Synthesis of coumarins by Pt-catalyzed hydroarylation of propiolic acids with phenols

Synthesis of coumarins from phenols and propiolic acids was examined by using a Pt catalyst such as PtCl₂/AgOTf, K₂PtCl₄/AgOTf, and K₂PtCl₄/AgOAc. Propiolic acid reacted even with less reactive phenols in trifluoroacetic acid to give coumarins and dihydrocoumarins. In the case of substituted propiolic acids, phenylpropiolic acid and 2-octynoic acid, the reactions proceeded selectively to afford coumarins in good to high yields.     

Ether-directed diastereoselectivity in catalysed Overman rearrangement: comparative studies of metal catalysts

Ether-directed diastereoselectivity in Overman rearrangement of δ-methoxy and δ-TBDMSO substituted allylic trichloroacetimidates has been explored using PtCl₂, PtCl₄, AuCl and AuCl₃ catalysts in comparison with commonly used Pd(II) catalysts. For both substrates the use of PtCl₂ catalyst gave notably improved anti/syn-ratio of 1,2-aminoalcohol derivatives (anti/syn=11:1 for δ-methoxy; 6:1 for δ-TBDMSO) compared to all metal catalysts known to promote Overman rearrangement. Formation of 2-trichloromethyloxazoline was observed as a dominant side reaction in the metal catalysed rearrangement of δ-methoxy substituted allylic trichloroacetimidates considerably reducing the yield of the desired product. This side reaction was suppressed when δ-TBDMS-ether was used as a directing group.     

Efficient and selective hydroarylation of propiolic acids and their esters with arenes catalyzed by a PtCl2/AgOTf system

PtCl₂/AgOTf-catalyzed hydroarylation of ethyl propiolate proceeded effectively to give ethyl (2Z)-cinnamate derivatives in good to high yields, without the formation of diethyl (1E,3Z)-4-arylbuta-1,3-diene-1,3-dicarboxylates that was observed in Pd(OAc)₂-catalyzed reaction. Especially, PtCl₂/AgOTf-catalyzed hydroarylation of propiolic acids proceeded effectively to give (2Z)-cinnamic acids exclusively.     

Electrochemical quartz crystal microbalance study on Au-supported Pt adlayers for electrocatalytic oxidation of methanol in alkaline solution

Underpotential deposition (UPD) of Cu on an Au electrode followed by redox replacement reaction (RRR) of Cu_UPD with a Pt source (H₂PtCl₆ or K₂PtCl₄) yielded Au-supported Pt adlayers (for short, Pt(CuUPD-Pt⁴⁺)n/Au for H₂PtCl₆, or Pt(CuUPD-Pt²⁺)n/Au for K₂PtCl₄, where n denotes the number of UPD-redox replacement cycles). The electrochemical quartz crystal microbalance (EQCM) technique was used for the first time to quantitatively study the fabricated electrodes and estimate their mass-normalized specific electrocatalytic activity (SECA) for methanol oxidation in alkaline solution. In comparison with Pt(CuUPD-Pt²⁺)n/Au, Pt(CuUPD-Pt⁴⁺)n/Au exhibited a higher electrocatalytic activity, and the maximum SECA was obtained to be as high as 35.7 mA μg^?1 at Pt(CuUPD-Pt⁴⁺)3/Au. The layer-by-layer architecture of Pt atoms on Au is briefly discussed based on the EQCM-revealed redox replacement efficiency, and the calculated distribution percentages of bare Au sites agree with the experimental results deduced from the charge under the AuO _x -reduction peaks. The EQCM is highly recommended as an efficient technique to quantitatively examine various electrode-supported catalyst adlayers, and the highly efficient catalyst adlayers of noble metals are promising in electrocatalysis relevant to biological, energy and environmental sciences and technologies.     

Mechanochemical Activation of K2PtCl6: Heterogeneous Catalyst for Gas-Phase Hydrochlorination of Acetylene

A heterogeneous catalyst for hydrochlorination of acetylene by gas-phase HCl is formed as a result of mechanical treatment of the solid salt K₂PtCl₆ under an acetylene, ethylene, or propylene atmosphere. We used X-ray photoelectron spectroscopy (XPS) to prove that under these conditions, in the near-surface layers of the K₂PtCl₆ matrix, there was formation of Pt(II) complexes and platinum complexes with vacancies in the coordination sphere. We hypothesized that the active centers of the catalyst are defects in the K₂PtCl₆ lattice in the form of impurity platinum(II) ions in the K₂PtCl₆ matrix.     

