Chiral diaza ligand

In conclusion, mention should be made of dendronised chiral salen ligands and their Co2+ and Ni2+ complexes, which were prepared for use as Jacobsen-type catalysts by diaza-Cope rearrangement [24]. However, instead of the meso compounds produced, the enantiomers will have to be synthesised directly in enantioselective manner (Fig. 4.69). 

A chiral bisphosphine such as 2,2 -h -(diphenylphosphino)-l,F-binaphthyl (BINAP) has been extensively used as a chiral chelator in asymmetric catalysis. When Stang et al. reacted the chiral metal complex 42 with 40, they synthesized a square box (Figure 25) and asymmetric induction was observed [79,82] with the formation of an excess of one of the preferred diastereoisomers as measured by NMR spectroscopy. The same reaction has been carried out with 42 and 6is-4-(4 -pyridyl)phenyl)iodonium triflate, but in this case the diaza ligands of the iodonium species possess rotational symmetry about their linkages. Consequently, the optical activity of the molecular squares obtained is due exclusively to the chiral transition metal auxiliary BINAP. 

Nomacemic binaphthol (BINOL) ligands are heavily utilized in asymmetric synthesis. They can be readily fashioned from 2-naphthol precursors employing Cu(I) or Cu(ll) salts. With either an external source of chirality (e.g. 1,5-diaza-cfr-decalin, l),ii or an internal chiral center (e.g. as in the proline-derived amide 2), derivatives substituted at the key 3- and 3 -sites are realized under mild conditions with ee s (see Enantioselectivity) up to 94%. 

Stang extended this approach to prepare chiral supramolecular squares featuring only chiral metal comers. Thus the C2h-symmetrical diaza bridging ligands, 2,6-diazaanthracene (DAA, 59) and 2,6-diazaanthracene-9,10-dione (DAAD, 60) were used (Figure 5.37). ... 

Diaza-cis-decalin, the bicychc analogue of tetramethyl-ethylenedia-mine, shown in Scheme 6.58, is an interesting (chiral) ligand [185, 186]. Is there a problem with the possible bicyclization approach shown ... 

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