Self-Assembly, Chiroptical Properties, and Host−Guest Chemistry of Chiral Pt−Pt and Pt−Pd Tetranuclear Macrocycles. Circular Dichroism Studies on Neutral Guest Inclusion Phenomena

Abstract

The synthesis, characterization, and circular dichroism (CD) spectra of optically active mixed, neutral-charged Pt/Pt and Pt/Pd macrocyclic complexes are described as well as the CD spectra of their corresponding precursors. Interaction between the chiral monomers (R(−)-DIOP or S(+)-DIOP) of cis-Pt(DIOP)(4-ethynylpyridine)2 and the bistriflates of chiral (R(+)-BINAP or S(−)BINAP)) Pt(II) or Pd(II) bisphosphines or cis-Pd(PEt3)2(OSO2CF3)2, in CH2Cl2 at room temperature results in the formation of cyclic, chiral molecular squares in 84−99% yields via self-assembly. CD studies and optical rotation of the chiral macrocycles and their corresponding precursors reveal that the chiroptical properties are mainly determined by the BINAP moiety. The host−guest chemistry of the chiral 4-ethynylpyridine tetramers with silver triflate and the capture of neutral guests via the resulting square Lewis acid/base receptors have been monitored by CD.