Diamine ligand

Table 3.1 summarises the influence of the diamine ligands on the equilibrium constant for binding of 3.8c to the ligand-metal ion complex (K ) and the second-order rate constant for reaction of the ternary complex (ICjat) (Scheme 3.5) with diene 3.9. 

In summary, for the most active of catalysts, the copper(II) ion, the diamine ligands that were investigated seriously hamper catalysis mainly by decreasing the efficiency of coordination of the dienophile. With exception of the somewhat deviant behaviour of N,N -dimethylethylenediamine, this conclusion also applies to catalysis by Ni" ions. Hence, significant ligand-accelerated catalysis using the diamine ligands appears not to be feasible. 

NMR signals of the amino acid ligand that are induced by the ring current of the diamine ligand" ". From the temperature dependence of the stability constants of a number of ternary palladium complexes involving dipeptides and aromatic amines, the arene - arene interaction enthalpies and entropies have been determined" ". It turned out that the interaction is generally enthalpy-driven and counteracted by entropy. Yamauchi et al. hold a charge transfer interaction responsible for this effect. 

In recent years, enantioselective variants of the above transannular C-H insertions have been extensively stiidied. The enantiodetermining step involves discrimination between the enantiotopic protons of a meso-epoxide by a homochiral base, typically an organolithium in combination with a chiral diamine ligand, to generate a chiral nonracemic lithiated epoxide (e.g., 26 Scheme 5.8). Hodgson... 

Hodgson and coworkers have demonstrated that the use of diamine ligands in combination with s-BuLi allows the direct deprotonation/electrophile trapping of... 

There is one report of a chiral reagent based on allylaluminum chemistry1 2 3 4 5 10. Bis(2-methyl-propyl)-2-propenylaluminum is treated with tin(II) triflate and chiral diamine ligand 4 to give a reagent, presumably a chiral allyltin species, that reacts with aldehydes at — 78 "C. Good enantioselectivity (80 -84% ee) is obtained with aromatic aldehydes, but with aliphatic aldehydes the selectivity is somewhat lower (53-64%)10. 

Carbene gold(III) with diamine ligand can coordinate a second metallic center, since the N -ligand contains a free N H 2 group and can react with a new gold isocyanide under the formation of double dinuclear carbenes [46] (32). 

Other tetradentate thiophene diamine ligands have been previously involved in the palladium-catalysed test reaction by Kim et al., in 2004. Prepared from (i ,i )-l,2-diaminocyclohexane, these ligands were proved to be very efficient in terms of enantioselectivity in this reaction since an enantioselectivity of up to 98% ee was observed when the ligand/palladium ratio was 4/1 (Scheme 1.61). 

Scheme 1.61 Test reaction with thiophene diamine ligands.

It was independently found by two groups that the exo-diol derived from bis(camphorsulfonyl)-substituted tra .s-cyclohexane-1,2-diamine ligand (HOCSAC) was an excellent promoter for the enantioselective addition of dialkyIzinc reagents to any type of ketones, even dialkyl ketones, in the presence of Ti(Oi-Pr)4. As shown in Scheme 4.11, excellent enantioselectivities of up to 99% ee were obtained in these conditions in combination with high yields and with a low catalyst loading of 2-10 mol%. 

In order to improve the performance of Noyori s catalytic system, Ru(II)-TsDPEN, which is very efficient but suffers from a long reaction time and a low activity in some cases, Mohar et al. have modified the diamine ligand by... 

Scheme 9.18 Ru-catalysed reductions of ketones with (r 6-arene)-Af-perfluorosulfonyl-1,2-diamine and Af-(Af,Af-dialkylamino)sulfamoyl-l,2-diamine ligands.

In 1991, Kobayashi el al. prepared novel chiral S/N ligands for the tin-mediated aldol reaction of silyl enol ethers with aldehydes. As an example, the reaction of benzaldehyde afforded the expected syn aldol product as the major product with a good yield and an enantioselectivity of up to 92% ee (Scheme 10.26). Moreover, other aldehydes such as substituted benzaldehydes or aliphatic unsaturated aldehydes were converted into their corresponding aldol products with enantioselectivities of more than 90% ee. It was checked that the corresponding diamine ligands provided less active complexes for the same reactions. 

For reduction of monofunctional ketones, the most effective catalysts include diamine ligands. The diamine catalysts exhibit strong selectivity for carbonyl groups over carbon-carbon double and triple bonds. These catalysts have a preference for equatorial approach in the reduction of cyclohexanones and for steric approach control in the reduction of acyclic ketones.51... 

