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Review
. 2017 Feb 8;117(3):2059-2107.
doi: 10.1021/acs.chemrev.6b00636. Epub 2017 Jan 19.

Copper-Oxygen Complexes Revisited: Structures, Spectroscopy, and Reactivity

Courtney E Elwell  1 , Nicole L Gagnon  1 , Benjamin D Neisen  1 , Debanjan Dhar  1 , Andrew D Spaeth  1 , Gereon M Yee  1 , William B Tolman  1
Affiliations
Review

Copper-Oxygen Complexes Revisited: Structures, Spectroscopy, and Reactivity

Courtney E Elwell et al. Chem Rev. .

Abstract

A longstanding research goal has been to understand the nature and role of copper-oxygen intermediates within copper-containing enzymes and abiological catalysts. Synthetic chemistry has played a pivotal role in highlighting the viability of proposed intermediates and expanding the library of known copper-oxygen cores. In addition to the number of new complexes that have been synthesized since the previous reviews on this topic in this journal (Mirica, L. M.; Ottenwaelder, X.; Stack, T. D. P. Chem. Rev. 2004, 104, 1013-1046 and Lewis, E. A.; Tolman, W. B. Chem. Rev. 2004, 104, 1047-1076), the field has seen significant expansion in the (1) range of cores synthesized and characterized, (2) amount of mechanistic work performed, particularly in the area of organic substrate oxidation, and (3) use of computational methods for both the corroboration and prediction of proposed intermediates. The scope of this review has been limited to well-characterized examples of copper-oxygen species but seeks to provide a thorough picture of the spectroscopic characteristics and reactivity trends of the copper-oxygen cores discussed.

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Conflict of interest statement

Notes

The authors declare no competing financial interest.

