Palladium(<Emphasis Type="SmallCaps">I</Emphasis>) and palladium(0) carbonyl bromide complexes

New Pd^I and Pd⁰ carbonyl bromide complexes co-existing in the same crystal were synthesized and studied by X-ray diffraction analysis. The crystals consist of dimeric complex anions composed of the central Pd(μ-CO)₂Pd fragment and four partially disordered terminal ligands (CO and Br⁻). The complexes were characterized by IR, ESR, and X-ray photoelectron spectroscopy. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1349–1355, June, 2005.     

Unusual selective allylation of norbornadiene in the presence of palladium nanoclusters

The reaction of norbornadiene (NBD) with allyl acetate in the presence of the nanocluster Pd₁₄₇phen₃₂O₆₀(OCOBu^t)₃₀ (Pd-147; phen is 1,10-phenanthroline) and PPh₃ in acetonitrile is nonselective and is accompanied by the decomposition of the cluster, affording the same allylation products of NBD as the reaction with Pd₃(OAc)₆ or Pd(dba)₂ (dba is dibenzylideneacetone) combined with PPh₃. In contrast, in the ionic liquid [bmim][BF₄] (bmim is 1-butyl-3-methylimidazolinium), the Pd-147 is not decomposed and the reaction occurs selectively to give methylidene(vinyl)norbornene as the sole product. The data obtained suggest that in an ionic liquid, the reaction under study is catalyzed by the nanocluster Pd-147 rather than by the products of its decomposition.     

Polymerization of 5-norbornene-2-methyl acetate catalyzed by air-stable cationic (η-substituted allyl) palladium complexes of N-heterocyclic carbene

In situ generated cationic (η³-substituted allyl) palladium N-heterocyclic carbene (NHC) complexes are air-stable active catalysts for the olefin polymerization of (bicyclo[2.2.1]hept-5-en-2-yl)methyl acetate (5-norbornene-2-methyl acetate) (endo:exo = 7:3). Catalytic activities, polymer yields, molecular weights, and molecular weight distributions of polymers were investigated under various reaction conditions. The catalytic activity was highly dependent not only on the reaction condition such as a solvent or the reaction temperature but also on the structure of the catalyst that include substituents of the allyl group in the catalyst and the counter anion. As the bulkiness of the allyl group increased, the catalytic activity of the catalysts increased.     

Pincer‐Type Heck Catalysts and Mechanisms Based on PdIV Intermediates: A Computational Study

Pincer‐type palladium complexes are among the most active Heck catalysts. Due to their exceptionally high thermal stability and the fact that they contain Pd^II centers, controversial Pd^II/Pd^IV cycles have been often proposed as potential catalytic mechanisms. However, pincer‐type Pd^IV intermediates have never been experimentally observed, and computational studies to support the proposed Pd^II/Pd^IV mechanisms with pincer‐type catalysts have never been carried out. In this computational study the feasibility of potential catalytic cycles involving Pd^IV intermediates was explored. Density functional calculations were performed on experimentally applied aminophosphine‐, phosphine‐, and phosphite‐based pincer‐type Heck catalysts with styrene and phenyl bromide as substrates and (E)‐stilbene as coupling product. The potential‐energy surfaces were calculated in dimethylformamide (DMF) as solvent and demonstrate that Pd^II/Pd^IV mechanisms are thermally accessible and thus a true alternative to formation of palladium nanoparticles. Initial reaction steps of the lowest energy path of the catalytic cycle of the Heck reaction include dissociation of the chloride ligands from the neutral pincer complexes [{2,6‐C₆H₃(XPR₂)₂}Pd(Cl)] [X=NH, R=piperidinyl ( 1 a ); X=O, R=piperidinyl ( 1 b ); X=O, R=iPr ( 1 c ); X=CH₂, R=iPr ( 1 d )] to yield cationic, three‐coordinate, T‐shaped 14e^? palladium intermediates of type [{2,6‐C₆H₃(XPR₂)₂}Pd]⁺ ( 2 ). An alternative reaction path to generate complexes of type 2 (relevant for electron‐poor pincer complexes) includes initial coordination of styrene to 1 to yield styrene adducts [{2,6‐C₆H₃(XPR₂)₂}Pd(Cl)(CH₂?CHPh)] ( 4 ) and consecutive dissociation of the chloride ligand to yield cationic square‐planar styrene complexes [{2,6‐C₆H₃(XPR₂)₂}Pd(CH₂?CHPh)]⁺ ( 6 ) and styrene. Cationic styrene adducts of type 6 were additionally found to be the resting states of the catalytic reaction. However, oxidative addition of phenyl bromide to 2 result in pentacoordinate Pd^IV complexes of type [{2,6‐C₆H₃(XPR₂)₂}Pd(Br)(C₆H₅)]⁺ ( 11 ), which subsequently coordinate styrene (in trans position relative to the phenyl unit of the pincer cores) to yield hexacoordinate phenyl styrene complexes [{2,6‐C₆H₃(XPR₂)₂}Pd(Br)(C₆H₅)(CH₂?CHPh)]⁺ ( 12 ). Migration of the phenyl ligand to the olefinic bond gives cationic, pentacoordinate phenylethenyl complexes [{2,6‐C₆H₃(XPR₂)₂}Pd(Br)(CHPhCH₂Ph)]⁺ ( 13 ). Subsequent β‐hydride elimination induces direct HBr liberation to yield cationic, square‐planar (E)‐stilbene complexes with general formula [{2,6‐C₆H₃(XPR₂)₂}Pd(CHPh?CHPh)]⁺ ( 14 ). Subsequent liberation of (E)‐stilbene closes the catalytic cycle.     

