Acid−Base Reactions of Methylnickel Hydroxo, Alkoxo, and Amide Complexes with Carbon Acids. Studies on the Reactivity of Noncyclic Nickel Enolates

Cámpora, Juan; Matas, Inmaculada; Palma, Pilar; Álvarez, Eleuterio; Graiff, Claudia; Tiripicchio, António

doi:10.1021/om7007259

Cited by 22 publications

(12 citation statements)

References 69 publications

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“…Accordingly, the reaction of [( iPr PCP)Ni(OH)] with equimolar amounts of acetophenone in C 6 D 6 is incomplete and gives rise to equilibrium mixtures of the hydroxide and the corresponding O‐ enolate, unambiguously identified in the solution NMR spectra of the reaction mixtures on the basis of its characteristic 1 H and 13 C signals of the vinyl enolate fragment. The apparent equilibrium constant, K eq ≈2×10 −2 , is very similar to that measured for the analogous reaction of acetophenone with the monomeric hydroxide complex [Ni(Me)(OH)(dippe)] [29a] . Removing water with molecular sieves shifts the equilibrium to the enolate side until the hydroxide/enolate ratio reaches 3 : 7, but the O‐ enolate product was reluctant to crystallize and could not be isolated pure (see Experimental Section).…”

Section: Resultssupporting

confidence: 64%

Nucleophilic Nickel and Palladium Pincer Hydroxides: A Study of Their Reactions with Dimethyl Carbonate and Other Non‐Alkylating Organic Electrophiles

et al. 2021

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The reactions of the pincer hydroxide complexes [(iPrPCP)M(OH)] (M=Ni, Pd) with dimethyl carbonate (DMC), and a set of organic electrophiles including benzaldehyde have been investigated in the context of our ongoing investigation on the synthesis of alkyl carbonates from CO2 and alcohols. The final outcome of such reactions is diverse, but for PhCHO and DMC the first step is a mechanistically similar addition of the [M]−OH linkage across the carbonyl functionality, that leads to unstable adducts. DMC is cleaved irreversibly by both Ni and Pd hydroxides, affording the corresponding methylcarbonates [(iPrPCP)MOCO2Me] and methanol, whereas PhCHO affords benzoate complexes [[(iPrPCP)MOCO2Ph]. The main kinetic and thermodynamic features of these reactions were reproduced satisfactorily by computational DFT models. The calculations throw light on the true causes of irreversibility of DMC cleavage by nucleophilic hydroxide complexes, which is the primary cause that prevents methanol carboxylation from being catalysed by the Ni or Pd pincers.

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Section: Resultssupporting

confidence: 64%

Nucleophilic Nickel and Palladium Pincer Hydroxides: A Study of Their Reactions with Dimethyl Carbonate and Other Non‐Alkylating Organic Electrophiles

et al. 2021

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“…[36] However,i nt he present case, the participation of the pentacoordinated iridium species of the type [Ir(cod)(MeImZ)(enolate)(aldehyde)] (Z = benzyloxycarbonyl) is unlikely.I nt his context,i ti sw orth of notingt he rich chemistry of the square-planar complex [Ni(CH 3 )(OC(=CH 2 )Ph)(dippe)] (dippe = 1,2-bis(diisopropylphosphino)ethane) having an acetophenone enolate ligand. [37] Mechanism of the b-alkylation of alcohols catalysedb y [Ir(cod)(NHC)] + + complexes:D FT studies…”

Section: Mechanistic Studiesmentioning

confidence: 99%

Oxidation and β‐Alkylation of Alcohols Catalysed by Iridium(I) Complexes with Functionalised N‐Heterocyclic Carbene Ligands

