Sulfoxide-olefin ligands

Figure 5.17 Chiral hybrid sulfoxide-olefin ligands and their application in the Hayashi-Miyaura reaction...

Rhodium Conjugate addition of aryl boronic acids to cyclohex-2-enone, catalysed by [Rh(diene)(OH)]2 complexes, afforded the corresponding product with the following enantioselectivities 96% ee with (508) ligand, 83% with (509), and 90% with (510). DFT calculations were used to shed light on the transition state structures and energies. " The sulfoxide-olefin ligand (511) exhibited >99% ee " ... 

Diallylsulfide can also be oxidized selectively to the sulfone without oxidation of the unsaturated side chain [144]. Coordination of the sulfur is apparently strong enough to exclude the olefinic ligand from the reactive center since in the absence of the sulfur, olefins are readily epoxidized by r-BuOOH in the presence of molybdenum complexes. The product of hydroperoxide oxidation of sulfides depends on the reaction conditions [143]. Sulfoxides are obtained at temperatures below 50 °C using excess sulfide whereas sulfones are the predominant product at temperatures above 55 °C using excess hydroperoxide. 

Satoh, T., Yamada, N., Asano, T. Ligand exchange reaction of sulfoxides in organic synthesis sulfoxide version of the Julia-Lythgoe olefination. Tetrahedron Lett. 1998, 39, 6935-6938. 

The palladium-catalysed arylation of olefins with aryl halides, the Heck reaction, is usually performed in polar solvents such as acetonitrile or dimethyl sulfoxide, in combination with a base and a Pd(ii) pre-catalyst that may or may not be associated with a phosphorus ligand. Given that quaternary ammonium or phosphonium salts are known to increase reaction rates, ILs emerged as promising solvents for this reaction.In the case of imidazolium-based ionic liquids, the solvent, beside providing an unusual coulombic environment. 

All the examples to be discussed are of square-planar platinum(II) complexes, recorded in Scheme 2. Thus Boucher and Bosnich (8) have prepared a series of olefin complexes derived from ( -tolylmethylsulfoxide)dichloroplatinum(II) in which the ligand is S-bonded. The S-methyl protons provide a convenient and sensitive NMR probe for the determination of diastereomer ratios. In the cases of but-l-ene, 3-methylbut-l-ene, styrene and 3,3-dimethylbut-l-ene crystals of a single diastereomer can be isolated in all but the last of these, however, there is rapid equilibration between diastereomers in solution, with relatively little discrimination between them (typically 55-75% of the major species). Since several rotamers are possible in the sulfoxide ligand it is not easy to specify the origin of chiral discrimination. 

Rhodium complexes generated from the water-insoluble carboxylated surfactant phosphine 17 (n = 3, 5, 7, 9, 11) were used as catalysts in the micellar hydrogenation of a- and cyclic olefins, such as 1-octene, 1-dodecene, and cyclohexene, in the presence of conventional cationic or anionic tensides such as cetyltrimethylammo-nium bromide (CTAB) or SDS and co-solvents, e.g., dimethyl sulfoxide [15], After the reaction the catalyst was separated from the organic products by decantation and recycled without loss in activity. There is a critical relationship between the length of the hydrocarbon chain of the ligand 17 and the length and nature of the added conventional surfactant, for obtaining maximum reactivity. For example,... 

Recently, Grela and coworkers [38] formed the pyridine monosolvate of a chelated complex related to the Hoveyda chelate. Exposure of the sulfoxide-based catalyst 27 to excess 3-bromopyridine resulted in the quantitative formation of complex 28 (Eq. (9.3)). In the RCM of diethyl allyl dimethallylmalonate, the initiation of complex 28 was much faster than that for the parent complex. Through various structural modifications as well as supplemental DFT calculations on the 6-coordinate complex, it was determined that 28 likely initiates by a different pathway than 27. Somewhat surprisingly, dissociation of the sulfoxide ligand from the metal center in 28 was found to precede olefin coordination and the subsequent loss of the pyridine ligand. Relative to 27, the overall initiation process was determined to be 5 kcalmol" lower for 28, having an energy barrier of 11.7 kcal mol versus 17.4 kcal mol . ... 

Thermal decarbonylation to the 77-allyl compound has been observed with a-allyl derivatives of Co(CO)4, CsH5Fe(CO)2, and CsHsM(CO)3 (M = Cr, Mo, W). Other ligands displaced by the olefin function of the allyl group are dimethyl sulfoxide in ff-C3H5PdCl(Me2SO)2 163) and cyanide ion in [<7-C3H5Co(CN)5] H6). 

The first example of Pd-catalyzed asymmetric nucleophilic substitutions of chiral j8-sulfinyl allylic systems was reported in 1995. The reaction of a chiral olefinic sulfoxide (5s)-l with dimethyl sodiomalonate was carried out in THF at room temperature (r.t.) in the presence of Pd(OAc)2 (0.1 equiv) and a phosphine ligand (0.2 equiv), giving (5,5s)-(Z)-2 with 29-79% de (Scheme 1). The degree of the asymmetric induction was largely dependent on the phosphine ligand used. With dpph as a ligand, the highest enantioselectivity was obtained. 

Dror and Manassen hydrogenated a- and cyclic olefins such as 1-octene, 1 -dodecene and cyclohexene in micellar systems using rhodium catalysts modified with water-insoluble carboxylated tenside phosphines 45 (Table 3 n=3,5,7,9,l 1) in the presence of conventional tensides such as sodium dodecylsulfate (SDS) or cetyltrimethylammonium bromide (CTAB) and cosolvents e.g. dimethyl sulfoxide. Linear olefins were more reactive than cyclic olefins. Maximum efficiency was observed in the presence of the anionic surfactant SDS when 45 contained a chain of 5-7 carbon atoms. In contrast, using the cationic tenside CTAB the ligand 45 with 5 C atoms was almost inactive but became active again with dodecyl trimethylammonium bromide. 

Thereafter, a serial of palladium-catalyzed intramolecular C-ff activation of allylic C-H bonds (Scheme 2.4) was reported by White [9], who first developed a novel route for accessing chiral syn-l,2-amino alcohols enabled through the discovery of a Pd/sulfoxide-catalyzed diastereoselective allylic C-H activation reaction of chiral homoallylic Af-tosyl carbamates. The author discovered that the addition of bis-sulfoxide ligands (L-1) to Pd(OAc)2 promoted allylic C-H cleavage of a-olefins versus oxypalladation in the presence of weak oxygen nucleophiles (i.e., carboxylic acids). Evidences presented that the mechanism proceeds via Pd(ll)/sulfoxide-promoted allylic C-H cleavage to furnish a n-allylic palladium intermediate followed by counterion-promoted functionalization with the tethered Af-tosyl carbamate nucleophile. 

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