Diamines, chelating-type

In a parallel study, it was found that chelating chiral diamines 208 or 209 are well suited as ligands to promote Kumada-type couplings of primary and secondary alkyl halides 202 with aryl Grignard reagents 203 (entry 4) [281]. This reaction was applicable to alkyl bromides and alkyl iodides, while alkyl chlorides gave only low yields. Acetal and ester functions are tolerated. A notable feature is the stereoretentive arylation of fra s-a-bromo acetals with excellent diastereo-selectivity. The involvement of radicals is supported by the stereoconvergent formation of cxo-phenvI norbornane from both endo- or exo-bromonorbomane (cf. Part 1, Fig. 9) and radical 5-exo cyclizations (see below). 

Based on the consideration that suitable ligand should be able to coordinate to the divalent tin metal center of the intermediate enolate, which has a vacant d orbital, the achiral, chelate-type asymmetric reaction was examined employing the diamines 1 s-z as chiral auxiliaries. 

Within the tris-chelate type of chiral coordination compound, the most extensively studied are the series of diamine chelates of cobalt(III), containing the octahedral [Cot )N6] cluster. The principal d—d transition of interest for the optical activity of these complexes is the Aj -> Tj octahedral excitation near 465 nm (Fig. 2), made up of the three single-orbital promotions, dxy dx -y , and the analogues obtained by the cyclic permutations of the electronic coordinates. The leading moments of the one-electron transition, dxy - , are the z-component of a magnetic dipole... 

A number of substituted propane-l,3-diamine (64) compounds of the type [PtL2] and [PtX2L2] (X = Cl, Br, or NH3) have been described. Several of the latter species exhibited polymorphism which was attributed to either different H-bonded linkages or different chelate ring conformations in the two forms.In solution their n.m.r. spectra are consistent with a preference for a chair-type conformation with the Cl or OH axial.Similar n.m.r. spectral studies have also been reported for some related N-methyl substituted... 

Simple macrocyclic quadridentate complexes can be synthesized by template reactions from ethers derived from salicylaldehyde and diamines in the presence of appropriate metal ions such as nickel(II) (equation 3).35>36 However, these reactions can also be carried out quite effectively in the absence of metal ions to yield the free ligands, which can be obtained by hydrolysis of the complexes. An iron(II) macrocyclic quinquedentate chelate of this type has been produced by template synthesis (equation 4).37... 

The diamine ligands of the type 587 have considerable importance for the formation (3.26) of chelates with metal-cycles of different size 588 ... 

For complexes with bidentate 1,2-diamines only one type of chelate ring conformation could be ascertained. The six-membered chelate rings of 1,3-diamines may exist in a chair 6a, skew boat 6b or boat 6c conformation. The least stable of the three types is 6c and was not taken into account so far. When the chelate ring carries... 

The lithium derivative of the chiral chelating diamine (3 )-2-(l-pyrrolidinylmethyl)-pyrrolidine (6) has been used extensively in stereoselective synthesis, i.e. in the deprotonation of ketones and rearrangement of epoxides to homoallylic alcohols. The lithium amide has been crystallized from toluene solution, and X-ray analysis revealed that it forms a ladder-type tetramer with the two pyrrolidine nitrogens solvating the two lithiums at the end of the ladder38, (Li-6)4. 

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