Metal Phthalocyanines Catalyzed Selective Organic Transformations: Recent Developments and Promising Future
Received Date: Jul 25, 2012 / Accepted Date: Jul 27, 2012 / Published Date: Jul 30, 2012
Achieving high levels of selectivity is one of the most daunting challenges of synthetic chemistry. In chemical synthesis, the term “selectivity” refers to the discrimination displayed by a reagent, when it reacts with two different reactants or functional groups. Highly selective reactions proceed with minimal reliance on protecting groups and contribute to both atom and step economy. Biological and synthetic systems operate somewhat differently when it comes to impose selectivity in chemical transformations. In nature, the biological catalysts, more particularly porphyrins such as cytochromes, are responsible for catalyzing oxidation-reduction processes and electron transfer reactions on which all forms of life are dependent. These enzymes are tailored towards a specific substrate and work with high levels of stereo-, regio- and chemoselectivity. However, high price, stability and bulk availability issues limit their practical utility.
Phthalocyanines (Pcs) have structural similarity with porphyrins and are very stable π-conjugated macrocyclic compounds that can form complexes with almost all metals and offer a high architectural flexibility in structure. Due to their greater stability than porphyrins, metal phthalocyanines (MPcs) attract great attention for their applications as catalysts for selective organic transformations including oxidation-reduction processes and electron transfer reactions.
Chauhan et al. have utilized CoPc for the selective reduction of flavones and isoflavones with sodium borohydride as reducing agent [1,2]. The mechanistic study revealed the involvement of electron transfer mechanism through the formation of hydridocobalt (III) complex. Our group employed phthalocyanine complexes of Fe, Co, Cu and Zn for chemo- and regio-selective reduction of nitroarenes to corresponding amines tolerating a large range of reducible functional groups such as acid, amide, ester, halogen, lactone, nitrile, N-benzyl, O-benzyl, hydroxy and heterocycles [3-5]. The mechanistic investigation on Co(II)Pc catalyzed reduction showed the formation of Co(I)Pc . However, in another study on Co(II)Pc catalyzed chemo-selective reductive amination of carbonyl compounds using diphenylsilane as reducing agent, the involvement of a different mechanism was disclosed . The Lewis acidic character of Co(II)Pc was found to be responsible for imine activation via a Lewis acid-base interaction. Ni(II)Pc showed excellent activity towards the selective reduction of carbonyl compounds . High regio-selectivity in the reduction of dicarbonyl compounds was remarkable, which was observed for the first time.
Sorokin et al. have reported selective oxidations of phenols and condensed aromatics to quinones and alkynes to α,β-acetylenic ketones mediated by supported iron phthalocyanine complexes . They reported a very different mechanistic features consistent with involvement of iron phthalocyanine centered species and free radicals as evidenced by 18O labelling and kinetic isotope effect studies. In a bioinspired approach, they further reported μ-nitrido iron phthalocyanine catalyzed oxidation of benzene for the formation of benzene oxide using H2O2 . Contrary to this, replacing H2O2 with t-BuOOH resulted in industrially important selective oxidation of alkylaromatic compounds such as toluene or xylene to corresponding acids . In addition to this, selective oxidation of various challenging substrates such as cyclooctene, cyclohexene, styrene etc. have also been reported .
Some other examples of catalytic applications of MPcs include AlPc catalyzed cyanosilylation of aldehydes and ketones [12,13], PdPc catalyzed Suzuki and Heck coupling reactions  and CoPc catalyzed oxidation of alcohols and thiols . MPcs have also been utilized in several photocatalytic transformations such as degradation of pollutants, oxidation of alkanes and alkenes, ene reaction etc. [16-18].
Although several catalyzed synthetic methodologies are being developed, controlling reaction selectivity still stands as one of the major challenges in organic synthesis. In this regards, these recent advances clearly evidenced the promising future of MPcs in catalyzing challenging organic transformations in which high selectivity is required. Currently, visible light absorbing photocatalysts are emerging as powerful tools in synthetic organic chemistry in which their electron/energy transfer potential is being utilized for sensitization of organic molecules. In this regard, MPc photosensitizers, which strongly absorb in the visible region and have long triplet lifetime, have great potential to be developed for efficient photocatalytic reactions.
- Kumari P, Poonam, Chauhan SM (2009) Efficient cobalt(II) phthalocyanine-catalyzed reduction of flavones with sodium borohydride. Chem Commun (Camb) 14: 6397-6399.
