Carbon dioxide fixation by Main-group Compounds
Bibaswan Biswas
Chem 681
Advisor: Dr. F.P.Gabbai
Introduction
The role of carbon dioxide as a greenhouse gas contributing to global warming is widely
recognized as one of the biggest environmental issues. To deal with this problem, methods for
the fixation of carbon dioxide are becoming increasingly needed. While carbon dioxide can be
stored as a gas, either underground or in porous solids, its conversion into useful chemical
compounds is a much more viable
alternative. While many different
routes have been pursued over the
years, the use of main group
compounds that react with CO2 has
become a topical theme.1-3 Earlier
examples of such compounds include
triphenylstibine oxide which catalyzes
the formation of 2-oxazolidinones by
reaction of CO2 with 2-amino alcohols(1) (Scheme 1).4 Related reactions have also been
reported for in which organotin compounds can serve for the conversion of CO2 into organic
carbonates. These early precedents illustrate the potential that main group Lewis acids hold in
the domain of CO2 fixation. In this presentation, I will report on the recent developments that
this field of research has witnessed.
CO2 fixation by nucleophilic main group compounds.
The electrophilic nature of the carbon
center in CO2 allows this small molecule to be
reactive towards bases. This reactivity pattern is at
the heart of the amine CO2 scrubbing process,5 one
of the most widely used fixation method. More
recently, it has been demonstrated that strong
neutral bases such as TBD can react with CO2 to afford the corresponding guanidinium
carboxylate which has been structurally characterized (Scheme 2).6 However in presence of
water, this zwitterionic species 2 was not formed, instead an ammonium bicarbonate species was
formed. Related results have also been obtained with N-heterocyclic carbenes (NHC) which
react with CO2 to form imidazolium carboxylates (Scheme 3).7 The stability of the resulting
adducts can be tuned by varying the nature of the nitrogen substituents. In the case of 6, CO2
binding is reversible; with dissociation occurring at 136°C. This CO2 fixation reaction constitutes
a first step of several
reduction reactions.
For
example, reaction of 8 with
diphenyl silane
leads to
formation of methanol.8 This
reaction can be run catalytically with 7 as the catalyst. Other studies have shown that the
reaction of CO2 with aldehyde, in the presence of 7, affords CO and the corresponding
carboxylic acid (Scheme 4).9
CO2 fixation by frustrated Lewis pairs.
The use of Frustrated Lewis acid Pairs (FLPs) to activate small molecules was pioneered by
Stephan.10 They first reported the activation of hydrogen molecule by Frustrated Lewis pair of
phosphino borate.11 Since then
FLPs have been used to
activate
several
small
molecules including CO2.
The
FLPs
(Me3C6H2)2PCH2CH2B(C6F5)2
(9) and tBu3P/ B(C6F5)3(11)
which both react with CO2 to
afford the corresponding
activation products 10 and 12
(Scheme 5). These reactions
are reversible with CO2
release occurring at -20°C for
9 and 80°C for 10 under
vacuum. Related results have been obtained with Lewis pairs involving AlX3 (X=Cl, Br) as the
Lewis acid and PMes3 as the Lewis base.12 In this case, the resulting adducts, which show
coordination of two Lewis acids to the carboxylate group, can be reduced by NH3-BH3 to
ultimately produce methanol.
CO2 fixation by hypervalent organobismuth compounds.
Recently hypervalent organobismuth compounds has been found to activate carbon dioxide
under very mild condition. Shimada reported that 13 and 14 can absorb carbon dioxide forming
15 (Scheme 6).13It is worthwhile to note that 12 and 13 also can absorb carbon dioxide under
ambient conditions, showing its potential as a capture agent. Also this hypervalent bismuth
species having a non nucleophilic counter anion (B(C6F5)4-) effectively catalyzes cyclic
carbonate formation from epoxides.14
CO2 fixation by organoantimony compound.
While it has long been known that organostibine oxides react with CO2, related reactions
have only recently been uncovered
for antimony compounds such as
16.15 This compounds reacts with
CO2 to form 17 which is very stable
and
does
not
undergo
decarboxylation until heated to
129ºC.
CO2 fixation by organo Sn-Te compound.
The reversible activation of CO2 has also been demonstrated the binary system of
(tBuSnO)3/ (p-MeOC6H4)2TeO((18/19) which reacts with CO2 to form a monomeric compound
[{(p-MeOC6H4)2TeOSn(tBu2)CO3}2](20) (Scheme 8).16
Conclusion
Main group compounds are becoming increasingly prominent in the domain of CO2
activation. When compared to transition metal based systems, these main group compounds
provide cheaper, less toxic, and more commercially viable alternatives. For now the study of
these new systems remains an academic exercise unlikely to dislodge the current CO2 scrubbing
technology based on simple amines.
References
(1)
Fletcher, A. J.; Cussen, E. J.; Prior, T. J.; Rosseinsky, M. J.; Kepert, C. J.;
Thomas, K. M. J. Am. Chem. Soc 2001, 123, 10001.
(2)
Lee, K. B.; Beaver, M. G.; Caram, H. S.; Sircar, S. Industrial & Engineering Chemistry
Research 2008, 47, 8048.
(3)
Surblé, S.; Millange, F.; Serre, C.; Düren, T.; Latroche, M.; Bourrelly, S.; Llewellyn, P.
L.; Férey, G. J. Am. Chem. Soc 2006, 128, 14889.
(4)
Matsuda, H.; Baba, A.; Nomura, R.; Kori, M.; Ogawa, S. Industrial & Engineering
Chemistry Product Research and Development 1985, 24, 239.
(5)
Rochelle, G. T. Science 2009, 325, 1652.
(6)
Villiers, C.; Dognon, J. P.; Pollet, R.; Thuéry, P.; Ephritikhine, M. Angew. Chem.,Int. Ed.
2010, 49, 3465.
(7)
Duong, H. A.; Tekavec, T. N.; Arif, A. M.; Louie, J. Chem. Commun. 2004, 112.
(8)
Riduan, S.; Zhang, Y.; Ying, J. Angew. Chem.,Int. Ed. 2009, 48, 3322.
(9)
Gu, L.; Zhang, Y. J. Am. Chem. Soc,2009 132, 914.
(10) Welch, G. C.; Juan, R. R. S.; Masuda, J. D.; Stephan, D. W. Science 2006, 314, 1124.
(11) Mömming, C.; Otten, E.; Kehr, G.; Fröhlich, R.; Grimme, S.; Stephan, D.; Erker, G.
Angew. Chem.,Int. 2009, 48, 6643.
(12) Ménard, G.; Stephan, D. W. J. Am. Chem. Soc 2010, 132, 1796.
(13) Yin, S. F.; Maruyama, J.; Yamashita, T.; Shimada, S. Angew. Chem.,Int. Ed. 2008, 47,
6590.
(14) Zhang, X.; Dai, W.; Yin, S.; Luo, S.; Au, C.-T. Frontiers of Environmental Science
& Engineering in China 2009, 3, 32.
(15) Dostál, L.; Jambor, R.; Růžička, A.; Erben, M.; Jirásko, R.; Černošková, E.; Holeček, J.
Organometallics 2009, 28, 2633.
(16) Beckmann, J.; Dakternieks, D.; Duthie, A.; Lewcenko, N. A.; Mitchell, C. Angew.
Chem.,Int. Ed.2004, 43, 6683.