Ligand-assisted templating mechanism

Fig. 4 Ligand assisted templating mechanism for the synthesis of niobium oxide. The amine surfactant forms covalent bonds with the niobium (V) ethoxide, resulting in the formation of a hybrid interface. Upon exposure to water, the system organizes into various structures such as bidimensional hexagonal (Nb-TMSl), three-dimensional hexagonal (Nb-TMS2), lamellar (Nb-TMS4), or a cubic phase. (Nb-TMS3 is not shown in the figure.) (From Ref...

The above mechanism is novel in that it does not require the interaction of a carbonyl moiety with the metal center. Neither a ketone/Ru complex nor a Ru alkoxide is involved in the mechanism, and the alcohol forms directly from the ketone. This non-classical mechanism also explains the high functional selectivity for the C=0 group. When the chiral molecular surface of the Ru hydride recognizes the difference of ketone enantiofaces, asymmetric hydrogenation is achieved. This is different from the earlier BINAP Ru chemistry where the enantio-face differentiation is made within the chiral metal template with the assistance of heteroatom/metal coordination. Similar heterolyses of H2 ligands have been shown by Morris and others (92) to be the critical step in the mechanism of reaction processes related to the Noyori systems. 

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