DOI: 10.1002/adsc.200700224 Tungsten- and Molybdenum-Based Coordination Polymer- Catalyzed N-Oxidation of Primary Aromatic Amines with Aqueous Hydrogen Peroxide Ankur Bordoloi a and S. B. Halligudi a, * a Inorganic Chemistry & Catalysis Division, National Chemical Laboratory, Pune – 411 008, India Phone: (+ 91)-20-2590-2107; fax: (+ 91)-20-2590-2633; e-mail: sb.halligudi@ncl.res.in Received: May 3, 2007; Published online: September 11, 2007 Supporting information for this article is available on the WWW under http://asc.wiley-vch.de/home/. Abstract: Recyclable tungsten- and molybdenum- based coordination polymers efficiently catalyzed the oxidation of primary aromatic amines to the corresponding nitroso derivatives with 30% aque- ous hydrogen peroxide in high yields at room tem- perature. Keywords: coordination polymers; hydrogen perox- ide; oxidation; primary aromatic amines; recyclable catalyst Oxidative biotransformation is amongst the most useful of all identified biologically mediated conver- sions. Environmentally friendly technologies accepta- ble with efficient formation of the desired products and with negligible waste and recyclability of the cata- lyst systems are the major aspects which must be con- sidered when designing a new catalyst for selective oxidation reactions. One of the most attractive ap- proaches is the catalytic oxidation reaction by hetero- geneous means. [1–3] Oxidation of amines is widespread in the area of biological science, reflecting the diverse roles for amine compounds. Amine compounds play important roles in neurotransmission, [4] cell growth and differentiation, [5] and neoplastic cell prolifera- tion. [6,7] On the other hand, the oxidation of amines is a fundamentally important reaction for industrial ap- plications, particularly for the synthesis of oxygenated derivatives such as hydroxylamine, nitroso, nitro, oxime, azo and azoxy compounds. Among these, the preparations of nitro, oxime and azoxy compounds have assumed special importance as synthetically useful intermediates. Nitroso derivatives hold a key position in the chemistry of heterocycles offering functional group manipulation and structural modifi- cation possibilities that are not accessible by any other methods. [8] Aromatic nitroso compounds are used in the vulcanization of rubber, stabilization of halogenated materials and as antioxidants in lubricat- ing oil. [9] Few homogeneous metal-catalyzed methods report- ed in the literature are able to yield aromatic nitroso compounds. [10] These include the use of Caro)s acid, 3- chloroperoxybenzoic acid (MCPBA), potassium per- manganate, peracetic acid, peroxyformic acid, peroxy- benzoic acid, oxaziridinium salts, oxygen difluoride, nitrous acid, trifluoroperacetic acid and, more recent- ly, molybdic peroxo complexes. Catalytic methods using H 2 O 2 or tert-butyl hydroperoxide as oxidant and sodium tungstate, oxomolybdate complexes, phospho- tungstate, phosphomolybdate and zirconate salts were published later. Dimeric products due to condensa- tion reactions such as azo or azoxy derivatives as well as over-oxidation to the nitro compounds are often observed as by-products or sometimes as main prod- ucts. Some methods for the direct oxidation of aro- matic amines to nitro derivatives with peracids were described and, more recently dioxirane, tert-butyl hy- droperoxide and H 2 O 2 have been used as oxidants whereas metal peroxo complexes, FeCl 3 , PbACHTUNGTRENNUNG(AcO) 4 and chromium silicalite have been employed as cata- lysts. [11] Nitroso compounds can also be produced by the direct reduction of nitro compounds with Mn 3 O 4 . [12] But organic synthetic methods have not yet provided an easy and mild path to obtain the aromat- ic nitroso compounds. Our earlier report shows that [(n-Bu 3 Sn) 2 MO 4 ], (M = Mo and W) is able to transfer one peroxidic oxygen atom to an olefin to yield epox- ides. [13] Hence, to the best of our knowledge we pres- ent here for the first time a heterogeneous catalytic system based on tungsten and molybdenum coordina- tion polymers [(n-Bu 3 Sn) 2 MO 4 ] for the selective oxi- dation of primary aromatic amines to the correspond- ing nitroso derivatives with 30% aqueous H 2 O 2 as ox- idant at ambient conditions such as room temperature and under an air atmosphere (Scheme 1). This is a simple and clean process where the desired com- Adv. Synth. Catal. 2007, 349, 2085–2088 # 2007 Wiley-VCH Verlag GmbH&Co. KGaA, Weinheim 2085 COMMUNICATIONS