Heterolytic H2 Activation

The examples covered in this chapter demonstrate that multistep catalytic cycles are simply composed of the following mixture of elementary organometallic reaction steps (i) ligand addition/dissociation, (ii) oxidative addi-tion/reductive elimination, (iii) hydrogenolysis (four-center concerted reactions, heterolytic H2 activation), and (iv) migratory insertion/elimination. The vast majority of catalytic reactions can be described using these basic reactions. 

Heterolytic H2 Activation We now look at the second mechanistic class of hydrogenation catalyst. RuCl2(PPh3)3 is believed to activate H2 heterolyt-ically, a reaction accelerated by bases, such as NEt3. The base may either be external or one of the ligands on the metal abstracts a proton from H2, leaving an H bound to the metal (Eq. 9.10). 

Seino H, Misumi Y, Hojo Y, Mizobe Y. Heterolytic H2 activation by rhodinm thiolato complexes bearing the hydrotris(pyrazolyl)borato hg3nd and apphcation to catalytic hydrogenation under mild conditions. Dalton Trans. 2010 39 3072-3082. 

Brown SD, Mehn MP, Peters JC. Heterolytic H2 activation mediated by low-coordinate L3Fe-(n-N)-FeL3 complexes to generate Fe(ti-NH)(n-H)Fe species. J Am Chem Soc. 2005 127 13146-13147. 

Generation of the catalytically active species by heterolytic H2 activation... 

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