Syntheses, Structures, and Theoretical Insights of Homobimetallic Ruthenium Complexes Comprising Mercaptobenzothiazolyl Ligands

This article presents the synthesis, structural characterization, and variable coordination modes of the 1,3-N,S-mercaptobenzothiazolyl ligand at the ruthenium center. Room-temperature reaction of [(η6-p-cymene)Ru(μ2-Cl3)Ru(Cl)(CO)(PPh3)] (1) with the potassium salt of Mbz (Mbz = 2-mercaptobenzothiazolyl) led to the formation of complexes [(η6-p-cymene)Ru{(μ2-k2-N,S-(NS2C7H4))(μ2-k2-S-(NS2C7H4))(μ2-k1-S,k2-N,S-(NS2C7H4))}Ru{k1-S-(NS2C7H4)}(CO)] (2) and [(η6-p-cymene)Ru{(μ2-k2-N,S-(NS2C7H4))(μ2-k2-S-(NS2C7H4))(μ2-k1-S,k2-N,S-(NS2C7H4))}Ru{k1-S-(NS2C7H4)}(PPh3)] (3). The solid-state X-ray structure of 2 shows unusual coordination modes of the three bridging mercaptobenzothiazolyl units at the ruthenium(II) center. Two of the bridging mercaptobenzothiazolyl ligands adopted μ2-k2-S-(NS2C7H4) and μ2-k2-N,S-(NS2C7H4) coordination modes, while the third bridging ligand binds through both nitrogen and sulfur atoms in a μ2-k1-S,k2-N,S-(NS2C7H4) fashion, forming a four-membered chelate ring with a metal center. Further, the reaction of 3 with the sodium salt of the [H2B(Mbz)2] ligand led to the formation of bimetallic ruthenium(II) borate complex, [(η6-p-cymene)Ru{μ2-k2-N,S-(NS2C7H4)(μ2-k2-S-(NS2C7H4)2)}Ru(k3-H,S,S′-H2B(NS2C7H4)2)] (4). The solid-state X-ray structure of 4 shows μ2-k2-S-(NS2C7H4) and μ2-k2-N,S-(NS2C7H4) coordination modes of the bridging mercaptobenzothiazolyl units, which are similar to those observed in 3. Comparative cyclic voltammetry was conducted to compare the electronic behavior of these bimetallic complexes. To understand the electronic structures of these complexes, DFT has been carried out.