Hydrogenation aryl substituted phosphines

The reduction of 4 was run in the presence of a series of aryl substituted phosphines. Hydrogenation profiles similar to that shown in Figure 5 were obtained. The rates of hydrogenation of 7 using aliquots... 

Moreover, the Nb complex hydrogenates catalytically aryl- and benzyl-substituted phosphine under similar conditions (Scheme 6.16) [149]. Kinetic studies show that the hydrogenation of triphenylphosphine into the monocyclohexyl, dicyclohexyl, and tricyclohexylphosphine are successive reactions, and the rate of hydrogenation of the arylphosphine decreases as the number of cyclohexyl substituents increases [153]. 

In the sixties it was recognized that ligand substitution on the cobalt carbonyl might influence the performance of the catalyst. It has been found that aryl phosphines or phosphites have little influence in fact they may not even coordinate to cobalt under such high CO pressures. Tertiary alkyl phosphines, however, have a profound influence [5] the reaction is much slower, the selectivity to linear products increases, the carbonyl complex formed, HCoL(CO)3, is much more stable, and the catalyst acquires activity for hydrogenation. This process has been commercialized by Shell. As a result of the higher stability of the cobalt complex, the Shell process can be operated at lower pressures and higher temperatures (50-100 bar vs 200-300 bar for HCo(CO)4, 170°C vs 140°C). 

In general, phosphines are tricoordinated phosphorus compounds that bear only hydrogen or carbon (alkyl, aryl, alkenyl) substituents at phosphorus. Subcategorization of phosphines is based on the degree of carbon substitution about phosphorus. Primary phosphines [RPH2] are those... 

A mixture of 2-t-butylfuran and 2,5-di-t-butylfuran is obtained by the action of t-butyl chloride on furan in the presence of mesitylene nolybdenum tricarbonyl." The intermediate in the nitration of furan-2-aldehyde in acetic anhydride has been identified as compound (26). Treatment of 5-bromo-2-furoic acid with sulphur tetrafluoride in hydrogen fluoride yields the dihydrofuran (27). Bromo-furans are converted into aryl-furans by crosscoupling with aryl Grignard reagents in the presence of nickel(II)-phosphine complexes. 2-Furoic acid is lithiated at position 5, 3-furoic acid at C-2. 2-Methylfuran yields the 5-methylthio-derivative by lithiation and subsequent treatment with dimethyl disulphide. The corresponding phenylthio-compound (28) has been converted into a series of 4-substituted 2-methyl-furans (29 R = alkyl, MeaSi, CO2H, or RCHOH) by the sequence bromi-nation, lithiation, treatment with the appropriate electrophile, and, finally, desulphurization with Raney nickel. 2-Lithiofuran reacts with copper(II)... 

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