Synthesis and characterisation of new bimetallic alkali metal–magnesium mixed diisopropylamide-acetylides: structural variations in bimetallic lithium- and sodium-heteroleptic magnesiates

García‐Álvarez, Joaquín; Graham, David V.; Hevia, Eva; Kennedy, Alan R.; Mulvey, Robert E.

doi:10.1039/b716215d

Cited by 29 publications

(48 citation statements)

References 51 publications

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“…[4] This complication contrasts with the apparent simplicity of turbo-TMP 1 which under the same conditions shows only one type of TMP resonance ( 1 H spectrum: d = 1.57/1.17/1.16 ppm for g-CH 2 /b-CH 2 /CH 3 ). The presence of lithium in 2 was confirmed by a singlet in the 7 Li NMR spectrum (at d = 0.25 ppm), [4] 8 ]THF solution) reveals a singlet at 0.51 ppm, this a priori rules out the possibility that 2 a and 2 b are monometallic magnesium species and that LiCl is "swimming" free in solution (unless the chemical shift difference is due to the dielectric constant varying between solutions [8] ). Knochel hypothesized the ionic formula "[Li(THF) 4 …”

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confidence: 80%

“…This is again consistent with one lithium-containing species common to 2 a and 2 b, and now to 2 c. A 1 H-1 H EXSY NMR [9] experiment confirmed dynamic equilibria between all three species. [4] In addition, 1 H and 7 Li spectra run at 25 8C on three different concentrations (0.46 m, 0.23 m, and < 0.10 m) of 2 in [D 8 ]THF established that 2 a predominates at higher concentrations whereas 2 b predominates at lower concentrations, suggestive of a possible dimer (2 a)-monomer (2 b) equilibrium. The same singlet 7 Li resonance was seen during these variableconcentration studies.…”

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confidence: 98%

“…[4] In addition, 1 H and 7 Li spectra run at 25 8C on three different concentrations (0.46 m, 0.23 m, and < 0.10 m) of 2 in [D 8 ]THF established that 2 a predominates at higher concentrations whereas 2 b predominates at lower concentrations, suggestive of a possible dimer (2 a)-monomer (2 b) equilibrium. The same singlet 7 Li resonance was seen during these variableconcentration studies. [4] To gain further information about the solution chemistry of 1 and 2, we studied their diffusion properties using diffusion-ordered NMR spectroscopy (DOSY).…”

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confidence: 99%

“…À " to account for the high reactivity of the alkyl turbo-Grignard reagent "iPrMgCl·LiCl", [1a,b] and this known solvent-separated cation would fit 7 Li NMR data for 2 a/2 b. As 1 H and 13 C resonances of 2 appeared broad, hinting at fluxional processes, a variable-temperature study (from À78 8C to 408C) [4] was undertaken.…”

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confidence: 99%

“…Widening the search to tetranuclear motifs of composition "AM(m-X) 2 Mg(m-X) 2 Mg-(m-X) 2 AM" (where AM = Li or Na; X = any ligand) revealed only four hits. [6,7] Poorly soluble in nonpolar solvents, 2 was dissolved in [D 8 ]THF solution (0.23 m) [4] for NMR spectroscopic characterization to attempt to reconstruct the actual conditions employed when turbo-DA is utilized in synthesis. Two different species labeled 2 a and 2 b were discernible from routine ambient-temperature 1 H and 13 C{ 1 H} NMR spectra …”

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confidence: 99%

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Diisopropylamide and TMP Turbo‐Grignard Reagents: A Structural Rationale for their Contrasting Reactivities

