Chiral iodonium-transition metal

Oenyuk, B., Whiteford, J.A. and Stang, P.J. (1996) Design and study of synthetic chiral nanoscopic assemblies. Preparation and characterization of optically active hybrid, iodonium-transition-metal and all-transition-metal macrocyclic molecular squares. J. Am. Chem. Soc., 118 (35), 8221-8230. 

Stang and coworkers have also reported the synthesis of the related mixed iodonium-transition metal squares 189-192 [74]. Unlike the previous examples, the pyridyl ligands used possess rotational symmetry and thus, the squares 189-192 are chiral solely due to the presence of the chiral (R)-BINAP ligands. 

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. 

When the reactive chiral building unit [M(/ -(+)-BINAP)(H20)][0Tf]2 with M = Pd (5.84) or M = Pt (5.85) was treated with the bridging ligand bis [4-(4 -pyridyl)phenyl) iodonium triflate (57), the related chiral hybrid supramolecular squares were formed (5.86-5.87) (hybrid = presence of iodonium and transition metal comers in the assembly). These hybrid molecular squares are optically active due to the chiral transition metal auxiliary (BINAP) in the assembly. Interestingly chiral induction was observed in these metallo-macrocycles since the preferred diastereomer in each preparation was formed in excess compared with the other isomers (Figure 5.34). ... 

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