Styrene platinum complex

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... 

Platinum complexes [PtCl2(diphosphine)] and [PtCl(SnCl3)(diphosphine)] of the ferrocenyl diphosphine ligands (35a), (35b), and (36) have been synthesized. Complexes [PtCl2(35)] and [PtCl2(36)] have been structurally characterized by XRD. Both the preformed and the in situ catalysts have been used in the hydroformylation of styrene.112... 

Platinum complexes with chiral phosphorus ligands have been extensively used in asymmetric hydroformylation. In most cases, styrene has been used as the substrate to evaluate the efficiency of the catalyst systems. In addition, styrere was of interest as a model intermediate in the synthesis of arylpropionic acids, a family of anti-inflammatory drugs.308,309 Until 1993 the best enantio-selectivities in asymmetric hydroformylation were provided by platinum complexes, although the activities and regioselectivities were, in many cases, far from the obtained for rhodium catalysts. A report on asymmetric carbonylation was published in 1993.310 Two reviews dedicated to asymmetric hydroformylation, which appeared in 1995, include the most important studies and results on platinum-catalogued asymmetric hydroformylation.80,81 A report appeared in 1999 about hydrocarbonylation of carbon-carbon double bonds catalyzed by Ptn complexes, including a proposal for a mechanism for this process.311... 

The cA-PtCl2(diphosphine)/SnCl2 constitutes the system mostly used in catalyzed hydroformylation of alkenes and many diphosphines have been tested. In the 1980s, Stille and co-workers reported on the preparation of platinum complexes with chiral diphosphines related to BPPM (82) and (83) and their activity in asymmetric hydroformylation of a variety of prochiral alkenes.312-314 Although the branched/normal ratios were low (0.5), ees in the range 70-80% were achieved in the hydroformylation of styrene and related substrates. When the hydroformylation of styrene, 2-ethenyl-6-methoxynaphthalene, and vinyl acetate with [(-)-BPPM]PtCl2-SnCl2 were carried out in the presence of triethyl orthoformate, enantiomerically pure acetals were obtained. 

The influence of steric and electronic effects of diphosphites (111) and (112) have been studied with regard to their catalytic performance on the hydroformylation of styrene catalyzed by platinum complexes. The highest chemoselectivity to aldehyde (71%) and regioselectivity to branched aldehyde (85%), with an enantiomeric excess of 86%, was obtained with the plat-inum(II)-SnCl2 catalytic system associated with ligand (25, 45)-bis(5)-(lll).340... 

Chiral bis-(binaphthophosphole) (bis(BNP)) ligands have been used in the asymmetric hydroformylation of styrene. In solution, the free diphospholes display fluxional behavior. Consistent with their structure, the reaction of the bis(BNP) compounds with platinum(II) derivatives gives either cis chelate mononuclear complexes or trans phosphorus-bridged polynuclear derivatives. Coordination to platinum enhances the conformational stability of bis(BNP)s and diastereomeric complexes can be detected in solution. In the presence of SnCl2, the platinum complexes give rise to catalysts that exhibit remarkable activity in the hydroformylation of styrene. Under optimum conditions, reaction takes place with high branched selectivity (80-85%) and moderate enantio-selectivity (up to 45% ee). 

Rhodium (I) complexes of chiral phosphines have been the archetypical catalysts for the hydrocarbonylation of 1-alkenes, with platinum complexes such as (61) making an impact also in the early 1990s[1461. More recently, rhodium(I)-chiral bisphosphites and phosphine phosphinites have been investigated. Quite remarkable results have been obtained with Rh(I)-BINAPHOS (62), with excellent ee s being obtained for aldehydes derived for a wide variety of substrates1 471. For example, hydroformylation of styrene gave a high yield of (R)-2-phenylpropanal (94% ee). The same catalyst system promoted the conversion of Z-but-2-ene into (5)-2-methylbutanal (82% ee). 

The majority of studies of asymmetric hydroformylation with rhodium and platinum complexes have made use of DIOP (49) as a ligand. With either the complex [RhCl(CO)(DIOP)] or [RhCl(C2H4)2]2 plus DIOP, styrene was hydroformylated to 2-phenylpropanal with optical yields of only 16%.366 When a-monodeuterostyrene was used as substrate, with DIOP and complex (34) as catalyst, essentially the same optical yield was obtained.367 The same catalyst with non-deuterated styrene under different conditions gave an optical yield of 25%.368... 

