A Solid‐State, Solution, and Theoretical Structural Study of Kinetic and Thermodynamic Lithiated Derivatives of a Simple Diazomethane and Their Reactivities Towards Aryl Isothiocyanates

Armstrong, David R.; Davies, Robert P.; Haigh, Robert; Hendy, Mark A.; Raithby, Paul R.; Snaith, Ronald; Wheatley, Andrew E. H.

doi:10.1002/ejic.200300244

Cited by 21 publications

(19 citation statements)

References 68 publications

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“…Initial DLPNO-CCSD(T) computations established a thermally feasible pathway from acetophenone ( 1 -Me,Ph) to 1-phenylpropyne ( 6 -Me,Ph), Figure . Consistent with Colvin and Hamill’s original proposal and later work by Gilbert, the diazoalkene MePhCCN 2 ( 4 -Me,Ph) was identified as a key intermediate, formed via a nucleophilic addition, , [1,3]-silyl migration, and elimination sequence. Although the ionic nature of the intermediates mean that quantitative comparisons made in the absence of explicit solvation should be interpreted with caution, lithiated silyl ether 3 -Me,Ph appears to be marginally favored over lithium alkoxide 2 -Me,Ph (Δ G 195K = −5 kJ mol –1 ), in a delicately balanced [1,3]-Brook equilibrium, − , in which pre-equilibrium between lithium α-diazoalkoxide 2 -Me,Ph and cyclic siliconate 7 -Me,Ph is kinetically insignificant.…”

Section: Resultssupporting

confidence: 66%

Systematic Evaluation of 1,2-Migratory Aptitude in Alkylidene Carbenes

et al. 2021

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Alkylidene carbenes undergo rapid inter-and intra-molecular reactions and rearrangements, including 1,2-migrations of β-substituents to generate alkynes. Their propensity for substituent migration exerts profound influence over the broader utility of alkylidene carbene intermediates, yet prior efforts to categorize 1,2-migratory aptitude in these elusive species have been hampered by disparate modes of carbene generation, ultrashort carbene lifetimes, mechanistic ambiguities, and the need to individually prepare a series of 13 C-labelled precursors. Herein we report on the rearrangement of 13 C-alkylidene carbenes generated in situ by the homologation of carbonyl compounds with [ 13 C]-Li-TMS-diazomethane, an approach that obviates the need for isotopically labelled substrates and has expedited a systematic investigation ( 13 C{ 1 H} NMR, DLPNO-CCSD(T)) of migratory aptitudes in an unprecedented range of more than 30 alkylidene carbenes. Hammett analyses of the reactions of 26 differentially substituted benzophenones reveal several counterintuitive features of 1,2-migration in alkylidene carbenes that may prove of utility in the study and synthetic application of unsaturated carbenes more generally.

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Section: Resultssupporting

confidence: 66%

Systematic Evaluation of 1,2-Migratory Aptitude in Alkylidene Carbenes

et al. 2021

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“…In contrast to the symmetrical binding of TMEDA observed in solution by NMR spectroscopy, only one molecule is bidentate with the other molecule coordinating through a single nitrogen atom (i.e., “dangling”), generating what may be considered a “Na(TMEDA) 1.5 ” unit. Although an η 1 -coordination of TMEDA has been previously observed at lithium − and potassium, the bonding of a single nitrogen donor group of TMEDA at sodium has only been structurally characterized within a bridging TMEDA ligand. , The resulting Al–Na bond in 2 -Na (3.1397(6) Å) is 4.2% longer than in I -Na(Et 2 O) 2 and 5.0% longer than in 1 -Na, reflecting the more sterically encumbered environment at sodium. Compound 2 -K contains two molecules of TMEDA that are both bidentate at potassium.…”

Section: Resultsmentioning

confidence: 96%

Controlling Al–M Interactions in Group 1 Metal Aluminyls (M = Li, Na, and K). Facile Conversion of Dimers to Monomeric and Separated Ion Pairs

et al. 2021

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The aluminyl compounds [M{Al(NON Dipp )}] 2 (NON Dipp = [O(SiMe 2 NDipp) 2 ] 2− , Dipp = 2,6-iPr 2 C 6 H 3 ), which exist as contacted dimeric pairs in both the solution and solid states, have been converted to monomeric ion pairs and separated ion pairs for each of the group 1 metals, M = Li, Na, and K. The monomeric ion pairs contain discrete, highly polarized Al−M bonds between the aluminum and the group 1 metal and have been isolated with monodentate (THF, M = Li and Na) or bidentate (TMEDA, M = Li, Na, and K) ligands at M. The separated ion pairs comprise group 1 cations that are encapsulated by polydentate ligands, rendering the aluminyl anion, [Al(NON Dipp )] − "naked". For M = Li, this structure type was isolated as the [Li(TMEDA) 2 ] + salt directly from a solution of the corresponding contacted dimeric pair in neat TMEDA, while the polydentate [2.2.2]cryptand ligand was used to generate the separated ion pairs for the heavier group 1 metals M = Na and K. This work shows that starting from the corresponding contacted dimeric pairs, the extent of the Al−M interaction in these aluminyl systems can be readily controlled with appropriate chelating reagents.

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“…The isomers of [Li][C(SiMe 3 )N 2 ] have been reported to be in equilibrium, with a preference for N- or C-lithiation that is similarly dependent on the coordinating ability of the solvent. − Computations suggest that the N-lithiated species is thermodynamically favored but solvation of the metal diminishes this preference until, in pure THF, the C-lithiated species is favored (Figure ). This is the same preference that we observed in the iron complexes 2 (favored in Et 2 O) and 3 (favored in THF), although we also observe a silyl shift.…”

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confidence: 99%

Diazoalkanes in Low-Coordinate Iron Chemistry: Bimetallic Diazoalkyl and Alkylidene Complexes of Iron(II)

et al. 2017

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Addition of trimethylsilyldiazomethane and its conjugate base to β-diketiminate-iron precursors gives novel dinuclear complexes in which the bridges are either diazomethane derivatives or an alkylidene. One product is an unusual bridging alkylidene complex containing two three-coordinate iron(II) centers. On the other hand, syntheses using the deprotonated diazomethane give two bridging diazomethyl species with binding modes that have not been observed in iron complexes previously. In the presence of coordinating THF solvent, a diiron(II) compound with μ-N bridges rearranges to a more stable isomer with μ-N,C bridges, a process that is accompanied by a 1,3-shift of a silyl group.

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A Solid‐State, Solution, and Theoretical Structural Study of Kinetic and Thermodynamic Lithiated Derivatives of a Simple Diazomethane and Their Reactivities Towards Aryl Isothiocyanates

Cited by 21 publications

References 68 publications

Systematic Evaluation of 1,2-Migratory Aptitude in Alkylidene Carbenes

Systematic Evaluation of 1,2-Migratory Aptitude in Alkylidene Carbenes

Controlling Al–M Interactions in Group 1 Metal Aluminyls (M = Li, Na, and K). Facile Conversion of Dimers to Monomeric and Separated Ion Pairs

Diazoalkanes in Low-Coordinate Iron Chemistry: Bimetallic Diazoalkyl and Alkylidene Complexes of Iron(II)

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