Stephen E. Jacobson

Biphase and triphase catalysis. Arsonated polystyrenes as catalysts in the Baeyer-Villiger oxidation of ketones by aqueous hydrogen peroxide

Arsonated polystyrene resins, prepared by a novel procedure, proved to be versatile catalysts for the Baeyer-Villiger oxidation of ketones by hydrogen peroxide. The insoluble beads of the catalyst can be quantitatively separated from the reaction mixture and recycled. Extensive hydrolysis of the lactone and ester products is prevented. In solvents miscible w i t h aqueous hydrogen peroxide (biphase system), the catalysts facilitate oxidation of medium size cycloalkanones (C4-C7) and their alkyl and aryl derivatives, steroid ketones, and branched-chain aliphatic ketones. Larger size cycloalkanones, acetophenone, and straight-chain aliphatic ketones react very slowly or not at all. The arsonated polystyrene beads are effective catalysts and phase transfer agents i n solvents immiscible wi th aqueous hydrogen peroxide. This represents the first example of triphase catalysis in oxidations by hydrogen peroxide. Replacement of carboxylic peroxy acids by a hydrogen peroxide-catalyst system has been of long-standing interest in the Baeyer-Villiger oxidation of ketones. This effort is important in view of the following considerations. Hydrogen peroxide is cheaper and more convenient than carboxylic peroxy acids (water is the only side product). The carboxylic acids resulting from peroxycarboxylic acids cannot be readily separated, and their equilibration with hydrogen peroxide is extremely slow.’ Although this can be accelerated by catalytic quantities of strong acids, the presence of these acids results in hydrolysis of the product of the Baeyer-Villiger oxidation.’ Therefore, in situ recycle of carboxylic acids is impossible. Thus, it becomes obvious that a good catalyst for the Baeyer-Villiger oxidation of ketones by hydrogen peroxide has to fulfill several requirements: (1 ) fast reaction with hydrogen peroxide resulting in hydroperoxy or metal peroxo species; (2) easy separation of the catalyst from the reaction mixture; and (3) low or no protonic or Lewis acidity. Although several catalysts have been reported in the literature,2,3 they do not satisfy the above requirements and possess several shortcomings. We are now pleased to report the preparation and demonstration of a suitable catalyst based on polystyrene substituted by arsonic groups. Results and Discussion 1. Catalyst Selection. The OH/ I80H or O H / O O H exchange, and therefore formation of hydroperoxy and peroxo species, is known to be fast in oxides of groups 5, 5A, 6, and 6A element^.^ This fact has been employed in the preparation of benzeneperoxyseleninic acid in a two-phase system such as chloroform-aqueous hydrogen peroxide.s The preformed benzeneperoxyseleninic acid dissolved in the organic solvent has then been used as a stoichiometric oxidant of cyclic ketones to lactones.’ Even more interesting are the patent literature reports* suggesting that selenium and arsenic oxides may be used as catalysts for the Baeyer-Villiger oxidation of ketones by hydrogen peroxide. I n our work,3 similar properties have been demonstrated for molybdenum and tungsten peroxo complexes stabilized by pyridinecarboxylato ligands. Unfortunately, the above-mentioned catalysts cannot be easily separated from the reaction mixtures. Furthermore, selenium and arsenic oxides are toxic, and in the presence of aqueous hydrogen peroxide they exhibit protonic and Lewis acidity causing extensive solvolysis of lactones.6 Inspection of the literature revealed that the acidity of toluenearsonic acidh (pK, = 3.82) is very close to that of mchlorobenzoic acid’ (pK, = 3.82), the peroxy form of which 0002-7863/79/15Ol-6938

Sulphur dioxide insertion : XX. The reaction of sulfur dioxide with some alkyl complexes of chromium, manganese, molybdenum, rhenium, and ruthenium. A comparative study of reactivity

