Imines coordinated

NMR experiments where undertaken to determine the site of coordination of the two other complexes. The thioether complex showed an upheld shift for the N-atom in the thioether gold complex and a similar result was obtained in the case of the thiazole compound, confirming imine coordination. 

In Sn(II) complexes, the tin atom was located above the di-Schiff base coordination plane, while in Sn(IV) complexes, it was coplanar with the imine coordination framework. The position of the metal was supported by X-ray data. For the compounds studied, the 119Sn chemical shift values varied from 501.4 to —1015.9 ppm. Increase in the coordination number from Sn(II) to Sn(IV) led to an increase in the tin shielding. The differences of up to 3.0 ppm between 5119Sn values for the complexes, being derivatives of R,R and S,S 1,2-diaminocyclohexane, were observed. 

An even more active related catalytic system has recently been reported by Lee s group. This (salen)cobalt(III) catalyst containing the salen ligand depicted in Fig. 12 exhibits a highly unusual coordination mode for the normally tetradentate salen ligand [35]. That is, whereas the f-butyl-substituted phenolate analog displays conventional imine coordination, the salen ligand in Fig. 12 is proposed to be bound... 

Sargeson and his coworkers have developed an area of cobalt(III) coordination chemistry which has enabled the synthesis of complicated multidentate ligands directly around the metal. The basis for all of this chemistry is the high stability of cobalt(III) ammine complexes towards dissociation. Consequently, a coordinated ammonia molecule can be deprotonated with base to produce a coordinated amine anion (or amide anion) which functions as a powerful nucleophile. Such a species can attack carbonyl groups, either in intramolecular or intermolecular processes. Similar reactions can be performed by coordinated primary or secondary amines after deprotonation. The resulting imines coordinated to cobalt(III) show unusually high stability towards hydrolysis, but are reactive towards carbon nucleophiles. While the cobalt(III) ion produces some iminium character, it occupies the normal site of protonation and is attached to the nitrogen atom by a kinetically inert bond, and thus resists hydrolysis. 

In the presence of water-free late transition metalphosphine cation complexes as Lewis acids, glyoxylatetosylamine imine reacted with silicon enolates stereoselectivity [23-26]. It was proposed that imine coordinated to the metal such as Ag(I), Pd(II), and Cu(I) in a bidentate manner [23]. The copper-based catalyst was the most effective, and the desired product was obtained in high yields with high enantioselectivities [(Eq. (4)]. 

The dimeric iron compound proved to be robust both in solution and the soHd state. Although catalyticaUy inactive, the electronic structure of [( PDAl)Fe]2 was of interest Observation of a single Mdssbauer doublet with an isomer shift of 0.84mms i estabhshed equivalent high-spin iron centers. These data, in combination with the distortions to the pincer ligand observed by X-ray diffraction, estabhshed overall two-electron reduction of the chelate, one in the unperturbed portion of the ligand and the other in the q -imine coordinated to the adjacent iron. 

They carried out some experiments in order to clarify the mechanism of the reaction that allowed them to propose the transition state depicted in the Figure 12.7, where the in situ generated imine coordinates to the catalyst in the equatorial position, avoiding the steric repulsion of the ligand. In addition, after coordination of the oxygen atom of the P-component to the metallic center, the active phosphite is formed, which then attacks to the azomethine carbon of the imine by its si face, thus providing the experimentally observed (5)-enantiomer. 

The design of polyether/imines coordinated to cyclopentadienyliron moieties (39) has been achieved via the reaction of a dialdehyde complex of cyclopentadienyliron with a number of aliphatic and aromatic diamines. The polycondensation reactions resulted in the isolation of the polyether/imines in good yields. 

In the initial mechanistic studies of the Ir-catalyzed hydrogenation of imines catalytic cycles involving imine coordination to the metallic center have been considered. - However, in the recent computational study of Hopmann and Bayer it has been shown that in the case of asymmetric hydrogenation with [lr(PHOX)(cod)]+BArF" 9 various catalytic cycles containing coordinated imine are characterized with unreasonably high activation barriers (35-50 kcal/mol). On the other hand, a catalyhc cycle resembling that outlined in 2006 by Oro et al. (Figure 1.30) - has been found kinetically feasible. 

As a result of the second imine coordination occurring much more slowly than the first, the opportunity was afforded to bring about tandem couplings involving imines and additional unsaturated organic molecules. Thus, even though 29... 

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