- Poonam, Kumari P, Nagpal R, Chauhan SMS (2011) Formation of hydridocobalt(III) phthalocyanine by reaction of cobalt(II) phthalocyanines with sodium borohydride and its reactions with antioxidant isoflavones. New J Chem 35: 2639-2646.
- Sharma U, Kumar P, Kumar N, Kumar V, Singh B (2010) Highly chemo-and regioselective reduction of aromatic nitro compounds catalyzed by recyclable copper (II) as well as cobalt (II) phthalocyanines. Adv Synth Catal 352: 1834-1840.
- Sharma U, Verma PK, Kumar N, Kumar V, Bala M, et al. (2011) Phosphane-free green protocol for selective nitro reduction with an iron-based catalyst. Chemistry 17: 5903-5907.
- Sharma U, Kumar N, Verma PK, Kumar V, Singh B (2012) Zinc phthalocyanine with PEG-400 as a recyclable catalytic system for selective reduction of aromatic nitro compounds. Green Chem 14: 2289-2293.
- Kumar V, Sharma U, Verma PK, Kumar N, Singh B (2012) Cobalt(II) phthalocyanine-catalyzed highly chemoselective reductive amination of carbonyl compounds in a green solvent. Adv Synth Catal 354: 870-878.
- Verma PK, Sharma U, Kumar N, Bala M, Kumar V, et al. (2012) Nickel phthalocyanine assisted highly efficient and selective carbonyl reduction in polyethylene glycol-400. Catal Lett 142: 907-913.
- Perollier C, Pergrale-Mejean C, Sorokin AB (2005) Mechanistic diversity of the selective oxidations mediated by supported iron phthalocyanine complexes. New J Chem 29: 1400-1403.
- Kudrik EV, Sorokin AB (2008) N-bridged diiron phthalocyanine catalyzes oxidation of benzene with H2O2 via benzene oxide with NIH shift evidenced by using 1,3,5-[D3]benzene as a probe. Chemistry 14: 7123-7126.
- Isci U, Afanasiev P, Millet JM, Kudrik EV, Ahsen V, et al. (2009) Preparation and characterization of µ-nitrido diiron phthalocyanines with electron-withdrawing substituents: application for catalytic aromatic oxidation. Dalton Trans 7410-7420.
- Sorokin AB, Kudrik EV (2011) Phthalocyanine metal complexes: versatile catalysts for selective oxidation and bleaching. Cat Today 159: 37-46.
- Rajagopal G, Kim SS, George SC (2007) Aluminum phthalocyanine: an active and simple catalyst for cyanosilylation of aldehydes.Appl Organometal Chem 21: 198-202.
- Rajagopal G, Kim SS, Kwak JM (2006) Aluminium phthalocyanine: an active and simple catalyst for cyanosilylation of ketones. Bull Korean Chem Soc 27: 1907-1909.
- Rohlich C, Kohler K (2010) Macrocyclic palladium(II) complexes in C-C coupling reactions: efficient catalysis by controlled temporary release of active species. Adv Synth Catal 352: 2263–2274.
- Chauhan SM, Kumar A, Srinivas KA (2003) Oxidation of thiols with molecular oxygen catalyzed by cobalt(II) phthalocyanines in ionic liquid. Chem Commun 2348-2349.
- Nyokong T (2007) Effects of substituents on the photochemical and photophysical properties of main group metal phthalocyanines. Coordination Chem Rev 251: 1707-1722.
- Wohrle D, Suvorova O, Gerdes R, Bartels O, Lapok L, et al. (2004) Efficient oxidations and photooxidations with molecular oxygen using metal phthalocyanines as catalysts and photocatalysts. J Porphyrins Phthalocyan 8: 1020.
- D’Ambrosio P, Tonucci L, d’Alessandro N, Morvillo A, Sortino S, et al. (2011) Water-Soluble Transition-Metal-Phthalocyanines as Singlet Oxygen Photosensitizers in Ene Reactions. Eur J Inorg Chem 4: 503-509.
Citation: Kumar N (2012) Metal Phthalocyanines Catalyzed Selective Organic Transformations: Recent Developments and Promising Future. Organic Chem Curr Res 1: e109. Doi: 10.4172/2161-0401.1000e109
Copyright: ©2012 Kumar N, et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
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