V. Yu. Kukushkin

1,3-dipolar cycloaddition of nitrones to free and coordinated nitriles: Routes to control the synthesis of 2,3-dihydro-1,2,4-oxadiazoles

Data on 1,3-dipolar cycloaddition of nitrones to free and coordinated nitriles producing 2,3-dihydro-1,2,4-oxadiazoles (or Δ4-1,2,4-oxadiazolines) are summarized. The latter compounds belong to the virtually unknown class of heterocyclic systems. The main factors responsible for the cycloaddition reactions are discussed. Particular attention is given to the role of metal centers in controlling the synthesis of 2,3-dihydro-1,2,4-oxadiazoles.

Coupling of C-amino aza-substituted heterocycles with an isocyanide ligand in palladium(ii) complex

The reaction of cis-dichlorobis(2,6-xylylisocyanide)palladium(ii) with 2-aminopyrazine affords a binuclear palladium complex, in which one of the metal atoms is involved in the palladacyclic ligand. In the contrast, the coupling of isocyanide ligands in cis-dichlorobis-(2,6-xylylisocyanide)palladium(ii) with another C-amino aza-substituted heterocycle, viz.,4-acetyl-3-amino-5-methylpyrazole, gives a mononuclear cationic palladium diaminocarbene complex. Both compounds were characterized by elemental analysis, IR spectroscopy, 1H, 13C{1H}, DEPT90/DEPT135, and 1H,13C-HSQC/1H,13C-HMBC NMR spectroscopy, high-resolution electrospray ionization mass spectrometry, and X-ray diffraction.

Hydrogen bonding effects on coordinated sulfoxides and relative role of intra- and inter-molecular interactions determining the dmso orientation in [RR′NHOH][ fac -RuCl 3 (dmso) 3 ] compounds: a crystallographic and molecular mechanics study

Abstract Compounds with hydroxyl ammonium cations, [RR′NHOH][ fac -RuCl 3 (dmso–S) 3 ], with R=R′=H ( 1 ), R=Me, R′=H ( 2 ) and R=R′=Et ( 3 ), have been prepared and structurally characterized by X-ray analyses. The three compounds display chain-like structures, formed by hydrogen bonding between the hydroxyl ammonium cations and the chlorine and oxygen atoms of the ruthenium anion. H-bonding involving the dmso oxygen atoms causes a lengthening of the S–O bonds. The comparison of the solid state structures with results of Molecular Mechanics calculations show that the arrangement of the fac -dmso–S ligands is not determined by H-bonding or packing effects, but from intramolecular steric and electrostatic interactions. These give rise to hindered rotation about the Ru–S bonds.

Theoretical study of nucleophilic addition of amines to organic nitriles

The mechanism of nucleophilic addition of a series of amines to acetonitrile MeC≡N both free and activated in a platinum complex trans-[PtCl2(N ≡CMe)2] was studied in detail by the theoretical methods of quantum chemistry. The influence of the nature of a particular nucleophile on the mechanism, kinetic and thermodynamic characteristics of the processes was elucidated. These reactions proceed according to a concerted highly synchronous mechanism that includes formation of 6-membered transition state consisting of the nitrile, amine, and water molecules. Hydrazine, aliphatic amines, and methylendiamine exhibit the highest reactivity from both kinetic and a thermodynamic viewpoint, while aromatic amines and amidine are the most inert.

Reactivity of ligands

The review systematizes and thoroughly discusses main factors responsible for variation of the reactivity of molecules upon coordination to a metal center. Principal types of ligand reactions inside co-ordination compounds are also categorized.

Versatility and reactivity of salicylaldehyde S-methylisothiosemicarbazone in palladium(II) complexes

New palladium(II) complexes, [Pd(HL)Cl] · H2O (I) and {K[Pd(L1)(NO2)] · H2O}2, with S-methylisothiosemicarbazone of salicylaldehyde (H2L) and its derivative (H2L1) were synthesized. X-ray diffraction analysis demonstrated the ambident nature of S-alkylated thiosemicarbazone, which is attached to palladium(II) through O, N, and S donor atoms in I and through O, N, and N atoms in II. This is the first known case of metal coordination of the alkylated sulfur atom of a thiosemicarbazide moiety of the ligand. A mechanism of nitrosation of the terminal amide nitrogen atom of the H2L1 ligand during complexation was proposed.

Theoretical study of ammonia nucleophilic addition to nitriles in platinum complexes

The mechanism of the reaction of the ammonia nucleophilic addition to nitriles RC≡N, both free and activated in the platinum complex trans-[PtCl2(N≡CCH3)2], was studied in detail by theoretical quantumchemical methods. The reaction resulting in the formation of free or coordinated amidines proceeds through consecutive formation of an orientation complex, a six-membered cyclic transition state, and a final reaction product, in which an amidine is in the E-configuration. Water containing in a solvent plays a role of a promoter of this process. The activation effect is interpreted from the viewpoint of both kinetic and thermodynamic factors. It was shown that the mechanism of the reaction product E-Z-isomerization includes the deprotonation of the amino-group nitrogen atom, the change of the coordinated ligand conformation, and the protonation of the nitrogen atom.

Platinum complexes bearing 2,2′-dipyridylamine ligand

The replacement of the iodide ligands in the complex [PtI2(dpa)] (1) (dpa is 2,2′-dipyridylamine) by silver triflate in acetonitrile afforded the compound [Pt(dpa)(MeCN)2](SO3CF3)2 (2). Homoleptic complexes [Pt(dpa)2](X)2 (3·(X)2) were synthesized by the treatment of [PtI2(dpa)] (1) with 2,2′-dipyridylamine in the presence of silver salts AgX in methanol (X = NO3) or acetonitrile (X = SO3CF3). The deprotonation of the complex [3](SO3CF3)2 to give the homoleptic complex [Pt(dpa-H)2] (4) was performed by two methods, e.g., by the treatment of [3](SO3CF3)2 with 2 equiv. of NaOH in methanol or by the addition of excess Et3N to a suspension of [3](SO3CF3)2 in methanol. The structures of compounds 1–4 were established by elemental analyses, high resolution electrospray ionization mass spectrometry, IR and NMR spectroscopy; the crystal structure of complexes [2](SO3CF3)2, [3](NO3)2·H2O, [3](SO3CF3)2·2H2O, and 4 were determined by single-crystal X-ray diffraction.

FORMATION OF RING SYSTEMS WITHIN SULFIMIDES AND THEIR METAL COMPLEXES

There are a number of ways we have developed for the incorporation of sulfimide units into ring systems. Simple coordination of Ph2SNH to a metal followed by hydrogen-bonding to anions and solvates...

Theoretical Investigation of Cycloaddition Reactions with Lewis Acid Mediation

This review covers theoretical investigations of cycloaddition reactions with Lewis acid (LA) mediation, except for Diels-Alder reactions. The key factors influencing these processes are analyzed, as well as the details of the reaction mechanisms.