In spite of extensive studies on the asymmetric hydroformylation of olefins using chiral rhodium and platinum complexes as catalysts in early days, enantioselectivity had not exceeded 60% ee until the reaction of styrene catalyzed by PtCl2[DBP-DIOP (l)]/SnCl-> was reported to attain 95% ee in 1982 [8]. Although the value was corrected to 73% ee in 1983 [9], this result spurred further studies of the reaction in connection to possible commercial synthesis of antiinflammatory drugs such as (S)-ibuprofen and (S)-naproxen. The catalyst PtCl2[BPPM... 

Platinum complexes, [PtCl2 (l ,l )-XantBino ] (2) and its S,S analogue, were treated with tin(II) chloride to form the pre-catalyst for chemo-, regio-, and enantio-selective hydroformylation of styrene, vinyl acetate and allyl acetate. Although the reaction showed good chemo- and regio-selectivities, only moderate ee was obtained.103... 

T-Olefin platinum(O) complexes are important starting materials for oxidative addition see Oxidative Addition) or catalysts. Karstedt s catalysts, which are the most active ones for hydrosilylation, have been structurally characterized and found to show the structure of Pt2(M y M y )3 (9), wherein = divinyltetramethyldisiloxane." A styrene analogue Pt°(styrene)3 provides a convenient route to get an r-alkyne platinum complex by displacement (Scheme 27). DFT calculations indicate that aUcyne in the... 

Orchin and colleagues have studied (239, 325, 326, 514, 543-545) extensively the platinum complexes traws-(olefin)(4-ZC5H4NO)PtCl2 (212) in which the 4-substituent, Z, on pyridine-iV-oxide is OCH3, CH3, H, Cl, CO2CH3, CN, or NO2. The olefins have included ethylene (239), styrene, and 3- or 4-substituted styrenes (239, 544), 1-dodecene (544),... 

The addition of methyldichlorosilane to styrene has been carried out homogeneously in the presence of [PtCl2(CgH8)]2 246). This reaction is first-order with respect to the styrene and the silane, and first-order with respect to the platinum complex. In aromatic solvents, an induction period was observed which was attributed to coordination of the aromatic or a second molecule of styrene to the platinum. This necessity of a vacant site was further emphasized by the finding that addition did not occur in donor solvents such as tetrahydrofuran, ether, or pyridine. 

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. 

Cobalt, rhodium and platinum complexes modified with numerous chiral phosphanes have been used in asymmetric hydroformylation of styrene. The results are compiled in Table 4. Iso-product selectivities of >95% and stereoselectivities of >90% ce are reported, in many cases, however, only with low conversion rates and yields. Early results based on optical rotation measurements had to be reevaluated due to wrongly adopted rotation values for hydra tropaldehyde4-. ... 

Discovered more than 70 years ago, hydroformylation is nowadays one of the most important reactions in the chemical industry because aldehydes can be transformed to many other products. In the enantioselective version, rhodium/ diphosphorus ligand complexes are the most important catalytic precursors, although cobalt and platinum complexes have also been widely used. For these systems, the active species are pentacoordinated trigonal-bipyramidal rhodium hydride complexes, [HRh(P-P)(CO)2]. In those complexes, the coordination mode of the bidentate ligand (equatorial-equatorial or equatorial-apical) is an important parameter to explain the outcome of the process. The most common substrates of enantioselective hydroformylation are styrenes followed by vinyl acetate and allyl cyanide. With these substrates, mixtures of the branched (b, chiral) and linear (1, not chiral) aldehydes are usually obtained. In addition, some hydrogenation of the double bond is often observed. Therefore, chemo- and regioselectivity are prerequisites to enan-tioselectivity and all of them must be controlled. An additional eomplieation is that chiral aldehydes are prone to racemise in the presenee of rhodium spe-... 

Basic methods for their production involve the hydrosilylation of alkylacetylenes catalyzed by platinum complexes [8] and the dehydrogenative silylation of olefins, e.g. styrene [9], 1-hexene [10,11], are catalyzed by rhodium [10], ruthenium [9,12, 13] and iridium [11] complexes and photocatalyzed by iron and cobalt [14,15] carbonyls. 

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