Dinuclear rhodium(II) pivalate complexes with N-donor ligands

Eight dinuclear rhodium(II) complexes containing various, (primarily, polyfunctional) N-donor ligands in the trans position with respect to the Rh-Rh bond were synthesized and characterized by X-ray diffraction. In the Chinese-lantern dinuclear rhodium(II) pivalates, RhII2 (μ-OOCCMe3)4(L)2 (L is 2,3-diaminopyridine (2), 7,8-benzoquinoline (4), 2,2′:6′,2″-terpyridine (5), N-phenyl-o-phenylenediamine (7)), and RhII2 (μ-OOCCMe3)4L1L2 (3, L1 is 2-phenylpyridine, L2 = MeCN), the steric effects of the axial ligands are most strongly reflected in the Rh-N(L) and Rh-Rh bond lengths. The introduction of chelating ligands containing a conformationally rigid chelate ring leads to the cleavage of two carboxylate bridges to form the dinuclear double-bridged structure RhII2 (μ- OOCCMe3)2(OCCMe3)2(η2-L3)2, where L3 is 8-amino-2,4-dimethylquinoline (6). The reaction of complex 7 containing coordinated N-phenyl-o-phenylenediamine with pyrrole-2,5-dialdehyde afforded the new RhII2(μ-OOCCMe3)4(L4)2 complex (8) containing 5-(1-phenyl-1-H-benzimidazol-2-yl)-1H-pyrrole-2-carbaldehyde (L4) in the axial positions of the dirhodium tetracarboxylate fragment. The coordinated diamine differs in reactivity from the free diamine. The reaction of the former with the above dialdehyde affords the [1+1]-condensation product, viz., 5-{(E)-[(2-anilinophenyl)imino]methyl}-1-H-pyrrole-2-carbaldehyde, whereas the reaction of unsubstituted o-phenylenediamine gives 5-{(E)-[(2-aminophenyl)imino]methyl}-1-H-pyrrole-2-carbaldehyde (L5) . The reaction of the latter with RhII2(μ-OOCCMe3)4(H2O)2 affords the dinuclear complex RhII2(μ-OOCCMe3)2(OOCCMe3)2(η2-L5)2 (9), which is an analog of complex 6 containing only two bridging carboxylate groups.