metal carbon dioxide complex

:File:MCO2structures.png)₂), the metallacarboxylic ester CpFe(CO)₂(η¹:η¹-CO₂)Re(CO)₅, and another dimetalla-ester.]]

Carbon dioxide binds to metals in only a few ways. The bonding mode depends on the electrophilicity and basicity of the metal centre.{{cite journal |last1= Gibson |first1= Dorothy H. |year= 1996 |title= The Organometallic Chemistry Carbon Dioxide |journal= Chem. Rev. |volume= 96 |issue= 6|pages= 2063–2095 |doi= 10.1021/cr940212c|pmid= 11848822 }} Most common is the η²-CO₂ coordination mode as illustrated by Aresta's complex, Ni(CO₂)(PCy₃)₂, which was the first reported complex of CO_2.{{cite journal|last1=Aresta|first1=Michele|last2=Gobetto|first2=Roberto|last3=Quaranta|first3=Eugenio|last4=Tommasi|first4=Immacolata|title=A bonding-reactivity relationship for (carbon dioxide)bis(tricyclohexylphosphine)nickel: a comparative solid-state-solution nuclear magnetic resonance study (phosphorus-31, carbon-13) as a diagnostic tool to determine the mode of bonding of carbon dioxide to a metal center|journal=Inorganic Chemistry|date=October 1992|volume=31|issue=21|pages=4286–4290|doi=10.1021/ic00047a015}}{{cite journal|last1=Yeung|first1=Charles S.|last2=Dong|first2=Vy M.|title=Beyond Aresta's Complex: Ni- and Pd-Catalyzed Organozinc Coupling with CO|journal=Journal of the American Chemical Society|date=June 2008|volume=130|issue=25|pages=7826–7827|doi=10.1021/ja803435w|pmid=18510323}} This square-planar compound is a derivative of Ni(II) with a reduced CO₂ ligand. In rare cases, CO₂ binds to metals as a Lewis base through its oxygen centres, but such adducts are weak and mainly of theoretical interest. A variety of multinuclear complexes are also known often involving Lewis basic and Lewis acidic metals, e.g. metallacarboxylate salts (C₅H₅)Fe(CO)₂CO₂⁻K⁺. In multinuclear cases (compounds containing more than one metal), more complicated and more varied coordination geometries are observed. One example is the unsymmetrical compound containing four rhenium centres, [(CO)₅ReCO₂Re(CO)₄]₂.{{Citation needed|date=May 2020}} Carbon dioxide can also bind to ligands on a metal complex (vs just the metal), e.g. by converting hydroxy ligands to carbonato ligands.{{Citation needed|date=May 2020}}

Transition metal carbon dioxide complexes undergo a variety of reactions. Metallacarboxylic acids protonate at oxygen and eventually convert to metal carbonyl complexes:

:[L_nMCO₂]⁻ + 2 H⁺ → [L_nMCO]⁺ + H₂O

This reaction is relevant to the potential catalytic conversion of CO₂ to fuels.{{cite journal | last1 = Benson | first1 = Eric E. | last2 = Kubiak | first2 = Clifford P. | last3 = Sathrum | first3 = Aaron J. | last4 = Smieja | first4 = Jonathan M. | year = 2009 | title = Electrocatalytic and homogeneous approaches to conversion of CO₂ to liquid fuels | journal = Chem. Soc. Rev. | volume = 38 | issue = 1| pages = 89–99 | doi = 10.1039/b804323j | pmid = 19088968 }}

N-heterocyclic carbene (NHC) supported Cu^I complexes catalyze carboxylation of organoboronic esters.{{cite journal|last1=Ohishi|first1=Takeshi|last2=Nishiura|first2=Masayoshi|last3=Hou|first3=Zhaomin|title=Carboxylation of Organoboronic Esters Catalyzed by N‐Heterocyclic Carbene Copper(I) Complexes|journal=Angewandte Chemie International Edition|date=21 July 2008|volume=47|issue=31|pages=5792–5795|doi=10.1002/anie.200801857|pmid=18576463}} The catalyst forms in situ from CuCl, an NHC ligand, and KO^tBu. Copper tert-butoxide can transmetallate with the organoboronic ester to generate the Cu^I-C bond, which intermediate can insert into CO₂ smoothly to get the respective carboxylate. Salt metathesis with KO^tBu releases product and regenerates catalyst (Scheme 2).

