Toward the synthesis of tetrametallic terminal oxo complexes supported by aminopyrazole ligands

Abstract

A proposed mechanism for the O-O bond formation in the oxygen-evolving complex (OEC) of Photosystem II (PSII) involves a terminal Mn-oxo intermediate. Thus, synthesizing multi- metallic clusters contg. such a terminal oxo group is expected to provide further mechanistic insight for the catalytic water oxidn. reaction. Here we report the synthesis and characterization of a series of tetranuclear complexes LM_3OM(L')(PhNHPz)_3 (L = 1,3,5-tris(2-(di(2-pyridyl)hydroxymethyl)phenyl) benzene; M = Mn, Fe; L' = OH, Cl; PhNHPz = 3-phenylamino-pyrazolate). Three metal centers are coordinated by a previously reported ligand, based on three dipyridyl-alkoxide units on a 1,3,5- triarylbenzene motif. The fourth metal center is site- differentiated, and is supported by three PhNHPz ligands and a μ_4-oxo. The PhNHPz bridging ligands were found to provide a hydrogen-bonding network which interacts with terminal ligands bound to the site- differentiated metal. The effect of the second coordination sphere interactions on structure and reactivity will be discussed.