The molecular structure of 1,10-phenanthroline-5,6-dione has been determined by X-ray diffraction analysis. The compound reacts with the tetrachlorides of Group 4 metals affording adducts of general formula [MCl₄(C₁₂H₆N₂O₂)] (M = Ti, Zr or Hf) and [(MCl₄)₂(C₁₂H₆N₂O₂)] (M = Ti or Hf), N,N′- and N,N′,O,O′-co-ordinated respectively. The compound [HfCl₄(C₁₂H₆N₂O₂)] is reactive towards TiCl₄ affording the bimetallic compound [Cl₄Hf(C₁₂H₆N₂O₂)TiCl₄]. The reaction of the dione with bis-cyclopentadienyl derivatives of titanium(II), zirconium(II), [MCp₂(CO)₂], and vanadium(II), VCp₂, affords derivatives O,O′-co-ordinated to the MCp₂ moiety. By reaction of [TiCp₂(C₁₂H₆N₂O₂)] with [TiCp₂(CO)₂] the bimetallic derivative [(TiCp₂)₂(C₁₂H₆N₂O₂)] is obtained, which is suggested to contain two TiCp₂ fragments, O,O′- and N,N′-co-ordinated to 1,10-phenanthroline-5,6-dione. The [MCp₂(C₁₂H₆N₂O₂)] (M = Ti, Zr or V) derivatives react with M′Cl₄ (M′ = Ti or Hf) to give [Cp₂M(C₁₂H₆N₂O₂)M′Cl₄] bimetallics.

The chemistry of niobium and tantalum pentahalides, MX₅ , with oxygen compounds is reviewed herein. The polynuclear structure of MX₅ is readily broken by addition of oxygen-containing organic molecules, L, to give either mononuclear or ionic dinuclear coordination adducts. Then activation of the organic ligand may take place favoured by several factors, i.e. low M–X bond energy, high temperature, presence of more than one oxygen function within L, L/M molar ratio ≥ 2. The activation reactions are often uncommon in the context of metal halides; they include the cleavage of C_sp3–O, C_sp2–O, C–H and C–C bonds, and eventual successive rearrangements proceeding with C–O or C–C couplings. The recently elucidated reactivity of MX₅ with limited amounts of oxygen compounds will be presented, and possible connections with the relevant MX₅-directed syntheses reported in the literature will be outlined.

α-Diimines are among the most robust and versatile ligands available in synthetic coordination chemistry, possessing finely tunable steric and electronic properties. A series of novel cationic ruthenium(II) p-cymene complexes bearing simple α-diimine ligands, [(η⁶-p-cymene)RuCl{κ²N-(HCNR)₂}]NO₃ (R = Cy, [1]NO₃; R = 4-C₆H₁₀OH, [2]NO₃; R = 4-C₆H₄OH, [3]NO₃), were prepared in near-quantitative yields as their nitrate salts. [2]NO₃ displays high water solubility. The potential of the α-diimine ligand in [3]NO₃ as a carrier of bioactive molecules was investigated via esterification reactions with the hydroxyl groups. Thus, the double-functionalized derivatives [(η⁶-p-cymene)RuCl{κ²N-(HCN(4-C₆H₄OCO-R))₂}]NO₃ (R = aspirinate, [5]NO₃; valproate, [6]NO₃) and also [4]Cl (R = Me) were obtained in good-to-high yields. UV–vis and multinuclear NMR spectroscopy and cyclic voltammetric studies in aqueous solution revealed only minor ruthenium chloride hydrolytic cleavage, biologically accessible reduction potentials, and pH-dependent behavior of [3]NO₃. Density functional theory analysis was performed in order to compare the Ru–Cl bond strength in [1]⁺ with the analogous ethylenediamine complex, showing that the higher stability observed in the former is related to the electron-withdrawing properties of the α-diimine ligand. In vitro cytotoxicity studies were performed against tumorigenic (A2780 and A2780cisR) and nontumorigenic (HEK-293) cell lines, with the complexes bearing simple α-diimine ligands ranging from inactive to IC₅₀ values in the low micromolar range. The complexes functionalized with bioactive components, i.e., [5]NO₃ and [6]NO₃, exhibited a marked increase in the cytotoxicity with respect to the precursor [3]NO₃.