Crescent-Shaped Rhodium(I) Complexes with Bis(<i>o</i>-carboxymethylphenyl)triazenide

Reaction of [{Rh(μ-Cl)(CO)2}2] with the triazene ArNNNHAr (Ar = o-CO2MeC6H4) produced the mononuclear complex [RhCl(ArNNNHAr)(CO)2] (1). Complex 1 reacted with KOH in methanol to give the dinuclear compound [{Rh(μ-ArNNNAr)(CO)2}2] (2), which showed a “μ-(1κN1,2κN3)-ArNNNAr” coordination mode for both bridging ligands. The dinuclear complex [{Rh(μ-ArNNNAr)(CO)2}2] (2) easily undergoes redistribution reactions in which the eight-membered “Rh2(NNN)2” core is broken. Thus, reaction of 2 with the anionic complex (NHEt3)[RhCl2(CO)2] gave the single-bridged complex (NHEt3)[Rh2(μ-ArNNNAr)Cl2(CO)4] (4), while the trinuclear complexes [Rh3(μ-ArNNNAr)(μ-Cl)(μ-CO)Cl(CO)4] (5) and [Rh3(μ-ArNNNAr)2(μ-Cl)(μ-CO)(CO)3] (6) were isolated by addition of the neutral compound [{Rh(μ-Cl)(CO)2}2] to 2, depending on the molar ratio employed. The formation of 5 and 6 involved the loss of carbonyl groups and the coordination of the oxygen atoms of the CO2Me groups. The structures of 4, 5, and 6 have been determined by X-ray diffraction methods, which show the ability of bis(o-carboxymethylphenyl)triazenide to act as bi-, tri-, and tetra-dentate ligand-spanning dinuclear moieties in trinuclear complexes.