Chiral dinuclear metal complex

O. Picazo et al., Bonding properties related with chiral discrimination in dinuclear metal complexes of group 10. Eur. J. Inorg. Chem. 2, 324-332 (2007)... 

Serrano and co-workers have reported the synthesis of two interesting series of chiral, hexacatenar metal complexes, that is, mono- and dinuclear, derived from chiral oxazoline-based ligands.None of the pure dinuclear compounds (136 X = OAc, Cl) was mesomorphic and most were room-temperature oils or glassy materials. This is likely due to the sterically demanding central chiral unit preventing molecular stacking and, hence, mesophase formation. 

The ophcally active Pd complex with a chiral allenyl ligand undergoes epimer-izahon in the presence of a catalytic amount of Pd(0) complex. This reaction does not involve the isomerization to the propargyl complex, but takes place via a dinuclear intermediate as depicted in Scheme 5.39. The -allenyl ligand in the dinuclear palladium intermediate may racemize via a vinyl-vinyidene intermediate. This type of reaction is prohahly involved in a kinetic resolution of racemic propargyl alcohols promoted hy chiral transihon metal complex [203]. The intermolecular allyl ligand transfer from Pd to Ee complexes occurs under... 

ABSTRACT. In this chapter several approaches to achieve assembly of mono- and dinuclear metal complexes, which can be considered structural and ftinctional models for metalloenzymes, are described. The emphasis lies on oxidation chemistry, summarizing O2 binding, hydroxylation, demethylation, dehalogenation and dehydrogenation. Furthermore self-assembly of chiral mono- and dinuclear complexes is illustrated. 

The formation of circular or linear forms seems to depend on balances between kinetic and thermodynamic control iron(II)-poly-2,2 -diimine systems with their substitutionally inert metal centers provide useful systems for disentangling thermodynamic and kinetic contributions. The mechanism of formation of circular helicates is believed to entail a kinetically favored triple helicate intermediate. Self-assembly of chiral dinuclear binaphthol-linked iron(III) porphyrin complexes into extended polynuclear species takes place through the intermediacy of fi-oxo dimers. Predetermined //-oxo-di-iron-dimers may be used in this type of synthesis. 

We list in Table 2 a few of the systems that have been reported in the recent literature to show metal complexes supported on amorphous, non-porous oxides. We also include a few recent reports on the decorating of mesoporous supports with metal complexes. Complexes have also been introduced into porous, crystalline oxides as well as placed on organic supports." We reported the use of metal complexes as templates for forming familiar crystalline solids and new crystalline materials, some of them adopting the chirality of the metal complex. " Preparations have appeared recently using dinuclear Pd(II) complexes [Pd2Me2Cl2(dppm)2] as the precursor and these were reacted with a silica surface to produce the grafted dinuclear Pd complex with the elimination of methane from the complex. ... 

Doye s group [81] showed that a dinuclear titanium-sulfonamidate complex (Scheme 21), with a tetrahedral sulfur in the ligand backbone, can be used for intermo-lecular hydroaminoalkylation as well. This system gives mixtures of branched and linear products, although to date there has been no mechanistic rationale provided for the reduced regioselectivity of group 4 metal complexes in this transformation. There has been one report by Zi s group [44] that describes axially chiral bis(sulfonamidate) tantalum and niobium complexes for application as precatalysts for hydroamination and hydroaminoalkylation. Unfortunately, these complexes did not show any reactivity for either of these reactions. 

The two or three bis(chelate) ligands that are coordinated to the metal centre may in fact be equivalent, it is the actual geometry of the whole stmcture, resembling a three-bladed propeller, which determines the chiral character of the molecule. In the area of helical chirality, other types of chiral complexes have been described, in particular the two-bladed dinuclear acetylenic complexes (2.18)(BF4)2 which represent a rare example in organometallic chemistry (Figure 2.26). ... 

The role of stoichiometric amount of zinc compounds in the aldol reaction was studied 30 years ago (107). The first study of asymmetric zinc-catalyzed aldol reaction was carried out by Mukaiyama and co-workers the chiral zinc catalyst was prepared from diethylzinc and chiral sulfonamides and was effective in the reaction of ketene silyl ethers with aldehydes (108). Among the subsequent studies on zinc-catalyzed aldol reactions, Trost s group gave important contribution to zinc/prophenol ligand complexes (109,110). The chiral dinuclear zinc catalyst promotes the direct aldol reaction of ketones, including a-hydroxyketones, and aldehydes with excellent enantioselectivity (Scheme 17). It is proposed that one zinc metal coordinated different substrates to form zinc enolate, and another zinc metal center provided the bridge between the interaction of donor and acceptor. 

Transition metals complexes of tartaric acid have been the subject of research in all the main areas of practical applications of chirality biochanistry and medicinal chan-istry [1], asymmetric catalysis [2-4], and chiral separations [5-9]. It is not surprising that the rapid development of the chemistry of vanadium in recent decades smoothly covered all of these areas by itself. The main attention has been devoted to the insulin-mimetic activity of vanadium complexes of tartaric acid [10,11]. Chirality of some insu-linomimetic dinuclear vanadyl(IV)-tartrate complexes has been considered as well, resulting in an interesting finding that both the complexes of naturally occurring L-tartaric acid and racemic tartaric acid are highly active [12]. 

Novel chiral Robson-type tetraimine macrocyclic complexes with Co(II), Co(III), Mn(II), and Mn(III) have been synthesized by metal template condensation of 2,6-diformyl-4-methylphenol with (l/f,2/f)-diaminocyclohexane or (lR,2R)-diphenyl-ethylenediamine. The dinuclear Co(II) and Co(III) complexes were shown to catalyse asymmetric cyclopropanation of styrene with diazoacetate cooperatively and with high enantioselectivity.118... 

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