A high hydroarylation activity of K2PtCl4/AgOTf catalyst in the reaction of propiolic acid with unactivated and activated arenes

A mixed catalyst K₂PtCl₄/AgOTf showed the highest activity for hydroarylation of propiolic acid, among palladium and platinum catalysts. This catalyst was effective for hydroarylation with less reactive benzene to give cis-cinnamic acid in good yield. The hydroarylation with toluene gave a higher yield of hydroarylation products than that with benzene and resulted in ortho/para orientation with an almost statistical ratio, suggesting that the result is very close to that of the Friedel-Crafts alkylation with methyl bromide or p-nitrobenzyl chloride. Hydroarylation of propiolic acid with other electron-rich arenes proceeded efficiently in the presence of the K₂PtCl₄/AgOTf catalyst in trifluoroacetic acid forming cis-cinnamic acids in good to high yields. This method was also applied to hydroarylation of ethyl propiolate.     

Highly selective hydroarylation of propiolic acid derivatives using a PtCl2/AgOTf catalytic system

Hydroarylation of propiolic acid derivatives with arenes in trifluoroacetic acid efficiently proceeded in the presence of PtCl₂/AgOTf catalyst to give cis-cinnamic acid derivatives in good to high yields. This PtCl₂/AgOTf-catalyzed reaction did not afford any 4-arylbuta-1,3-diene-1,3-dicarboxylic acid derivatives formed by Pd(OAc)₂-catalyzed hydroarylation. The specific optimization of the catalytic hydroarylation and application to electron-rich arenes are reported.     

Reaction of platinum complexes with (+)-α-pinene and (+)-limonene. Synthesis, molecular structure, and catalytic activity of dichloro(η4-[p-mentha-1,8{9}-diene])platinum(II)

The transformations of platinum(II) and platinum(IV) complexes with inner-and outer-sphere ligands by the action of (+)-α-pinene and (+)-limonene were studied. Reduction of the metal complex is the main process whose rate increases in the following outer-sphere ligand series: (Me₂SO)₂H⁺ < Et₃NH⁺ < K^? < H⁺. The reaction of K₂PtCl₄ with α-pinene gave cis-terpine monohydrate and dichloro-η⁴-[p-mentha-1,8(9)-diene]platinum(II), and their structure was proved by X-ray analysis. The complex belongs to monoclinic crystal system, the Pt-Cl and Pt-C bonds therein have different lengths, the ClPtCl angle is 85.88°, and the C=C bond plane is orthogonal to the square coordination core. Dichloro-η⁴-[p-mentha-1,8(9)-diene]-platinum(II) was tested as catalyst in the hydrosilylation of acetophenone with diphenylsilane.     

Electron paramagnetic resonance of Mn(II) in [M(H2O)6]PtCl6 (M=Zn,Mg, Cd) single crystals

EPR studies have been carried out on Mn(II)-doped single crystals of [Zn(H₂O)₆]PtCl₆, [Mg(H₂O)₆]PtCl₆ and [Cd(H₂O)₆]PtCl₆ from room temperature to 77 K at X-band frequencies (⋍9.5 GHz). MN(II) ions substituting the divalent metals exhibit a unique magnetic behavior with the z-axes directed along the c-axes of the crystals. A non-linear iterative least-squares fitting procedure for the analysis of EPR spectra is presented. In this method calculation of the spin-Hamiltonian parameters can be carried out for any orientation of the external magnetic field with respect to the crystal symmetry axis.     

W(II)-catalyzed hydroarylation of bicyclo[2.2.1]hept-2-ene by simple arenes

The tungsten(II) carbonyl compound (CO)₄W(μ-Cl)₃W(SnCl₃)(CO)₃ has been found to be a very effective catalyst for the hydroarylation of bicyclo[2.2.1]hept-2-ene (norbornene) conducted in arene solution at room temperature. Norbornene adducts with benzene, toluene, para-xylene, and mesitylene have been isolated and their structures have been unambiguously established by means of ¹H and ¹³C NMR spectroscopy. On the basis of ¹H NMR monitoring of several catalytic reactions, a possible mechanism involving coordination of norbornene to the W(II) atom and its activation has been proposed.     

