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. 2019 Apr 15;58(8):4706-4711.
doi: 10.1021/acs.inorgchem.9b00090. Epub 2019 Mar 22.

Revisiting the Synthesis and Nucleophilic Reactivity of an Anionic Copper Superoxide Complex

Wilson D Bailey  1 , Nicole L Gagnon  2 , Courtney E Elwell  2 , Anna C Cramblitt  2 , Caitlin J Bouchey  1   2 , William B Tolman  1   2
Affiliations

Revisiting the Synthesis and Nucleophilic Reactivity of an Anionic Copper Superoxide Complex

Wilson D Bailey et al. Inorg Chem. .

Abstract

The addition of 1 equiv of KO2 and Kryptofix222 (Krypt) in CH3CN to a solution of LCu(CH3CN) [L = N, N'-bis(2,6-diisopropylphenyl)-2,6-pyridinecarboxamide] in tetrahydrofuran at -80 °C yielded [K(Krypt)][LCuO2], the enhanced stability of which enabled reexamination of its reactivity with 2-phenylpropionaldehyde (2-PPA). Mechanistic and product analysis studies revealed that [K(Krypt)][LCuO2] reacts with wet 2-PPA to form [LCuOH]-, which then deprotonates 2-PPA to yield the copper(II) enolate complex [LCu(OC═C(Me)Ph)]-. Acetophenone was observed upon workup of this complex or mixtures of KO2 and 2-PPA alone, in support of an alternative mechanism(s) to the one proposed previously involving an initial nucleophilic attack at the carbonyl group of 2-PPA.

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Conflict of interest statement

Notes

The authors declare no competing financial interest.

Figures

Figure 1
Figure 1
UV−vis spectra as a function of time for the reaction of [LCuO2]− (red) and 375 equiv of 2-PPA to form [LCu(OC═C(Me)Ph)]− (blue) via the intermediate (purple). Inset: Two-phase process illustrated by the absorbance at 628 nm versus time.
Figure 2
Figure 2
Representation of the anionic portion of the X-ray crystal structure of [NBu4][LCu(OC═C(Me)Ph)]. All non-H atoms are shown as 50% thermal ellipsoids. Select bond distances (Å) and angles (deg): Cu1−N1, 2.0197(18); Cu1−N2, 1.9221(19); Cu1−N3, 2.013(2); Cu1−O1, 1.865(2); O1−C1, 1.285(3); C1−C2, 1.371(4); C2−C3, 1.504(4); N1−Cu1−N3, 158.89(8); N1−Cu1−N2, 79.40(8); N2−Cu1−O1, 165.84(9); N2−Cu1−N3, 80.63(8); Cu1−O1−C1, 135.5(2); C1−C2−C3, 119.5(3).
Scheme 1
Scheme 1
Previously Proposed Mechanism for the Initial Nucleophilic Attack of [K(18-crown-6)][LCuO2] on Aldehydes
Scheme 2
Scheme 2
Synthesis of [K(Krypt)][LCuO2]
Scheme 3
Scheme 3
Proposed Pathway for the Formation of an Enolate Complex
See this image and copyright information in PMC

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