2020

2020

Intramolecular 1,2-Dipp migration of seven mesoionic carbenes (iMICAr) 2a-g (iMICAr = ArC{N(Dipp)}2CHC; Ar = aryl; Dipp = 2,6-iPr2C6H3) under nickel catalysis to give 1,3-imidazoles (IMDAr) 3a-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.

82. Isolation of a 16π-Electrons 1,4-Diphosphinine-1,4-diide with a Planar C4P2 Ring

       D. Rottschäfer, B. Neumann, H.-G. Stammler,  T. Sergeieva, D. M. Andrada,* R. S. Ghadwal*

       Chem. Eur. J. 2020, xx, doi: 10.1002/chem.202003617.

   

Herein, we report the first 1,4‐diphosphinine‐1,4‐diide compound [(ADC Ph )P]2 ( 5‐Ph ) (ADC Ph = PhC{(NDipp)C}2 ; Dipp = 2,6‐iPr2C6H3) derived from an anionic dicarbene (ADC-Ph ) 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 Ph )PCl2]2 (4‐Ph) with Mg (or KC8 ) in a quantitative yield. Experimental and computational results imply that the central 8π‐electrons C4P2 ring of 5‐Ph, which is fused between two 6π‐electrons C3N2 aromatic rings, is antiaromatic. Thus, each of the phosphorus atoms of 5‐Ph has two electron‐lone‐pairs, one in a p‐type orbital is in conjugation with the C=C bonds of the C4P2 ring, while the second resides in a σ‐symmetric orbital. This can be shown with the gold complex [(ADC-Ph )P(AuCl)2]2 (6‐Ph) obtained by reacting 5‐Ph with (Me 2S)AuCl. A mixture of 5‐Ph and 4‐Ph undergoes comproportionation in the presence of MgCl2 to form the intermediate oxidation state compound [(ADC-Ph)P]2(MgCl4) (7‐Ph), which is an aromatic species.

81. Saturated NHC Derived Dichalcogen Dications

       D. Rottschäfer, D. E. Fuhs, B. Neumann, H.-G. Stammler, R. S. Ghadwal*

       Z. Anorg. Allg. Chem. 2020, 646, 574–579.

   

Herein, the synthesis and characterization of dicationic di-halcogenide compounds [(SIPr)E]2(OTf)2 (3a-E) (E = S, Se, Te) based on a saturated N-heterocyclic carbene (NHC), SIPr [SIPr = C{N(Dipp)CH2}2, Dipp = 2,6-iPr2C6H3] are reported. Treatment of SIPr (1a) with elemental chalcogens affords the heavier ketone derivatives (SIPr)E (2a-E), which readily undergo oxidative E–E coupling reactions with triflic anhydride to yield the corresponding products 3a-E. Compounds 3a-E are air-stable crystalline solids and were characterized by NMR and UV/Vis spectroscopy as well as by X-ray diffraction methods.

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

       D. Rottschäfer, B. Neumann, H.-G. Stammler,  D. M. Andrada, R. S. Ghadwal*

       J. Org. Chem. 2020, 85, 435114339.

   

Phosphinidene complexes of a general formula RPM(CO)n (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 so far a challenge. In this contribution, we report the first terminal phosphinidene complexes [{(NHC)C(Ph)}P]Fe(CO)4 (NHC = IPr = C{(NDipp)CH}2, 3; Me-IPr = C{(NDipp)CMe}2, 4; Dipp = 2,6-iPr2C6H3; NHC = N-heterocyclic carbene) as red crystalline solids containing a π-donor N-heterocyclic vinyl (NHV) substituent at the phosphorus atom.

79. Distannabarrelenes with three Coordinated Sn(II) atoms

       M. K. Sharma, T. Glodde, B. Neumann, H.-G. Stammler,  R. S. Ghadwal*

      Chem. Eur. J. 2020, 26, 11113‒11118.

 

Crystalline 1,4-distannabarrelene compounds [(ADC-Ar)3Sn2]SnCl3 (3-Ar) (ADC-Ar = {CC(NDipp)CAr}; Dipp = 2,6-iPr2C6H3, Ar = Ph or DMP; DMP = 4-Me2NC6H4)) have been reported. The cationic moiety of 3-Ar (see below, Ar = Ph) features a barrelene framework with three coordinated Sn(II) atoms at the 1,4-positions, whereas the anionic unit SnCl3 is formally derived from SnCl2 and chloride ion.

