Dirhodium (ii) carboxylate complexes as building blocks. cis-Chelating dicarboxylic acids designed to bridge the dinuclear core

Abstract

The syntheses and crystal structures of a series of dicarboxylic acids of general structure HO₂CCR₂OArOCR₂CO₂H (LH₂) designed to span a pair of cis sites on the dirhodium(II) tetracarboxylate framework are described. Monochelate complexes LRh₂(OAc)₂ and bischelate complexes L₂Rh₂ were prepared by heating the diacids with Rh₂(OAc)₄ in N,N-dimethylaniline. Chelates were formed under kinetic control and the best yields were obtained from diacids with methyl groups on the ether side arms and bulky substituents on the aromatic ring next to the ether links. Effective molarities for chelation were measured under thermodynamic control by ¹H NMR in tetrachloroethane. The stability of chelates and the conformational properties of diacids were investigated by molecular mechanics and quantum chemical techniques.