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A century on since Grignard won the Nobel Prize in Chemistry for their development, Grignard reagents "RMgX" are still widely utilized today and still stand at the cutting edge of synthetic research. Current innovation centers on Knochels exciting 21st century models "turbo-Grignard reagents" especially those formulated as "R 2 NMgCl·LiCl". [1] Equipped with enhanced kinetic basicity, these commercially available turbo-Grignard reagents can outperform their illustrious ancestors by executing magnesiation reactions of excellent regioselectivity and high functional group tolerance upon a large number of aromatic and heteroaromatic substrates. Since the exceptional reactivities of these special bases must be dictated by cooperative effects between their different component parts (Li, Mg, R 2 N, Cl, any solvent ligands), it is important to understand how these components organize and interact with each other, both in solid state and most importantly in solution where they operate. To date, little structural information has been gathered and, what is more, only in the solid state through one X-ray crystallographic study of the TMP (2,2,6 6-tetramethylpiperidide) turbo-Grignard reagent or Knochel-Hauser base "(TMP)MgCl·LiCl" (turbo-TMP). It exists in the crystal as the tris(THF)-solvated contact ion pair [(THF) 2 Li(m-Cl) 2 Mg-(THF)TMP] (1).[2] A terminal (TMP)N À Mg bond is its salient feature. Here we present a more detailed characterization, in both the solid state and solution, of "(TMP)MgCl·LiCl" and its DA (diisopropylamide, iPr 2 N) analogue, the turboGrignard reagent "(DA)MgCl·LiCl" (turbo-DA). A complementary combination of X-ray crystallographic and NMR spectroscopic studies [including diffusion-ordered (DOSY) and exchange (EXSY) experiments] reveals that both in its crystalline form, [{(THF) 2 Li(m-Cl) 2 Mg(m-DA)} 2 ] (2), and most significantly in solution turbo-DA differs markedly from turbo-TMP, enabling a rationalization of their markedly different observed reactivities.[1c] Furthermore, looking more generally across the whole field of modern metalation chemistry, these results allow a key distinction to be drawn between TMP-magnesiation reactions performed by these halide-activated regents and by mixed alkyl-amido formulations that dispense alkali metal mediated magnesiation (AMMMg). [3] In a variation of the original literature synthesis, [1c] we prepared turbo-DA by mixing LDA (iPr 2 NLi) with magnesium chloride in THF.[4] The crystalline form of turbo-DA 2 (60 % yield) came from a hexane/THF mixture. Dimeric aggregation is the main feature of the centrosymmetric molecular structure of 2 (Figure 1). Its tetranuclear arrangement consists of a central (MgN) 2 planar ring, lying orthogonal to and separating two (LiCl) 2 non-planar outer rings. The Li atoms carry two THF ligands. All four metal atoms and N atoms of the amido bridges exhibit distorted tetrahedral geometries, while the chloro bridges have two-coordinate bent geometries. The THF ligands, one iPr arm of each DA ligand, and the chloride atoms...

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confidence: 98%

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confidence: 99%

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confidence: 99%

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confidence: 99%

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Diisopropylamide and TMP Turbo‐Grignard Reagents: A Structural Rationale for their Contrasting Reactivities

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Mixed Lithium Complexes: Structure and Applicationin Synthesis

Mulvey

O’Hara

2014

Lithium Compounds in Organic Synthesis

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IntroductionFor half a century, organolithium (C-Li bonded) reagents and lithium amides (N-Li bonded) have played a pivotal role in the development of modern day synthetic chemistry. Reagents in these categories, in particular the butyllithiums (the normal-, secondary-, and tertiary-isomers), lithium diisopropylamide (LDA), lithium 2,2,6,6-tetramethylpiperid-1-ide (LiTMP), and lithium 1,1,1,3,3,3-hexamethyldisilazide (LiHMDS) are utilized in most synthetic laboratories around the world and are especially important in the metallation reaction (that is, the conversion of a relatively inert C-H bond into a more reactive (more chemically pliable) C-Li bond) and in the kinetically operative metal-halogen exchange reactions. The past two decades have witnessed several new classes of constitutionally more complex reagents that contain multimetal and/or multianion formulations that have challenged the dominance of these unimetallic/unianionic reagents in deprotonative/metal-halogen exchange chemistry. This chapter covers some of the rich structural and synthetic chemistry of these new and still emerging systems, detailing only a small selection of what these classes of compounds can offer the chemist at the present time. Structural Chemistry of Heterometallic Lithium ComplexesStructure is inextricably and mutually linked to reactivity; hence, much recent research activity has focused on the elucidation of solid-state and solution structures of lithium organometallics and amides. This section concentrates on the structural chemistry of lithium-containing mixed-metal complexes, focusing particularly on mixed s-block (Group 1/Group 1 or Group 1/Group 2) complexes, and those containing the Group 12 d 10 metal zinc, which is commonly regarded as a displaced alkaline earth metal. In recent years, heterometallic sodium reagents (particularly sodium zincates, magnesiates, aluminates, etc.) have received a great Lithium Compounds in Organic Synthesis: From Fundamentals to Applications, First Edition. Edited by Renzo Luisi and Vito Capriati.

