,4-positions, whereas the anionic unit SnCl is formally derived from SnCl and chloride ion. The all carbon substituted bis-stannylenes 3-Ar have been characterized by NMR spectroscopy and X-ray diffraction.