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Carbonation of ribulose bisphosphate is the starting point of the incorporation of carbon dioxide into the biosphere.

In chemistry, carbonation refers to two chemical processes involving the binding of carbon dioxide to substrates. Various applications or manifestations of this reaction are listed in order of their relative scale.

In biochemistry. Carbon-based life originates from a carbonation reaction that is most often catalysed by the enzyme RuBisCO. This carbonation process is so important that a significant fraction of leaf mass consists of this carbonating enzyme.[1]

The production of urea, a widely used fertilizer, involves the combination of carbon dioxide and ammonia:

2 NH3 + CO2 → (H2N)2CO + H2O

In inorganic chemistry, carbonation occurs widely. Metal oxides and metal hydroxides react with CO2 to give complexes of carbonate and bicarbonate. In reinforced concrete construction, the chemical reaction between carbon dioxide in the air and calcium hydroxide and hydrated calcium silicate in the concrete is known as neutralisation. Low valent metal complexes react with CO2 to give metal carbon dioxide complexes. In organometallic chemistry, carbonation involves the insertion of CO2 into metal-carbon bonds. The topic has attracted great interest for organic synthesis and even as a means of utilizing CO2 as a feedstock.[2]


Carbonation of metal-carbon bondsEdit

Carbonation is a means of generating carbon-carbon bonds.[3], stoichiometric and catalytic CO2[4]

Insertion into Mg-C and Li-C bondsEdit

Carbonation of Grignard reagents and organolithium compounds provides a way to convert organic halides into carboxylic acids.

Insertion into Cu-C bondsEdit

N-heterocyclic carbene (NHC) supported CuI complexes catalyze carboxylation of organoboronic esters.[5]. The catalyst forms in situ from CuCl, an NHC ligand, and KOtBu. Copper tert-butoxide can transmetallate with the organoboronic ester to generate the CuI-C bond, which intermediate can insert into CO2 smoothly to get the respective carboxylate. Salt metathesis with KOtBu releases product and regenerates catalyst (Scheme 2).

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[6] NHC-Cu-H species to deprotonate acidic proton to effect carboxylation of terminal alkynes.[7] 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[8][9]

Cabometallation to alkynes and allenes using organozinc and organoaluminum reagents followed by transmetallation to copper is also a strategy to initiate carboxylation. Trimethylaluminum 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[10]. 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[11][12].

Insertion in Pd-C bondsEdit

In the presence of palladium acetate under 1-30 bar of CO2, simple aromatic compounds convert to aromatic carboxylic acids.[13][14][15][16][17]. A PSiP-pincer ligand (5) promotes carboxylation of allene without using pre-functionalized substrates.[18]. 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[19]. In 2015, Iwasawa et al. reported the germanium analogue (6) and combined CO2 source together with hydride source to formate salts[20].

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[21]. 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.

Insertion by Rh-C bondsEdit

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.[22]. 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[23][24][25].

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[26]. In this system, excess amount of diethylpropylethylamine works as sacrificial electron donor (Scheme 5).

Insertion by Ni-C bondEdit

Carboxylation of benzyl halides has been reported[27]. 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[28], alkyl halides[29][30], and allyl esters[31].

Henry's LawEdit

Henry's Law states that PCO2=KBxCO2 Where PCO2 is the partial pressure of CO2 gas above the solution. KB is Henry's Law Constant. KB increases as temperature increase. xCO2 is the mole fraction of CO2 gas in the solution. According to Henry's Law carbonation increases in a solution as temperature decreases.[32]

