I n d i u m ( I I I ) B r o m i d e -C a t a l y z e d C h e m i o s e l e c t i v e D i m e r i z a t i o n o f V i n y l a r e n e sAbstract: Indium(III) bromide catalyzes the dimerization of a-substituted vinylarenes. Chemioselectivity towards open chain or cyclic dimers depends on the nature of the substituent at the aryl group of the vinylarene.Acid-catalyzed dimerization of vinyl arenes has been known for long time. 1 Since this pioneer work, several acid catalysts have been used. 2 Aminium salts acting as one electron oxidants also promote the dimerization. 3 The products which were obtained from these reactions (Scheme 1) are all derived from a common intermediate 2.Scheme 1 Acid-catalyzed of a-methylstyrene derivatives Open chain unsaturated dimers 3 and 4 are generated by proton elimination, while production of indan cyclodimers 5 is the result of an intramolecular FriedelCrafts reaction within intermediate 2. Frequently, the formation of higher oligomers (trimers, tetramers) 6 as the result of reaction between intermediate 2 with the vinyl arene starting material 1 is observed. A common feature of these reactions is that, in most cases, a mixture of products is obtained. Therefore, the search for new chemoselective catalysts is still of importance.Recently, a protocol using palladium(II)-indium triflate catalyst was reported to transform a-methylstyrene into a mixture of the open chain unsaturated dimers 3 and 4. 4As a part of our interest to apply indium compounds in organic synthesis, we describe here the results of our investigation on such dimerization reactions catalyzed by indium(III) bromide.We first examined the catalytic activity of InBr 3 (10 mol%) on a-methylstyrene 1a (1 mmol) in CH 2 Cl 2 (2 mL) at 0°C (Scheme 2). After 2 hours of continuous stirring under nitrogen atmosphere, we observed (TLC) the complete consumption of 1a. The reaction was quenched with H 2 O, and the aqueous phase extracted with CH 2 Cl 2 . The organic phase was dried in vacuo and the product 2,4-diphenyl-4-methyl-1-pentene (4a) was purified by column chromatography on silica gel with hexanes. This procedure afforded 90% of yield of an analytically pure compound. When the reaction mixture was allowed to stir at 0°C for longer periods (>5 h), heavier oligomers 6a were obtained in 30% of yield together with 65% of the cyclic dimer 5a. At room temperature, 1a is directly transformed into 5a, when all other experimental conditions were kept constant. We further observed the isomerization of the open chain unsaturated dimer 4a into the corresponding indan derivative 5a. These results demonstrate that chemoselectivity towards dimers 4 is determined by kinetically controlled conditions; while thermodynamic control produces dimers 5. Further, the results suggest that oligomerization is achieved under kinetic conditions.

The indium(III) selenolate obtained from indium(I) bromide and diphenyldiselenide promotes, alternatively, the Markovnikov hydroselenation, diselenation or hydration of terminal alkynes, depending on the experimental conditions. For many years, the interest in indium chalcogenates was related to their use as precursors of semiconductors type InE (E = chalcogene). 1 Only recently, it was demonstrated that some of these compounds can, conveniently, be used as useful reagents in organic transformations (Scheme 1). IIn(EPh) 2 (E = Se, Te) promotes the hydrochalcogenation of 2-alkyn-1-ol derivatives, in non-aqueous media, with rigorous regio-, and stereochemical control; the products correspond to Markovnikov adducts resulting of an anti addition of the chalcogenol constituents across the triple bonds. 2 IIn(SePh) 2 promotes the ring-opening reaction of epoxydes to the corresponding bhydroxy selenides with rigorous regioselectivity; the nucleophile incorporation at the less hindered carbon atom was observed for alkyl-substituted epoxides, and at the benzylic carbon atom for aryl derivatives. 3 Further, IIn(SePh) 2 was used to prepare unsymmetrical selenides from organyl halides. 4 Scheme 1 Organic reactions promoted by indium chalcogenatesContinuing our studies on the applications of indium compounds in organic synthesis, we examine here the hydroselenation of unactivated alkynes with indium(III) selenolates in aqueous media. We envisaged this reaction on observing that the compounds XIn(SePh) 2 (X = Br, I), prepared from InX and PhSeSePh in THF, MeCN or CH 2 Cl 2 and X 2 InSePh, obtained from InX and PhSeX in THF or CH 2 Cl 2 , readily decompose under moisture. Therefore, we first examined the nature of this decomposition. To a freshly prepared solution of Br 2 InSePh in THF, under N 2 atmosphere, was added an equivalent amount of 2,2¢-dipyridyl followed by a 5-fold excess of water; the resulting solution was allowed to contact with air. This treatment resulted in the slow deposition of colorless crystals of [Br 2 InOH(bipy)] 2 ·4THF (Scheme 2). 5 Benzeneselenol could not be isolated, since it was completely oxidized to diphenyldiselenide by air.Scheme 2 Decomposition of Br 2 InSePh by moisture [Br 2 InOH(bipy)] 2 ·4THF was characterized by X-ray means. 6 The compound, in the solid state, is a centrosymmetric dimer. The dimerization occurs through the hydroxylic oxygen atom, leading to a planar In 2 O 2 fourmembered ring. Two bromine and one bidentate 2,2-dipyridyl ligands complete the hexacoordination at each metal center. The geometrical arrangement around the indium centers is a distorted octahedron guarding a cis-relationship between each pair of similar ligands. The THF molecules are loosely held in the lattice and do not show any interaction with the indium complex. IIn(EPh) 2 + R-Y R-EPh CH 2 Cl 2 (E = Se; Y = Cl, Br, I, R = alkyl, benzyl, allyl, etc.) H EPh OH R 2 R 3 (E = Se, Te; R 1 , R 2 , R 3 = alkyl and aryl) i ii iii SePh In Br Br H 2 O bipy 2 O In O In Br Br Br Br H H bipy bipy 2 InBr + 2 BrSePh THF O...

Indium(III) benzenechalcogenolates (chalcogen = sulfur and selenium) promote the rigorous Markovnikov hydrochalcogenation of terminal alkynes. The generality and limitations of the reaction with aminoalkynes leading to allylic amines bearing vinylic chalcogenide substituents are discussed.

The structure of the title compound, C25H22P2, at 293 K is isostructural with those determined at 153 K [Di Nicola, Effendy, Fazaroh, Pettinari, Skelton, Somers & White (2005), Inorg. Chim. Acta, 358, 720–734] and 233 K [Schmidbaur, Reber, Schier, Wagner & Muller (1998), Inorg. Chim. Acta, 147, 143–150]. The diphenylphosphine groups are staggered relative to the PCP backbone such that the lone pairs are at an angle of 75.12 (7)° to each other. There are no classical intermolecular interactions.

The reactivity of indium(III) benzenechalcogenolates (chalcogen = sulfur, selenium) towards organyl halides (organyl = alkyl, allyl, benzyl, acyl) was examined. A practical one-pot method to prepare organyl phenyl chalcogenides from indium metal and diphenyl dichalcogenide was found. The coupling is fairly broad in scope and generally works better for organyl halides capable to produce stable carbocations.