File:Scheme 2 Copper catalyzed carboxylation of organoboronic ester.jpg Apart from transmetallation, there are other approaches forming Cu-C bond. C-H functionalization is a straightforward and atom economic method. Base can help deprotonate acidic C-H protons and form Cu-C bond. [(Phenanthroline)Cu(PR₃)] catalyst effect C-H carboxylation on terminal alkynes together with Cs₂CO₃.{{cite journal|last1=Gooßen|first1=Lukas J.|last2=Rodríguez|first2=Nuria|last3=Manjolinho|first3=Filipe|last4=Lange|first4=Paul P.|title=Synthesis of Propiolic Acids via Copper-Catalyzed Insertion of Carbon Dioxide into the C-H Bond of Terminal Alkynes|journal=Advanced Synthesis & Catalysis|date=22 November 2010|volume=352|issue=17|pages=2913–2917|doi=10.1002/adsc.201000564}} NHC-Cu-H species to deprotonate acidic proton to effect carboxylation of terminal alkynes.{{cite journal|last1=Fujihara|first1=Tetsuaki|last2=Xu|first2=Tinghua|last3=Semba|first3=Kazuhiko|last4=Terao|first4=Jun|last5=Tsuji|first5=Yasushi|title=Copper-Catalyzed Hydrocarboxylation of Alkynes Using Carbon Dioxide and Hydrosilanes|journal=Angewandte Chemie International Edition|date=10 January 2011|volume=50|issue=2|pages=523–527|doi=10.1002/anie.201006292|pmid=21157832}} Cu-H species were generated from Cu-F and organosilanes. The carboxylate product was trapped by silyl fluoride to get silyl ether. For non-acidic C-H bonds, directed metalation with ⁱBu₃Al(TMP)Li is adopted followed by transmetallation with copper to get Cu-C bond. Allylic C-H bonds and phenyl C-H bonds got carboxylated with this approach by Hou and co-workers:{{cite journal|last1=Ueno|first1=Atsushi|last2=Takimoto|first2=Masanori|last3=O|first3=Wylie W. N.|last4=Nishiura|first4=Masayoshi|last5=Ikariya|first5=Takao|last6=Hou|first6=Zhaomin|title=Copper-Catalyzed Formal C-H Carboxylation of Aromatic Compounds with Carbon Dioxide through Arylaluminum Intermediates|journal=Chemistry: An Asian Journal|date=April 2015|volume=10|issue=4|pages=1010–1016|doi=10.1002/asia.201403247|pmid=25491488}}{{cite journal|last1=Ueno|first1=Atsushi|last2=Takimoto|first2=Masanori|last3=Hou|first3=Zhaomin|title=Synthesis of 2-aryloxy butenoates by copper-catalysed allylic C–H carboxylation of allyl aryl ethers with carbon dioxide|journal=Org. Biomol. Chem.|date=2017|volume=15|issue=11|pages=2370–2375|doi=10.1039/C7OB00341B|pmid=28244535}}

File:Scheme 3 Copper catalysed boracarboxylation of internal alkynes.jpg Carbometallation to alkynes and allenes using organozinc and organoaluminum reagents followed by transmetallation to copper is also a strategy to initiate carboxylation. Trimethylaluminium is able to insert into unbiased aliphatic internal alkynes with syn fashion directed by ether directing group. Vinyl copper complexes are formed by transmetallation and carboxylation is realized with a similar pathway giving tetrasubstituted aliphatic vinyl carboxylic acids.{{cite journal|last1=Takimoto|first1=Masanori|last2=Hou|first2=Zhaomin|title=Cu-Catalyzed Formal Methylative and Hydrogenative Carboxylation of Alkynes with Carbon Dioxide: Efficient Synthesis of α,β-Unsaturated Carboxylic Acids|journal=Chemistry: A European Journal|date=19 August 2013|volume=19|issue=34|pages=11439–11445|doi=10.1002/chem.201301456|pmid=23852827}} In this case, regioslectivity is controlled by the favor of six-membered aluminum ring formation. Furthermore, carboxylation can be achieved on ynamides and allenamides using less reactive dimethyl zinc via similar approach.{{cite journal|last1=Gholap|first1=Sandeep Suryabhan|last2=Takimoto|first2=Masanori|last3=Hou|first3=Zhaomin|title=Regioselective Alkylative Carboxylation of Allenamides with Carbon Dioxide and Dialkylzinc Reagents Catalyzed by an N-Heterocyclic Carbene-Copper Complex|journal=Chemistry: A European Journal|date=13 June 2016|volume=22|issue=25|pages=8547–8552|doi=10.1002/chem.201601162|pmid=27167688}}{{cite journal|last1=Takimoto|first1=Masanori|last2=Gholap|first2=Sandeep Suryabhan|last3=Hou|first3=Zhaomin|title=Cu-Catalyzed Alkylative Carboxylation of Ynamides with Dialkylzinc Reagents and Carbon Dioxide|journal=Chemistry: A European Journal|date=19 October 2015|volume=21|issue=43|pages=15218–15223|doi=10.1002/chem.201502774|pmid=26346513}}

