Synthesis, structure, and electrochemical characterization of a mixed-ligand diruthenium(iii,ii) complex with an unusual arrangement of the bridging ligands

Abstract

A mixed-ligand metal-metal bonded diruthenium complex having the formula Ru(2)(2,4,6-(CH(3))(3)ap)(3)(O(2)CCH(3))Cl where ap is the anilinopyridinate anion was synthesized from the reaction of Ru(2)(O(2)CCH(3))(4)Cl and H(2,4,6-(CH(3))(3)ap), after which the isolated product was structurally, spectroscopically and electrochemically characterized. The crystal structure reveals an unusual arrangement of the bridging ligands around the dimetal unit where one ruthenium atom is coordinated to one anilino and two pyridyl nitrogen atoms while the other ruthenium atom is coordinated to one pyridyl and two anilino nitrogen atoms. To our knowledge, Ru(2)(2,4,6-(CH(3))(3)ap)(3)(O(2)CCH(3))Cl is the only example of a mixed-ligand diruthenium complex of the type [Ru(2)L(3)(O(2)CCH(3))](+), where L is an unsymmetrical anionic bridging ligand that has been structurally characterized with a "(2,1)" geometric conformation of the bridging ligands, all others being "(3,0)". The initial Ru(2)(5+) compound in CH(2)Cl(2) or CH(3)CN containing 0.1 M tetra-n-butylammonium perchlorate (TBAP) undergoes up to four one-electron redox processes involving the dimetal unit. The Ru(2)(5+/4+) and Ru(2)(5+/6+) processes were characterized under N(2) using thin-layer UV-visible spectroelectrochemistry and this data is compared to UV-visible spectral changes obtained during similar electrode reactions for related diruthenium compounds having the formula Ru(2)L(4)Cl or Ru(2)L(3)(O(2)CCH(3))Cl where L is an anionic bridging ligand. Ru(2)(2,4,6-(CH(3))(3)ap)(3)(O(2)CCH(3))Cl was also examined by UV-visible and FTIR spectroelectrochemistry under a CO atmosphere and two singly reduced Ru(2)(4+) species, [Ru(2)(2,4,6-(CH(3))(3)ap)(3)(O(2)CCH(3))(CO)Cl](-) and Ru(2)(2,4,6-(CH(3))(3)ap)(3)(O(2)CCH(3))(CO) were in situ generated for further characterization. The CO-bound complexes could be further reduced and exhibited additional reductions to their Ru(2)(3+) and Ru(2)(2+) oxidation states.

Effect of Axial Ligands on the Spectroscopic and Electrochemical Properties of Diruthenium Compounds

“…This is consistent with two stepwise one-electron additions. The difference between the electrochemical behavior at room temperature and that at low temperature is attributed to a chemical reaction involving the electrogenerated Ru 2 3+ form of the compound and the CH 2 Cl 2 solvent, as has been shown in the case of related Ru 2 5+ complexes …”

“…The structural, electrochemical, and spectroscopic properties of numerous diruthenium complexes with a Ru 2 5+ core and a paddle-wheel structure have been reported in the literature − since the first synthesis and physical characterization of Ru 2 (OAc) 4 Cl (OAc = acetate anion) by Stephenson and Wilkinson in 1966 . The majority of investigated Ru 2 5+ complexes have contained an axially bound chloride anion and are formulated in their neutral form as Ru 2 L 4 Cl or Ru 2 (OAc) x ­(L) 4‑ x Cl ( x = 1–4) where L is a symmetrical or unsymmetrical anionic bridging ligand. ,,,,,,,− ,, …”

Electronic Structure of Ru2(II,II) Oxypyridinates: Synthetic, Structural, and Theoretical Insights into Axial Ligand Binding

“…This explanation is supported by a recent study of M–M and M–L bond orders in M 2 (O 2 CR) 4 (L) 1–2 type complexes at the CASSCF level of theory . The complexes with O,O- and N,O-donor equatorial ligands are degraded by strong σ-donors, whereas complexes with N,N-donor equatorial ligands are not, − because the Ru–N eq bond is stronger than the Ru–O eq bond, stabilizing Ru 2 (N,N) 4 complexes to weakening of the Ru–Ru bond. This Ru ion abstraction is not observed in PPh 3 adduct 4 , which, to our knowledge, has the greatest π* stabilization of any triplet d 6 –d 6 M 2 complex that has been synthesized.…”

Side-Arm Functionalized Silylene Copper(I) Complexes in Catalysis

“…Starting materials were purchased commercially and used without further purification. MesNHPy and PhC­(N t Bu) 2 SiCl were synthesized according to literature procedures. ,,, 1 H, 13 C, and 29 Si NMR spectroscopic data were recorded on a Bruker Avance 401 MHz and a Bruker Avance 300 MHz spectrometer and referenced to the deuterated solvent (benzene- d 6 , dcm- d 2 , thf- d 8 ). Deuterated solvents were dried over activated molecular sieves (3 Å) and stored in an argon drybox.…”