Macrocycles asymmetric 60°-based ligands

Inversion at the N center is coupled to conformational changes in a chelate ring. The kinetics of inversion at asymmetric N centers in complexes of tetraaza linear or macrocyclic ligands have received scant attention. There are five configurational isomers of the planar complex Ni([14]aneN4) +, Sec. 3.1.1. The interconversions between such structures are base catalyzed with second-order rate constants covering a small range from 1.2 x 10 to 2.4 x 10 M- s- Refs. 108-110. 

As with any modern review of the chemical Hterature, the subject discussed in this chapter touches upon topics that are the focus of related books and articles. For example, there is a well recognized tome on the 1,3-dipolar cycloaddition reaction that is an excellent introduction to the many varieties of this transformation [1]. More specific reviews involving the use of rhodium(II) in carbonyl ylide cycloadditions [2] and intramolecular 1,3-dipolar cycloaddition reactions have also appeared [3, 4]. The use of rhodium for the creation and reaction of carbenes as electrophilic species [5, 6], their use in intramolecular carbenoid reactions [7], and the formation of ylides via the reaction with heteroatoms have also been described [8]. Reviews of rhodium(II) ligand-based chemoselectivity [9], rhodium(11)-mediated macrocyclizations [10], and asymmetric rho-dium(II)-carbene transformations [11, 12] detail the multiple aspects of control and applications that make this such a powerful chemical transformation. In addition to these reviews, several books have appeared since around 1998 describing the catalytic reactions of diazo compounds [13], cycloaddition reactions in organic synthesis [14], and synthetic applications of the 1,3-dipolar cycloaddition [15]. 

Much research have been focused on compartmental SB macrocycles derived from 2,6-diformyl (diacetyl)phenols as head units (see Scheme 19). The coordination chemistry of the phenol-based compartmental ligands was reviewed.2 A series of symmetrical and less extensively asymmetrical macrocycles (having dissimilar lateral chains) have been prepared (Scheme 19). The variation of the lateral chains of the macrocycle gives ligands with different cavity size and flexibility. Thus, the N202 cavity of the ethylenediamine derivative (65a) can accommodate only the small Cu11 and Ni11 ions because it has little flexibility. The replacement of the dimethylene by a trimethylene... 

Sterically more demanding copper(II) chelates based on trans-cyclohexane-1,2-diamine reveal similar condensation chemistry [165]. The yield of macrocyclic products, however, decreases compared to the reaction with ethane-1,2-diamine-containing chelates. The formation of copper(II) complexes of half-capped ligands is favoured compared to capped species for steric reasons. The presence of two asymmetric carbon atoms in the starting ligson allows synthesis of new chiral macrocycles. The most suitable for macrocyclisation has proved to be the R,R S,S bis(cyclohexane-l,2-diamine)copper(II). The three isomers of H2LI36 possible... 

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