Dataset Information

Spectroscopic Characterization of a Reactive [Cu₂ (μ-OH)₂ ]²⁺ Intermediate in Cu/TEMPO Catalyzed Aerobic Alcohol Oxidation Reaction.

ABSTRACT: Cu^I /TEMPO (TEMPO=2,2,6,6-tetramethylpiperidinyloxyl) catalyst systems are versatile catalysts for aerobic alcohol oxidation reactions to selectively yield aldehydes. However, several aspects of the mechanism are yet unresolved, mainly because of the lack of identification of any reactive intermediates. Herein, we report the synthesis and characterization of a dinuclear [L1₂ Cu₂ ]²⁺ complex 1, which in presence of TEMPO can couple the catalytic 4 H⁺ /4 e^- reduction of O₂ to water to the oxidation of benzylic and aliphatic alcohols. The mechanisms of the O₂ -reduction and alcohol oxidation reactions have been clarified by the spectroscopic detection of the reactive intermediates in the gas and condensed phases, as well as by kinetic studies on each step in the catalytic cycles. Bis(μ-oxo)dicopper(III) (2) and bis(μ-hydroxo)dicopper(II) species 3 are shown as viable reactants in oxidation catalysis. The present study provides deep mechanistic insight into the aerobic oxidation of alcohols that should serve as a valuable foundation for ongoing efforts dedicated towards the understanding of transition-metal catalysts involving redox-active organic cocatalysts.

SUBMITTER: Warm K

PROVIDER: S-EPMC8518518 | biostudies-literature | 2021 Oct

REPOSITORIES: biostudies-literature

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Publications

Spectroscopic Characterization of a Reactive [Cu2 (μ-OH)2 ]2+ Intermediate in Cu/TEMPO Catalyzed Aerobic Alcohol Oxidation Reaction.

Warm Katrin K Tripodi Guilherme G Andris Erik E Mebs Stefan S Kuhlmann Uwe U Dau Holger H Hildebrandt Peter P Roithová Jana J Ray Kallol K

Angewandte Chemie (International ed. in English) 20210908 42

CuI /TEMPO (TEMPO=2,2,6,6-tetramethylpiperidinyloxyl) catalyst systems are versatile catalysts for aerobic alcohol oxidation reactions to selectively yield aldehydes. However, several aspects of the mechanism are yet unresolved, mainly because of the lack of identification of any reactive intermediates. Herein, we report the synthesis and characterization of a dinuclear [L12 Cu2 ]2+ complex 1, which in presence of TEMPO can couple the catalytic 4 H<sup ...[more]

PMID: 34309168

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Project description:Reaction of [CoCp2][TpiPrMoOS(OAr)] [Cp = η5-cyclopentadienyl; TpiPr = hydrotris(3-isopropylpyrazol-1-yl)borate; OAr = phenolate or derivative thereof] with [Cu(NCMe)(Me3tcn)]BF4 (Me3tcn = 1,4,7-trimethyl-1,4,7-triazacyclononane) in MeCN at -30 °C results in the formation of red-brown/black, paramagnetic, μ-sulfido-Mo(v)/Cu(i) complexes, TpiPrMoO(OAr)(μ-S)Cu(Me3tcn). The complexes possess the MoO(μ-S)Cu core found in aerobic carbon monoxide dehydrogenases (CODHs) and exhibit X-band EPR spectra closely related to those of semi-reduced CODH, with g iso ∼ 1.937, hyperfine coupling to 95,97Mo (a iso = 39-42 × 10-4 cm-1) and strong superhyperfine coupling to 63,65Cu (a iso = 34-63 × 10-4 cm-1). Anisotropic spectra exhibit monoclinic symmetry with g 1 ∼ 1.996, g 2 ∼ 1.944 and g 3 ∼ 1.882, and nearly isotropic A Cu values (75-90 × 10-4 cm-1). The X-ray structures of four derivatives (Ar = Ph, C6H4 t Bu-2, C6H4 sBu-2, C6H4Ph-4) are reported and discussed along with that of the Ar = C6H3 t Bu2-3,5 derivative (communicated in C. Gourlay, D. J. Nielsen, J. M. White, S. Z. Knottenbelt, M. L. Kirk and C. G. Young, J. Am. Chem. Soc., 2006, 128, 2164). The complexes exhibit distorted octahedral oxo-Mo(v) and distorted tetrahedral Cu(i) centres bridged by a single bent μ-sulfido ligand, with Mo-S and Cu-S distances and Mo-S-Cu angles in the ranges 2.262-2.300 Å, 2.111-2.134 Å and 115.87-134.27°, respectively. The 2 t-butyl derivative adopts a unique phenolate conformation with O[double bond, length as m-dash]Mo-O-Cα and O[double bond, length as m-dash]Mo-S-Cu torsion angles of 92.7 and 21.1°, respectively, very different from those of the other structurally characterized derivatives (31-47 and 33-45°, respectively) and exhibits a relatively short Mo···Cu distance [3.752(2) Å vs. 3.806(7)-4.040(2) Å]. As well, the a Cu value of this complex (34.3 × 10-4 cm-1) is much lower than the values observed for other members of the series (55-63 × 10-4 cm-1), supporting the hypothesis that the electronic structure of the MoO(μ-S)Cu core unit and the degree of intermetallic communication are strongly dependent on the geometry of the MoO(OR)(μ-S)Cu unit. The complexes participate in an electrochemically reversible Mo(vi)/Mo(v) redox couple and react with cyanide undergoing decupration and desulfurization reactions of the type observed for CODH.

Dataset Information

Spectroscopic Characterization of a Reactive [Cu₂ (μ-OH)₂ ]²⁺ Intermediate in Cu/TEMPO Catalyzed Aerobic Alcohol Oxidation Reaction.

Publications

Spectroscopic Characterization of a Reactive [Cu<sub>2</sub> (μ-OH)<sub>2</sub> ]<sup>2+</sup> Intermediate in Cu/TEMPO Catalyzed Aerobic Alcohol Oxidation Reaction.

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