Figures

Figure 1
Figure 1
Proposed copper–oxygen intermediates involved in the reactions of the indicated enzymes. (a) and (b) Superoxo, hydroperoxo, and oxyl intermediates proposed for the monocopper sites in the indicated enzymes, R = H or Me. (c) Possible equilibrium between putative substrate-bound intermediates, either of which could undergo electrophilic attack at the substrate to yield a catecholate species in the monooxygenase reaction of coupled binuclear polyphenol oxidases such as tyrosinase (N indicates nitrogen donor atom of histidine imidazoles). (d) Selected copper–oxygen intermediates speculated to be responsible for C–H bond attack of substrate by particulate methane monooxygenase. (e) Selected tricopper intermediates proposed for reduction of O2 to H2O by the multicopper oxidases. The proximate type 1 Cu electron transfer center is not shown. (f) Two key intermediates proposed for reduction of O2 to H2O by the Fe–Cu core of cytochrome c oxidase.
Figure 2
Figure 2
(a) Proposed transition state for hydrogen atom abstraction from methane by the (μ-oxo)dicopper core of Cu-ZSM-5 (ref 112). (b) Alternative O2 activation pathway calculated by DFT for Cu-ZSM-5 (ref 115). (c) Structure and location of [Cu3(μ-O)3]2+ core in mordenite. Reprinted with permission from ref . Copyright 2015 Nature Publishing Group.
Figure 3
Figure 3
Overall catalytic reaction and proposed mechanism for the hydroxylation of benzoate derivatives (TMAO is trimethylamine-N-oxide) (ref 121).
Figure 4
Figure 4
1:1 Cu:O2 core structures.
Figure 5
Figure 5
1:1 Cu:O2 adducts defined by X-ray crystallography, supported by ligands L39a,b (1a,b), L44 (2), L2d,e (3a,b), or L3b (4). Reprinted from ref . Copyright 2007 American Chemical Society.
Figure 6
Figure 6
DFT calculated spin down (β) MO diagram of 2. Reprinted from ref . Copyright 2010 American Chemical Society.
Figure 7
Figure 7
Proposed hydrogen bonding interactions in 2·CF3CO2H and 5 (refs and 130) supported by ligands L44 and L41d, respectively.
Figure 8
Figure 8
Proposed dual pathway for the oxygenation reaction resulting in formation of complex 3a. Adapted from ref .
Figure 9
Figure 9
Reaction of a 1:1 Cu:O2 adduct (6, supported by ligand L28a) with a Cu(I) complex to yield a (trans-1,2-peroxo)dicopper complex (7; ref 128).
Figure 10
Figure 10
Reversible O2 binding to yield 1:1 Cu:O2 adduct 8 (supported by L74, X = Me or Ph) and its conversion to a bis(μ-oxo)dicopper complex 9. Adapted from ref .
Figure 11
Figure 11
Intramolecular aryl ring hydroxylation/oxidation reaction of 3a (ref 170).
Figure 12
Figure 12
Reactivity of 5 with hydride donors, proposed to involve initial HAT (ref 130).
Figure 13
Figure 13
Proposed mechanism for intramolecular hydroxylation by 10 (supported by L33c, refs and 162).
Figure 14
Figure 14
Proposed pathways for the generation of oxidized products (in boxes) from the reaction of Cu(II)-O2−• complexes supported by L (L41b and L41c; similar products formed for L44) (refs , , and 175).
Figure 15
Figure 15
Routes by which [CuOOR]+ (R = H, alkyl, or acyl) complexes may be generated. S–H = substrate C–H or O–H bond. Supporting ligands not shown.
Figure 16
Figure 16
Proposed mechanism for generation of [CuOOH]+ complexes supported by ligand L35b and L35c. Only the donor N atoms of the supporting ligand are shown; S = solvent molecule (ref 179).
Figure 17
Figure 17
Proposed mechanism for generation of [CuOOH]+ complexes supported by ligand L41h (ligand not shown; ref 188).
Figure 18
Figure 18
Generation of alkylperoxide complexes supported by L18 via functionalization of acetone solvent. Y = ClO4− or H2O; S = MeCN or H2O; X = NO2, Cl, H, Me, OMe; n = 1 or 2, depending on Y (refs , , and 185).
Figure 19
Figure 19
Proposed mechanism for the generation of 18 from reaction of cumene hydroperoxide with the Cu(I) complex (14) of L42c (X = TIPT), R = dimethylbenzyl (cumyl), S = CH3CN (ref 195).
Figure 20
Figure 20
X-ray structures of the [CuOOH]+ complex of L41e (19), also drawn in Figure 21), and the [CuOOCm]+ (Cm = cumyl) complex of L39c (20). Selected interatomic distances (Å): (19) Cu–O, 1.888(4); O–O, 1.460(6) (20) Cu–O, 1.816(4); O–O, 1.460(6). (19) Reprinted from ref . Copyright 2005 Elsevier. (20) Reprinted from ref . Copyright 1993 American Chemical Society.
Figure 21
Figure 21
