An Isolable Magnesium(II)-Radical Dianion Complex

Pan, Jinjing; Zhang, Li; He, Yuhao; Yu, Qian; Tan, Gengwen

doi:10.1021/acs.organomet.1c00512

“…Similar destruction of the aromatic solvent was found when the Mg−Mg bond was cleaved by UV‐irradiation [19] . An attempt to trap the Mg I radical in the cleft of a bulky carbazole ligand gave ligand reduction [20] . Using a superbulky BDI ligand, we found that in situ formed (BDI)Mg⋅ is easily over‐reduced to give an unique closed‐shell Mg 0 complex ( VII ) [21] .…”

Section: Methodssupporting

confidence: 62%

“…[19] An attempt to trap the Mg I radical in the cleft of a bulky carbazole ligand gave ligand reduction. [20] Using a superbulky BDI ligand, we found that in situ formed (BDI)Mg * is easily over-reduced to give an unique closedshell Mg 0 complex (VII). [21] More recently, Hill and coworkers reported a dianionic Mg I complex with a very long, but intact MgÀ Mg bond (VIII).…”

mentioning

confidence: 98%

Access to a Labile Monomeric Magnesium Radical by Ball‐Milling

Jędrzkiewicz

¹

,

Mai

²

,

Langer

³

et al. 2022

Angewandte Chemie

5

0

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In order to isolate a monometallic Mg radical, the precursor (Am)MgI⋅(CAAC) (1) was prepared (Am=tBuC(N‐DIPP)2, DIPP=2,6‐diisopropylphenyl, CAAC=cyclic (alkyl)(amino)carbene). Reduction of a solution of 1 in toluene with the reducing agent K/KI led to formation of a deep purple complex that rapidly decomposed. Ball‐milling of 1 with K/KI gave the low‐valent MgI complex (Am)Mg⋅(CAAC) (2) which after rapid extraction with pentane and crystallization was isolated in 15 % yield. Although a benzene solution of 2 decomposes rapidly to give Mg(Am)2 (3) and unidentified products, the radical is stable in the solid state. Its crystal structure shows planar trigonal coordination at Mg. The extremely short Mg−C distance of 2.056(2) Å indicates strong Mg−CAAC bonding. Calculations and EPR measurements show that most of the spin density is in a π* orbital located at the C−N bond in CAAC, leading to significant C−N bond elongation. This is supported by calculated NPA charges in 2: Mg +1.73, CAAC −0.82. Similar metal‐to‐CAAC charge transfer was calculated for M0(CAAC)2 and [MI(CAAC)2+] (M=Be, Mg, Ca) complexes in which the metal charges range from +1.50 to +1.70. Although the spin density of the radical is mainly located at the CAAC ligand, complex 2 reacts as a low‐valent MgI complex: reaction with a I2 solution in toluene gave (Am)MgI⋅(CAAC) (1) as the major product.

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“…Despite this, it is worthy of mention that the EPR spectra of two related amido‐magnesium radical complexes, in which the unpaired electron is ligand based, have been recently reported, viz . Harder's [(Amid)Mg(CAAC⋅)] [20] and Tan's [Mg(THF) 2 (Carbazol⋅)] (Carbozol=3,6‐di‐ tert ‐butyl‐1,8‐bis(10‐phenylanthracen‐9‐yl)carbazolyl) [32] . A very small 25 Mg hfc (1.6 G) was observed for the former, whereas none was recorded for the latter.…”

Section: Resultsmentioning

confidence: 99%

“…Harder's [(Amid)Mg(CAAC * )] [20] and Tan's [Mg-(THF) 2 (Carbazol * )] (Carbozol = 3,6-di-tert-butyl-1,8-bis(10-phenylanthracen-9-yl)carbazolyl). [32] A very small 25 Mg hfc (1.6 G) was observed for the former, whereas none was recorded for the latter.…”

Section: Chemistry-a European Journalmentioning

confidence: 91%

C−H Activation of Inert Arenes using a Photochemically Activated Guanidinato‐Magnesium(I) Compound