Related catalysts include both a chiral BINAP-type phosphine and a chiral diamine ligand. A wide range of aryl ketones gave more than 95% enantioselectivity when substituted-l,l -binaphthyl and ethylene diamines were used.52... 

Scheme 6.7 shows some other examples of enantioselective catalysts. Entry 1 illustrates the use of a Co(III) complex, with the chirality derived from the diamine ligand. Entry 2 is a silver-catalyzed cycloaddition involving generation of an azome-thine ylide. The ferrocenylphosphine groups provide a chiral environment by coordination of the catalytic Ag+ ion. Entries 3 and 4 show typical Lewis acid catalysts in reactions in which nitrones are the electrophilic component. 

More recently, asymmetric Mannich-type reactions have been studied in aqueous conditions. Barbas and co-worker reported a direct amino acid catalyzed asymmetric aldol and Mannich-type reactions that can tolerate small amounts of water (<4 vol%).53 Kobayashi found that a diastereo- and enantioselective Mannich-type reaction of a hydrazono ester with silyl enol ethers in aqueous media has been successfully achieved with ZnF2, a chiral diamine ligand, and trifluoromethanesul-fonic acid (Eq. 11.31).54 The diastereoselective Mannich-type reaction... 

Hultgren, V. M. Atkinson, I. M. Beddoes, R. L. Collison, D. Garner, C. D. Helliwell, M. Lindoy, L. F. Tasker, P. A. Formation of folded complexes retaining intramolecular H-bonding in the extraction of nickel(II) by phenolic oxime and aliphatic diamine ligands. Chem. Commun. 2001, 573-574. 

The 1,2-diol is liberated easily from cyclic osmate ester by either reductive or oxidative hydrolysis.213 Importantly, the ligand acceleration has been utilized extensively for the production of chiral 1,2-diols from (achiral) olefins using optically active amine bases (such as L = dihydroquinidine, dihydroquinine and various chiral diamine ligands).215... 

In 1996, Noyori and co-workers discovered that Ru(II) ri-arene complexes containing either a chiral 1,2-amino alcohol such as in 41 or a chiral N-monotosylated 1,2-diamine ligand, see 42, serve as excellent catalysts. It was a breakthrough for catalytic ATH reactions to ketones in terms of enantioselectivities, catalyst loading and... 

To improve the rate of reduction the amino alcohol ligand of the ruthenium complexes was exchanged for monotosylated 1,2-diamine ligands. For exploratory experiments AT-tosylethane-1,2-diamine was prepared hy monotosylation of ethane-1,2-diamine and attached to the primary face of P-CD yielding 80. With P-CD as the only chiral unit the ruthenium complex of 80 could reduce aromatic and aliphatic standard ketones 63 and 69 in 91% 5deld, 25% ee (S) and 68% 5deld, 58% ee, respectively, within only 4h under standard conditions (Fig. 24). 

Asymmetric C=0 hydrogenations in water were also reported by Lemaire et al. This catalytic system is based on Ir(cod)L complexes, where L is a hydrophilic chiral C2-symmetric diamine ligand such as p-substituted (IR 2R)-(-i-)-l,2-diphenylethylenediamine derivatives (29a-e Scheme 4.12). The use of such ligands allowed catalyst recovery without loss of activity and enantioselectivity in at least four acetophenone hydrogenation cycles [29]. The ee-values observed in the reduction of phenyl glyoxylate in the water phase were, however, lower than were found when running the tests in THF (Table 4.3), when the substituents were H and Me, and about the same with OH, OMe and 0-(C2H40)3Me. 

Gabrielsson et al. reported the aerobic oxidation of alcohols catalyzed by a cationic Cp Ir complexes bearing diamine ligands such as bipyrimidine 10 (Scheme 5.8) [35], the mechanism of which is closely related to the Oppenauer-type oxidation mentioned above. In this reaction, the deprotonation of Ir hydrido species to afford Ir species, and the reoxidation of Ir to Ir by O2, are crucial. 

Ikariya and Noyori et al. also reported the synthesis of new chiral Cp Rh and Cp Ir complexes (13 and 14) bearing chiral diamine ligands [(R,R)-TsCYDN and (R,R)-TsDPEN] (Scheme 5.10) these are isoelectronic with the chiral Ru complex mentioned above, and may be used as effective catalysts in the asymmetric transfer hydrogenation of aromatic ketones [42], The Cp Ir hydride complex [Cp IrH(R,R)-Tscydn] (14c) and 5-coordinated amide complex (14d), both of which would have an important role as catalytic intermediates, were also successfully prepared. 

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