Catalytic system dinuclear

A breakthrough was reported by Stack and co-workers in 1998 (212) who reported the first biomimetic catalytic system for the oxidation of primary alcohols by air. Independently, in the same year Chaudhuri, et al. (216) reported efficient aerobic oxidation of primary and secondary alcohols by the dinuclear catalyst [Cu2 2(Ls )2]C12 (216). Next, we will briefly review the salient features of these two systems. 

As pointed out by several mechanistic studies, a binary or a dinuclear catalytic system is likely needed for CCVepoxide copolymerization with high activities. 

Wieghardtis group have described two generations of their catalytic system, both of which will oxidise some saturated as well asP -unsaturated alcohols. The first of these is an isolable dinuclear his-phenoxyl complex [III] (Figure 8) whieh retains its strueture in solution and is the active oxidation catalyst (Chaudhuri et al., 1998). The second generation catalyst IV, (Figure 9), however, forms a mononuelear phenoxyl eomplex upon oxida-... 

The Trost group has developed an efficient ProPhenol dinuclear zinc catalytic system, which is used in many reactions. Recendy, they expanded the... 

Fig. 6 (a) A homogeneous catalytic system containing exactly two independent unicyclic mechanisms for hydroformylation of a symmetric alkene. X, Y, Z are organometallic present which do not participate in a catalytic mechanism and do not interact with any intermediates. They are just spectator species, (b) The system after addition of a chelated dinuclear rhodium complex which also performs hydroformylation... 

Chiral amines have been conveniently prepared also by asymmetric reductive amination of ketones using iridium catalysts and intriguing results with up to 96% ee have been obtained by Zhang and co-workers employing a catalytic system based on Ir./-binaphane in the presence of Ti(OPr )4 and iodine (Scheme 61). Water-soluble aquo complexes [Cp lr(H20)3](0Tf)2 494, [CpP Ir(H20)2](0Tf)2 504, and [Cp Ir(bpy)(H20)](0Tf)2 505 have been used to catalyze the reductive amination of hydrosoluble aldehydes and ketones as well as the dehalogenation of alkyl halides. The activity is markedly pH dependent and inactivation of the catalyst takes place reversibly on increasing the solution basicity due to Ir(H20), deprotonation and formation of mono- or dinuclear hydroxo complexes which are catalytically inactive. The structure of one of these compounds, [Cp Ir(bpy)(OH)]OTf 506, which reversibly forms from 494 around pH 6.6, is presented in Figure 42. 

Other metals can also be used as a catalytic species. For example, Feringa and coworkers <96TET3521> have reported on the epoxidation of unfunctionalized alkenes using dinuclear nickel(II) catalysts (i.e., 16). These slightly distorted square planar complexes show activity in biphasic systems with either sodium hypochlorite or t-butyl hydroperoxide as a terminal oxidant. No enantioselectivity is observed under these conditions, supporting the idea that radical processes are operative. In the case of hypochlorite, Feringa proposed the intermediacy of hypochlorite radical as the active species, which is generated in a catalytic cycle (Scheme 1). 

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