Imidazole-based mesoionic carbenes (iMICs) are a very promising class of carbon-donor ligands in synthesis and catalysis. However, a systematic study of the quantification of stereoelectronic properties of iMICs is lacking. This is most likely due to the absence of rational synthetic routes to suitable iMIC compounds. Herein, we report the synthesis of the appropriate phosphinidene (iMIC Ar )PPh (iMIC Ar = :CCH(NDipp) 2 CAr; Ar = Ph (5a), DMP (5b); DMP = 4-Me 2 NC 6 H 4 ; Dipp = 2,6-iPr 2 C 6 H 3 ), selenium (iMIC Ar )Se (Ar = Ph (6a), DMP (6b)), and nickel carbonyl compounds (iMIC Ar )Ni(CO) 3 (Ar = Ph (7a), DMP (7b)). The π-accepting property of iMIC Ar (Ar = Ph (2a), DMP (2b)) has been evaluated by 31 P and 77 Se NMR spectroscopic analyses of 5 and 6, respectively. The overall donor property of 2 has been assessed by determining the Tolman electronic parameter (TEP) of 7. Studies suggest that iMIC Ar (2) are stronger σ donors and weaker π acceptors compared to classical N-heterocyclic carbenes (NHCs). The steric profile of iMIC Ar (2) has been obtained by calculating the percentage buried volume (%V bur ) for (iMIC Ar

Intramolecular 1,2‐Dipp migration of seven mesoionic carbenes (iMICAr) 2 a–g (iMICAr=ArC{N(Dipp)}2CHC; Ar=aryl; Dipp=2,6‐iPr2C6H3) under nickel catalysis to give 1,3‐imidazoles (IMDAr) 3 a–g (IMDAr=ArC{N(Dipp)CHC(Dipp)N}) has been reported. The formation of 3 indicates the cleavage of an N−CDipp bond and the subsequent formation of a C−CDipp 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. The quantification of the stereoelectronic properties reveals the superior σ‐donor strength of 5 compared to that of classical NHCs. Remarkably, the percentage buried volume of 5 (%Vbur=45) is the largest known amongst thus far reported iMICs. Catalytic studies show a remarkable activity of 5, which is consistent with their auspicious stereoelectronic features.

Fluorescent styryl‐tryptophans have been synthesized by a Mizoroki–Heck cross‐coupling from unprotected bromotryptophan in aqueous medium showing promising spectrophotometric properties for possible application in fluorescence labelling of biomolecules. Moreover, this strategy permits a modular combination of biocatalytic halogenation by using immobilized FAD‐dependent tryptophan halogenases and Pd‐mediated chemocatalysis in a multistep one‐pot process.

Die Ni‐katalysierte intramolekulare 1,2‐Verschiebung eines 2,6‐Diisopropylphenyl‐Substituenten (Dipp) von sieben mesoionischen Carbenen (iMICAr) 2 a–g (iMICAr=ArC{N(Dipp)}2CHC; Ar=Aryl) unter Bildung von 1,3‐Imidazolen (IMDAr) 3 a–g (IMDAr=ArC{N(Dipp)CHC(Dipp)N}) wird berichtet. Dieser Prozess impliziert die Spaltung einer N‐CDipp‐Bindung in 2 und die anschließende Knüpfung einer C‐CDipp‐Bindung, was in der NHC‐Chemie bislang unbekannt war. Die Überführung von 3 in Super‐iMICs (5) (S‐iMIC=ArC{N(Dipp)N(Me)C(Dipp)}C) wurde mit der Herstellung von Selen‐ (6), Gold‐(7) und Palladium‐Derivaten (8) gezeigt. Die Quantifizierung der stereoelektronischen Eigenschaften lässt hierbei eine deutliche Erhöhung der σ‐Donorstärke von 5 relativ zu klassischen NHCs erkennen. Bemerkenswert hierbei ist das “Buried Volume” von 5 (%Vbur=45), welches in iMICs dem bisher größten bekannten Wert entspricht. Katalytische Studien weisen auf eine hervorragende Aktivität von 5 hin, was mit den stereoelektronischen Eigenschaften der Liganden im Einklang ist.

Phosphino-functionalized mesoionic olefins (p-MIOs), (iMIC)CHR (iMIC = PhC{N(Dipp)}2C(PPh2)C, Dipp = 2,6-iPr2C6H3; R = H 4a or Ph 4b) derived from a 1,3-imidazole based mesoionic carbene (iMIC) are reported. The p-MIOs...

Herein, the first stable anions K[SIPr Bp ] (4 a-K) and K[IPr Bp ] (4 b-K) (SIPr Bp = BpC{N(Dipp)CH 2 } 2 , IPr Bp = BpC{N(Dipp)CH} 2 ; Bp = 4-PhC 6 H 4 ; Dipp = 2,6-iPr 2 C 6 H 3 ) derived from classical N-heterocyclic carbenes (NHCs) (i.e. SIPr and IPr) have been isolated as violet crystalline solids. 4 a-K and 4 b-K are prepared by KC 8 reduction of the neutral radicals [SIPr Bp ] (3 a) and [IPr Bp ] (3 b), respectively. The radicals 3 a and 3 b as well as [Me-IPr Bp ] 3 c (Me-IPr Bp = BpC{N(Dipp)CMe} 2 ) are accessible as crystalline solids on treatment of the respective 1,3-imidazoli(ni)um bromides (SIPr Bp )Br (2 a), (IPr Bp )Br (2 b), and (MeÀ IPr Bp )Br (2 c) with KC 8 . The cyclic voltammograms of 2 a-2 c exhibit two oneelectron reversible redox processes in À 0.5 to À 2.5 V region that correspond to the radicals 3 a-3 c and the anions (4 a-4 c) À . Computational calculations suggest a closed-shell singlet ground state for (4 a-4 c) À with the singlet-triplet energy gap of 17-24 kcal mol À 1 .

Cyclic organoalane compounds [(ADCAr)AlH2]2 (ADCAr = ArC{(DippN)C}2; Dipp = 2,6‐iPr2C6H3; Ar = Ph or 4‐PhC6H4 (Bp)) based on anionic dicarbene (ADC) frameworks have been reported as crystalline solids. Treatments of Li(ADCAr) with LiAlH4 at room temperature afford [(ADCAr)AlH2]2 with the concomitant release of LiH. Compounds [(ADCAr)AlH2]2 are stable crystalline solids and are freely soluble in common organic solvents. They are annulated tricyclic compounds with an almost planar central C4Al2‐core embedded between two peripheral 1,3‐imidazole (C3N2) rings. At room temperature, [(ADCPh)AlH2]2 readily reacts with CO2 to form two‐ and four‐fold hydroalumination products [(ADCPh)AlH(OCHO)]2 and [(ADCPh)Al(OCHO)2]2, respectively. Further hydroalumination reactivity of [(ADCPh)AlH2]2 has been shown with isocyanate (RNCO) and isothiocyanate (RNCS) species (R=alkyl or aryl group). All compounds have been characterized by NMR spectroscopy, mass spectrometry, and single‐crystal X‐ray diffraction.

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