The new diprotic ligand 3,5-di-tert-butylsalicylaldehyde 4-ethyl-3-thiosemicarbazone, abbreviated H2(3,5-t-Bu2)-sal4eT, exists as the thio-keto tautomer and adopts the E-configuration with respect to the imine double bond as evidenced by single-crystal X-ray analysis and corroborated by spectroscopic characterisation. Upon treatment with Cu(OAc)2·H2O in the presence of either 2,9-dimethyl-1,10-phenanthroline (2,9-Me2-phen) or 1,10-phenanthroline (phen) as a co-ligand in MeOH, this thiosemicarbazone undergoes conformational transformation (relative donor-atom orientations: syn,anti → syn,syn) concomitantly with tautomerization and double deprotonation to afford the ternary copper(II) complexes [Cu{(3,5-t-Bu2)-sal4eT}(2,9-Me2-phen)] (1) and [Cu2{3,5-t-Bu2)-sal4eT}2(phen)] (2). Crystallographic elucidation has revealed that complex 1 is a centrosymmetric dimer of mononuclear copper(II) complex molecules brought about by intermolecular H-bonding. The coordination geometry at the copper(II) centre is best described as distorted square pyramidal in accord with the trigonality index (τ = 0.14). The co-ligand adopts an axial-equatorial coordination mode; hence there is a disparity between its two Cu–N coordinate bonds arising from weakening of the apical one as a consequence of the tetragonal distortion. The axial X-band ESR spectrum of complex 1 is consistent with retention of this structure in solution. Complex 2 is a centrosymmetric dimer of dinuclear copper(II) complex molecules exhibiting intermolecular H-bonding and π-π-stacking interactions. The two copper(II) centres, which are 4.8067(18) Å apart and bridged by the thio-enolate nitrogen of the quadridentate thiosemicarbazonate ligand, display two different coordination geometries, one distorted square planar (τ4 = 0.082) and the other distorted square pyramidal (τ5 = 0.33). Such dinuclear copper(II) thiosemicarbazone complexes, which are crystallographically characterised, are extremely rare. In vitro, complexes 1 and 2 outperform cisplatin as antiproliferative agents in terms of potency and selectivity towards HeLa and MCF-7 cancer cell lines.

Two types of heterometallic (Fe(III),Na) silsesquioxanes [Ph₅Si₅O₁₀]₂[Ph₁₀Si₁₀O₂₁]Fe₆(O^2‒)₂Na₇(H₃O⁺)(MeOH)₂(MeCN)_4.5.1.25(MeCN), I, and [Ph₅Si₅O₁₀]₂[Ph₄Si₄O₈]₂Fe₆Na₆(O^2‒)₃(MeCN)_8.5(H₂O)_8.44, II, were obtained and characterized. X-Ray studies established distinctive structures of both products, with pair of Fe(III)-O-based triangles surrounded by siloxanolate ligands, giving fascinating cage architectures. Complex II proved to be catalytically active in the formation of amides from alcohols and amines, thus becoming a rare example of metallasilsesquioxanes performing homogeneous catalysis. Benzene, cyclohexane and other alkanes, as well as alcohols, can be oxidized in acetonitrile solution to phenol, the corresponding alkyl hydroperoxides and ketones, respectively, by hydrogen peroxide in air in the presence of catalytic amounts of complex II and trifluoroacetic acid. Thus, the cyclohexane oxidation at 20 °C gave oxygenates in very high for alkanes yield (48% based on alkane). The kinetic behaviour of the system indicates that the mechanism includes the formation of hydroxyl radicals generated from hydrogen peroxide in its interaction with diiron species. The latter are formed via monomerization of starting hexairon complex with further dimerization of the monomers.

A series of polynuclear, dinuclear, and mononuclear Mo(VI) complexes were synthesized with the hydrazonato ligands derived from 5-methoxysalicylaldehyde and the corresponding hydrazides (isonicotinic hydrazide (H2L1), nicotinic hydrazide (H2L2), 2-aminobenzhydrazide (H2L3) or 4-aminobenzhydrazide (H2L4)). The metallosupramolecular compounds obtained from non-coordinating solvents, [MoO2(L1,2)]n (1 and 2) and [MoO2(L3,4)]2 (3 and 4), formed infinite structures and metallacycles, respectively. By blocking two coordination sites with cis-dioxo ligands, the molybdenum centers have three coordination sites occupied by the ONO donor atoms from the rigid hydrazone ligands and one by N atom of pyridyl or amine-functionalized ligand subcomponents from the neighbouring Mo building units. The reaction in methanol afforded the mononuclear analogues [MoO2(L1-4)(MeOH)] (1a-4a) with additional monodentate MeOH ligand. All isolated complexes were tested as catalysts for cyclooctene epoxidation using tBuOOH (TBHP) as an oxidant in water. The impact of the structure and ligand lability on the catalytic efficiency in homogeneous cyclooctene epoxidation was elucidated through theoretical considerations. Thus, dinuclear assemblies exhibited better catalytic activity than mononuclear or polynuclear complexes.

As a candidate for bifunctional asymmetric catalysts containing a half-sandwich C–N chelating Ir(III) framework (azairidacycle), a dinuclear Ir complex with an axially chiral linkage is newly designed. An expedient synthesis of chiral 2,2’-bis(aminomethyl)-1,1’-binaphthyl (1) from 1,1-bi-2-naphthol (BINOL) was accomplished by a three-step process involving nickel-catalyzed cyanation and subsequent reduction with Raney-Ni and KBH4. The reaction of (S)-1 with an equimolar amount of [IrCl2Cp*]2 (Cp* = 5-C5(CH3)5) in the presence of sodium acetate in acetonitrile at 80 °C gave a diastereomeric mixture of new dinuclear dichloridodiiridium (5) through the double C–H bond cleavage, as confirmed by 1H NMR spectroscopy. A loss of the central chirality on the Ir centers of 5 was demonstrated by treatment with KOC(CH3)3 to generate the corresponding 16e amidoiridium complex 6. The following hydrogen transfer from 2-propanol to 6 provided diastereomers of hydrido(amine)iridium with retaining the bis(azairidacycle) architecture. The dinuclear chlorido(amine)iridium 5 can serve as a catalyst precursor for the asymmetric transfer hydrogenation of acetophenone with a substrate to catalyst ratio of 200 in the presence of KOC(CH3)3 in 2-propanol, leading to (S)-1-phenylethanol with up to 67% ee.