Synthesis, structure, and quaternization and complexation reactions of κ3SCS pincer palladium complexes having 3,5-pyridinediyl unit

Meguro, Hikaru; Koizumi, Toru; Yamamoto, Takakazu; Kanbara, Takaki

doi:10.1016/j.jorganchem.2007.12.033

Cited by 32 publications

(17 citation statements)

References 52 publications

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“…The drastic reactivity difference between 5 and 7 and the DFT computations provide insights into the enzyme reaction mechanism. Additionally, the pyridinium-based pincer SCS ligand developed here is new in molecular chemistry (28,29) and may find novel applications in coordination chemistry and homogeneous catalysis.…”

Section: Discussionmentioning

confidence: 99%

Nickel pincer model of the active site of lactate racemase involves ligand participation in hydride transfer

Wodrich

Scopelliti

et al. 2017

Proc. Natl. Acad. Sci. U.S.A.

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Lactate racemase is the first enzyme known to possess a metal pincer active site. The enzyme interconverts D-and L-lactic acid, which is important for the assembly of cell walls in many microorganisms. Here, we report a synthetic model of the active site of lactate racemase, which features a pyridinium-based SCS pincer ligand framework bound to nickel. The model complex mediates the dehydrogenation of alcohols, a reaction relevant to lactate racemization. Experimental and computational data indicate ligand participation in the dehydrogenation reaction.biomimetic chemistry | lactate racemase | nickel | pincer ligands | hydride transfer P incer complexes are widely applied in homogeneous catalysis thanks to their stability, diversity, and tunability (1-4). However, only very recently has the first pincer complex been discovered in the active site of a metalloenzyme (5-7). It was reported that lactate racemase, an enzyme responsible for the racemization of lactic acid and hence important for cell wall assembly in many microorganisms, hosts a nickel pincer cofactor (Fig. 1). The nickel center is coordinated by an SCS pincer ligand derived from a nicotinic acid mononucleotide, in addition to histidine (200) (5, 6). Based on the structure of this active site, it was proposed that the pincer ligand could reversibly capture a hydride from lactate at the carbon atom coordinated to nickel, in a manner similar to nicotinamide adenine dinucleotide in hydride transfer enzymes (Fig. 1). Nevertheless, evidence for this mechanism is still lacking.Although several nickel SCS pincer complexes have previously been reported (8-10), none exhibited an essential feature present in the active site of lactate racemase, namely a pyridinium-based pincer backbone. According to the proposed enzyme mechanism, the pyridinium group enables ligand participation in the hydride transfer reaction, which is likely impossible for a more conventional pyridine group. This hypothesis might be tested using model complexes containing either a pyridinium or a pyridine backbone. A further motivation for synthetic models of this unusual active site is the perspective of developing a new, bioinspired pincer ligand platform that enables metal ligand cooperation in catalysis (11,12). With these considerations in mind, we began investigating the biomimetic chemistry of lactate racemase. Here, we report the synthesis and characterization of a synthetic mimic of lactate racemase. Using dehydrogenation of alcohols as a model reaction, we show that the pyridinium functionality indeed facilitates hydride transfer by ligand participation. ResultsSynthesis. The pyridine-based ligand precursor (4) was synthesized from 4-chloro-3,5-dimethyl pyridine (1, Fig. 2). Oxidation of 1 by KMnO 4 gave 4-chloropyridine-3,5-dicarboxylic acid (2), which was converted to a dicarboxamide (3) by amidation. Reaction of 3 with Lawesson's reagent [2,4-bis(4-methoxyphenyl)-2,4-dithioxo-1,3,2,4-dithiadiphosphetane] yielded the ligand precursor 4 containing thioamides (13). Upon treatment o...

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Section: Discussionmentioning

confidence: 99%

Nickel pincer model of the active site of lactate racemase involves ligand participation in hydride transfer

Wodrich

Scopelliti

et al. 2017

Proc. Natl. Acad. Sci. U.S.A.

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“…short lateral bonds. 49 It could be reasoned, that coordination to the metal centre already induces localization of double bonds in a carbenoid fashion (Figure 3 -A'). Indeed, according to electron decomposition analysis (EDA), σ and π orbital contributions in pyridyl-metal and pyridylidene-metal bonds are remarkably similar.…”

Section: Figurementioning

confidence: 99%

Pyridine-Derived N-Heterocyclic Carbenes: An Experimental and Theoretical Evaluation of the Bonding in and Reactivity of Selected Normal and Abnormal Complexes of Nickel(II) and Palladium(II)

et al. 2010

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“…Metallacycles possessing the pincer ligand framework could be an efficient system because of their considerable thermal and oxidative stabilities [1][2][3][4][5][6][7][8][9]. Various types (e.g., PCP-, NCN-, CNC-) of pincer complexes of transition metals have been reported to date; among them, palladium-pincer complexes have been widely investigated and employed as catalysts for cross-coupling reactions [10][11][12][13][14][15]. Much less attention has been paid to the nickel-pincer complexes [16][17][18][19][20][21][22], although the use of nickel catalysts instead of palladium catalysts sometimes offers advantages, such as cost effectiveness and distinct catalytic abilities [23][24][25][26][27][28][29][30][31][32][33].…”

Section: Introductionmentioning

confidence: 99%

Pincer-type bis(carbene)-derived complexes of nickel(II): Synthesis, structure, and catalytic activity

Inamoto

Kuroda

Kwon

et al. 2009

Journal of Organometallic Chemistry

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Synthesis, structure, and quaternization and complexation reactions of κ3SCS pincer palladium complexes having 3,5-pyridinediyl unit

Cited by 32 publications

References 52 publications

Nickel pincer model of the active site of lactate racemase involves ligand participation in hydride transfer

Nickel pincer model of the active site of lactate racemase involves ligand participation in hydride transfer

Pyridine-Derived N-Heterocyclic Carbenes: An Experimental and Theoretical Evaluation of the Bonding in and Reactivity of Selected Normal and Abnormal Complexes of Nickel(II) and Palladium(II)

Pincer-type bis(carbene)-derived complexes of nickel(II): Synthesis, structure, and catalytic activity

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