Crystallographic Characterisation of Organolithium and Organomagnesium Intermediates in Reactions of Aldehydes and Ketones

Abstract

We report reactions of LiNacNac and NacNacMg(TMP) with common organic substrates (TMP=2,2,6,6‐tetramethylpiperidide). Using bulky β‐diketiminate compound NacNac (Me, Dipp), we have trapped metalated intermediates amenable to X‐ray crystallographic study. LiNacNac and acetone produced the NacNac‐free hexameric diacetone alkoxide [{LiO(MeC(=O)CH2C(Me)2}6]; whereas pinacolone gave the simple monomeric donor–acceptor complex [Li{(MeCN‐2,6‐iPr2C6H3)2CH}{O=C(Me)tBu}]. Benzaldehyde produced dimeric [Li{(MeCN‐2,6‐iPr2C6H3)2CC(=O)Ph}{O=C(Ph)OCH2Ph}]2, where one benzaldehyde molecule has inserted in to the γ‐carbon position of the NacNac ligand, with a molecule of benzyl benzoate derived from a Tishchenko reaction of the aldehyde acting as a terminal donor to lithium. Tetranuclear, mixed dimer [{LiO(MeCN‐2,6‐iPr2C6H3)2CH‐CH(Ph)}2{LiO(PhC(=O)}2] containing the same modified NacNac ligand was the fortuitous product from repeating the reaction of LiNacNac and benzaldehyde in a solution presumably contaminated with benzoic acid. Combining NacNacMg(TMP) with pinacolone affords monomeric heteroleptic [Mg{(MeCN‐2,6‐iPr2C6H3)2CH}{OC(tBu)(Me)CH2C(=O)tBu}] with an aldolate constituting the second anion. Completing the set is dimeric [Mg{(MeCN‐2,6‐iPr2C6H3)2CH}{O(C=CH2)Ph}2], where the enolate derived from acetophenone bridges the magnesium centres.

Li vs Na: Divergent Reaction Patterns between Organolithium and Organosodium Complexes and Ligand-Catalyzed Ketone/Aldehyde Methylenation

“…Reactions between Group-1 metal complexes and ketones/aldehydes are not only important tools in organic synthesis, but also can provide insights into the two fundamental and essential reactivity aspects of Group-1 metal complexes: Brønsted basicity and nucleophilicity . We first employed benzophenone ( 2a ) as the model substrate to test the reactivity of 1 -Li and 1 -Na.…”

“…Stoichiometric Reactions between the Li/Na Monomeric Alkyl Complexes [M(CH 2 SiMe 3 )(Me 6 Tren)] (1-Li, 1-Na) and Ketones/Aldehydes: Nucleophilic Addition, C− H Deprotonation, or C�O Olefination? Reactions between Group-1 metal complexes and ketones/aldehydes 60 are not only important tools in organic synthesis, but also can provide insights into the two fundamental and essential reactivity aspects of Group-1 metal complexes: Brønsted basicity and nucleophilicity. 62 We first employed benzophenone (2a) as the model substrate to test the reactivity of 1-Li and 1-Na.…”

Preparation and Characterization of N,N′‐Dialkyl‐1,3‐propanedialdiminium Chlorides, N,N′‐Dialkyl‐1,3‐propanedialdimines, and Lithium N,N′‐Dialkyl‐1,3‐propanedialdiminates

“…Compounds 3a – 3d are insoluble in benzene but soluble in diethyl ether and THF; they decompose in chlorocarbons. The NMR spectra of 3a – 3d in THF show that the 3 J HH couplings are all near 6 Hz, so that these compounds adopt the closed U‐shaped conformation in solution; presumably, the β‐dialdiminate anions coordinate in a chelating fashion to the lithium cations, as seen in lithium β‐diketiminates [13,15,65,66] and lithium β‐dialdiminates [35,37] …”

“…The NMR spectra of 3a-3d in THF show that the 3 J HH couplings are all near 6 Hz, so that these compounds adopt the closed U-shaped conformation in solution; presumably, the β-dialdiminate anions coordinate in a chelating fashion to the lithium www.helv.wiley.com (9 of 18) e202200152 © 2023 The Authors. Helvetica Chimica Acta published by Wiley-VHCA AG cations, as seen in lithium β-diketiminates [13,15,65,66] and lithium β-dialdiminates. [35,37]…”

Atom-economic access to cationic magnesium complexes

“…These ligands were already particularly prevalent in s-block chemistry in for example the stabilization of low-valent [(Mg( i ), Ca( i )] or reactive hydrido-equipped alkaline-earth metal complexes, 3 the stabilization of dihydropyridyl ligands and hydrogen-rich B/N ligands 4 and the development of magnesium complexes for deprotonation or C–H/C–F bond activation and consequent stabilization of the resulting sensitive products. 5 However, it is now established that these ligands are not as innocent as they were initially thought to be, with recent alkali–metal research in this area showing that NacNac is susceptible to attack at the backbone site 6 on account of the HOMO being located at the C γ position, which renders it nucleophilic. 7…”