General referencesEdit

  1. ^ Stryer, Lubert; Berg, Jeremy Mark; Tymoczko, John L. (2002). Biochemistry (5th ed.). San Francisco: W. H. Freeman. ISBN 0-7167-3051-0. 
  2. ^ Behr, Arno (May 1988). "Carbon Dioxide as an Alternative C1 Synthetic Unit: Activation by Transition-Metal Complexes". Angewandte Chemie International Edition in English. 27 (5): 661–678. doi:10.1002/anie.198806611. 
  3. ^ Gibson, Dorothy H. (January 1996). "The Organometallic Chemistry of Carbon Dioxide". Chemical Reviews. 96 (6): 2063–2096. doi:10.1021/cr940212c. 
  4. ^ Braunstein, Pierre; Matt, Dominique; Nobel, Dominique (August 1988). "Reactions of carbon dioxide with carbon-carbon bond formation catalyzed by transition-metal complexes". Chemical Reviews. 88 (5): 747–764. doi:10.1021/cr00087a003. 
  5. ^ Ohishi, Takeshi; Nishiura, Masayoshi; Hou, Zhaomin (21 July 2008). "Carboxylation of Organoboronic Esters Catalyzed by N‐Heterocyclic Carbene Copper(I) Complexes". Angewandte Chemie International Edition. 47 (31): 5792–5795. doi:10.1002/anie.200801857. 
  6. ^ Gooßen, Lukas J.; Rodríguez, Nuria; Manjolinho, Filipe; Lange, Paul P. (22 November 2010). "Synthesis of Propiolic Acids via Copper-Catalyzed Insertion of Carbon Dioxide into the C-H Bond of Terminal Alkynes". Advanced Synthesis & Catalysis. 352 (17): 2913–2917. doi:10.1002/adsc.201000564. 
  7. ^ Fujihara, Tetsuaki; Xu, Tinghua; Semba, Kazuhiko; Terao, Jun; Tsuji, Yasushi (10 January 2011). "Copper-Catalyzed Hydrocarboxylation of Alkynes Using Carbon Dioxide and Hydrosilanes". Angewandte Chemie International Edition. 50 (2): 523–527. doi:10.1002/anie.201006292. 
  8. ^ Ueno, Atsushi; Takimoto, Masanori; O, Wylie W. N.; Nishiura, Masayoshi; Ikariya, Takao; Hou, Zhaomin (April 2015). "Copper-Catalyzed Formal C-H Carboxylation of Aromatic Compounds with Carbon Dioxide through Arylaluminum Intermediates". Chemistry - An Asian Journal. 10 (4): 1010–1016. doi:10.1002/asia.201403247. 
  9. ^ Ueno, Atsushi; Takimoto, Masanori; Hou, Zhaomin (2017). "Synthesis of 2-aryloxy butenoates by copper-catalysed allylic C–H carboxylation of allyl aryl ethers with carbon dioxide". Org. Biomol. Chem. 15 (11): 2370–2375. doi:10.1039/C7OB00341B. 
  10. ^ Takimoto, Masanori; Hou, Zhaomin (19 August 2013). "Cu-Catalyzed Formal Methylative and Hydrogenative Carboxylation of Alkynes with Carbon Dioxide: Efficient Synthesis of α,β-Unsaturated Carboxylic Acids". Chemistry - A European Journal. 19 (34): 11439–11445. doi:10.1002/chem.201301456. 
  11. ^ Gholap, Sandeep Suryabhan; Takimoto, Masanori; Hou, Zhaomin (13 June 2016). "Regioselective Alkylative Carboxylation of Allenamides with Carbon Dioxide and Dialkylzinc Reagents Catalyzed by an N-Heterocyclic Carbene-Copper Complex". Chemistry - A European Journal. 22 (25): 8547–8552. doi:10.1002/chem.201601162. 
  12. ^ Takimoto, Masanori; Gholap, Sandeep Suryabhan; Hou, Zhaomin (19 October 2015). "Cu-Catalyzed Alkylative Carboxylation of Ynamides with Dialkylzinc Reagents and Carbon Dioxide". Chemistry - A European Journal. 21 (43): 15218–15223. doi:10.1002/chem.201502774. 
  13. ^ Sugimoto, Hiroshi; Kawata, Itaru; Taniguchi, Hiroshi; Fujiwara, Yuzo (May 1984). "Preliminary communication: Palladium-Catalyzed Carboxylation of Aromatic-Compounds with Carbon-Dioxide". Journal of Organometallic Chemistry. 266 (3): c44–c46. doi:10.1016/0022-328X(84)80150-3. 
  14. ^ Shi, Min; Nicholas, Kenneth M. (May 1997). "Palladium-Catalyzed Carboxylation of Allyl Stannanes". Journal of the American Chemical Society. 119 (21): 5057–5058. doi:10.1021/ja9639832. 
  15. ^ Johansson, Roger; Jarenmark, Martin; Wendt, Ola F. (September 2005). "Insertion of Carbon Dioxide into (PCP)Pd-II-Me bonds". Organometallics. 24 (19): 4500–4502. doi:10.1021/om0505561. 
  16. ^ Johansson, Roger; Wendt, Ola F. (2007). "Insertion of CO2 into a palladium allyl bond and a Pd(II) catalysed carboxylation of allyl stannanes". Dalton Trans. (4): 488–492. doi:10.1039/B614037H. 
