Iridium complexes colloidal

Hydrogenation using the rhodium complex may involve the formation of colloid particles, as it was shown that the reaction is inhibited by metallic mercury [167]. Selective hydrogenation of the carbonyl group in a,P-unsatu-rated carbonyl compounds can be done with immobilized ruthenium or iridium complexes by using either the supported aqueous phase technique... 

The mechanism for this ostensibly homogeneous process, the Chalk-Harrod mechanism, [264] was based on classical organometallic synthetic and mechanistic research. Its foundation lies in the oxidative addition of the silane Si-H bond to the low oxidation state metal complex catalyst, a reaction which is well established in the organometallic literature. Lewis reported in 1986 that the catalyti-cally active solutions contained small (2.0 nm) platinum particles, and demonstrated that the most active catalyst in the system was in fact the colloidal metal. [60, 265] Subsequent studies established the relative order of catalytic activity for several precious metals to be platinum > rhodium > ruthenium = iridium > osmium. [266] In addition, a dependence of the rate on colloid particle morphology for a rhodium colloid was observed. [267]... 

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