Sulfur-olefin ligand

Asymmetric addition of arylboroxines to cyclic N-sulfonylimines 92 or arylborates to iV-sulfonylimines 95 in the presence of a newly developed rhodium catalyst 93 coordinated with a sulfur-olefin ligand (L ) is a facile method to obtain benzosultams 94 or 97, wherein a stereogenic quaternary... 

Enantioselective arylation of ketimines has been carried out using rhodium catalysis with chiral sulfur-olefin ligands arylboronic acids are added in up to 99/99% yield/cc. 0... 

In recent years, the asymmetric hydrogenation of prochiral olefins have been developed in the presence of various chiral sulfur-containing ligands combined with rhodium, iridium or more rarely ruthenium catalysts. The best results have been obtained by using S/P ligands, with enantioselectivities of up to 99% ee in... 

Sulfuric acid stack emission limit, 23 774 Sulfuric acid storage tanks, 23 783 Sulfur impregnation, 23 593-594 Sulfur-iodine (S-I) cycle, 73 848 Sulfurized olefins, 23 642 Sulfur ligands, platinum, 79 656 Sulfur linkages... 

MCS) remains uncoordinated. It is important to note that on the contrary to what is typically observed with most other complexes, the olefin does not form an adduct with the metal center, but reacts directly with the sulfur-based ligand. After reduction of complex 48 the olefin can be released and complex 46 recovered, thus closing the cycle. This mechanism of the trapping of ethylene probably involves thiy 1-radical ligands as intermediates. 

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. 

The use of molybdenum catalysts in combination with hydrogen peroxide is not so common. Nevertheless, there are a number of systems in which molybdates have been employed for the activation of hydrogen peroxide. A catalytic amount of sodium molybdate in combination with monodentate ligands (e.g., hexaalkyl phosphorus triamides or pyridine-N-oxides), and sulfuric acid allowed the epoxidation of simple linear or cyclic olefins [46]. The selectivity obtained by this method was quite low, and significant amounts of diol were formed, even though highly concentrated hydrogen peroxide (>70%) was employed. 

Palladium(II) complexes possessing bidentate ligands are known to efficiently catalyze the copolymerization of olefins with carbon monoxide to form polyketones.594-596 Sulfur dioxide is an attractive monomer for catalytic copolymerizations with olefins since S02, like CO, is known to undergo facile insertion reactions into a variety of transition metal-alkyl bonds. Indeed, Drent has patented alternating copolymerization of ethylene with S02 using various palladium(II) complexes.597 In 1998, Sen and coworkers also reported that [(dppp)PdMe(NCMe)]BF4 was an effective catalyst for the copolymerization of S02 with ethylene, propylene, and cyclopentene.598 There is a report of the insertion reactions of S02 into PdII-methyl bonds and the attempted spectroscopic detection of the copolymerization of ethylene and S02.599... 

Going around the reaction system in Fig. 16, the first problem are poisons for rhodium such as traces of sulfur compounds in the raw materials. 3 valent P-compounds as ligands are highly prone to oxidation according to PR3 + [O] -> 0=PR3. In a continuous process, even traces of peroxides in the starting olefin and traces of oxygen in the synthesis gas accumulate over the time, so meticulous purification steps are a must if ligand-modified rhodium catalysts are used. 

Hydrides of Ni(I) and Ni(II) are known (37). A Ni(II) hydride appears to be an intermediate in the catalysis of olefin isomerization by phosphine complexes of nickel (61). Dilworth (62) has pointed out that stable hydride species are not obtained in model complexes with sulfur ligands. However, they may be possible within the confines of a protein chelate. 

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