Transition metal dioxygen complex

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Dioxygen complexes are coordination compounds that contain O2 as a ligand. [1] [2] The study of these compounds is inspired by oxygen-carrying proteins such as myoglobin, hemoglobin, hemerythrin, and hemocyanin. [3] Several transition metals form complexes with O2, and many of these complexes form reversibly. [4] The binding of O2 is the first step in many important phenomena, such as cellular respiration, corrosion, and industrial chemistry. The first synthetic oxygen complex was demonstrated in 1938 with cobalt(II) complex reversibly bound O2. [5]

Contents

Mononuclear complexes of O2

O2 binds to a single metal center either "end-on" (η1-) or "side-on" (η2-). The bonding and structures of these compounds are usually evaluated by single-crystal X-ray crystallography, focusing both on the overall geometry as well as the O–O distances, which reveals the bond order of the O2 ligand.

TMdioxygenCmpx.png

Complexes of η1-O2 ligands

A picket-fence porphyrin complex of Fe, with axial coordination sites occupied by methylimidazole (green) and dioxygen (R = amide groups). PicketFenceGenericRevised.png
A picket-fence porphyrin complex of Fe, with axial coordination sites occupied by methylimidazole (green) and dioxygen (R = amide groups).

O2 adducts derived from cobalt(II) and iron(II) complexes of porphyrin (and related anionic macrocyclic ligands) exhibit this bonding mode. Myoglobin and hemoglobin are famous examples, and many synthetic analogues have been described that behave similarly. Binding of O2 is usually described as proceeding by electron transfer from the metal(II) center to give superoxide (O−
2) complexes of metal(III) centers. As shown by the mechanisms of cytochrome P450 and alpha-ketoglutarate-dependent hydroxylase, Fe-η1-O2 bonding is conducive to formation of Fe(IV) oxo centers. O2 can bind to one metal of a bimetallic unit via the same modes discussed above for mononuclear complexes. A well-known example is the active site of the protein hemerythrin, which features a diiron carboxylate that binds O2 at one Fe center. Dinuclear complexes can also cooperate in the binding, although the initial attack of O2 probably occurs at a single metal.

Complexes of η2-O2 ligands

η2-bonding is the most common motif seen in coordination chemistry of dioxygen. Such complexes can be generated by treating low-valent metal complexes with oxygen. For example, Vaska's complex reversibly binds O2 (Ph = C6H5):

IrCl(CO)(PPh3)2 + O2⇌ IrCl(CO)(PPh3)2O2

The conversion is described as a 2 e− redox process: Ir(I) converts to Ir(III) as dioxygen converts to peroxide. Since O2 has a triplet ground state and Vaska's complex is a singlet, the reaction is slower than when singlet oxygen is used. [7] The magnetic properties of some η2-O2 complexes show that the ligand, in fact, is superoxide, not peroxide. [8]

Most complexes of η2-O2 are generated using hydrogen peroxide, not from O2. Chromate ([CrO4)]2−) can for example be converted to the tetraperoxide [Cr(O2)4]2−. The reaction of hydrogen peroxide with aqueous titanium(IV) gives a brightly colored peroxy complex that is a useful test for titanium as well as hydrogen peroxide. [9]

Binuclear complexes of O2

O2-bound form of hemocyanin, the O2 carrier for certain molluscs. Oxyhemocyanin full.png
O2-bound form of hemocyanin, the O2 carrier for certain molluscs.

These binding modes include μ2-η2,η2-, μ2-η1,η1-, and μ2-η1,η2-. Depending on the degree of electron-transfer from the dimetal unit, these O2 ligands can again be described as peroxo or superoxo. Hemocyanin is an O2-carrier that utilizes a bridging O2 binding motif. It features a pair of copper centers. [10]

Dimetal dioxygen complexes (molecular diagrams).png
Structure of [Co(salen)(dmf)]2O2. DOESCF10.svg
Structure of [Co(salen)(dmf)]2O2.

.

Salcomine, the cobalt(II) complex of salen ligand is the first synthetic O2 carrier. [12] Solvated derivatives of the solid complex bind 0.5 equivalent of O2:

2 Co(salen) + O2 → [Co(salen)]2O2

Reversible electron transfer reactions are observed in some dinuclear O2 complexes. [13]

Oxidation of the dicobalt peroxy complex gives the complex of superoxide (O2 ). The Co-O-O-Co core flattens in the process and the O-O distance contracts by 10%. Co2O2noparam.svg
Oxidation of the dicobalt peroxy complex gives the complex of superoxide (O2 ). The Co-O-O-Co core flattens in the process and the O-O distance contracts by 10%.

