Synthesis and Characterization of a Dinuclear Manganese(III,III) Complex with Three Phenolate Ligands

Abstract

A dinuclear manganese complex ([Mn 2 L(µ-OAc) 2 ]PF 6 ) has been synthesized, where L is the trianion of 2,6-bis{[(2-hydroxy-3,5-di-tert-butylbenzyl)(2-pyridylmethyl)amino]-methyl}-4-methylphenol, a ligand with three phenolate groups. The two pseudo-octahedrally coordinated Mn ions are bridged via the two bidentate acetate ligands and the 4-methylphenolate group of the ligand. We have characterized the complex with electrochemistry, spectroelectrochemistry and EPR spectroscopy. Electrochemically the Mn 2 III,III complex undergoes two metal-centered quasi-reversible oneelectron reduction steps (E 1/2 = 0.04 and −0.32 V vs. SCE). Reduction to the Mn 2 II,III state results in transformation into

Role of ligands in catalytic water oxidation by mononuclear ruthenium complexes

“…Sun and co-workers [78] used the dianionic ligand 2,2′-bipyridine-6,6′-dicarboxylic acid (bda) to prepare the neutral mononuclear Ru WOC, [Ru(bda)(pic) 2 ] (52, Chart 12) that shows an excellent catalytic performance in both thermal and visible light-driven water oxidation [79,80]. The strong electron donating ability of the carboxylate ligands stabilizes the higher oxidation states of the metal center [81], making isolation of high valence intermediates possible. By mass spectrometry, two isolated oxidation states were identified as 52a and 52b (Chart 12).…”

A new, dinuclear high spin manganese(III) complex with bridging phenoxy and methoxy groups. Structure and magnetic properties

“…A Mn V @O moiety has been proposed to play a key-role in OAO bond formation in photosynthesis as well as a model complex [9][10][11]. It is therefore of interest to study and characterize highvalent dinuclear manganese complexes, and we and others have prepared a number of dinuclear manganese complexes, which have oxidation states between Mn II and Mn IV and a varied number of coordinating phenoxy groups, which could be expected to stabilize high oxidation states of manganese [12][13][14][15][16][17][18]. These studies include the dinuclear Mn II,III complex 3, which was first prepared by Hendrickson et al [19] This complex was found to give a fairly stable Mn III,IV complex, which, however, appears to decompose on further oxidation [20,21].…”

EPR investigations of synthetic manganese complexes as bio-mimics of the water oxidation complex in photosystem II

“…We performed stepwise electrolysis and EPR to characterize all these redox states. One-electron reduction resulted in an antiferromagnetically coupled Mn~ ull species as described above for 9 and 10 [39]. In contrast, by two-electron reduction a so far stmcturally noncharacterized species was formed that displays a very well structured 23-to 25-1ine EPR spectmm (Fig.…”

“…From a series of synthesized dinuclear Mn comp|exes, we present here comptexes 9-11 shown in Fig. 4 [35][36][37][38][39].…”

“…Complex 9 is prepared asa Mn2 u'u complex, 10 Table 1) assigned as M. 2, ,lvul 2, and M. 2, ,lvu~ z , redox couples, respectively [37]. As the number of oxygen ligands to manganese was increased, manganese oxidation became more facile: the corresponding oxidation potentials for complex 10 were determined as -0.14 and +0.78 V and for complex 11 as -0.09 and +0.42 V [35,39]. At higher potentials, complexes 9-11 show irreversible oxidations to species of manganese oxidation states higher than Mn m,m.…”