Cobalt-catalyzed benzylic C-H amination via dehydrogenative-coupling reaction

An efficient direct benzylic C-H amination via dehydrogenative-coupling by using an inexpensive catalyst/oxidant (CoBr₂/^tBuOO^tBu) system is described. Various unmodified amides including primary or secondary sulfonamides, carboxamides, and carbamates preformed well with benzylic hydrocarbons with moderate to good yields.     

Direct arylation of oxazole and benzoxazole with aryl or heteroaryl halides using a palladium-diphosphine catalyst

Through the use of PdCl(dppb)(C₃H₅) as a catalyst, a range of aryl bromides and chlorides undergoes coupling via C-H bond activation/functionalization reaction with oxazole or benzoxazole in good yields. This air-stable catalyst can be used at low loadings with several substrates. Surprisingly, better results in terms of substrate/catalyst ratio were obtained in several cases using electron-excessive aryl bromides than with the electron-deficient ones. This seems to be mainly due to the relatively low thermal stability of some of the 2-arylbenzoxazoles formed with electron-deficient aryl halides. With these substrates, in order to obtain higher yields of product, the reactions had to be performed at a lower temperature (100-120 °C) using a larger amount of catalyst. On the other hand, in the presence of the most stable products, the reactions were performed at 150 °C using as little as 0.2 mol% catalyst. Arylation of benzoxazole with heteroaryl bromides also gave the coupling products in moderate to high yields using 0.2-5 mol% catalyst. With this catalyst, electron-deficient aryl chloride such as 4-chlorobenzonitrile, 4-chloroacetophenone or 2-chloronitrobenzene have also been used successfully.     

Crystal and molecular structures of the olefin complexes trichloro(π-allylammonium)platinum(II), trichloro(π-but-3-enylammonium)platinum(II) and trichloro(π-hex-5-enylammonium)platinum(II)

The crystal and molecular structures of the title compounds, [PtCl₃(C₃H₈N)] (I), [PtCl₃(C₄H₁₀N)] (II), and [PtCl₃(C₆H₁₄N)] (III) have been determined by single-crystal X-ray methods. I crystallizes in the orthorombic system (Pbca) with a 10.444(3), b 8.782(2), c 17.036(5)Å, Z 8; II is monoclinic (P2₁/n) with a 7.953(5), b 11.254(6), c 10.722(6)Å, β 111.07(4)°, Z 4; III is orthorombic (P2₁2₁2₁) with a 17.080(6), b 6.768(2), c 9.541(4)Å, Z 4. Full-matrix least-squares refinements have given final R-factors of 0.051 (1077 reflections for I), 0.043 (1325 reflections for II) and 0.041 (1123 reflections for III). The reflections were collected by counter methods and only those having I τ 3σ(I) were used in the analyses.In all three complexes platinum is four-coordinate, having as ligands the three chlorine atoms and the double bond of the

(n=1, 2 or 4) cationic species. The structures are discussed, and compared with that of the analogous complex containing the pent-4-enylammonium cation,

.     

Modified palladium-catalyzed regioselective ortho-arylation of sp C-H bond substrates with a low catalyst loading

A novel and generally applicable system for ortho-arylation of a broad range of sp² C-H bond substrates such as arylated benzoxazoles, acylated anilines, and pyridines has been developed. The arylation was performed in trifluoroacetic acid (TFA) under air by using PdCl₂ as the catalyst with a low catalyst loading of 1 mol %. And it was found for the first time that the addition of weak base K₃PO₄ to the acidic solvent could remarkably enhance the reaction rate. The arylated products were isolated in moderate to good yields with high regioselectivity for the substrates containing a meta-substituent. This arylation is tolerant with various functional groups such as CH₃, CH₃O, CH₃CO, Br, and Cl.     