Relationship to other oxygenic ligands and applications

Dioxygen complexes are the precursors to other families of oxygenic ligands. Metal oxo compounds arise from the cleavage of the O–O bond after complexation. Hydroperoxo complexes are generated in the course of the reduction of dioxygen by metals. The reduction of O2 by metal catalysts is a key half-reaction in fuel cells.

Metal-catalyzed oxidations with O2 proceed via the intermediacy of dioxygen complexes, although the actual oxidants are often oxo derivatives. The reversible binding of O2 to metal complexes has been used as a means to purify oxygen from air, but cryogenic distillation of liquid air remains the dominant technology.

Related Research Articles

<span class="mw-page-title-main">Ligand</span> Ion or molecule that binds to a central metal atom to form a coordination complex

In coordination chemistry, a ligand is an ion or molecule with a functional group that binds to a central metal atom to form a coordination complex. The bonding with the metal generally involves formal donation of one or more of the ligand's electron pairs, often through Lewis bases. The nature of metal–ligand bonding can range from covalent to ionic. Furthermore, the metal–ligand bond order can range from one to three. Ligands are viewed as Lewis bases, although rare cases are known to involve Lewis acidic "ligands".

In chemistry, a superoxide is a compound that contains the superoxide ion, which has the chemical formula O−2. The systematic name of the anion is dioxide(1−). The reactive oxygen ion superoxide is particularly important as the product of the one-electron reduction of dioxygen O2, which occurs widely in nature. Molecular oxygen (dioxygen) is a diradical containing two unpaired electrons, and superoxide results from the addition of an electron which fills one of the two degenerate molecular orbitals, leaving a charged ionic species with a single unpaired electron and a net negative charge of −1. Both dioxygen and the superoxide anion are free radicals that exhibit paramagnetism. Superoxide was historically also known as "hyperoxide".

<span class="mw-page-title-main">Hemerythrin</span> InterPro Family

Hemerythrin (also spelled haemerythrin; Ancient Greek: αἷμα, romanized: haîma, lit. 'blood', Ancient Greek: ἐρυθρός, romanized: erythrós, lit. 'red') is an oligomeric protein responsible for oxygen (O2) transport in the marine invertebrate phyla of sipunculids, priapulids, brachiopods, and in a single annelid worm genus, Magelona. Myohemerythrin is a monomeric O2-binding protein found in the muscles of marine invertebrates. Hemerythrin and myohemerythrin are essentially colorless when deoxygenated, but turn a violet-pink in the oxygenated state.

<span class="mw-page-title-main">Metalloprotein</span> Protein that contains a metal ion cofactor

Metalloprotein is a generic term for a protein that contains a metal ion cofactor. A large proportion of all proteins are part of this category. For instance, at least 1000 human proteins contain zinc-binding protein domains although there may be up to 3000 human zinc metalloproteins.

<span class="mw-page-title-main">Vaska's complex</span> Chemical compound

Vaska's complex is the trivial name for the chemical compound trans-carbonylchlorobis(triphenylphosphine)iridium(I), which has the formula IrCl(CO)[P(C6H5)3]2. This square planar diamagnetic organometallic complex consists of a central iridium atom bound to two mutually trans triphenylphosphine ligands, carbon monoxide and a chloride ion. The complex was first reported by J. W. DiLuzio and Lauri Vaska in 1961. Vaska's complex can undergo oxidative addition and is notable for its ability to bind to O2 reversibly. It is a bright yellow crystalline solid.

<span class="mw-page-title-main">Salen ligand</span> Chemical compound

Salen refers to a tetradentate C2-symmetric ligand synthesized from salicylaldehyde (sal) and ethylenediamine (en). It may also refer to a class of compounds, which are structurally related to the classical salen ligand, primarily bis-Schiff bases. Salen ligands are notable for coordinating a wide range of different metals, which they can often stabilise in various oxidation states. For this reason salen-type compounds are used as metal deactivators. Metal salen complexes also find use as catalysts.

