Dimeric oxo

SCF + MBPT + ZPE calculations [92THE(277)313] and MP2/6-31+G calculations [97JPC(B)9199] of the three possible dimers (oxo-oxo, oxo-hydroxy, and hydroxy-hydroxy). 

The iron protein has been found in animals, viruses and some prokaryotic organisms. The best studied example is from Escherichia coli.S19 The enzyme consists of two subunits, Bi and B2. Subunit B, has a molecular weight of 160 000 and is made up of two polypeptide chains. It contains redox-active SH groups, which play a role in the reaction, and has two binding sites for substrates and sites for effector molecules. It can bind any of the four ribonucleotide substrates. Subunit B2 has a molecular weight of 78 000 and also has two polypeptide chains. It contains a dimeric oxo-bridged iron site associated with a remarkably stable tyrosine radical. The formation of the active enzyme from B, and B2 requires the presence of magnesium ions. 

A major contaminant of many of the earlier preparations of K3[Mn(CN)6],575 and often described as a different form of this, was a golden brown dimeric oxo-bridged species [(CN)5Mn—O— Mn(CN)5]6-. It is also formed when KMn04 is reacted with KCN, and an X-ray analysis of the crystalline compound K7[Mn2O(CN)I0l,CN showed a linear Mn—O—Mn bridge, with Mn— O = 1.72 A and Mn—CN = 1.97-2.06 A. It is almost diamagnetic because of antiferromagnetism. 

Dimeric oxo-bridged V111 complexes with bipy or phen as supportive ligands (186) were found to cleave DNA without the addition of exogenous oxidants or reductants.740 The dinuclear V111 complex formed from 2-(dimethylamino)ethanethiol has a linear V—O—V 41 unit (187).793 This compound was the first example of a class of dinuclear complexes containing NS donors.793... 

Recently, controlled procedures for the covalent anchoring of iron tetrasul-fophthalocyanine onto amino-modified silicas have been developed to fix the complex either in a monomer or dimer form.80 Remarkably, the normally inactive dimeric oxo iron tetrasulfophthalocyanine is an active and selective... 

Tridentate red dimeric / -oxo-bridged complexes, [ MoOjlLXDjfAz-O)], prepared in high yield and purity, are used as catalysts in the epoxidation of several alkenes with TBHP as the oxidant. The epoxides are obtained in moderate to good yields and high... 

In confirmation of the modeling predictions outlined above, complex 4 did not form an isolable pyridine complex. In fact, NMR monitoring of the reaction of 4 with pyridine (5 equivs) in chloroform-d did not show any detectable coordination of the pyridine. However, treatment of 4 with pyridine (5-6 equivs) in refluxing acetonitrile (containing ca. 0.5% water) afforded the dimeric oxo complex [(l,3-C5(Si(CH3)3)2H3)Ti((tBuCOCHCOtBu)(0)]2 (77%). This complex possessed the same gross dimeric structure as 7 (31), but required much more vigorous conditions to effect its synthesis. 

---