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.