<span class="mw-page-title-main">Hapticity</span> Number of contiguous atoms in a ligand that bond to the central atom in a coordination complex

In coordination chemistry, hapticity is the coordination of a ligand to a metal center via an uninterrupted and contiguous series of atoms. The hapticity of a ligand is described with the Greek letter η ('eta'). For example, η2 describes a ligand that coordinates through 2 contiguous atoms. In general the η-notation only applies when multiple atoms are coordinated. In addition, if the ligand coordinates through multiple atoms that are not contiguous then this is considered denticity, and the κ-notation is used once again. When naming complexes care should be taken not to confuse η with μ ('mu'), which relates to bridging ligands.

<span class="mw-page-title-main">Transition metal dinitrogen complex</span> Coordination compounds with N2

Transition metal dinitrogen complexes are coordination compounds that contain transition metals as ion centers the dinitrogen molecules (N2) as ligands.

<span class="mw-page-title-main">Radical (chemistry)</span> Atom, molecule, or ion that has an unpaired valence electron; typically highly reactive

In chemistry, a radical, also known as a free radical, is an atom, molecule, or ion that has at least one unpaired valence electron. With some exceptions, these unpaired electrons make radicals highly chemically reactive. Many radicals spontaneously dimerize. Most organic radicals have short lifetimes.

<span class="mw-page-title-main">Salcomine</span> Chemical compound

Salcomine is a coordination complex derived from the salen ligand and cobalt. The complex, which is planar, and a variety of its derivatives are carriers for O2 as well as oxidation catalysts.

<span class="mw-page-title-main">Potassium tetraperoxochromate(V)</span> Chemical compound

Potassium peroxochromate, potassium tetraperoxochromate(V), or simply potassium perchromate, is an inorganic compound having the chemical formula K3[Cr(O2)4]. It is a red-brown paramagnetic solid. It is the potassium salt of tetraperoxochromate(V), one of the few examples of chromium in the +5 oxidation state and one of the rare examples of a complex stabilized only by peroxide ligands. This compound is used as a source of singlet oxygen.

A transition metal oxo complex is a coordination complex containing an oxo ligand. Formally O2-, an oxo ligand can be bound to one or more metal centers, i.e. it can exist as a terminal or (most commonly) as bridging ligands (Fig. 1). Oxo ligands stabilize high oxidation states of a metal. They are also found in several metalloproteins, for example in molybdenum cofactors and in many iron-containing enzymes. One of the earliest synthetic compounds to incorporate an oxo ligand is potassium ferrate (K2FeO4), which was likely prepared by Georg E. Stahl in 1702.

In organometallic chemistry, metal sulfur dioxide complexes are complexes that contain sulfur dioxide, SO2, bonded to a transition metal. Such compounds are common but are mainly of theoretical interest. Historically, the study of these compounds has provided insights into the mechanisms of migratory insertion reactions.

<span class="mw-page-title-main">Metal salen complex</span> Coordination complex

A metal salen complex is a coordination compound between a metal cation and a ligand derived from N,N′-bis(salicylidene)ethylenediamine, commonly called salen. The classical example is salcomine, the complex with divalent cobalt Co2+, usually denoted as Co(salen). These complexes are widely investigated as catalysts and enzyme mimics.

<span class="mw-page-title-main">Transition metal fullerene complex</span>

A transition metal fullerene complex is a coordination complex wherein fullerene serves as a ligand. Fullerenes are typically spheroidal carbon compounds, the most prevalent being buckminsterfullerene, C60.

In organometallic chemistry, a transition metal alkene complex is a coordination compound containing one or more alkene ligands. The inventory is large. Such compounds are intermediates in many catalytic reactions that convert alkenes to other organic products.

The Mukaiyama hydration is an organic reaction involving formal addition of an equivalent of water across an olefin by the action of catalytic bis(acetylacetonato)cobalt(II) complex, phenylsilane and atmospheric oxygen to produce an alcohol with Markovnikov selectivity.

<span class="mw-page-title-main">Metal peroxide</span>

Metal peroxides are metal-containing compounds with ionically- or covalently-bonded peroxide (O2−
2) groups. This large family of compounds can be divided into ionic and covalent peroxide. The first class mostly contains the peroxides of the alkali and alkaline earth metals whereas the covalent peroxides are represented by such compounds as hydrogen peroxide and peroxymonosulfuric acid (H2SO5). In contrast to the purely ionic character of alkali metal peroxides, peroxides of transition metals have a more covalent character.