Structure of polynuclear palladium(ii) hydroxocomplexes formed upon alkaline hydrolysis of palladium(ii) chloride complexes

The structure of polynuclear Pd^II hydroxocomplexes (PHC) formed as a result of alkaline hydrolysis of Pd^II chloride complexes was studied by EXAFS, SAXS, and TEM methods. It is established that in aqueous solutions a hydroxocomplex particle is a filament curled into a ball containing about 100 Pd atoms. The filament consists of planar coordination squares of PdO₄ units linkedvia one or two oxygen bridges of different geometry. Aging of samples results in an increase in the number of single bridging ligands and a decrease in the diameter of particles. Interatomic distances around palladium atoms were determined.Translated fromIzvestiya Akademii Nauk. Seriya Khimlcheskaya, No. 10, pp. 1901–1905, October, 1995.     

Reactivity of fluorinated sulfur-containing heterocycles towards nucleophilic and oxidizing reagents

The reaction of 5,5-bis(trifluoromethyl)-6-thia-bicyclo[2.2.1]hept-2-ene, 5,5-bis(trifluoromethyl)-6-thia-bicyclo[2.2.2]oct-2-ene and 2,2-bis(trifluoromethyl)-3,6-dihydro-4,5-dimethyl-2H-thiopyran with i-C₃H₇MgCl leads to the formation of ring opening products as the result of nucleophilic attack of the Grignard reagent on the sulfur atom. According to DFT calculations the reactivity of the sulphur-containing substrate correlates with the strain energy of the heterocycle. The oxidation of 3-thia-4,4-bis(trifluoromethyl)tricyclo[5.2.1.0^2,5]non-7-ene by hydrogen peroxide in hexafluoro-iso-propanol solvent resulted in formation of the corresponding sulfoxide however, the reaction with m-chloroperoxybenzoic acid produced the product of exhaustive oxidation of sulfur and the double bond. In sharp contrast, the oxidation of 5,5-bis(trifluoromethyl)-6-thia-bicyclo[2.2.1]hept-2-ene and 5,5-bis(trifluoromethyl)-6-thia-bicyclo[2.2.2]oct-2-ene by MCPBA (2d, 25 °C) proceeds with the preservation of the double bond, leading to the selective formation of the corresponding sulfones.     

