2021

Metalloradical Cations and Dications Based on Divinyldiphosphene and Divinyldiarsene Ligands

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M. K. Sharma, D. Rottschäfer, B. Neumann, H.-G. Stammler, S. Danés, D. M. Andrada,* M. van Gastel,
A. Hinz, R. S. Ghadwal*

Metalloradicals are key species in synthesis, catalysis, and bioinorganic chemistry. Herein, two iron radical cation complexes (3-E)GaCl4 [(3-E)•+ = [{(IPr)C(Ph)E}2Fe(CO)3]•+, E = P or As; IPr = C{(NDipp)CH}2, Dipp = 2,6-iPr2C6H3] are reported as crystalline solids. Treatment of the divinyldipnictenes {(IPr)C(Ph)E}2 (1-E) with Fe2(CO)9 affords [({(IPr)C(Ph)E}2)Fe(CO)3] (2-E), in which 1-E binds to the Fe atom in an allylic (η3-EEC-vinyl) fashion and functions as a 4e-donor ligand. 2-E undergo 1e-oxidation with GaCl3 to yield (3-E)GaCl4. Spin-density analysis reveals that the unpaired electron in (3-E)•+ is mainly located on the Fe (52-64%) and vinylic C (30-36%) atoms. Further 1e-oxidation of (3-E)GaCl4 leads to an unprecedented η3-EEC-vinyl to η3-ECvinylCPh coordination shuttling to form the dications (4-E)(GaCl4)2.

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An Open‐Shell Singlet Sn(I) Diradical and H2 Splitting

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

Angew. Chem. Int. Ed. 2021, 60, 64146418.

Angewandte Chemie 2021, 133,  64856489.

The first Sn(I) diradical [(ADCPh)Sn]2 (4) based on an anionic dicarbene (ADCPh = {CN(Dipp)}2CPh, Dipp = 2,6-iPr2C6H3) scaffold has been isolated as a green crystalline solid by KC8 reduction of the corresponding bis-chlorostannylene [(ADCPh)SnCl]2 (3). The six-membered C4Sn2-ring of 4 containing 6π-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 (ΔEOS-T = 4.4 kcal/mol), which is consistent with CASSCF (ΔES-T = 6.6 kcal/mol and diradical character y = 37%) calculations. The diradical 4 splits H2 at room temperature to yield the bis-hydridostannylene [(ADCPh)SnH]2 (5). Further reactivity of 4 has been studied with PhSeSePh and MeOTf.

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

1,4-Diarsinine-1,4-diide compound [(ADCPh)As]2 (5) (ADCPh = {C(DippN)}2CPh, Dipp = 2,6-iPr2C6H3) with a planar C4As2-ring fused between two 1,3-imidazole scaffolds has been isolated as a red crystalline solid. Compound 5, formally comprising an 8π-electron C4As2-ring, is antiaromatic and undergoes 2e-oxidation with AgOTf to form the 6π-electron aromatic system [(ADCPh)As]2(OTf)2 (6).

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Isolation of a Ge(I) Diradicaloid and Dihydrogen Splitting

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

The cyclic Ge(I) compound [(ADCPh)Ge]2 (4) (ADCPh = {CN(Dipp)}2CPh, Dipp = 2,6-iPr2C6H3) containing a 6π-electron C4Ge2 framework has been isolated as a red crystalline solid. CASSCF calculations reveal a closed-shell singlet ground state for 4 with a considerable diradical character (y = 34%). Thus, the diradicaloid 4 readily splits dihydrogen at room temperature to yield the elusive bis-hydridogermylene [(ADCPh)GeH]2 (5).

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

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A. Merschel, T. Glodde, B. Neumann, H.-G. Stammler, R. S. Ghadwal*

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.

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Isolation of a 16π‐Electrons 1,4‐Diphosphinine‐1,4‐diide with a Planar C4P2 Ring

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

Herein, we report the first 1,4-diphosphinine-1,4-diide compound [(ADCPh)P]2 (5-Ph) (ADCPh=PhC{(NDipp)C}2; Dipp=2,6-iPr2C6H3) derived from an anionic dicarbene (ADCPh) as a red crystalline solid. Compound 5-Ph containing a 16p-electron planar fused-tricyclic ring system was obtained by the 4e reduction of [(ADCPh)PCl2]2 (4-Ph) with Mg (or KC8) in a quantitative yield. Experimental and computational results imply that the central 8p-electrons C4P2 ring of 5-Ph, which is fused between two 6p-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 sigma-symmetric orbital. This can be shown with the gold complex [(ADCPh)P(AuCl)2]2 (6-Ph) obtained by reacting 5-Ph with (Me2S)AuCl. A mixture of 5-Ph and 4-Ph undergoes comproportionation in the presence of MgCl2 to form the intermediate oxidation state compound [(ADCAr)P]2(MgCl4) (7-Ph), which is an aromatic species.

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