  17. ^ Johnson, Magnus T.; Johansson, Roger; Kondrashov, Mikhail V.; Steyl, Gideon; Ahlquist, Mårten S. G.; Roodt, Andreas; Wendt, Ola F. (23 August 2010). "=Mechanisms of the CO2 Insertion into (PCP) Palladium Allyl and Methyl sigma-Bonds. A Kinetic and Computational Study". Organometallics. 29 (16): 3521–3529. doi:10.1021/om100325v. 
  18. ^ Takaya, Jun; Iwasawa, Nobuharu (19 November 2008). "Hydrocarboxylation of Allenes with CO2 Catalyzed by Silyl Pincer-Type Palladium Complex". Journal of the American Chemical Society. 130 (46): 15254–15255. doi:10.1021/ja806677w. 
  19. ^ Takaya, Jun; Sasano, Kota; Iwasawa, Nobuharu (April 2011). "Efficient One-to-One Coupling of Easily Available 1,3-Dienes with Carbon Dioxide". Organic Letters. 13 (7): 1698–1701. doi:10.1021/ol2002094. 
  20. ^ Zhu, Chuan; Takaya, Jun; Iwasawa, Nobuharu (3 April 2015). "Use of formate salts as a hydride and a co2 source in PGeP-palladium complex-catalyzed hydrocarboxylation of allenes". Organic Letters. 17 (7): 1814–1817. doi:10.1021/acs.orglett.5b00692. 
  21. ^ Sasano, Kota; Takaya, Jun; Iwasawa, Nobuharu (31 July 2013). "Palladium(II)-Catalyzed Direct Carboxylation of Alkenyl C–H Bonds with CO2". Journal of the American Chemical Society. 135 (30): 10954–10957. doi:10.1021/ja405503y. 
  22. ^ Ukai, Kazutoshi; Aoki, Masao; Takaya, Jun; Iwasawa, Nobuharu (2006-07-01). "Rhodium(I)-Catalyzed Carboxylation of Aryl- and Alkenylboronic Esters with CO2". Journal of the American Chemical Society. 128 (27): 8706–8707. doi:10.1021/ja061232m. ISSN 0002-7863. 
  23. ^ Mizuno, Hajime; Takaya, Jun; Iwasawa, Nobuharu (2011-02-09). "Rhodium(I)-Catalyzed Direct Carboxylation of Arenes with CO2 via Chelation-Assisted C−H Bond Activation". Journal of the American Chemical Society. 133 (5): 1251–1253. doi:10.1021/ja109097z. ISSN 0002-7863. 
  24. ^ Suga, Takuya; Mizuno, Hajime; Takaya, Jun; Iwasawa, Nobuharu (2014-10-23). "Direct carboxylation of simple arenes with CO2 through a rhodium-catalyzed C–H bond activation". Chemical Communications. 50 (92). doi:10.1039/C4CC06188H. ISSN 1364-548X. 
  25. ^ Suga, Takuya; Saitou, Takanobu; Takaya, Jun; Iwasawa, Nobuharu (2017-01-30). "Mechanistic study of the rhodium-catalyzed carboxylation of simple aromatic compounds with carbon dioxide". Chemical Science. 8 (2). doi:10.1039/C6SC03838G. ISSN 2041-6539. 
  26. ^ Murata, Kei; Numasawa, Nobutsugu; Shimomaki, Katsuya; Takaya, Jun; Iwasawa, Nobuharu (2017-03-09). "Construction of a visible light-driven hydrocarboxylation cycle of alkenes by the combined use of Rh(I) and photoredox catalysts". Chemical Communications. 53 (21). doi:10.1039/C7CC00678K. ISSN 1364-548X. 
  27. ^ León, Thierry; Correa, Arkaitz; Martin, Ruben (2013-01-30). "Ni-Catalyzed Direct Carboxylation of Benzyl Halides with CO2". Journal of the American Chemical Society. 135 (4): 1221–1224. doi:10.1021/ja311045f. ISSN 0002-7863. 
  28. ^ Correa, Arkaitz; León, Thierry; Martin, Ruben (2014-01-22). "Ni-Catalyzed Carboxylation of C(sp2)– and C(sp3)–O Bonds with CO2". Journal of the American Chemical Society. 136 (3): 1062–1069. doi:10.1021/ja410883p. ISSN 0002-7863. 
  29. ^ Liu, Yu; Cornella, Josep; Martin, Ruben (2014-08-13). "Ni-Catalyzed Carboxylation of Unactivated Primary Alkyl Bromides and Sulfonates with CO2". Journal of the American Chemical Society. 136 (32): 11212–11215. doi:10.1021/ja5064586. ISSN 0002-7863. 
  30. ^ Börjesson, Marino; Moragas, Toni; Martin, Ruben (2016-06-22). "Ni-Catalyzed Carboxylation of Unactivated Alkyl Chlorides with CO2". Journal of the American Chemical Society. 138 (24): 7504–7507. doi:10.1021/jacs.6b04088. ISSN 0002-7863. 
  31. ^ Moragas, Toni; Cornella, Josep; Martin, Ruben (2014-12-24). "Ligand-Controlled Regiodivergent Ni-Catalyzed Reductive Carboxylation of Allyl Esters with CO2". Journal of the American Chemical Society. 136 (51): 17702–17705. doi:10.1021/ja509077a. ISSN 0002-7863. 
  32. ^ "Henry's Law". ChemEngineering. Tangient LLC. Retrieved 7 November 2017.