Providing Support in Favor of the Existence of a PdII/PdIV Catalytic Cycle in a Heck‐Type Reaction

The complex [Pd(O,N,C‐L)(OAc)], in which L is a monoanionic pincer ligand derived from 2,6‐diacetylpyridine, reacts with 2‐iodobenzoic acid at room temperature to afford the very stable pair of Pd^IV complexes (OC‐6‐54)‐ and (OC‐6‐26)‐[Pd(O,N,C‐L)(O,C‐C₆H₄CO₂‐2)I] (1.5:1 molar ratio, at ?55 °C). These complexes and the Pd^II species [Pd(O,N,C‐L)(OX)] and [Pd(O,N,C‐L′)(NCMe)]ClO₄, (X=MeC(O) or ClO₃, L′=another monoanionic pincer ligand derived from 2,6‐diacetylpyridine), are precatalysts for the arylation of CH₂?CHR (R?CO₂Me, CO₂Et, Ph) using IC₆H₄CO₂H‐2 and AgClO₄. These catalytic reactions have been studied and a tentative mechanism is proposed. The presence of two Pd^IV complexes was detected by ESI(+)‐MS during the catalytic process. All the data obtained strongly support a Pd^II/Pd^IV catalytic cycle.     

Kinetics and mechanism of catalytic oxidation of alcohols to carbonyl compounds with dioxygen in the Pd-containing aqua system

The oxidation of lower aliphatic alcohols C₁–C₄ with dioxygen to form the corresponding carbonyl compounds in the presence of the PdII tetraaqua complexes and Fe^II-Fe^III aqua ions in an aqueous medium was studied at 40–80 °C. The introduction of an aromatic compound (acetophenone, benzonitrile, phenylacetonitrile, o-cyanotoluene, nitrobenzene) and Fe^II aqua ion instead of the Fe^III aqua ion into the reaction system increases substantially the catalytic activity and the yield of the carbonyl compound. The key role of the Pd species in the intermediate oxidation state stabilized by the aromatic additive in the catalytic cycle of alcohol oxidation with dioxygen to the carbonyl compound was shown. An increase in the kinetic isotope effect with an increase in the temperature of methanol oxidation indicates a change in the rate-determining step of alcohol oxidation with dioxygen in the presence of Pd^II-Fe^II-Fe^III and the aromatic compound. At temperatures below 60 °C, the catalytically active palladium species are mainly formed upon the reduction of the Pd^II tetraaqua complex with the Fe^II aqua ion, whereas at higher temperatures the reaction between the alcohol and Pd^II predominates. The mechanism and kinetic equation of the process were proposed. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 842–848, May, 2007.     

Analytical ion cyclotron resonance spectrometry. Spectereochemical factors and a functional group interaction in some norbornyl systems

Ion cyclotron resonance results show that the rate of the acetylation of endo-bicyclo-[2.2.1]hept-5-en-2-ol by [(CH₃CO)₃]⁺ in the gas phase is similar to that of its exo-isomer and greater than that of endo-norborneol by the same ion. This suggests that steric interference of the 6-endo hydrogen is removed by making it vinylic. Additionally, the acetates of the isomeric norborneols and of exo- and endo-bicyclo[2.2.1]hept-5-en-2-ol have relative rates 1.0, 0.9, 1.1 and 0.5; these figures may be interpreted to indicate that acetylation may occur on the carbonyl oxygen here and that in the last compound the carbonyl function is protected by interaction with the olefinic bond.     

Co<Superscript>II</Superscript> and Rh<Superscript>I</Superscript> complexes with <Emphasis Type="Italic">C</Emphasis><Subscript>2</Subscript>-symmetric chiral diamines of the dioxolane series

The reaction of di-μ-chlorobis(1,5-cyclooctadiene)dirhodium with (4S, 5S)-2,2-dimethyl-4,5-bis(methylaminomethyl)-1,3-dioxolane (1) gave the complex [Rh(cod)(1)]Cl (cod is 1,5-cyclooctadiene). The composition of the complexes CoCl₂ · L₂ and [Rh(cod)(L₂)]X (L₂ = 1, (4S,5S)-2,2-dimethyl-4,5-bis(aminomethyl)-1,3-dioxolane, and (4S, 5S)-2,2-dimethyl-4,5-bis(dimethylaminomethyl)-1,3-dioxolane; X = Cl, TfO) was studied using IR and ¹H NMR spectroscopy. In the Rh^I cyclooctadienediamine complexes, the diene molecule forms a stronger bond with the metal atom than that in the cyclooctadienediphosphine analogs. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2270–2274, October, 2005.     

