Hydrogenolysis heterocyclic halides

Hydrogenolysis of metal carbonyls, such as Mnj(CO)jg [250 atm (25 MPa), 200°C] or COjCCOg [250 atm (25 MPa), 110°C], leads to metal-metal bond cleavage, forming HMn(CO)j or HCo(CO) The conversion of CoJiCO to HCo(CO) is the rate-determining step in Co-catalyzed hydroformylations at high P and T. Tertiary amines, nitrogen heterocycles, tertiary phosphorus bases or halide ions enhance the rate of HCo(CO) formation e.g., pyridine can increase the rate of HCo(CO).j formation 300-fold at 40°C. 

The removal of a halogen from an aromatic heterocycle takes place more readily than the hydrogenolysis of a phenyl halide of the same type (Eqn. 20.61). 45 The relative difference between the ease of dehalogenation of a phenyl and a heterocyclic halide is more pronounced over Raney nickel in basic medium than it is over palladium (Eqn. 20.62). 46... 

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