Hydrogenolysis homogeneous catalytic

Scheme 12 The mechanism of homogeneous catalytic hydrogenolysis of benzothiophene.

Stereoselective alkylation of chiral oxazolopyrrolidine phosphonate (458) occurred with a complete retention of stereochemistry on the a-stereogenic center. Removal of the chiral auxiliary from the resultant diastereomeri-cally pure phosphonates (459) by catalytic hydrogenolysis gave rise to enantiomerically homogenous cx-substituted pyrrolidin-2-yl-phosphonates (460) (Scheme 106). ° ... 

These unprecedented homogeneous transformations have been achieved for a variety of substrates, viz. T [72], BT [72-74], DBT [29, 72], and dinaphthothiophene (DNT) [75], by use of the electron-rich 16-electron neutral or anionic fragments [(triphos)MH]" (M = Rh, Ir, n = 0 M = Ru, n = -1). The reactions have been typically performed at about 160 °C under 30 atm H, conditions that are well tolerated by the very stable triphos derivatives the presence of strong bases such as NaOH or KO Bu dramatically increases the overall rate of the catalytic hydrogenolysis. 

The first homogeneous catalytic HDS reaction reported involved the conversion of DBT to biphenyl plus H2S, together with some hydrogenolysis products by use of [(triphos)IrH], generated by thermolysis of [(triphos)IrH2(Et)] in THF solution. The reaction proceeds slowly at 170 °C. The catalytic cycle (Scheme 13) was established from the isolation of most of the intermediates involved and the independent study of the individual reactions implicated. ... 

Scheme 13 Homogeneous catalytic HDS and hydrogenolysis of dibenzothiophene on Ir-triphos complexes.

The striking advances in borane chemistry during the period of 1940-1960 led to the successful development of the new field of metal hydride chemistry within the past 50 years. Especially transition-metal hydride complexes not only aroused academic interest but also established an exceptional position as participants in many important homogeneous catalytic reactions such as C==C and C=0 hydrogenation, C—H activation, and hydroformylation. For example, HCo(CO)4 and HCo(CO)3 which are produced by hydrogenolysis of Co2(CO)g ... 

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