Synthesis and electrochemical study of 2-(2-pyridyl)benzothiazole complexes with transition metals (CoII, NiII, and CuII). Molecular structure of aquabis[2-(2-pyridyl)benzothiazole]copper(II) diperchlorate

The reactions of 2-(2-pyridyl)benzothiazole (1) with MX₂·nH₂O salts (M = Ni^II, Co^II, or Cu^II; X = Cl or ClO₄; n = 0–2) in EtOH afforded the corresponding complexes. Depending on the nature of the counterion in the starting metal salt, the reactions give compounds of composition M(1)Cl₂·nH₂O or Cu(1)₂(ClO₄)₂·H₂O. The molecular and crystal structure of the Cu^II(1)₂(ClO₄)₂·H₂O complex was established by X-ray diffraction. The copper atom in this complex has a distorted tetragonal-pyramidal ligand environment and is coordinated by four nitrogen atoms of two ligand molecules and one water molecule. Electrochemical study of the ligand and the resulting complexes by cyclic voltammetry and at a rotating disk electrode demonstrated that ligand 1 stabilizes reduced forms of complexes containing Ni, Co, or Cu atoms in the oxidation state +1. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1738–1744, October, 2006.     

Synthesis,spectroscopic characterization and study the effect of gamma irradiation on VO2+, Mn2+, Zn2+, Ru3+, Pd2+, Ag+ and Hg2+ complexes and antibacterial activities

Novel complexes of VO²⁺, Mn²⁺, Zn²⁺, Ru³⁺, Pd²⁺, Ag⁺ and Hg²⁺ have been prepared by reacting their metal salts with ligand, named (4-(4-chlorophenyl)-1-(2-(phenylamino) acetyl) thiosemicarbazone). Study of synthesized metal complexes was confirmed by different analytical and spectral techniques (¹H NMR, MS, FT-IR, UV–Vis, EPR and Powder X-ray diffraction), thermogravimetric studies as well as molecular modeling. FT-IR spectra showed that the compound behave as neutral or monobasic tetradentate. In case of complexes of Mn²⁺, Zn²⁺, Ag⁺ and VO²⁺, through (N2H), (CO) or (CO) groups. While, the ligand behave as neutral bidentate in case of complexes with Pd²⁺ and Hg²⁺. X-ray diffraction pattern of Mn²⁺, Pd²⁺ and Ag⁺ complexes before and after irradiation are recorded. XRD studies exhibited that decrease in the crystalline size of sample Mn²⁺ as compared of samples Ag⁺ and Pd²⁺ upon irradiation and irradiation influenced the crystallinity of the complexes. The possible structures of the ligand, Mn²⁺, Pd²⁺ and Hg²⁺complexes have been computed by means of the molecular mechanic calculations using the hyper chem. 8.03 molecular modeling program. The bond length, bond angle, HOMO, LUMO and dipole moment have been studied to verify the geometry of Mn²⁺, Pd²⁺ and Hg²⁺ complexes. The effect of gamma irradiation was investigated by recording the new results of pervious spectroscopic techniques and other measurements. Thermal studies of these chelates before and after γ-irradiation showed that the complexes after γ-irradiation were more thermally stable than before γ-irradiation. The compound and its metal complexes have been experienced for their inhibitory outcome on the growth of microorganisms against gram positive and gram negative. The results proved that the complexes B₁–B₇ have potent antibacterial activity as compared to that of ligand.     

