Dinuclear Pyridine-4-thiolate-Bridged Rhodium and Iridium Complexes as Ditopic Building Blocks in Molecular Architecture

A series of dinuclear
pyridine-4-thiolate (4-Spy)-bridged rhodium and iridium compounds
[M­(μ-4-Spy)­(diolef)]2 [diolef = 1,5-cyclooctadiene
(cod), M = Rh (1), Ir (2); diolef = 2,5-norbornadiene
(nbd), M = Rh (3)] were prepared by the reaction of Li­(4-Spy)
with the appropriate compound [M­(μ-Cl)­(diolef)]2 (M
= Rh, Ir). The dinuclear compound [Rh­(μ-4-Spy)­(CO)­(PPh3)]2 (4) was obtained by the reaction of [Rh­(acac)­(CO)­(PPh3)] (acac = acetylacetonate) with 4-pySH. Compounds 1–4 were assessed as metalloligands in self-assembly
reactions with the cis-blocked acceptors [M­(cod)­(NCCH3)2]­(BF4) [M = Rh (a), Ir (b)] and [M­(H2O)2(dppp)]­(OTf)2 [M
= Pd (c), Pt (d); dppp = 1,3-bis­(diphenylphosphino)­propane].
The homometallic hexanuclear metallomacrocycles [{M2(μ-4-Spy)2(cod)2}2{M­(cod)}2]­(BF4)2 (M = Rh [(1a)2], Ir [(2b)2]) and the
heterometallic hexanuclear metallomacrocycles [{Rh2(μ-4-Spy)2(cod)2}2{Ir­(cod)}2]­(BF4)2 [(1b)2],
[{Rh2(μ-4-Spy)2(cod)2}2{M′(dppp)}2]­(OTf)4 (M′
= Pd [(1c)2], Pt [(1d)2]), and [{Ir2(μ-4-Spy)2(cod)2}2{M′(dppp)}2]­(OTf)4 (M′ = Pd [(2c)2], Pt [(2d)2]) were obtained.
NMR spectroscopy in combination with electrospray ionization mass
spectrometry was used to elucidate the nature of the metalloligands
and their respective supramolecular assemblies. Most of the synthesized
species were found to be nonrigid in solution, and their fluxional
behavior was studied by variable-temperature 1H NMR spectroscopy.
An X-ray diffraction study of the assemblies (1a)2 and (1d)2 revealed the formation of rectangular (9.6 Å × 6.6 Å)
hexanuclear metallomacrocycles with alternating dinuclear (Rh2) and mononuclear (Rh or Pt) corners. The hexanuclear core
is supported by four pyridine-4-thiolate linkers, which are bonded
through the thiolate moieties to the dinuclear rhodium units, exhibiting
a bent-anti arrangement, and through the peripheral pyridinic nitrogen
atoms to the mononuclear corners.