In the presence of palladium acetate under 1-30 bar of CO₂, simple aromatic compounds convert to aromatic carboxylic acids.{{cite journal|last1=Sugimoto|first1=Hiroshi|last2=Kawata|first2=Itaru|last3=Taniguchi|first3=Hiroshi|last4=Fujiwara|first4=Yuzo|title=Preliminary communication: Palladium-Catalyzed Carboxylation of Aromatic-Compounds with Carbon-Dioxide|journal=Journal of Organometallic Chemistry|date=May 1984|volume=266|issue=3|pages=c44–c46|doi=10.1016/0022-328X(84)80150-3}}{{cite journal|last1=Shi|first1=Min|last2=Nicholas|first2=Kenneth M.|title=Palladium-Catalyzed Carboxylation of Allyl Stannanes|journal=Journal of the American Chemical Society|date=May 1997|volume=119|issue=21|pages=5057–5058|doi=10.1021/ja9639832}}{{cite journal|last1=Johansson|first1=Roger|last2=Jarenmark|first2=Martin|last3=Wendt|first3=Ola F.|title=Insertion of Carbon Dioxide into (PCP)Pd-II-Me bonds|journal=Organometallics|date=September 2005|volume=24|issue=19|pages=4500–4502|doi=10.1021/om0505561}}{{cite journal|last1=Johansson|first1=Roger|last2=Wendt|first2=Ola F.|title=Insertion of CO2 into a palladium allyl bond and a Pd(II) catalysed carboxylation of allyl stannanes|journal=Dalton Trans.|date=2007|issue=4|pages=488–492|doi=10.1039/B614037H|pmid=17213935}}{{cite journal|last1=Johnson|first1=Magnus T.|last2=Johansson|first2=Roger|last3=Kondrashov|first3=Mikhail V.|last4=Steyl|first4=Gideon|last5=Ahlquist|first5=Mårten S. G.|last6=Roodt|first6=Andreas|last7=Wendt|first7=Ola F.|title==Mechanisms of the CO2 Insertion into (PCP) Palladium Allyl and Methyl sigma-Bonds. A Kinetic and Computational Study|journal=Organometallics|date=23 August 2010|volume=29|issue=16|pages=3521–3529|doi=10.1021/om100325v}} A PSiP-pincer ligand (5) promotes carboxylation of allene without using pre-functionalized substrates.{{cite journal|last1=Takaya|first1=Jun|last2=Iwasawa|first2=Nobuharu|title=Hydrocarboxylation of Allenes with CO2 Catalyzed by Silyl Pincer-Type Palladium Complex|journal=Journal of the American Chemical Society|date=19 November 2008|volume=130|issue=46|pages=15254–15255|doi=10.1021/ja806677w|pmid=18942785}} Catalyst regeneration, Et₃Al was added to do transmetallation with palladium. Catalyst is regenerated by the following β-H elimination. Apart from terminal allenes, some of internal allenes are also tolerated in this reaction, generating allyl carboxylic acid with the yield between 54% and 95%. This system was also applied to 1,3-diene, generating carboxylic acid in 1,2 addition fashion.{{cite journal|last1=Takaya|first1=Jun|last2=Sasano|first2=Kota|last3=Iwasawa|first3=Nobuharu|title=Efficient One-to-One Coupling of Easily Available 1,3-Dienes with Carbon Dioxide|journal=Organic Letters|date=April 2011|volume=13|issue=7|pages=1698–1701|doi=10.1021/ol2002094|pmid=21370864}} In 2015, Iwasawa et al. reported the germanium analogue (6) and combined CO₂ source together with hydride source to formate salts.{{cite journal|last1=Zhu|first1=Chuan|last2=Takaya|first2=Jun|last3=Iwasawa|first3=Nobuharu|title=Use of formate salts as a hydride and a co2 source in PGeP-palladium complex-catalyzed hydrocarboxylation of allenes|journal=Organic Letters|date=3 April 2015|volume=17|issue=7|pages=1814–1817|doi=10.1021/acs.orglett.5b00692|pmid=25794110}}

