Styrenes palladium

The relative sensitivity of furan to electrophilic attack stands in the order benzene < naphthalene < ferrocene < furan as found from competition experiments with styrene palladium(II) acetate.441 Relative rales for acylation by trifluoroacetic anhydride (no catalyst) arc observed to be thiophene (1), selenophene (6.5), furan (1.4 x 102), pyrrole (5.3 x I07), and... 

Moritani, I. and Fujiwara, Y. (1967) Aromatic substitution of styrene palladium chloride complex. Tetrahedron Lett., 8, 1119-22. 

The first waste-free vinylation of arenes under C—H activation is as old as the Mizoroki-Heck reaction itself already in 1967, Moritani and Fujiwara [6] revealed a stoichiometric reaction of styrene-palladium(II) chloride dimers with benzene in the presence of acetic acid to give stilbenes in a modest 24% yield. During this process, the palladium(II) precursor is reduced to palladium(O), so that the key to closing the catalytic cycle was to add an efficient reoxidation step to regenerate an active palladium(II) species. One year later, the same group presented a first approach, substoichiometric in palladium. 

Fujiwara and Moritani discovered in 1%7 that when styrene-palladium chloride complex 1 was heated in benzene (2a), toluene (2b) or p-xylene (2c), in the presence of acetic acid, tra 5-stilbene (3a), rram -methylstilbene (3b) or tra -2,5-dimethylstilbene (3c) were produced respectively, albeit in low yields (Equation (9.1)) [3], No stilbene derivative was obtained, however, in the case of mesitylene, which may be attributed to the steric hindrance of three methyl groups on the benzene ring [3]. Shortly thereafter, Fujiwara and coworkers [4] found that arylation of styrene (4a) occurred much more efficiently in the presence of stoichiometric palladium acetate instead of the styrene-palladium chloride complex (1). Thus, equimolar amounts of styrene (4a) and palladium acetate were refluxed in benzene (2a) in the presence of acetic acid, affording a 90% yield of rran -stilbene (3a). In the case of toluene (2b) and p-xylene (2c), fran5-4-methylstilbene (3b, 58%) and rran5-2,5-dimethylstilbene (3c, 47%) were obtained (Equation (9.2)). 

As early as 1963, Tsuji and colleagues described the reaction of olefin-palladium chloride complexes with CO to produce jS-chloroacyl chlorides [1,2]. Both internal and terminal aliphatic olefins were transformed into the corresponding chloroesters when the reaction was conducted in alcohols. Later on, in 1969, Yukawa and Tsutsumi reported on the reaction of a styrene-palladium complex with CO in alcohols [3]. Here, various cinnamates and phenylsuccinates were synthesized. Compared with Tsuji s work, they proposed a different reaction mechanism. They assumed that the oxidative addition of the alkyloxycarbonyl groups into styrenes is the key step, but a stoichiometric amount of palladium was stiU necessary to perform the reaction. Another version of a dialkoxycarbonylation of olefins was reported by Heck [4], using mercuric chloride as additive. 

It has been discovered that styrene forms a linear alternating copolymer with carbon monoxide using palladium II—phenanthroline complexes. The polymers are syndiotactic and have a crystalline melting point - 280° C (59). Shell Oil Company is commercializing carbon monoxide a-olefin plastics based on this technology (60). 

Another appHcation for this type catalyst is ia the purification of styrene. Trace amounts (200—300 ppmw) of phenylacetylene can inhibit styrene polymerization and caimot easily be removed from styrene produced by dehydrogenation of ethylbenzene using the high activity catalysts introduced in the 1980s. Treatment of styrene with hydrogen over an inhibited supported palladium catalyst in a small post reactor lowers phenylacetylene concentrations to a tolerable level of <50 ppmw without significant loss of styrene. 

The oxidative carbonylation of styrene with carbon monoxide, oxygen, and an aUphatic alcohol in the presence of a palladium salt, a copper salt, and sodium propionate also provides the requisite cinnamate. 

A mechanism for alkene arylation by palladium(II) is given below. The isotope effect was found to be 5 when benzene-dg was used. When styrene-/S,i5-d2 was used. 

Hydrogenation of styrene oxide over palladium in methanol 66 gives exclusively 2-phenylethanol, but in buffered alkaline methanol the product is l-phenylelhanol. If alcoholysis of the epoxide by the product is troublesome, the problem can be eliminated by portion-wise addition of the epoxide to the reaction, so as always to maintain a high catalyst-to-substrate ratio. The technique is general for reactions in which the product can attack the starting material in competition with the hydrogenation. 

