Synthesis, characterization, and electrochemical properties of molecular rectangles of half-sandwich iridium complexes containing bridging chloranilate Ligands

Binuclear complex [Cp*Ir-2(2)(mu-CA)Cl-2] (2) (CA = chloranilate) was obtained by the reaction of [Cp*IrCl2](2) (1) with H(2)CA in the presence of base. Treatment of 2 with pyridine or 4-(4-bromophenyl)pyridine in the presence of AgOTf (OTf = CF3SO3) in CH3OH gave the corresponding binuclear complexes [Cp*Ir-2(2)(mu-CA)(pyridine)(2)](OTf)(2) (4a) and [Cp*Ir-2(2)(mu-CA)(4-(4-bromophenyl) pyridine}(2)]-(OTf)(2) (4b). Reactions of 2 with bidentate ligands gave tetranuclear complexes [Cp*Ir-4(4)(mu-CA)(2)(mu-L)(2)](OTf)(4) (L = pyrazine, 5a; 4,4'-dipyridyl, 5b; 2,5-bis(4-pyridyl)-1,3,5-oxadiazole, 5c; 1,4-bis(4pyridyl)benzene, 5d; (E)-1,2-bis(4-pyridyl)ethene, 5e). X-ray analyses of 5a, 5b, and 5e revealed that each of four Cp*Ir moieties was connected by pyridyl ligands and a bis-bidentate chloranilate (CA) ligand to construct a rectangular cavity with the dimensions 8.03 x 6.92 angstrom for 5a, 8.03 x 11.24 angstrom for 5b, and 8.01 x 13.55 angstrom for 5e. Toluene molecules are contained as solvent molecules in the crystals of 5a and 5b. For 5a, the toluene molecules appeared between the independent rectangles, but the toluene molecules appeared in the rectangle cavity for 5b. The electrochemical properties of 5b and 5e were investigated preliminarily, using cyclic voltammetry.