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, Accepted article, https://pubs.acs.org/doi/10.1021/acs.joc.0c00176.


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, xx, https://doi.org/10.1002/chem.2020014320.


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, xx, https://pubs.acs.org/doi/10.1021/acs.organomet.0c00045.


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, doi: 10.1039/D0CC00624F.


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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