Dinuclear Pyridine-4-thiolate-bridged rhodium and iridium complexes as ditopic building blocks in molecular architecture

Abstract

A series of dinuclear pyridine-4-thiolate rhodium and iridium compounds [M(μ-4-Spy)(diolef)]2 (diolef = 1,5-cyclooctadiene, cod; M = Rh (1), Ir (2); 2,5-norbornadiene, nbd; M = Rh (3)) have been prepared by 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) has been obtained by reaction of [Rh(acac)(CO)(PPh3] with 4-pySH. Compounds 1-4 have been assessed as metalloligands in self-assembly reactions with the cis-blocked [M(cod)(NCCH3)2](BF4) (M = Rh (a) and M = Ir (b)) and [M(H2O)2(dppp)](OTf)2 (M = Pd (c), Pt (d)) (dppp = 1,3-bis(diphenylphosphino)propane) acceptors. Homo [{M2(μ-4-Spy)2(cod)2}2{M(cod)}2](BF4)2 (M = Rh (1a)2, and M = Ir (2b)2), and hetero [{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 and M'= Pt (1d)2) and [{Ir2(μ-4-Spy)2(cod)2}2{M'(dppp)}2](OTf)4 ( M' = Pd (2c)2 and M'= Pt (2d)2) hexanuclear metallomacrocycles have been obtained. NMR spectroscopy, in combination with ESI mass spectrometry has been used to elucidate the nature of the metalloligands and their respective supramolecular assemblies. Most of synthesized species have shown to be non-rigid in solution and their fluxional behavior has been studied by VT 1H NMR spectroscopy. An X-ray diffraction study on the assemblies (1a)2 and (1d)2 revealed the formation of rectangular (9.6 x 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 moiety to the dinuclear rhodium units, exhibiting a bent-anti arrangement, and through the peripheral pyridinic nitrogen atoms to the mononuclear corners.