Recent Advances in the Domain of Cyclic (Alkyl)(Amino) Carbenes

Kushvaha, Saroj Kumar; Mishra, Ankush; Roesky, Herbert W.; Mondal, Kartik Chandra

doi:10.1002/asia.202101301

“…Charge transfer to CAAC and concomittant C−N bond elongation is not uncommon. In fact, it is the rationale for its property to stabilize low‐valent metals [36] . Also in Be 0 (CAAC) 2 and [Be I (CAAC) 2 + ] considerable charge transfer from Be to the CAAC ligands was observed, but atomic charges have not been discussed [24–26] .…”

Section: Methodsmentioning

confidence: 99%

“…In fact, it is the rationale for its property to stabilize low-valent metals. [36] Also in Be 0 -(CAAC) 2 and [Be I (CAAC) 2 + ] considerable charge transfer from Be to the CAAC ligands was observed, but atomic charges have not been discussed. [24][25][26] For comparison, we calculated the NPA charges at the B3PW91/def2TZVP// def2SVP level (Scheme 3f).…”

mentioning

confidence: 99%

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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“…In fact, it is the rationale for its property to stabilize low‐valent metals. [36] Also in Be 0 (CAAC) 2 and [Be I (CAAC) 2 + ] considerable charge transfer from Be to the CAAC ligands was observed, but atomic charges have not been discussed. [ 24 , 25 , 26 ] For comparison, we calculated the NPA charges at the B3PW91/def2TZVP//def2SVP level (Scheme 3 f).…”

mentioning

confidence: 99%

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.

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“…Their exceptional σ-donating and π-accepting abilities led to the isolation of a flurry of compounds of fundamental and applied interest. 2 Prominent examples include homoleptic late transition metal compounds in low oxidation states, 3 main-group and organoradical spin carriers, 4 elements in unusual oxidation states, 5 and high-performing transition metal catalysts. 6 The growing library of accessible CAACs is facilitating steric and electronic profile tuning of their complexes for tailored applications.…”

mentioning

confidence: 99%