<span class="mw-page-title-main">Water oxidation catalysis</span>

Water oxidation catalysis (WOC) is the acceleration (catalysis) of the conversion of water into oxygen and protons:

<span class="mw-page-title-main">Transition metal carboxylate complex</span> Class of chemical compounds

Transition metal carboxylate complexes are coordination complexes with carboxylate (RCO2−) ligands. Reflecting the diversity of carboxylic acids, the inventory of metal carboxylates is large. Many are useful commercially, and many have attracted intense scholarly scrutiny. Carboxylates exhibit a variety of coordination modes, most common are κ1- (O-monodentate), κ2 (O,O-bidentate), and bridging.

References

  1. ↑ Yee, Gereon M.; Tolman, William B. (2015). "Chapter 5: Transition Metal Complexes and the Activation of Dioxygen". In Kroneck, Peter M. H.; Sosa Torres, Martha E. (eds.). Sustaining Life on Planet Earth: Metalloenzymes Mastering Dioxygen and Other Chewy Gases. Metal Ions in Life Sciences. Vol. 15. Springer. pp. 131–204. doi:10.1007/978-3-319-12415-5_5. PMID   25707468.
  2. ↑ Holleman, A. F.; Wiberg, E. (2001). Inorganic Chemistry. San Diego, CA: Academic Press. ISBN   0-12-352651-5.
  3. ↑ Lippard, S. J.; Berg, J. M. (1994). Principles of Bioinorganic Chemistry. Mill Valley, CA: University Science Books. ISBN   0-935702-73-3.
  4. ↑ Berry, R. E. (2004). "Reactivity and Structure of Complexes of Small Molecules: Dioxygen". Comprehensive Coordination Chemistry II. Vol. 1. pp. 625–629. doi:10.1016/B0-08-043748-6/01161-0. ISBN   978-0-08-043748-4.
  5. ↑ Tsumaki, Tokuichi (1938). "Nebenvalenzringverbindungen. IV. Über einige innerkomplexe Kobaltsalze der Oxyaldimine" [Secondary valence ring compounds. IV. On some inner-complex cobalt salts of oxyaldimine ]. Bulletin of the Chemical Society of Japan . 13 (2): 252–260. doi: 10.1246/bcsj.13.252 .
  6. ↑ S. J. Lippard, J. M. Berg "Principles of Bioinorganic Chemistry" University Science Books: Mill Valley, CA; 1994. ISBN   0-935702-73-3.
  7. ↑ Selke, M.; Foote, C. S. (1993). "Reactions of Organometallic Complexes with Singlet Oxygen. Photooxidation of Vaska's Complex". J. Am. Chem. Soc. 115 (3): 1166–1167. doi:10.1021/ja00056a061.
  8. ↑ Egan, James W.; Haggerty, Brian S.; Rheingold, Arnold L.; Sendlinger, Shawn C.; Theopold, Klaus H. (1990). "Crystal structure of a side-on superoxo complex of cobalt and hydrogen abstraction by a reactive terminal oxo ligand". Journal of the American Chemical Society. 112 (6): 2445–2446. doi:10.1021/ja00162a069.
  9. ↑ Greenwood, N. N.; Earnshaw, A. (1997). Chemistry of the Elements (2nd ed.). Oxford: Butterworth-Heinemann. ISBN   0-7506-3365-4.
  10. ↑ Elwell, Courtney E.; Gagnon, Nicole L.; Neisen, Benjamin D.; Dhar, Debanjan; Spaeth, Andrew D.; Yee, Gereon M.; Tolman, William B. (2017). "Copper–Oxygen Complexes Revisited: Structures, Spectroscopy, and Reactivity". Chemical Reviews. 117 (3): 2059–2107. doi:10.1021/acs.chemrev.6b00636. PMC   5963733 . PMID   28103018.
  11. ↑ M. Calligaris; G. Nardin; L. Randaccio; A. Ripamonti (1970). "Structural Aspects of the Synthetic Oxygen-Carrier NN′-Ethylenebis(Salicylideneiminato)cobalt(II): Structure of the Addition Compound with Oxygen Containing Dimethylformamide". J. Chem. Soc. A: 1069. doi:10.1039/j19700001069.
  12. ↑ Tokuichi Tsumaki (1938). "Nebenvalenzringverbindungen. IV. Über einige innerkomplexe Kobaltsalze der Oxyaldimine". Bulletin of the Chemical Society of Japan . 13 (2): 252–260. doi: 10.1246/bcsj.13.252 .
  13. ↑ Schaefer, William Palzer (1968). "Structure of Decaammine-μ-Peroxo-Dicobalt Disulfate Tetrahydrate". Inorganic Chemistry. 7 (4): 725–731. doi:10.1021/ic50062a022.
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