Stepwise Formation of Quasi-Octahedral Macrocyclic Complexes of Rhodium(III) and Iridium(III) Bearing a Pentamethylcyclopentadienyl Group

Abstract

Reactions of [{MCl2(Cp*)}2] (1: M=Ir, 2: M=Rh) with bidentate ligands (L) such as 1,4-diisocyano-2,5-dimethylbenzene (a), 1,4-diisocyano-2,3,5,6-tetramethylbenzene (b), pyrazine (c) or 4,4′-dipyridyl (d) gave the corresponding dinuclear complexes [{MCl2(Cp*)}2(L)] (M=Ir: 3 a, 3 b, 5 c, 5 d; M=Rh: 4 b, 6 c, 6 d), which were converted into tetranuclear complexes [{M2(μ-Cl)2(Cp*)2}2(L)2](OTf)4 (M=Ir: 7 c, 7 d, 9 a, 9 b; M=Rh: 8 c, 8 d, 10 b) on treatment with Ag(OTf). X-ray analyses of 8 c and 8 d revealed that each of four pentamethylcyclopentadienyl metal moieties was connected by two μ-Cl-bridged atoms and a bidentate ligand to construct a rectangular cavity with the dimensions of 3.7×7.0 Å for 8 c and 3.7×11.5 Å for 8 d. Both the Rh2Cl2 and pyrazine (or 4,4′dipyridyl) ring planes are perpendicular to the Rh4 plane. Treatment of Cl-bridged complexes (7 c, 7 d, 8 c, 8 d, 9 b, and 10 b) with a different ligand (L′) resulted in cleavage of the Cl bridges to produce two-dimensional complexes [{MCl(Cp*)}4{(L)(L′)}2](OTf)4 (11 ac, 11 bc, 11 bd, 12 bc, and 12 bd) with two different ligand "edges". Complex 10 b reacted readily with 1,4-diisocyano-2,3,5,6-tetramethylbenzene (b) to give a tetranuclear rhodium(III) complex 12 bb. The structure of tetranuclear complexes was confirmed by X-ray analysis of 11 bc. Each {MCp*} moiety is surrounded by a Cl atom, isocyanide, and pyrazine (or 4,4′-dipyridyl) and the dimensions of its cavity are 7.0×11.6 Å.