Diamines bidentate

Amino-77/-dibenz[/),t/]azepin-7-ones, e.g. 7, prepared either by successive bromination, aminodebromination, and dehydrogenation of 5-tosyl-5A/-dihydro 7>,t/]azepin-7(6//)-ones, or by the oxidation of 6-ethoxy-6,7-dihydro-5//-dibenz 7>,r/]azepincs with lead(IV) acetate followed by aminodemethoxylation, on treatment with a bidentate nucleophile (e.g.. benzene-1,2-diamine or 2-aminobenzenethiol) yield the pentacyclic systems 8 and 9, respectively.27... 

Bidentate binding of two Lewis acidic boron centers to one methoxide anion was first reported in 1967 [241]. Further examples did not appear until 1985 [242]. Today, other bis(boronates) like 152 and 154-158 (Fig. 41) are known that can be applied to the selective complexation of amines and diamines [243-247]. 

In 1997 the first asymmetric aza-Claisen rearrangement was reported by Overman et al. [55], which made use of diamines as bidentate ligands for Pd(II), allowing for moderate enantioselectivities. In the same year, Hollis and Overman described the application of the planar chiral ferrocenyl palladacycle 38 as a catalyst for the enantioselective aza-Claisen rearrangement of benzimidates 39 (Fig. 19) [56]. A related ferrocenyl imine palladacycle provided slightly inferior results, while a benzylamine palladacycle lacking the element of planar chirality was not able to provide any enantioselectivity [57]. 

On the other hand, the enantioselective 1,4-addition of carbanions such as enolates to linear enones is an interesting challenge, since relatively few efficient methods exist for these transformations. The Michael reaction of p-dicarbonyl compounds with a,p-unsaturated ketones can be catalysed by a number of transition-metal compounds. The asymmetric version of this reaction has been performed using chiral diol, diamine, and diphosphine ligands. In the past few years, bidentate and polydentate thioethers have begun to be considered as chiral ligands for this reaction. As an example, Christoffers et al. have developed the synthesis of several S/O-bidentate and S/O/S-tridentate thioether... 

It has been found that a number of bidentate ligands greatly expand the scope of copper catalysis. Copper(I) iodide used in conjunction with a chelating diamine is a good catalyst for amidation of aryl bromides. Of several diamines that were examined, rra s-yV,yV -dimethylcyclohexane-l,2-diamine was among the best. These conditions are applicable to aryl bromides and iodides with either ERG or EWG substituents, as well as to relatively hindered halides. The nucleophiles that are reactive under these conditions include acyclic and cyclic amides.149... 

In catalytic enantioselective Diels-Alder reactions, Mg11 catalysts bearing chiral auxiliaries, such as chiral bidentate ligands containing oxazoline moieties,27-29 chiral diamines,30 and... 

Ligands for catalytic Mukaiyama aldol addition have primarily included bidentate chelates derived from optically active diols,26 diamines,27 amino acid derivatives,28 and tartrates.29 Enantioselective reactions induced by chiral Ti(IY) complex have proved to be one of the most powerful stereoselective transformations for synthetic chemists. The catalytic asymmetric aldol reaction introduced by Mukaiyama is discussed in Section 3.4.1. 

Several other enantiomeric ally pure bidentate ligands have been screened using [Ir (cod)Cl]2, including bis-oxazolines [48,49], amino oxazolines [50],Ai-heterocyclic carbenes [51], and diamines [52, 53]. Examples where the enantioselectivity was in excess of 90% ee include the use of ligands 45,46, and 47 [54-56]. Selected examples of the use of these ligands with [Ir(cod)Cl]2 are given in Scheme 12 for the reduction of ketones 48, 50, and 52. 

It has been tacitally assumed in this discussion that the second-order formation rate constants measure the simple water substitution process. Although this must apply when unidentate ligands replace coordinated water, a composite process could describe the replacement by multidentate ligands. However, consideration of rate constants for successive formation and dissociation processes suggests that the overall rate of complex formation with flexible bidentate (and probably multidentate) ligands such as diamines, dipyridyl, glycine is probably determined by the rate of expulsion of the first water molecule from the metal aqua ion (56, 80, cf. 3 and 84). 

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