Synthesis and electrochemical characterization of CoII, NiII, and CuII complexes with organic N2S2-type ligands derived from 2-thio-substituted benzaldehydes and aromatic amines

Transition metal complexes (Ni^II, Co^II, and Cu^II) with tetradentate N₂S₂-type ligands (L), which are reaction products of 2-thio-substituted benzaldehydes with aromatic amines (3-aminopyridine or 2-aminothiophenol), were synthesized for the first time. The complexes have the composition L·MX₂ or L·2MX₂ (X = Cl or ClO₄). The electrochemical behavior of the ligands and complexes was studied by cyclic voltammetry and rotating disk electrode voltammetry. Depending on the structure of the complexes, the metal atom in the latter is initially reduced in a one-or two-electron process. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2115–2124, November, 2007.     

Formation of polynuclear palladium complexes with the benzimidazole-2-thiolate anion

The reactions of palladium(II) salts with 2-mercaptobenzimidazole (HL) and its 5,6-difluorinated derivative (HL^F) were investigated. In the presence of hydrochloric acid, PdCl₂ and K₂PdCl₄ react with HL and HL^F in the ethanol—water and acetonitrile—water systems to form the mono-nuclear dicationic complexes [Pd(HL)₄]Cl₂ (1) and [Pd(L^F)₄]Cl₂ (2). In the absence of HCl, the reactions afford the tetranuclear complex Pd₄[(L)₂(μ₃-S,N-(L))₂(μS,N-(L))₄] (3). The reaction of triethylamine with an ethanolic solution of 3 leads to degradation of 3 and the formation of the lantern-type dinuclear complex Pd₂[(μ₂-(L)₄] (4), in which the palladium atoms are in the nonequivalent coordination environment, PdN₄ and PdS₄. The reaction of K₂PdCl₄ with HL or HL^F in the THF—water or acetonitrile—water systems (for the reaction with HL^F) in the presence of Et₃N produces the lantern-type dinuclear complexes Pd₂[(μS,N′-(L³))₄] and Pd₂[(μ-S,N′-(L^F))₄] (5), in which the metal atoms are in the equivalent coordination environment (cis-PdN₂S₂). Dedicated to Academician G. A. Tolstikov on the occasion of his 75th birthday. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 45–52, January, 2008.     

Palladium-catalyzed activation of E-E and C-E bonds in diaryl dichalcogenides (E = S,Se) under microwave irradiation conditions

The first example of palladium-catalyzed stereoselective addition of diphenyl disulfide and diphenyl diselenide to the triple bond of terminal alkynes under microwave irradiation conditions is described. It was found that both the element—element (E-E) and carbon—element bonds can be activated in the catalytic system studied. The products of both reactions were isolated in quantitative yields. According to quantum-chemical calculations, the reaction mechanism involves the oxidative addition of the E-E bond to Pd⁰. Depending on the microwave power and reaction conditions, the next stage is either the reaction with alkyne or the carbon—element bond activation. The product of the oxidative addition of Ph₂Se₂ to Pd⁰, namely, dinuclear complex [Pd₂(SePh)₄(PPh_{3 2}], was detected by ³¹P{¹H}NMR spectroscopy directly in the Ph₂Se₂/PPh₃ melt formed under microwave irradiation conditions.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 569–580, March, 2005.     

Redox Reaction of the Pd0 Complex Bearing the Trost Ligand with meso‐Cycloalkene‐1,4‐biscarbonates Leading to a Diamidato PdII Complex and 1,3‐Cycloalkadienes: Enantioselective Desymmetrization Versus Catalyst Deactivation

