Reductive Dimerization of CO by a Na/Mg(I) Diamide

Liu, Han‐Ying; Schwamm, Ryan J.; Neale, Samuel E.; Hill, Michael S.; McMullin, Claire L.; Mahon, Mary F.

doi:10.1021/jacs.1c09467

“…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 ) [22] …”

Section: Methodsmentioning

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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“…While the two-electron reduction of CO by a number of main group compounds to give systems of the type [CnOn] 2has been reported, 18,[20][21][22][23]29 four-electron processes yielding the topologically linear [C4O4] 4fragment have more limited literature precedent. 31,33 We were therefore keen to probe the mechanism of this transformation through both experimental and quantum chemical methods.…”

Section: (Ii) Mechanistic Studies: Co Coordination and C-c/c=c Bond F...mentioning

confidence: 99%

“…The amenability of homogeneous systems to small molecule characterization techniques has driven the investigation of organometallic compounds capable of modelling the homologation of CO via C-C bond formation. 4 Prominent examples include d-block metal compounds (mirroring the use of heterogeneous transition metal catalysts such as iron and cobalt in the Fischer-Tropsch process), [5][6][7][8][9][10][11][12][13][14][15][16][17] with examples derived from low-valent s-, p-, [18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33] and f-block compounds [34][35][36][37][38][39][40][41][42][43][44][45][46][47][48][49][50] having also been reported (e.g. I-VII, Figure…”

Section: Introductionmentioning

confidence: 99%

“…I-VII, Figure 1). Prevalent among the homologation products formed via reduction processes are cyclic systems of the type [CnOn] 2-(n = 3, 4, 6) and the related ethynediolate system [C2O2] 2-, [6][7][8]11,18,[20][21][22][23]29,40,41,[44][45][46][47][48] formed by a formal two-electron reduction process, although a number of systems featuring longer linear chains of carbon atoms have also been reported (Figure 1). 14,17,22,25,31,33,34,36,37,42,49 Within this sphere, a small number of studies have emerged which demonstrate the potential for control of homologation processes at a constant oxidation level: the selective formation of [CnOn] 2-(n = 2, 3 or 4) by the cooperative action of U(III) or Mg(I) centres has been shown to be influenced by the steric bulk of ancillary ligands, 21,48 and the stepwise growth of C3 chains by the addition of CO has been demonstrated at d-block metal systems derived from metal carbonyl precursors.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Coordination and homologation of CO at Al(I): mechanism and chain growth, branching, isomerization and reduction

Heilmann

¹

,

Roy

²

,

Crumpton

³

et al. 2022

Preprint

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Homologation of carbon monoxide is central to the heterogeneous Fischer Tropsch Process for the production of hydrocarbon fuels. C–C bond formation has been modelled by homogeneous systems, with [CnOn]2- fragments (n = 2-6) formed by two-electron reduction being commonly encountered. Here we show that four- or six-electron reduction of CO can be accomplished by the use of anionic aluminium(I) ('aluminyl') compounds, to give both topologically linear and branched C4/C6 chains. We show that the mechanism for homologation relies on the highly electron-rich nature of the aluminyl reagent, and on an unusual mode of interaction of the CO molecule, which behaves primarily as a Z-type ligand in initial adduct formation. The formation of [C6O6]4- from [C4O4]4- shows a solution-phase CO homologation process that brings about chain branching via complete C-O bond cleavage, while comparison of the linear [C4O4]4- system with the [C4O4]6- congener formed under more reducing conditions, models the net conversion of C–O bonds to C–C bonds in the presence of additional reductant.

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“… [21] More recently, Hill and co‐workers reported a dianionic Mg I complex with a very long, but intact Mg−Mg bond ( VIII ). [22] …”

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.

show abstract

Reductive Dimerization of CO by a Na/Mg(I) Diamide

Cited by 46 publications

References 54 publications

Access to a Labile Monomeric Magnesium Radical by Ball‐Milling

Access to a Labile Monomeric Magnesium Radical by Ball‐Milling

Coordination and homologation of CO at Al(I): mechanism and chain growth, branching, isomerization and reduction

Access to a Labile Monomeric Magnesium Radical by Ball‐Milling

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