Pendant nitrogen bases

The imidazohmn carbocation must be optimally positioned to extract a hydride from Ha, boimd to and activated by Fe° in [Fe]-Haase similarly, the other hydrogenases are well set up for cooperative interactions and the formation of iron hydrides. Positioned over the open site for the [FeFe]-Haase is the pendant nitrogen base built into the bridging dithiolate colactor. This pendant base is attractively available for rapid intramolecular shuttling of a proton into... 

Wilson AD, Shoemaker RK, Miedaner A, Muckerman JT, DuBois DL, Dubois MR. Nature of hydrogen interactions with Ni(II) complexes containing cyclic phosphine hgands with pendant nitrogen bases. Proc Natl Acad Sci USA 2007 104 6951-6956. 

The ligand L3 was initially intended to provide enforced tetrahedral coordination at the metal. Moore and co-workers (30,31) have successfully used the pendant arm macrocycle L5, also a derivative of [12]aneNs, for the same purpose (although in view of the foregoing discussion, enforcing the geometry may not have been necessary). The three macrocyclic nitrogen donors form the base of a tetrahedron and the pendant amine fills the apical site. If the pendant arm is shorter. 

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