Homobimetallic complexes

Belokon et al.83 have investigated the formation of the homo-and bimetallic titanium complexes with di-Schiff base ligands, by means of FT NMR spectroscopy. The ligands have been shown to adapt the ds-p configuration in titanium (IV) complexes. Analysis of the 1H NMR spectra has allowed determination of the population of the homobimetallic complexes derived from two different Ti(IV) complexes [34],... 

Trost et al. [11] reported another impressive example of bimetallic catalysts in which a Zn-Zn homobimetallic complex (17, Scheme 7) serves as an effective catalyst for direct aldol reactions [11-13]. The proposed structure of the catalyst was verified by mass spectrometry and the best ratio of Et2Zn and the ligand. The chemical yield was moderate in the reaction of methyl ketones (1) (Scheme 7, top) [11,12], but a highly atom-economic system was achieved when a-hydroxylated ketones (10) were used as a substrate (Scheme 7, bottom) [13]. Excellent diastereo- and enantioselectivity were obtained under mild conditions. In contrast to the case of Shibasaki s heteropolymetallic catalyst, syn-1,2-diols (syn-11) were obtained as the major diastereomers. 

Metal(II) species, homobimetallic complexes - During a rhodium insertion into H2(TPP) using [Rh(CO)2Cl]2 in HOAc/NaOAc, a paramagnetic rhodium(II) porphyrin was observed [57] which could be transformed into a hydridorho-dium(III) porphyrin with dihydrogen (path — p) and subsequently into its corresponding base, the anion [Rh(TPP)], which may be likewise regarded as... 

Bimetallic alkenes, with platinum heterobimetallic complexes, 8, 637 homobimetallic complexes, 8, 635 Bimetallic complexes... 

Polymetallic alkynes, with platinum heterobimetallic derivatives, 8, 647 homobimetallic complexes, 8, 645 polymetallic derivatives, 8, 648 Polymetallic cyclopentadienyl iridium complexes, preparation and characteristics, 7, 370... 

FIGURE 29. Some examples of homobimetallic complexes with p-CNR ligands. 

This type of reaction sometimes leads to formation of homobimetallic complexes. 

A triazole ligand, (28), leads to asymmetric coordination modes, giving inequivalent metal centers in homobimetallic complexes.94 Complexes of Ru,Os exhibit efficient energy transfer mediated by the triazole ring. Benzimidazole-based bridging ligands like 2,2 -bibenzimidazolate... 

Homobimetallic complexes of H4(DPX) and H4(DPD) are easily prepared by direct reaction of the free-base Pacman assemblies with the appropriate metal salts (Fig. 2) (79). The coordination chemistry of both H4(DPX) and H4(DPD)... 

Bridged homobimetallic complexes as models of dimetal active centers. ... 

Hydrides are one of the most commonly found bridging ligands in iridium homobimetallic complexes. The symmetry or asymmetry of the hydride bridge is usually determined by the nature of the trans-ligands in both metal centers. For example, the complexes depicted in Fig. 1 feature asymmetric hydride bridges in solution and in the solid state. Although the position of the bridging hydrides obtained from X-ray diffraction must be examined with care due to the limited accuracy of the technique for these situations, this assumption has been also supported by NMR studies in solution [63, 64]. 

In an early study (Dessy et at., 1966), reduction of homobimetallic complexes at a mercury electrode was used to generate the corresponding mononuclear anions in. situ as exemplified in (8). Although the reaction... 

Of the Group 8 homobimetallic complexes, those of diruthenium are the most numerous, perhaps because of their stability. Diruthenium complexes have many interesting electronic and redox properties. They can have multiple bonds, and they can be low or intermediate spin. Moreover, the spin states can be explained by the application of simple ligand field theory. Diruthenium complexes have been isolated in several redox states. Typically, oxidation state changes result in minimal reorganization of the diruthenium core, and hence, many of these complexes can transfer multiple electrons readily, albeit one at a time. 

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