Bis diimine

Commercially available chiral columns such as CHIRACEL OD-R or Crest-Pak [14-16]. Such columns have, for example, been successfully used for the separation of the enantiomers of the bis-diimine [Ru[(N-N)2 (dmso)Cl] ] complexes [14,17,18]. 

The cylindrical helical binuclear complex [Fe2L3]4+, where L is the bis-diimine Schiff base 1, exists as two enantiomers, whose interactions with DNA differ markedly. The more strongly interacting enantiomer targets the major groove (cf. ruthenium(II) complexes, Section II.E.l below) and induces dramatic tightening of the DNA coil (118). 

Square-planar metallo(diimine)(dithiolene) complexes generally display intense, solvatochromatic absorptions in the visible region of the spectrum that are not found in the corresponding metallo-bis(dithiolene) or metallo-bis (diimine) complexes. Futhermore, the LLCT transition energy does not vary appreciably as a function of the metal ion. Extended Hiickel calculations on Ni, Pt, and Zn metallo(diimine)(dithiolene) complexes indicate that the HOMO is comprised almost entirely of dithiolene orbital character (Figure 2), while the LUMO was found to possess essentially all diimine n orbital character (112, 252, 268). In stark contrast to the spectra of square-planar Ni and Pt metallo (diimine)(dithiolene) complexes, the psuedo-tetrahedral complexes of Zn possess extremely weak LLCT transitions. Now, it is of interest to discuss the differences in LLCT intensity as a function of geometry from a MO point of view. This discussion should help to explain important orientation-dependent differences in photoinduced electron delocalization and charge separation. 

These complexes are redox active. The two one-electron reductions resemble more closely the reduction of the corresponding bis(diimine) complex than those of the corresponding bis(dithiolene) complex. The redox potentials are more sensitive to diimine ligand variation than to dithiolene variation. One-electron oxidation is relatively insensitive to diimine ligand variation. However, the dependence of one-electron oxidation on dithiolene variation has not been assessed directly due to the limited amount of data available on the oxidation of the corresponding dithiolene complexes. It has been proposed that the LUMO of the neutral mixed-dithiolene diimine complexes possesses more diimine than dithiolene character and that the HOMO is mainly metal d orbital in nature (52). 

Ligand oxygenation (112 -> 113) of Fe11 complexes of bis(/ -diimine) macrocycles by molecular oxygen has also been observed. Again, an Feni-mediated radical mechanism has been suggested for this oxidation.397... 

The tris(diimine)Ru(II) complexes are potential mediators in the conversion of solar energy to chemical energy via electron-transfer mechanisms (see 13.4). Their spectra display intense visible-range absorption bands and the relative long lifetimes of the lowest-energy ES, MLCT in character, allow efficient bimolecular energy and electron-transfer processes in solution. The photolability of certain bis(diimine)Ru(II) complexes is of synthetic utility ... 

The preparation of ruthenium bis(diimine)sulfoxide complexes by reaction of cis-[Ru(bipyridine)2(Cl)2] (165) with enantiomerically pure chiral sulfoxides 166 was described by Ait-Haddou [94] as a new concept in the preparation of optically active octahedral ruthenium complexes (Scheme 5.47). The reaction produces two dia-stereomeric complexes 167 and 168 and the microwave-irradiated reactions resulted in excellent yields and high reaction rates with a notable increase in the observed diastereomeric excess. 

Ligand oxygenation (112 113) of Fe complexes of bis(/ -diimine) macrocycles by molecular... 

Whereas the substitutions discussed so far concern replacement of diimine ligands, substitution at iron(II) in the bis(diimine) 11 (R = p-C6H4Me) complex [FeL(MeCN)2] in acetonitrile solution involves... 

Bis(diimine) complexes of the type [Fe(phen)2Cl2] solvolyze very quickly in aqueous solution, but are stable in the solid state and in at least some aprotic... 

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