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Diisopropylamide and TMP Turbo‐Grignard Reagents: A Structural Rationale for their Contrasting Reactivities

et al. 2010

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A century on since Grignard won the Nobel Prize in Chemistry for their development, Grignard reagents "RMgX" are still widely utilized today and still stand at the cutting edge of synthetic research. Current innovation centers on Knochels exciting 21st century models "turbo-Grignard reagents" especially those formulated as "R 2 NMgCl·LiCl". [1] Equipped with enhanced kinetic basicity, these commercially available turbo-Grignard reagents can outperform their illustrious ancestors by executing magnesiation reactions of excellent regioselectivity and high functional group tolerance upon a large number of aromatic and heteroaromatic substrates. Since the exceptional reactivities of these special bases must be dictated by cooperative effects between their different component parts (Li, Mg, R 2 N, Cl, any solvent ligands), it is important to understand how these components organize and interact with each other, both in solid state and most importantly in solution where they operate. To date, little structural information has been gathered and, what is more, only in the solid state through one X-ray crystallographic study of the TMP (2,2,6 6-tetramethylpiperidide) turbo-Grignard reagent or Knochel-Hauser base "(TMP)MgCl·LiCl" (turbo-TMP). It exists in the crystal as the tris(THF)-solvated contact ion pair [(THF) 2 Li(m-Cl) 2 Mg-(THF)TMP] (1). [2] A terminal (TMP)N À Mg bond is its salient feature. Here we present a more detailed characterization, in both the solid state and solution, of "(TMP)MgCl·LiCl" and its DA (diisopropylamide, iPr 2 N) analogue, the turbo-Grignard reagent "(DA)MgCl·LiCl" (turbo-DA). A complementary combination of X-ray crystallographic and NMR spectroscopic studies [including diffusion-ordered (DOSY) and exchange (EXSY) experiments] reveals that both in its crystalline form, [{(THF) 2 Li(m-Cl) 2 Mg(m-DA)} 2 ] (2), and most significantly in solution turbo-DA differs markedly from turbo-TMP, enabling a rationalization of their markedly different observed reactivities. [1c] Furthermore, looking more generally across the whole field of modern metalation chemistry, these results allow a key distinction to be drawn between TMP-magnesiation reactions performed by these halide-activated regents and by mixed alkyl-amido formulations that dispense alkali metal mediated magnesiation (AMMMg). [3] In a variation of the original literature synthesis, [1c] we prepared turbo-DA by mixing LDA (iPr 2 NLi) with magnesium chloride in THF. [4] The crystalline form of turbo-DA 2 (60 % yield) came from a hexane/THF mixture. Dimeric aggregation is the main feature of the centrosymmetric molecular structure of 2 ( Figure 1). Its tetranuclear arrangement consists of a central (MgN) 2 planar ring, lying orthogonal to and separating two (LiCl) 2 non-planar outer rings. The Li atoms carry two THF ligands. All four metal atoms and N atoms of the amido bridges exhibit distorted tetrahedral geometries, while the chloro bridges have two-coordinate bent geometries. The THF ligands, one iPr arm of each DA ligand, and the chlori...

show abstract

Synthesis and characterisation of new bimetallic alkali metal–magnesium mixed diisopropylamide-acetylides: structural variations in bimetallic lithium- and sodium-heteroleptic magnesiates

Cited by 29 publications

References 51 publications

Diisopropylamide and TMP Turbo‐Grignard Reagents: A Structural Rationale for their Contrasting Reactivities

Diisopropylamide and TMP Turbo‐Grignard Reagents: A Structural Rationale for their Contrasting Reactivities

Mixed Lithium Complexes: Structure and Applicationin Synthesis

Diisopropylamide and TMP Turbo‐Grignard Reagents: A Structural Rationale for their Contrasting Reactivities

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