NEUTRAL CATECHOLATE DERIVATIVES OF MANGANESE AND IRON - SYNTHESIS AND CHARACTERIZATION OF THE METAL OXYGEN CUBANE-LIKE SPECIES M4(DBCAT)4(PY)6 (M = MN, FE), THE TRINUCLEAR COMPLEX MN3(DBCAT)4(PY)4, AND THE DIMERS M2(DBCAT)2(PY)N (M = MN, N = 6, M = FE, N = 4, 6)

The synthesis and characterization of several new catecholate derivatives of manganese and iron are described. The reaction of 3,5-di-tert-butycatechol (DBCatH2) with the amides M[N(SiMe3)2]2 (M = Mn, Fe) in the presence of pyridine (py) affords the title compounds in high yield. The dimers Mn2(DBCat)2(py)6 (1) and Fe2(DBCat)2(py)n (n = 4 (4a), 6 (4b)) are obtained by treatment of catechol with the appropriate amide in pyridine. In hexane or toluene, this reaction gives the tetrametallic species M4(DBCat)4(py)6 (M = Mn (2), Fe (5)) upon the addition of 2 equiv of pyridine or, in the case of 2, by recrystallization of the dimer from toluene. Mn3(DBCat)4(py)4 (3) is obtained by slow air oxidation of 2 or by addition of 1/3 equiv of 3,5-di-tert-butyl-omicron-benzoquinone to the reaction of Mn[N(SiMe3)2]2 with DBCatH2 in hexane with subsequent addition of pyridine. Compounds 1-5 were characterized by infrared, UV-visible, H-1 NMR, and EPR spectroscopy and X-ray crystallography. The crystal structures of 1, 4a, and 4b (which cocrystallize as 4) consist of centrosymmetric dimeric units in which both catecholate ligands bridge the two metal centers by one doubly bridging and one terminal oxygen. Three pyridine ligands per metal complete the distorted octahedral geometry in 1 and 4a. In 4b two pyridines are bound to each iron which have distorted trigonal bipyramidal geometry at the metal. The structure of 2 possesses a Mn4O6 core composed of four doubly bridging oxygens, two triply briding oxygens, and four manganese atoms. Further coordination by pyridine ligands gives rise to two manganese centers with trigonal bipyramidal geometry and two with distorted octahedral geometry. The overall geometry of the complex gives 2 a basket-like appearance. Compound 5 has an Fe4O4 distorted cubane core, with each iron bound to three triply bridging oxygens and one terminal oxygen. As in 2, the six pyridine ligands are arranged to give two octahedral and two trigonal bipyramidal metal centers. The structure of 3 consists of two five-coordinate Mn(III) centers (one square pyramidal and one trigonal bipyramidal), each bound by two doubly bridging catecholate oxygens to a central pseudooctahedral Mn(II) ion. The cis arrangement of the bridging units imposes a bent geometry on the compound. Spectroscopic studies suggest that complex 3 undergoes intramolecular electron transfer on dissolution in toluene to give the all-Mn(II) semiquinone form Mn3(DBSQ)2(DBCat)2(py)4.