Jiménez

Fernández-Tornos

Modrego

et al. 2015

Chemistry A European J

111

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The borrowing hydrogen methodology allows for the use of alcohols as alkylating agents for CC bond forming processes offering significant environmental benefits over traditional approaches. Iridium(I)-cyclooctadiene complexes having a NHC ligand with a O- or N-functionalised wingtip efficiently catalysed the oxidation and β-alkylation of secondary alcohols with primary alcohols in the presence of a base. The cationic complex [Ir(NCCH3 )(cod)(MeIm(2- methoxybenzyl))][BF4 ] (cod=1,5-cyclooctadiene, MeIm=1-methylimidazolyl) having a rigid O-functionalised wingtip, shows the best catalyst performance in the dehydrogenation of benzyl alcohol in acetone, with an initial turnover frequency (TOF0 ) of 1283 h(-1) , and also in the β-alkylation of 2-propanol with butan-1-ol, which gives a conversion of 94 % in 10 h with a selectivity of 99 % for heptan-2-ol. We have investigated the full reaction mechanism including the dehydrogenation, the cross-aldol condensation and the hydrogenation step by DFT calculations. Interestingly, these studies revealed the participation of the iridium catalyst in the key step leading to the formation of the new CC bond that involves the reaction of an O-bound enolate generated in the basic medium with the electrophilic aldehyde.

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“…The reactivity of organonickel complexes bearing a σ-bonded methyl group toward unsaturated compounds and carboxylic acids was investigated. , The authors investigated the process of the coordination of unsaturated hydrocarbons and carbonyl compounds to monoalkyl- and dialkylnickel complexes and made some conclusions concerning the mechanism of C–C bond formation under these conditions. The influence of the ligand nature on the stability of nickel–carbon σ-bonds in alkylnickel complexes and the mechanism of C–H bond activation leading to organonickel complexes containing a methyl substituent at the nickel center was also studied …”

Section: Main Types Of Organonickel Complexesmentioning

confidence: 99%

Electrochemical Synthesis and Properties of Organonickel σ-Complexes

2014

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The organonickel complexes are organometallic compounds containing a Ni−C σ-bond (σ-complexes). These species are very reactive and have been mainly characterized as the intermediates of catalytic processes of cross coupling and homocoupling involving organic and elementoorganic substrates such as organic halides, chlorophosphines, unsaturated hydrocarbons, etc. Thus, only a limited number of these complexes have been isolated and characterized as the free stable species. Although the organonickel complexes have been known since the 1960s, the chemistry of these species is currently at the beginning stages of development. The interest of the researchers in this class of compounds has significantly increased over the past decade, resulting in a plethora of scientific papers published on this topic. At the same time, electrochemical methods have become more and more popular in modern synthetic chemistry, due to easy access to high reactive intermediates, including organometallic species, which can be selectively generated in situ and used for subsequent synthetic processes. This review summarizes the elaborated electrochemical approaches for the preparation of organonickel complexes, including a discussion of the important role of the electrochemical cell construction and the influence of the electrode material nature on the electrochemical process. In order to give more insight into the importance of organonickel complexes in synthetic chemistry and introduce the reader to this problem of organometallic chemistry, focused on the development of new synthetic protocols for preparation of stable organonickel complexes, an overview of the most important catalytic processes proceeding with participation of these highly reactive intermediates and the main types of organonickel complexes are presented. However, in this review organonickel complexes will be limited by examples in which the organic fragment is singly bonded to the nickel center, because these species are responsible for the catalytic reactions.

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Acid−Base Reactions of Methylnickel Hydroxo, Alkoxo, and Amide Complexes with Carbon Acids. Studies on the Reactivity of Noncyclic Nickel Enolates

Cited by 22 publications

References 69 publications

Nucleophilic Nickel and Palladium Pincer Hydroxides: A Study of Their Reactions with Dimethyl Carbonate and Other Non‐Alkylating Organic Electrophiles

Nucleophilic Nickel and Palladium Pincer Hydroxides: A Study of Their Reactions with Dimethyl Carbonate and Other Non‐Alkylating Organic Electrophiles

Oxidation and β‐Alkylation of Alcohols Catalysed by Iridium(I) Complexes with Functionalised N‐Heterocyclic Carbene Ligands

Electrochemical Synthesis and Properties of Organonickel σ-Complexes

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