Transition metal complex systems, binuclear

Equally strong interactions do not necessarily have to exist in square planar binuclear complexes, a problem that is of great concern to us. There is very little information in the literature about the synthesis or properties of such materials. Possibly planar binuclear systems are the ethanetetraaldehyde-bridged nickel aminotroponeiminato complexes, 2, reported by Trofimenko (26). The preparation of the bisimidazole complexes 3 was described (27) of which the tetracarbonyl derivatives might well be the very first example of completely planar binuclear transition metal compounds that are capable of extended interactions. 

Some representative co-facial systems. The series (138)—(140) of mixed thiaaza donor ligands have been synthesized and all three have been shown to form binuclear complexes with transition metal ions (Lehn, 1980). In these, each metal ion is associated with one cyclic subunit as shown in (141) for (138). Complexes containing two Cu(n) ions or two Cu(i) ions have been obtained with each of (138)-(140) while (139), the... 

Fujita et al. used a catalytic amount of a binuclear titanium(IV) complex in an attempt to find an efficient system to oxidize sulfides with high enantioselectivity [102]. Prior to this study, they investigated other systems with several transition metals. A similar asymmetric sulfoxidation was discovered [105] using a catalytic amount of nonracemic Schiff base oxovanadium complex (Table 1.4) under atmospheric conditions at room temperature in dichloromethane. With 0.1 mol% of catalyst and cumene hydroperoxide as oxidant, oxidation produces sulfoxides in excellent yields. However, the reaction is limited to alkyl aryl sulfide substrates, and the best enantioselectivity obtained was 40% ee, for (S)-methyl p-methoxy phenyl sulfoxide. 

The transitions of type (c) are defined by two transition temperatures, one for decreasing (Ti/2j), and one for increasing temperature (Ti/2 ). Two-step transitions (Fig. Id), first reported in 1981 for an iron(III) complex of 2-bromo-salicylaldehyde-thiosemicarbazone [21], are relatively rare and have their origins in several sources. The most obvious is the presence of two lattice sites for the complex molecules. There are several examples of this [22]. In addition, binuclear systems can give rise to this effect, even when the environment of each metal atom is the same—in this instance the... 

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