Synthesis, Characterization, and Properties of Half-Sandwich Iridium/Rhodium-Based Metallarectangles

Tetranuclear half-sandwich iridium
or rhodium complexes were obtained
in good yields from the reactions of the binuclear half-sandwich metal
precursors [Cp*2M2(μ-CA)]­Cl2 (1a, M = Ir; 1b, M = Rh; CA = chloranilate)
or [Cp*2M2(μ-DHNA)]­Cl2 (2a, M = Ir; 2b, M = Rh; H2DHNA =
6,11-dihydroxynaphthacene-5,12-dione) with diPyNI (diPyNI = N,N-bis­(4-pyridyl)-1,4,5,8-naphthalene­tetra­carboxydiimide)
in the presence of AgOTf (OTf = CF3SO3) in CH3OH, respectively. The new metallarectangles have been characterized by elemental analysis,
FT-IR, 1H NMR, electrospray mass spectrometry (ESI-MS),
and UV/vis absorption spectroscopy. The interactions of these metallarectangles
with aromatic molecules, especially pyrene, in solution have been
studied by various NMR techniques (1D, DOSY, and ROESY) and UV–vis
absorption. DOSY measurements suggest that the interactions between
metallarectangle 4a and pyrene are outside of the cavity.
The strong π···π interactions between pyrene
and the naphthalene­tetra­carboxydiimide ring of metallarectangle 4a were further supported by single-crystal X-ray diffraction
data; pyrene molecules are found outside the cavity of the metallarectangle.