File:Scheme 4 Pincer Pd complexes for catalytic carboxylation.jpg Palladium has shown huge power to catalyze C-H functionalization. If the Pd-C intermediate in carboxylation reaction comes from C-H activation, such methodology must promote metal catalyzed carboxylation to a much higher level in utility. Iwasawa and co-workers reported direct carboxylation by styrenyl C-H activation generating coumarin derivatives.{{cite journal|last1=Sasano|first1=Kota|last2=Takaya|first2=Jun|last3=Iwasawa|first3=Nobuharu|title=Palladium(II)-Catalyzed Direct Carboxylation of Alkenyl C–H Bonds with CO2|journal=Journal of the American Chemical Society|date=31 July 2013|volume=135|issue=30|pages=10954–10957|doi=10.1021/ja405503y|pmid=23865901}} Benzene rings with different electronic properties and some heteroaromatic rings are tolerated in this reaction with yield from 50% to 90%. C-H activation was demonstrated by crystallography study.

Similar to Cu(I) chemistry mentioned above, Rh(I) complexes can also transmetallate with arylboronic esters to get aryl rhodium intermediates, to which CO₂ is inserted giving carboxylic acids.{{cite journal|last1=Ukai|first1=Kazutoshi|last2=Aoki|first2=Masao|last3=Takaya|first3=Jun|last4=Iwasawa|first4=Nobuharu|date=2006-07-01|title=Rhodium(I)-Catalyzed Carboxylation of Aryl- and Alkenylboronic Esters with CO2|journal=Journal of the American Chemical Society|volume=128|issue=27|pages=8706–8707|doi=10.1021/ja061232m|pmid=16819845|issn=0002-7863}} Later, Iwasawa et al. described C-H carboxylation strategy. Rh(I) undergoes oxidative addition to aryl C-H bond followed by transmetallation with alkyl aluminum species. Ar-Rh(I) regenerates by reductive elimination releasing methane. Ar-Rh(I) attacks CO₂ then transmetallates with aryl boronic acid to release the boronic acid of product, giving final carboxylic acid by hydrolysis. Directed and non-directed versions are both achieved.{{cite journal|last1=Mizuno|first1=Hajime|last2=Takaya|first2=Jun|last3=Iwasawa|first3=Nobuharu|date=2011-02-09|title=Rhodium(I)-Catalyzed Direct Carboxylation of Arenes with CO2 via Chelation-Assisted C−H Bond Activation|journal=Journal of the American Chemical Society|volume=133|issue=5|pages=1251–1253|doi=10.1021/ja109097z|pmid=21192682|issn=0002-7863}}{{cite journal|last1=Suga|first1=Takuya|last2=Mizuno|first2=Hajime|last3=Takaya|first3=Jun|last4=Iwasawa|first4=Nobuharu|date=2014-10-23|title=Direct carboxylation of simple arenes with CO2 through a rhodium-catalyzed C–H bond activation|journal=Chemical Communications|language=en|volume=50|issue=92|pages=14360–14363|doi=10.1039/C4CC06188H|pmid=25296263|issn=1364-548X}}{{cite journal|last1=Suga|first1=Takuya|last2=Saitou|first2=Takanobu|last3=Takaya|first3=Jun|last4=Iwasawa|first4=Nobuharu|date=2017-01-30|title=Mechanistic study of the rhodium-catalyzed carboxylation of simple aromatic compounds with carbon dioxide|journal=Chemical Science|language=en|volume=8|issue=2|pages=1454–1462|doi=10.1039/C6SC03838G|pmid=28616144|issn=2041-6539|pmc=5460598}}