Chemical reduction is used extensively nowadays for the deposition of nickel or copper as the first stage in the electroplating of plastics. The most widely used plastic as a basis for electroplating is acrylonitrile-butadiene-styrene co-polymer (ABS). Immersion of the plastic in a chromic acid-sulphuric acid mixture causes the butadiene particles to be attacked and oxidised, whilst making the material hydrophilic at the same time. The activation process which follows is necessary to enable the subsequent electroless nickel or copper to be deposited, since this will only take place in the presence of certain catalytic metals (especially silver and palladium), which are adsorbed on to the surface of the plastic. The adsorbed metallic film is produced by a prior immersion in a stannous chloride solution, which reduces the palladium or silver ions to the metallic state. The solutions mostly employed are acid palladium chloride or ammoniacal silver nitrate. The etched plastic can also be immersed first in acidified palladium chloride and then in an alkylamine borane, which likewise form metallic palladium catalytic nuclei. Colloidal copper catalysts are of some interest, as they are cheaper and are also claimed to promote better coverage of electroless copper. 

Phenoxy acetophenone, 46, 94 Phenylacetyleue, oxidative coupling to diphenyldiacetylene, 46, 39 partial reduction to styrene using palladium catalyst, 46, 90 reaction with sodium hypobromite to yield phenylbromoethyne, 46,86... 

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... 

Nickel and palladium react with a number of olefins other than ethylene, to afford a wide range of binary complexes. With styrene (11), Ni atoms react at 77 K to form tris(styrene)Ni(0), a red-brown solid that decomposes at -20 °C. The ability of nickel atoms to coordinate three olefins with a bulky phenyl substituent illustrates that the steric and electronic effects (54,141) responsible for the stability of a tris (planar) coordination are not sufficiently great to preclude formation of a tris complex rather than a bis (olefin) species as the highest-stoichiometry complex. In contrast to the nickel-atom reaction, chromium atoms react (11) with styrene, to form both polystyrene and an intractable material in which chromium is bonded to polystyrene. It would be interesting to ascertain whether such a polymeric material might have any catal3dic activity, in view of the current interest in polymer-sup-ported catalysts (51). 

These complexes can be isolated in some cases in others they are generated in situ from appropriate precursors, of which diazo compounds are among the most important. These compounds, including CH2N2 and other diazoalkanes, react with metals or metal salts (copper, palladium, and rhodium are most commonly used) to give the carbene complexes that add CRR to double bonds. Ethyl a-diazoacetate reacts with styrene in the presence of bis(ferrocenyl) bis(imine), for example, to give ethyl 2-phenylcyclopropane-l-carboxylate. Optically active complexes have... 

The palladium (II) NHC complexes 81 and 82 (Fig. 2.13) have also been used as catalysts in the diboration of styrene. In the presence of NaOOCCHj, (1 equiv.. 

Concerning enantioselective processes, Fujihara and Tamura have proved that palladium NPs containing (S)-BINAP (2,2 -bis(diphenylphosphino)-l,l -binaphthyl) as chiral stabiliser, catalyse the hydrosilylation of styrene with trichlorosilane, obtaining (S)-l-phenylethanol as the major isomer (ee = 75%) [42]. In contrast, the palladium complex [Pd(BINAP)(C3H5)]Cl is inactive for the same reaction [43]. 

Palladium-catalyzed hydrosilylation of styrene derivatives usually proceeds with high regioselectivity to produce benzylic silanes, 1-aryl-1-silyle thanes, because of the... 

In all of these cases, paUadium-catalyzed hydrosilylation proceeds via hydropalla-dation followed by reductive elimination of alkyl- and silyl group from the palladium. In the reaction of o-aUylstyrene (24) with trichlorosilane, which gives hydrosilylation products on the styrene double bond 25 and cycUzed product 26, the hy-dropalladation process is supported by the absence of side products which would result from the intermediate of the silylpaUadation process (Scheme 3-11) [37]. 

In addition, various chiral (p-A -sulfonylaminoalkyl)phosphine ligands were earlier employed by Achiwa et al. for the asymmetric palladium-catalysed hydrosilylations of cyclopentadiene and styrene, affording the corresponding... 

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