78. Quantifying the Electronic and Steric Properties of 1,3-Imidazol-based Mesoionic Carbenes (iMICs)

       A. Merschel, D. Rottschäfer, B. Neumann, H.-G. Stammler, R. S. Ghadwal*

      Organometallics 2020, 39, 1719‒1729.

    

Stereoelectronic properties of iMICs (2) have been quantified by systematic spectroscopic studies of the appropriate iMIC-phosphinidene (5), selenium (6), and nickel carbonyl complexes (7).

77. Isolation of Singlet Carbene Derived 2-Arsa-1,3-butadiene Radical Cations and Dications

       M. K. Sharma, S. Blomeyer, B. Neumann, H.-G. Stammler, A. Hinz, M. van Gastel, R. S. Ghadwal*

      Chem. Commun. 2020, 56, 3575‒3578.

 

2-Arsa-1,3-butadienes (L)As(cAAC) ((L = PhC=C{(NDipp)CH}2, Dipp = 2,6-iPr2C6H3; cAAC = C{(NDipp)CMe2CH2CMe2} (2a) or C{(NDipp)CMe2CH2C(Cy)} (2b), Cy = cyclohexyl) and the corresponding radical cations [(L)}As­(cAAC)]GaCl4 (3) and dications [(L)As(cAAC)]­(GaCl4)2 (4) featuring a C=C‒As=C π-conjugated framework are reported.

75. Isolation of Singlet Carbenes Derived 2-Phospha-1,3-butadienes and their Sequential One-electron Oxidation to Radical Cations and Dications

       M. K. Sharma, S. Blomeyer, T. Glodde, B. Neumann, H.-G. Stammler, A. Hinz, M. van Gastel, R. S. Ghadwal*

      Chem. Sci. 2020, 11, 19751984.

A synthetic strategy for the 2-phospha-1,3-butadiene derivatives [{(IPr)C(Ph)}P(cAACMe)] (3a) and [{(IPr)C(Ph)}P(cAACCy)] (3b) (IPr = C{(NDipp)CH}2, Dipp = 2,6-iPr2C6H3; cAACMe = C{(NDipp)CMe2CH2CMe2}; cAACCy = C{(NDipp)CMe2CH2C(Cy)}, Cy = cyclohexyl) containing a C=C‒P=C framework has been established. Compounds 3a and 3b have a remarkably small HOMO-LUMO energy gap (3a: 5.09; 3b: 5.05 eV) with a very high-lying HOMO (‒4.95 eV for each). Consequently, 3a and 3b readily undergo one-electron oxidation with the mild oxidizing agent GaCl3 to afford radical cations [{(IPr)C(Ph)}P(cAACR)]GaCl4 (R = Me 4a, Cy 4b) as crystalline solids. The main UV-vis absorption band for 4a and 4b is red-shifted with respect to that of 3a and 3b, which is associated with the SOMO related transitions. The EPR spectrum of compounds 4a and 4b each exhibits a doublet due to coupling with the 31P nucleus. Further one-electron removal from the radical cations 4a and 4b is also feasible with GaCl3, affording the dications [{(IPr)C(Ph)}P(cAACR)](GaCl4)2 (R = Me 5a, Cy 5b) as yellow crystals. The molecular structures of compounds 3-5 have been determined by X-ray diffraction and analyzed by DFT calculations.

76. A crystalline C5-protonated 1,3-imidazol-4-ylidene

       D. Rottschäfer, T. Glodde, B. Neumann, H.-G. Stammler, R. S. Ghadwal*

      Chem. Commun2020, 2027‒2030. 

 

The first C5-protonated 1,3-imidazol-based mesoionic carbene iMICBp (2) (iMICBp = :C{CH(NDipp)2C(Bp)}; Dipp = 2,6-iPr2C6H3; Bp = 4-PhC6H4) has been reported as a crystalline solid. Spectroscopic, X-ray diffraction, and computational studies clearly support the carbenic nature of 2, which has been further corroborated by its reactions with Ni(CO)4, (Me2S)AuCl, white phosphorus (P4), and CO2.

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