[CuOOH]+ complexes illustrating hydrogen bonding to the proximal O atom (19, supported by L41e) (refs and 211), distal O atom (21, supported by L43a; ref 207), and with no hydrogen bonding (22, supported by L43b; ref 207).
Figure 22
Figure 22
Reactivity of [CuOOH]+ complex 23 (L = L41h) (refs and 193).
Figure 23
Figure 23
Aryl group hydroxylations by [CuOOR]+ complexes. (a) Reaction of complex 24 supported by L41f (ref 181). (b) Reaction of 2-hydroxy-2-peroxypropane complexes 13, highlighting the proposed mechanism. X = NO2, Cl, H, Me, OMe (refs and 184).
Figure 24
Figure 24
Proposed mechanism for the conversion of the 2-hydroxy-2-peroxypropane complex of L18a to a Cu(II)-acetate complex (ref 184).
Figure 25
Figure 25
N-dealkylation reactions of complexes (27) of L41g (R = H) and L41i–k (R = aryl) (refs , , and 189).
Figure 26
Figure 26
Proposed conversion of 1:1 Cu:O2 complex 2 to copper(II)-alkoxide 30 upon reaction with H atom donor reagents (ref 175).
Figure 27
Figure 27
Hypothesized mechanism for N-dealkylation of 27, with only the attacked arm of the L41i–k ligand shown. All copper species have an overall charge of +1 (ref 189).
Figure 28
Figure 28
Reactivity of [CuOOR]+ (R = Cm) complex 31 with proposed mechanism involving O–O bond homolysis (ref 185).
Figure 29
Figure 29
Copper(I) complexes (a) 34 (supported by L18a) which proceeds via a 2:1 stoichiometry (not shown) and (b) the proposed pathway for reaction of cumyl hydroperoxide with 35 (supported by L69) to yield CmOH and the Cu(I) complex of the oxidized ligand 38 (refs and 192).
Figure 30
Figure 30
(left) Qualitative molecular orbital (MO) scheme for [CuO]+. Reprinted with permission from ref . Copyright 2011 AIP Publishing). (right) Orbital scheme for [CuO]+ unit in PHM. Reprinted with permission from ref . Copyright 2005 Elsevier Ltd.
Figure 31
Figure 31
Reaction of 39 (supported by L17) that results in hydroxylation of the ligand and the mechanism proposed on the basis of DFT calculations. Adapted from ref .
Figure 32
Figure 32
Complexes with a [CuOH]2+ core supported by L28a–c and L25, respectively (refs –239).
Figure 33
Figure 33
Plot of log(k) vs ΔH (equivalent to the ΔBDE between the aqua complexes and the C–H bonds of the substrates) for reactions of 40 (black), 43 (red), and 42 (blue) with the substrates DHA (filled circles), cyclohexene (open circles), diphenylmethane (filled squares), THF (open squares), toluene (filled stars), and cyclohexane (open stars) at −25 °C in 1,2-DFB. Reprinted from ref . Copyright 2016 American Chemical Society.
Figure 34
Figure 34
Isomeric cores of 2:1 Cu:O2 complexes.
Figure 35
Figure 35
X-ray crystal structure of the (μ-η2:η2-peroxo)dicopper complex dication supported by L20c. Selected interatomic distances (Å): O1a-O1b = 1.475(4), Cu···Cu = 3.6349(8). Reprinted from ref . Copyright 2016 American Chemical Society.
Figure 36
Figure 36
Reaction of (μ-η2:η2-peroxo)dicopper complexes 44 (supported by L1a) with 2,4-di-tert-butylphenolate, with proposed mechanism based on spectroscopy and theory (refs –253).
Figure 37
Figure 37
Synthesis of (μ-η2:η2-peroxo)dicopper complexes with simple imidazole ligands (refs –259).
Figure 38
Figure 38
Proposed (μ-η2:η2-peroxo)dicopper complexes supported by L58c (52; ref 268) and L58a (53; refs and 273).
Figure 39
Figure 39
Ligand hydroxylation reactions of (μ–η2:η2-peroxo)-dicopper complexes supported by L58f–h (54; refs and 277) or L58i (R3 = Me, R = H, OMe, tBu, and NO2) (55; ref 281).
Figure 40
Figure 40
Proposed formation of an intermediate CuICuII(O2−•) species (ref 280).
Figure 41
Figure 41
Proposed mechanisms for the catalytic reduction of O2 to H2O by 56 (L51a) in the presence of exogenous Fc* as a reductant (ref 288).
Figure 42
Figure 42
X-ray crystal structure of the bis(μ-oxo)dicopper complex supported by L6c. Reprinted from ref . Copyright 2005 American Chemical Society. Selected interatomic distances (Å): Cu(1)–O(1), 1.809(6); Cu(1)–O(2), 1.808(6); Cu(2)–O(1), 1.795(5); Cu(2)–O(2), 1.799(6); Cu(1)···Cu(2), 2.744(1); and O(1) ···O(2), 2.334(1).
Figure 43
Figure 43
Controlled formation of di- and tricopper complexes, [(L1c)Cu2O2]2+ and [(L1c)Cu3O2]3+, via selective addition of dioxygen (refs and 294).
Figure 44
Figure 44
Stability order of bis(μ-oxo)dicopper complexes. Adapted from ref .
Figure 45
Figure 45
Proposed mechanism for the reduction of O2 to H2O invoking the intermediacy of the bis(μ-oxo)dicopper (65) complex supported by L18a (ref 288).
Figure 46
Figure 46
