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

The synthesis and characterization of various optically active nanoscale-size tetranuclear assemblies held together by coordination bonds is described. Interaction of bis4-(4‘-pyridyl)phenyliodonium triflate and bistriflates of chiral transition metal (Pd(II) or Pt(II)) bisphosphines resulted in the formation of chiral hybrid iodonium-transition metal molecular squares. Restricted rotation of the coordinated bis4-(4‘-pyridyl)phenyliodonium moiety was detected in these squares and investigated by using variable-temperature NMR. The preparation of chiral hybrid squares which possess the elements of helicity (twist) in the assembly was accomplished using the above bisphosphines and bis(3-pyridyl)iodonium triflate. Interaction between the bistriflates of chiral (R(+)-BINAP or S(−)-BINAP)) transition metal (Pd(II) or Pt(II)) bisphosphines and a diaza ligand with C2h symmetry, 2,6-diazaanthracene (DAA) or 2,6-diazaanthracene-9,10-dione (DAAD), in acetone at ambient temperature results in chirality-directed assembly of a single stable diastereomer or highly enriched diastereomeric mixtures of optically active macrocyclic molecular squares. The stereochemical outcome of such self-assembly at the full combinatorial level was investigated as well by the use of achiral Pd(II) or Pt(II) bisphosphine complexes.