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Synthesis of five novel copper–arylhydrazone complexes and their catalytic activity for microwave-assisted click reaction in water and glycerol.

Chalcogen bonding as a synthetic tool in metal-mediated synthesis and engineering of the secondary coordination sphere of copper(ii) complexes.

Lanthanide complexes have attracted a widespread attention due to their structural diversity, as well as multifunctional and tunable properties. The development of lanthanide based functional materials has often relied on the design of the secondary coordination sphere of the corresponding lanthanide complexes. For instance, usually simple lanthanide salts (solvento complexes) do not catalyze effectively organic reactions or provide low yield of the expected product, whereas the presence of a suitable organic ligand with a noncovalent bond donor or acceptor centre (secondary coordination sphere) modifies the symmetry around the metal centre in lanthanide complexes which then successfully can act as catalysts in both homogenous and heterogenous catalysis. In this minireview, we discuss several relevant examples, based on X-ray crystal structure analyses, in which the hydrogen, halogen, chalcogen, pnictogen, tetrel and rare-earth bonds, as well as cation-π, anion-π, lone pair-π, π-π and pancake interactions, are used as a synthon in the decoration of the secondary coordination sphere of lanthanide complexes.

The pnictogen bond (PnB) is a noncovalent attraction between electrophilic pnictogen atoms, originated from the anisotropic distribution of electron density on Pn in a molecular entity, and a nucleophilic (Nu) region in the same (intramolecular) or another (intermolecular) molecular entity: R–Pn⋯Nu (Pn = N, P, As, Sb or Bi; R = electron withdrawing atom or group; Nu = Ha, Ch, Pn, π-system, anion, etc.). Like the halogen and chalcogen bonds, PnB is a directional noncovalent interaction with a preference for a linear geometry, R–Pn⋯Nu angle approaching 180°. In contrast to the halogen and chalcogen atoms, the pnictogen atoms are able to introduce three electrophilic centres on the Pn atom (on account of the existence of three species bonded to the pnictogen atom), which gives an additional advantage in the use of these weak forces in coordination chemistry. In this review we highlight several recent relevant examples, based on X-ray crystal structure analyses, in which PnB is used as a synthon in the construction and design of coordination and organometallic compounds.

Peroxides form an important class of chemicals in which two oxygen atoms are linked together by a single covalent bond (R−O−O−R, R=H, SO3K, alkyl, etc.), with a wide range of applications in medicine, industry, environmental protection, etc. The current version of the Cambridge Structural Database reveals more than 1400 structurally characterized metal-peroxy/peroxo complexes with diverse coordination modes having specific biological, catalytical and other functional properties. Both inorganic and organic peroxides are versatile oxidants and extensively used reagents for metal complex catalyzed functionalization of organic compounds. The utilization of peroxides in metal complex catalysis typically requires prior activation of O−O or O−R bonds at a metal centre leading to radical species with a reactivity and lifetime that are dependent on the substituents R and reaction medium (pH, solvent, etc.). In fact, the cooperation of a metal centre (coordination) with a peroxide can lead to a multifunctional catalytic system having a high performance towards selective functionalization of organic substrates. This review is intended to focus on the auxiliary/crucial role of peroxides in the transformations of various classes of organic compounds such as alkanes, alkenes, alkynes, aromatics, heterocycles, aldehydes, ketones and alcohols, catalyzed by metal complexes.

Nitroxyl radicals, illustrated by 2,2,6,6-tetramethylpiperidine-N-oxyl (TEMPO), constitute a versatile class of stable free radicals that are extensively used in metal complex catalyzed synthetic transformations of a great interest. The Cambridge Structural Database reveals more than 260 hits, concerning crystal structures of metal complexes of N-oxyl ligands and most of them (ca. 240) relate to complexes comprising TEMPO and its derivatives. In order to prepare multifunctional catalysts, supramolecular architectures, drugs, magnetic materials, etc., the para-position of TEMPO has been functionalized with OH, COOH, CN, NH2 or N3, leading to an increase of the coordination sites beyond the N O· synthon. Herein, we highlight the coordination mode and reactivity of TEMPO ligands in the design of coordination compounds, which can be applied in catalysis. The review mainly focuses on the auxiliary/crucial role of TEMPO in functionalization of alkanes, alkenes, alkynes, aromatics, heterocycles, aldehydes, ketones and alcohols, catalyzed by metal complexes.

Three known multinuclear Zn(II)-arylhydrazone complexes, [Zn{(CH3)2SO}(H2O)(L1)] (1), [Zn2(CH3OH)2(μ-L2)2] (2) and [Zn4(μ-OH)2(1κO:2κO-HL3)4(κO-HL3)2(H2O)4] (3) were prepared upon reaction of ZnCl2 or Zn(CH3COO)2·2H2O with 3-(2-(2-hydroxy-4-nitrophenyl) hydrazineylidene) pentane-2,4-dione (H2L1), 3-(2-(2-hydroxyphenyl)hydrazineylidene)pentane-2,4-dione (H2L2) and 2-(2-(2,4-dioxopentan-3-ylidene)hydrazineyl)benzoic acid (H2L3), respectively, in methanol solution. Compounds 1–3 were tested as catalysts for the cyanosilylation reaction of a diversity of both aliphatic and aromatic aldehydes with trimethylsilyl cyanide yielding the corresponding cyanohydrin trimethylsilyl ethers in high yields (72–98%) in methanol and at room temperature.