Trinuclear iridium hydride cluster

The counterion as well was found to strongly influence catalyst performance. Initial experiments with Ir-PHOX complexes gave high enantioselectivity and full conversion, but only at high catalyst loadings of 4 mol% (Scheme 2b) [9]. Lower catalyst loadings resulted in decreased conversion due to catalyst deactivation [14] with concomitant formation of an inactive trinuclear iridium hydride cluster 8 (Scheme 4) [15], analogous to the deactivation products observed with the Crabtree catalyst 6 [16]. 

Scheme 4 Formation of trinuclear iridium hydride cluster as main deactivation pathway of catalysts...

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