Styrene platinum catalysts

In comparison with the platinum catalysts, rhodium catalysts are much more reactive to effect addition of bis(catecholato)diboron even to non-strained internal alkenes under mild reaction conditions (Equation (5)).53-55 This higher reactivity prompted trials on the asymmetric diboration of alkenes. Diastereoselective addition of optically active diboron derived from (li ,2i )-diphenylethanediol for />-methoxystyrene gives 60% de (Equation (6)).50 Furthermore, enantioselective diboration of alkenes with bis(catecolato)diboron has been achieved by using Rh(nbd)(acac)/(A)-QUINAP catalyst (Equation (7)).55,56 The reaction of internal (A)-alkenes with / //-butylethylene derivatives gives high enantioselectivities (up to 98% ee), whereas lower ee s are obtained in the reaction of internal (Z)-alkenes, styrene, and a-methylstyrene. 

Some of the highest enantiomeric excesses in hydroformylation reactions of styrene (-70-80% ee) have been obtained with a platinum catalyst containing the chiral ligand (2S,4S)-4-(diphenylphosphino)-2-[(diphenylphosphino)methyl]pyrrolidine (17 (-)-BPPM).39... 

The two metals that have been found to give encouraging conversions and selectivities for the hydroformylation of styrene are platinum and rhodium. The platinum-based catalytic system uses tin chloride as a promoter. It also uses triethyl orthoformate as a scavenger that reacts with the aldehyde to form the acetal. By removing it as soon as it is formed, any further degradative reactions of the aldehyde are avoided. The chirality in these reactions is induced by the use of optically active phosphorus ligands. With the best platinum catalyst, branched and linear aldehydes are produced in about equal proportion, but the former has an e.e. of >96%. 

The Pd-catalyzed alkoxycarbonylation of styrenes was achieved in the biphasic system [BMIM]BF4-cyclohexane [27]. High regioselectivity of up to 199 1 in favor of the /50-ester was observed after optimization of the phosphine ligand. This reaction can also be run in cblorostannate melts using a platinum catalyst [12]. 

With respect to polymer-bound platinum catalysts, a dinuclear amidate-bridged platinum(III) complex was supported on pol3winylpyridine [95] and tested as catalyst in the epoxidation of cyclohexene and styrene by isobutyralde-hyde/O2. Its catalytic activity was found to be significantly lower compared to the same complex immobilized on inorganic supports. 

Since the reaction of styrene with o-bis(deuteriodimethylsilyl)benzene produced the expected disilacyclopentene with no deuterium incorporation, the mechanism of this reaction is believed to involve the intermediacy of the cyclic bis(silyl)platinum complex (116) first reported by Eaborn et al. <73JOM(63)107> from the reaction of (113) and the platinum catalyst. However, complex (116) itself did not react with styrene but when 1.1 equivalents of (113) was added, an 83% yield of (114 Ri = H, R2 = Ph) was obtained. 

Suppression of aldehyde product racemization under the reaction conditions can be achieved with ethyl orthoformate21-45, l34,158. Thus, nearly quantitative induction is observed when a BPPM-modified platinum catalyst is used for styrene hydroformylation in the presence of orthoformate as the trapping agent for the chiral aldehyde formed125-, 58. These results, however, are reported to be not reproducible48, S3-177. 

Following this oxidative addition, insertion of the olefin or alkyne occurs into the platinum-hydride bond to form an alkyl or vinyl hydride complex. The regioselectivity of the insertion step and the chemistry of the alkyl silyl complexes control the overall regioselectivity of the hydrosilylation of olefins. Recall that these platinum catalysts form terminal alkylsilane products. This regioselectivity indicates that insertions of terminal olefins occur in order to generate a linear alkylplatinum intermediate. Apparently, the insertions of styrene and acrylic acid derivatives into the platinum hydride in these catalysts occur with the same regiochemistry. 

Highly enantioselective hydroformylation catalyzed by chiral metal complexes has been obtained with oidy a few catalytic systems. Many chiral phosphorus ligands have been used in Pt(II) and Rh(I) systems in the asymmetric hydroformylation of styrene. The first highly enantioselective examples of asymmetric hydroformylation of styrene were reported by Consiglio et al. in 1991 and used Pt-Sn systems [5, 6]. They achieved an ee of 86%. Platinum catalysts have several disadvantages they have low reaction rates, they hydrogenate the substrate and their regioselectivity to the... 

Pd complexes of polymeric diphenylphosphinyl ferrocene are effective catalysts for the hydrosilylation of styrene and 1-hexene by SiHCls. They can be recycled with no loss of activity.Nitrile groups on macroporous copolymers of acrylonitrile/divinylbenzene/ styrene are effective ligands for the immobilization of Rh(I), Pt(II), and Pd(II) complexes, which can be used as hydrosilylation catalysts, with their effectiveness closely related to the morphology of the polymer matrix. Similar transformation was also effected by platinum catalyst immobilized by mercaptan groups over polysiloxane. ... 

Usually, platinum catalysts stimulate extensive isomerization of nonfunctional-ized olefins. Nevertheless, they have been screened for asymmetric hydroformylation, where migration of the double bond to a (achiral) terminus is not desired. Frequently, this problem has been overcome by use of styrenes as model substrates, which direct the hydroformylation to the position next to the aryl ring [118]. Whether the olefin insertion or the subsequent carbonylation is the regio-chemistry determining step is still under discussion [119,120]. 

Substituted styrene monomers have been used in various laboratories with the aim of reducing the intrinsic chemical susceptibility of sulfonated polystyrene to graft chain degradation in the PEFC induced by radical species (HO , HOO ), which are formed in situ in the presence of O, H, and the platinum catalyst (Liu... 

The isolated preformed platinum catalyst [Pt(PP3)(SnCl3)]SnCl3 (PP3 = tris[2-(diphenylphosphano)ethyl]-phosphane) from the precursor [Pt(PP3)Cl]Cl and SnCl2 was found to show high aldehyde selectivity (99%) in styrene hydroformylation at 100 °C and 100bar CO/H2 = l [71]. 

The choice of an appropriate support is of no less importance than that of active phase of a catalyst. We have focused our attention on the application of hydrophobic supports to prepare effective platinum catalysts for hydrosilylation since our preliminary experiments have shown that in a number of hydrosilylation reactions hydrophobic material-supported catalysts appeared to be superior to those based on hydrophilic supports such as alumina and silica. We have also aimed at selecting such supports which, in addition to their hydrophobicity, do not have acid centers on their surfaces, and due to this, they do not catalyze undesirable side reactions of isomerization. The supports selected for our study were styrene-divinylbenzene copolymer (SDB) and fluorinated carbon (FC), because nonfunctionalized SDB is free of acid sites and surface acidity of FC is extremely weak (H 9). The performance of SDB- and FC-supported platinum catalysts was studied in several reactions of hydrosilylation. 

Styrene, a-ethyl-asymmetric hydroformylation catalysts, platinum complexes, 6, 266 asymmetric hydrogenation catalysts, rhodium complexes, 6, 250 Styrene, a-methyl-asymmetric carbonylation catalysis by palladium complexes, 6, 293 carbonylation... 

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