Mullins

¹

,

Kuppusamy

²

,

Jiang

³

et al. 2022

Chemistry A European J

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UV irradiation of solutions of a guanidinate coordinated dimagnesium(I) compound, [{(Priso)Mg} 2 ] 3 (Priso = [(DipN) 2 CNPr i 2 ] À , Dip = 2,6-diisopropylphenyl), in either benzene, toluene, the three isomers of xylene, or mesitylene, leads to facile activation of an aromatic CÀ H bond of the solvent in all cases, and formation of aryl/hydride bridged magnesium(II) products, [{(Priso)Mg} 2 (μ-H)(μ-Ar)] 4-9. In contrast to similar reactions reported for β-diketiminate coordinated counterparts of 3, these CÀ H activations proceed with little regioselectivity, though they are considerably faster. Reaction of 3 with an excess of the pyridine, p-NC 5 H 4 Bu t (py But ), gave [(Priso)Mg(py But H)(py But ) 2 ] 10, presumably via reduction of the pyridine to yield a radical intermediate, [(Priso)Mg(py But* )(py But ) 2 ] 11, which then abstracts a proton from the reaction solvent or a reactant. DFT calculations suggest two possible pathways to the observed arene CÀ H activations. One of these involves photochemical cleavage of the MgÀ Mg bond of 3, generating magnesium(I) doublet radicals, (Priso)Mg * . These then doubly reduce the arene substrate to give "Birch-like" products, which subsequently rearrange via CÀ H activation of the arene. Circumstantial evidence for the photochemical generation of transient magnesium radical species includes the fact that irradiation of a cyclohexane solution of 3 leads to an intramolecular aliphatic CÀ H activation process and formation of an alkylbridged magnesium(II) species, [{Mg(μ-Priso À H )} 2 ] 12. Furthermore, irradiation of a 1 : 1 mixture of 3 and the β-diketiminato dimagnesium(I) compound, [{( Dip Nacnac)Mg} 2 ] ( Dip Nacnac = [HC(MeCNDip) 2 ] À ), effects a "scrambling" reaction, and the near quantitative formation of an unsymmetrical dimagnesium(I) compound, [(Priso)MgÀ Mg( Dip Nacnac)] 13. Finally, the EPR spectrum (77 K) of a glassed solution of UV irradiated 3 is dominated by a broad featureless signal, indicating the presence of a doublet radical species.

show abstract

“… [19] An attempt to trap the Mg I radical in the cleft of a bulky carbazole ligand gave ligand reduction. [20] Using a superbulky BDI ligand, we found that in situ formed (BDI)Mg⋅ is easily over‐reduced to give an unique closed‐shell Mg 0 complex ( VII ). [21] More recently, Hill and co‐workers reported a dianionic Mg I complex with a very long, but intact Mg−Mg bond ( VIII ).…”

mentioning

confidence: 98%

Access to a Labile Monomeric Magnesium Radical by Ball‐Milling

Jędrzkiewicz

¹

,

Mai

²

,

Langer

³

et al. 2022

View full text Add to dashboard Cite

In order to isolate a monometallic Mg radical, the precursor (Am)MgI⋅(CAAC) (1) was prepared (Am=tBuC(N‐DIPP)2, DIPP=2,6‐diisopropylphenyl, CAAC=cyclic (alkyl)(amino)carbene). Reduction of a solution of 1 in toluene with the reducing agent K/KI led to formation of a deep purple complex that rapidly decomposed. Ball‐milling of 1 with K/KI gave the low‐valent MgI complex (Am)Mg⋅(CAAC) (2) which after rapid extraction with pentane and crystallization was isolated in 15 % yield. Although a benzene solution of 2 decomposes rapidly to give Mg(Am)2 (3) and unidentified products, the radical is stable in the solid state. Its crystal structure shows planar trigonal coordination at Mg. The extremely short Mg−C distance of 2.056(2) Å indicates strong Mg−CAAC bonding. Calculations and EPR measurements show that most of the spin density is in a π* orbital located at the C−N bond in CAAC, leading to significant C−N bond elongation. This is supported by calculated NPA charges in 2: Mg +1.73, CAAC −0.82. Similar metal‐to‐CAAC charge transfer was calculated for M0(CAAC)2 and [MI(CAAC)2+] (M=Be, Mg, Ca) complexes in which the metal charges range from +1.50 to +1.70. Although the spin density of the radical is mainly located at the CAAC ligand, complex 2 reacts as a low‐valent MgI complex: reaction with a I2 solution in toluene gave (Am)MgI⋅(CAAC) (1) as the major product.

show abstract

An Isolable Magnesium(II)-Radical Dianion Complex

Cited by 9 publications

References 33 publications

Access to a Labile Monomeric Magnesium Radical by Ball‐Milling

Access to a Labile Monomeric Magnesium Radical by Ball‐Milling

C−H Activation of Inert Arenes using a Photochemically Activated Guanidinato‐Magnesium(I) Compound

Access to a Labile Monomeric Magnesium Radical by Ball‐Milling

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