Iwasawa and co-workers developed Rh(I) catalyzed carbonation reaction initiated by Rh-H insertion to vinylarenes. In order to regenerate reactive Rh-H after nucleophilic addition to CO₂, photocatalytic proton-coupled electron transfer approach was adopted.{{cite journal|last1=Murata|first1=Kei|last2=Numasawa|first2=Nobutsugu|last3=Shimomaki|first3=Katsuya|last4=Takaya|first4=Jun|last5=Iwasawa|first5=Nobuharu|date=2017-03-09|title=Construction of a visible light-driven hydrocarboxylation cycle of alkenes by the combined use of Rh(I) and photoredox catalysts|journal=Chemical Communications|language=en|volume=53|issue=21|pages=3098–3101|doi=10.1039/C7CC00678K|pmid=28243662|issn=1364-548X}} In this system, excess amount of diethylpropylethylamine works as sacrificial electron donor (Scheme 5).

File:Scheme 5. Photocatalyzed carboxylation.jpg

Carboxylation of benzyl halides has been reported.{{cite journal|last1=León|first1=Thierry|last2=Correa|first2=Arkaitz|last3=Martin|first3=Ruben|date=2013-01-30|title=Ni-Catalyzed Direct Carboxylation of Benzyl Halides with CO2|journal=Journal of the American Chemical Society|volume=135|issue=4|pages=1221–1224|doi=10.1021/ja311045f|pmid=23301781|issn=0002-7863}} The reaction mechanism is proposed to involve oxidative addition of benzyl chloride to Ni(0). The Ni(II) benzyl complex is reduced to Ni(I), e.g., by zinc, which inserts CO₂ delivering the nickel carboxylate. Reduction of the Ni(I) carboxylate to Ni(0) releases the zinc carboxylate (Scheme 6). Similarly, such carboxylation has been achieved on aryl and benzyl pivalate,{{cite journal|last1=Correa|first1=Arkaitz|last2=León|first2=Thierry|last3=Martin|first3=Ruben|date=2014-01-22|title=Ni-Catalyzed Carboxylation of C(sp2)– and C(sp3)–O Bonds with CO2|journal=Journal of the American Chemical Society|volume=136|issue=3|pages=1062–1069|doi=10.1021/ja410883p|pmid=24377699|issn=0002-7863|hdl=2072/305833|hdl-access=free}} alkyl halides,{{cite journal|last1=Liu|first1=Yu|last2=Cornella|first2=Josep|last3=Martin|first3=Ruben|date=2014-08-13|title=Ni-Catalyzed Carboxylation of Unactivated Primary Alkyl Bromides and Sulfonates with CO2|journal=Journal of the American Chemical Society|volume=136|issue=32|pages=11212–11215|doi=10.1021/ja5064586|pmid=25068174|issn=0002-7863|url=https://recercat.cat//bitstream/2072/305831/1/Ni-cat%20carboxylation%20alkyl%20electrophiles-final.pdf|hdl=2072/305831|hdl-access=free}}{{cite journal|last1=Börjesson|first1=Marino|last2=Moragas|first2=Toni|last3=Martin|first3=Ruben|date=2016-06-22|title=Ni-Catalyzed Carboxylation of Unactivated Alkyl Chlorides with CO2|journal=Journal of the American Chemical Society|volume=138|issue=24|pages=7504–7507|doi=10.1021/jacs.6b04088|pmid=27269443|issn=0002-7863|hdl=2072/305936|hdl-access=free}} and allyl esters.{{cite journal|last1=Moragas|first1=Toni|last2=Cornella|first2=Josep|last3=Martin|first3=Ruben|date=2014-12-24|title=Ligand-Controlled Regiodivergent Ni-Catalyzed Reductive Carboxylation of Allyl Esters with CO2|journal=Journal of the American Chemical Society|volume=136|issue=51|pages=17702–17705|doi=10.1021/ja509077a|pmid=25473825|issn=0002-7863|hdl=2072/305832|hdl-access=free}}

File:Scheme 6 Nickel catalysed carboxylation of benzyl halids.jpg

{{Reflist}}

{{Organometallics}}

{{Coordination complexes}}

Category:Coordination complexes

Category:Inorganic chemistry

Category:Organometallic chemistry

Category:Transition metals