Mono-, di-, and tri-ruthenium complexes with the ligand 2,2′-dipyridylamide (dpa): insights into the formation of extended metal atom chains

Reactions between Hdpa (2,2′-dipyridylamine) and either RuCl₃ · xH₂O and Ru₂(OAc)₄Cl produce mono-, di-, and tri-ruthenium complexes under various conditions. The ligand Hdpa and RuCl₃ · xH₂O react in boiling DMF to form the ionic species Ru(Hdpa)₂Cl₂]Cl (1). Reaction of Ru₂(OAc)₄Cl with molten Hdpa leads to scission of the Ru-Ru bond and formation of the vertex-sharing bioctahedral complex Ru₂(dpa)₃(OAc)_0.64Cl_1.36 (2). A mixture of both of these species results from the reaction of Ru₂(OAc)₄Cl with Hdpa and LiCl in refluxing o-dichlorobenzene/EtOH mixtures. This mixture of compounds reacts further with KOBu^t and n-butanol in refluxing naphthalene to give low yields of the extended metal atom chain (EMAC) complex Ru₃(dpa)₄Cl₂ (I).