Dirhodium(II) carboxylates as building blocks. Synthesis and structures of cis-chelate complexes

Abstract

Dirhodium tetracarboxylate complexes (C)Rh₂(OAc)₂ and (C)₂Rh₂, where C is a chelating dicarboxylate of general form meta-C₆H₄(OC(CH₃)₂CO₂⁻)₂, were prepared by heating Rh₂(OAc)₄ and diacids in N,N-dimethylaniline. The structures of six new complexes with one or two chelate rings were obtained, with pyridine ligands (or in one case N,N-dimethylaniline) co-ordinated to rhodium. The geometries of the molecules are similar, with the aromatic part of the chelate ring tilted out of the plane of the Rh–O cage by 57.5 to 66.6°. The monochelate Rh₂{C₆H₄(OC(CH₃)₂CO₂)₂-m}(OAc)₂·2Bu^tPy (Bu^tPy = 4-tert-butylpyridine) packed in the crystal to generate a hexagonal network of channels of (minimum) diameter 5 Å due to vertical stacking of its axial pyridine ligands. Several other instances of intramolecular CH–π and intermolecular π–π interactions were noted in the packing diagrams. The bischelate Rh₂{Ar(OC(CH₃)₂CO₂)₂-m}₂·PhNMe₂, with Ar = 4,6-di-tert-butylphenyl, has a polymeric structure displaying a new mode of arene co-ordination. The aromatic ring of the N-bound aniline co-ordinates to a neighbouring dirhodium complex via the para carbon atom with a Rh–C distance of 2.709 Å.