The Pd⁰ complex 1 that bears the Trost ligand 2 undergoes a facile redox reaction with 1,4‐biscarbonates 5 b – d and rac‐ 22 under formation of the diamidato–Pd^II complex 7 and the corresponding 1,3‐cycloalkadienes 8 b – d . The redox deactivation of complex 1 was the dominating pathway in the reaction of 5 b – d with HCO₃^? at room temperature. However, at 0 °C the six‐membered biscarbonate 5 b , catalytic amounts of complex 1 , and HCO₃^? mainly reacted in an allylic alkylation, which led to a highly selective desymmetrization of the substrate and gave alcohol 6 b with ≥99 % ee in 66 % yield. An increase of the catalyst loading in the reaction of 5 b with 1 and HCO₃^? afforded the bicyclic carbonate 12 b (96 % ee, 92 %). Formation of carbonate 12 b involves two consecutive inter‐ and intramolecular substitution reactions of the π‐allyl–Pd^II complexes 16 b and 18 b , respectively, with O‐nucleophiles and presumably proceeds through the hydrogen carbonate 17 b as key intermediate. The intermediate formation of 17 b is also indicated by the conversion of alcohol rac‐ 6 b to carbonate 12 b upon treatment with HCO₃^? and 1 . The Pd⁰‐catalyzed desymmetrization of 5 b with formation of 12 b and its hydrolysis allow an efficient enantioselective synthesis of diol 13 b . The reaction of the seven‐membered biscarbonate 5 c with ent‐ 1 and HCO₃^? afforded carbonate ent‐ 12 c (99 % ee, 39 %). The Pd⁰ complex 1 is stable in solution and suffers no intramolecular redox reaction with formation of complex 7 and dihydrogen as recently claimed for the similar Pd⁰ complex 9 . Instead, complex 1 is rapidly oxidized by dioxygen to give the stable Pd^II complex 7 . Thus, formation of the Pd^II complex 10 from 9 was most likely due to an oxidation by dioxygen. Oxidative workup (air) of the reaction mixture stemming from the desymmetrization of 5 c catalyzed by 1 gave the Pd^II complex 7 in high yield besides carbonate 12 c .     

Synthesis and electrochemical characterization of complexes of 1,2-bis[2-(pyridylmethylideneamino)phenylthio]ethanes with transition metals (CoII, NiII, CuII)

Transition metal (Ni^II, Co^II, and Cu^II) complexes with 1,2-bis[2-(3-pyridylmethylideneamino)phenylthio]ethane (1) and 1,2-bis[2-(4-pyridylmethylideneamino)phenylthio]ethane (2) were synthesized for the first time by slow diffusion of solutions of compounds 1 or 2 in CH₂Cl₂ into solutions of MX₂ · nH₂O (M = Ni, Co, or Cu; X = Cl or NO₃; n = 2 or 6) in ethanol. The reactions with Co^II and Cu^II chlorides afford complexes of composition M(L)Cl₂ (L = 1 or 2). The reactions of compound 1 with Ni^II salts produce complexes with 1,2-bis(2-aminophenylthio)ethane. The molecular structure of dinitrato[1,2-bis(2-aminophenylthio)ethane]nickel(ii) was confirmed by X-ray diffraction. The ligands and the complexes were investigated by cyclic voltammetry and rotating disk electrode voltammetry. The initial reduction of the complexes proceeds at the metal atom. The oxidation of the chlorine-containing complexes proceeds at the coordinated chloride anion. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 350–355, February, 2008.     

Palladium‐Catalyzed Alkoxycarbonylation of Terminal Alkenes To Produce α,β‐Unsaturated Esters: The Key Role of Acetonitrile as a Ligand

A mild protocol has been developed for the Pd^II‐catalyzed alkoxycarbonylation of terminal olefins to produce α,β‐unsaturated esters with a wide range of substrates. Key features are the use of MeCN as solvent (and/or ligand) to control the reactivity of the intermediate Pd complexes and the combination of CO with O₂, which facilitates the Cu^II‐mediated reoxidation of the Pd⁰ complex to Pd^II and prevents double carbonylation.     

Metallation of the methyl group ino-nitrosotoluene: synthesis and the molecular structure of the binuclear complex [o-(NO)(CH2)C6H4)]2Pd2(μ-OOCCF3)2

The reaction of the tetranuclear cluster Pd₄(CO)₄(OOCCF₃)₄ witho-nitrosotoluene afforded the Pd¹¹-containing complex [o-(NO)(CH₂)C₆H₄]₂Pd₂(μ-OOCCF₃)₂. The elimination of CO₂ and the formation of organic products of transformation of tolylnitrene species (azotoluene, ditolylamine, and tolylisocyanate) were observed in the course of the reaction. The title complex was characterized by IR and¹H NMR spectroscopy. Its structure was established by X-ray diffraction analysis. It was suggested that the reaction proceeds through intermediate formation of nitrene complexes. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 147–150, January, 2000.