0l .OO/O is the most common reagent for conversion of cyclic ketones to lactones. Also, the C-As bond8 in benzenearsonic acid, unlike the C-Se bond9 in benzeneseleninic acid, is very stable toward nucleophilic and electrophilic reagents. Indeed, preliminary experiments indicated that benzenearsonic acid is an efficient catalyst for oxidation of cyclic ketones to lactones. Nevertheless, only bonding of the benzenearsonic acid group to an insoluble support would allow the separation of this catalyst from the product. Our interest therefore centered on polystyrene arsonated on the benzene ring since, from all the polymers modified by peroxycarboxylic groups, only those based on polystyrene have been found stable.’O 11. Preparation and Characterization of the Catalyst. Previous attempts to derivatize polystyrene by arsonic groups have employed, as the key step, the Bart’s reaction which involves interaction of the diazotized phenyl rings with alkaline metal arsenite.’ The polystyrene derivatized by this method is contaminated’ l a x b by a substantial number of phenyl groups bearing azo, amino, and hydroxy groups which are incompatible with hydrogen peroxide. Therefore, a new procedure has been developed which is summarized in eq 1 :

14 N–31P, 15N–15P, and 31P–31P coupling constants from the 31P nuclear magnetic resonance spectra of square planar platinum(II) and palladium(II) thiocyanate complexes

Abstract The rates of the cleavage of the metal-carbon bond in h5-C5H5Cr(NO)2R, h5-C5H5Ru(CO)2R, h5-C5H5Mo(CO)3R, Mn(CO)5R, and Re(CO)5R have been investigated in neat SO2 at −65 to −18° by infrared and 1H NMR spectroscopy. The pseudo-first-order rate constants, obtained here and elsewhere, decrease in the following orders for various groups R: h5-C5H5Fe(CO)2CH3 > Re(CO)5CH3 > h5-C5H5Ru(CO)2CH3 ∼ Mn(CO)5CH3 ≳ h5-C5H5Mo(CO)3CH3 ⪢ h5-C5H5W(CO)3CH3; h5-C5H5Cr(NO)2CH2C6H5 ⪢ h5-C5H5Mo(CO)3CH2C6H5 ≳ h5-C5H5Fe(CO)2CH2C6H5 ≳ Mn(CO)5CH2C6H5 > h5-C5H5Ru(CO)2CH2C6H5 ⪢ h5-C5H5W(CO)3CH2C6H5; h5-C5H5Fe(CO)2C2H5 > h5-C5H5Mo(CO)3C2H5 ⪢ h5-C5H5W(CO)3C2H5; and h5-C5H5Cr(NO)2C6H5 ⪢ h5-C5H5Fe(CO)2C6H5. In general, the methyl complexes undergo the cleavage more rapidly than their benzyl counterparts. The foregoing trends are compared with those reported in the literature for the CO insertion and for other electrophilic scission reactions.

Oxidation of cyclic ketones by hydrogen peroxide catalysed by Group 6 metal peroxo complexes

The 31P n.m.r. spectra of cis-PtX2[P(OPh)3]2(X = CNS, C15NS) show the independent existence of dithiocyanato, diisothiocyanato and mixed linkage isomers in solution, and the appearance of distinct resolvable 31P–31P, 14N–31P and 15N–31P coupling in the spectra of the mixed species suggests a means of measuring these couplings in co-ordination complexes.

Selective catalytic oligomerizations and hydrogenations using polymer-anchored complexes of nickel and iridium

Molybdenum peroxo complexes stabilized by picolinato and pyridine 2,6-dicarboxylato ligands catalyse oxidation of cyclic ketones by H2O2 to lactones and their derivatives; this represents a catalytic analogue of the Baeyer–Villiger reaction.

Group 6 transition metal peroxo complexes stabilized by polydentate pyridinecarboxylate ligands

Polystyrene–divinylbenene resin-anchored [Ni(CO)2(PPh3)2] has been used selectively to oligomerize butadiene to either 4-vinylcyclohexene or cycloocta-1,5-diene, and anchored [Ir(Cl)(CO)(PPh3)2] selectively catalyses the hydrogenation of cyclo-octa-1,5-diene to cyclo-octene; the activity of these catalysts in some cases surpasses that of their homogeneous counterparts under identical conditions.