Proposed pathway for hydroxylation of an appended arene of the L7 ligand (ref 301).
Figure 47
Figure 47
DFT geometry-optimized structure for the bis(μ-oxo)-dicopper intermediate proposed in the oxidation of the appended phenol in L80a. Reprinted with permission from ref . Copyright 2015 the Royal Society of Chemistry.
Figure 48
Figure 48
Comparison of the reactivity of set of bis(μ-oxo)dicopper complexes 51 (L10a), 66 (L14), and 67 (L27) with 2,4-di-tertbutylphenol (“phenol”) and 2,4-di-tert-butylphenolate (“phenolate”) (ref 306).
Figure 49
Figure 49
Reaction of 68 (L48) with phenolates (69) identified for X = Cl (refs and 310).
Figure 50
Figure 50
Comparison of results of oxygenation of Cu(I) complexes of the indicated ligands (R = CH2CH2Ph), which yield either the indicated (μ-η2:η2-peroxo)- or bis(μ-oxo)dicopper cores (refs –317).
Figure 51
Figure 51
Variation in ratio of isomers formed as a function of the substituent in the L21 supporting ligand (ref 320).
Figure 52
Figure 52
Results of the reactions of the Cu(I) complexes of the indicated ligands with O2 (ref 326).
Figure 53
Figure 53
Comparison of the results of oxygenations of Cu(I) complexes of the indicated ligands (refs , , , and 331).
Figure 54
Figure 54
Synthesis of Cu-containing heterobimetallic complexes using 3a (L2d,e) and 70 (L81) as the starting materials (ref 167).
Figure 55
Figure 55
General scheme showing the synthesis of Cu-containing heterobimetallic complexes using 1:1 M:O2 adducts as starting materials (see Table 6 for specific M and L combinations).
Figure 56
Figure 56
Course of oxygenations of Cu(I)–Ge(II) complexes (ref 168).
Figure 57
Figure 57
Relationship of O–O bond strength and electron donation between complexes [(L41a)Cu2O2]+ (left), 78 (L67) (middle), and [(L82)Cu2O2]+ (right) (ref 342).
Figure 58
Figure 58
Ligand derivatives that yielded indicated copper–oxygen cores upon reaction of their Cu(I) complexes with O2 (refs , , and 348).
Figure 59
Figure 59
Proposed equilibrium between Ci (left) and C1 (right) isomers of (trans-1,2-peroxo)dicopper complexes with bis(μ-oxo)dicopper isomer (ref 345).
Figure 60
Figure 60
(top) X-ray crystal structures of the (1,2-peroxo)dicopper complexes 79 and 80 and (bottom) orthogonal molecular orbitals in 80 that give rise to its S = 1 ground state. Reprinted with permission from ref (top) and ref (bottom). Copyright 2015 Wiley-VCH.
Figure 61
Figure 61
(1,1-Hydroperoxo)dicopper complexes supported by L40f and L65b, respectively, that have been structurally characterized by Xray crystallography (refs and 359).
Figure 62
Figure 62
Oxygen reduction reactions involving intermediate 83 (refs and 363).
Figure 63
Figure 63
Proposed structure of a (μ-η1:η2-peroxo)dicopper complex supported by L64 (ref 364).
Figure 64
Figure 64
Examples of (μ-oxo)dicopper(II) complexes (references cited in text).
Figure 65
Figure 65
Examples of (μ-oxo)dicopper(II) complexes (refs –375).
Figure 66
Figure 66
X-ray crystal structures of hydroxo-bridged dicopper(II) complexes 92 (L59) and 93 (L55) that served as starting materials for the preparation of higher valent species. (left) Only anion shown; Cu–Cu = 2.6596(15) Å. Reprinted from ref . Copyright 2014 American Chemical Society. (right) Cation and one counterion shown; Cu–Cu = 2.7511(12) Å. Reprinted from ref . Copyright 2016 American Chemical Society.
Figure 67
Figure 67
Oxygenation of a tricopper(I) complex of a templated, preorganized ligand (L61a,b). Adapted from ref .
Figure 68
Figure 68
Results of room temperature oxygenation of Cu(I) complexes of L1a (ref 396).
Figure 69
Figure 69
(top) Proposed mechanism for generation of the hypothesized reactive intermediate in hydrocarbon oxidations by complexes of ligands L79a–f. Supporting ligands not shown. (bottom) Space-filling and ball-and-stick drawing of calculated structure for intermediate 97 supported by L79f. Reprinted with permission from ref . Copyright 2013 Wiley-VCH. *Corresponding Author: wtolman@umn.edu.
Chart 1
Chart 1
Ligands Containing Two Nitrogen Donors
Chart 2
Chart 2
Ligands Containing Three Nitrogen Donors
Chart 3
Chart 3
Ligands Containing Four Nitrogen Donors
Chart 4
Chart 4
Ligands Containing Five or More Nitrogen Donors
Chart 5
Chart 5
Ligands Containing a Mixture of Nitrogen, Sulfur, and Oxygen Donors
See this image and copyright information in PMC

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