Hydrogenolysis reactions

The activation of alkanes on transition metal surfaces is an important step in many catalytic reactions. Hydrogenolysis, steam reforming and isomerization of alkanes all involve alkane dissodation. Thus, much interest exists in the mechanistic and kinetic aspects of alkane dissociation. 

Earlier transition metals, as zirconium and hafnium, are still more active in hydrogenolysis, which allows zirconium hydrides to be used in depolymerization reactions (hydrogenolysis of polyethylene and polypropylene) [89], In this case, the zirconium hydride was supported on silica-alumina. Aluminum hydrides close to [(=SiO)3ZrH] sites would increase their electrophilicity and, thus, their catalytic activity. A catalyst prepared in this way was able to convert low-density polyethylene (MW 125000) into saturated oligomers (after 5h) or lower alkanes at 150°C (100% conversion). It was also able to cleave commercial isotactic polypropylene (MW 250000) under hydrogen at about 190 °C (40% of the starting polypropylene was converted into lower alkanes after 15 h of reaction). 

Conversion of phenolic OH to H.1 This reagent is superior to several related hcterocyclcs lor this reaction. Hydrogenolysis of the resulting 1-phenyltetrazolyl Siller is best conducted using Pd/C and hydrazine as the H-donor in C6H6 r,II,Oil 11,0(7 3 2). 

The synthesis of a pyrrole segment common to netropsin and distamycin is shown in Scheme 2ji°l Friedel-Crafts acylation of 1-methylpyrrole (1) followed by nitration at C4 provides 3 in 54% yield. After a haloform reaction, hydrogenolysis, N-protection with B0C2O, and saponification, the pyrrolecarboxylic derivative acid 7 was obtained in 30% overall yield from 3. This monomer is readily chain-extended to the pyrrole-imidazole derivative 9 (Scheme 3)J10 Furthermore, solid-phase synthesis with this and related pyrrole-containing building blocks leads to polyamides that have recently been used in the recognition of a 16 base-pair sequence in the minor groove of DNA.1" ... 

Apart from metal-catalyzed cross-coupling reactions, hydrogenolysis of halo-oxepine was used as a key step for the synthesis of 2-chloro-2-deoxy septanoside... 

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