Platinum(II) and platinum(IV) chloro complexes with (<Emphasis Type="Italic">RS</Emphasis>)-1-(4-chlorophenyl)-4,4-dimethyl-3-(1Н-1,2,4-triazol-1-ylmethyl)pentan-3-ol

Platinum(II) and platinum(IV) chloro complexes with (RS)-1-(4-chlorophenyl)-4,4-dimethyl-3-(1Н-1,2,4-triazol-1-ylmethyl)pentan-3-ol (L), namely, cis-[PtCl₂L₂], trans-[PtCl₂L₂], and trans-[PtCl₄L₂], were synthesized. The structures of their coordination cores and the coordination mode of the reagent to the metal ions via the N(4) atom of the triazole ring were determined by electronic, IR, and NMR ¹H and ¹³C spectroscopy. The ratio between treo and erythro diastereomers and the conformation of reagent L in the complexes were established from the complete assignment of signals in their NMR spectra.     

Catalysis of hydrosilylation: Part XXIV. H2PtCl6 in cyclohexanone as hydrosilylation catalyst—what is the active species in this catalytic system?

A cyclohexanone solution of H₂PtCl₆ was examined to find the catalytic species responsible for the hydrosilylation of the olefinic C=C bond. Similarly to other H₂PtCl₆–solvent systems (e.g. Speier's and Karstedt's catalysts), the real catalyst appeared to be colloidal platinum formed in situ by stepwise reduction [Pt(IV)→Pt(O)] and dechlorination of the platinum precursor. The role of cyclohexanone seems to be to form sufficiently stable platinum complexes to avoid rapid platinum precipitation and aggregation. The studies of H₂PtCl₆–solvent systems are of practical importance since these compounds are widely used catalyst precursors for hydrosilylation on an industrial scale.     

Kinetics of reaction of alkynes with some cobalt carbonyls

Pt(CO)₂Cl₂ reacts in benzene, toluene or tetrahydrofuran with 3-hexyne to give carbonylplatinumbis[di-μ-chloro,chloro(tetraethylcyclobutadiene)platinum](I), bis[dichloro(tetraethylcyclopentadienone)platinum] (III), dichloro-(tetraethyl-p-benzoquinone)platinum (IV) and dichloro(tetraethylcyclobutadiene)platinum (II). This last compound is also obtained by treating I with 1 to 3 moles of triphenylphosphine or p-toluidine. p ]The structure and reactions of III are discussed; the anion exchange reaction gives the iodo-analogue, while treatment with donor ligands gives adducts of formula [(C₂H₅)₄C₄CO]PtCl₂L(L = triphenylphosphine, p-toluidine, benzylamine and pyridine) and [(C₂H₅)₄C₄CO]PtCl₂L₂(L = benzylamine, 3-methylpyridine). p ]2-Butyne reacts with dichlorodicarbonylplatinum to give the methyl analogous of compounds I–III.     

Spectroscopic,theoretical, and antibacterial approach in the characterization of 5-methyl-5-(3-pyridyl)-2,4-imidazolidenedione ligand and of its platinum and palladium complexes

A series of Pt(IV), Pt(II), and Pd(II) complexes (PtCl₄L₂ (1), PtCl₂L₂ (2), PdCl₂L₂ (3), and Pd₂Cl₄L₂ (4)) with 5-methyl-5-(3-pyridyl)-2,4-imidazolidenedione ligand (L) have been synthesized by the reaction of metal chlorides (K₂[PtCl₆], K₂[PtCl₄], K₂[PdCl₄], and PdCl₂) with L in 1:2 (1-3) and 1:1 (4) molar ratios. The binding manner of L, and the composition and geometry of the metal complexes were examined by elemental analysis, IR, ¹H, and ¹³C NMR spectroscopies. Theoretical calculations invoking geometry optimization of different isomers, performed using density functional theory, suggested that in both gas and solution phases the trans isomers are more stable than the cis ones. The experimental results and calculated molecular parameters, bond distances and angles, revealed slightly distorted octahedral (1) and square-planar (2–4) geometry around the metallic center through the pyridine-type nitrogen (N_py) and chlorine atoms. In 4, the binuclear complex, each palladium atom is coordinated by one nitrogen and three chlorine atoms (one as terminal and two as bridging ligands). Antibacterial activity of L and the corresponding complexes was investigated against six species of microorganisms. Testing was performed by disk diffusion method and minimum inhibitory concentrations (MIC) have been determined. The results showed that the title compounds have the capacity of inhibiting the metabolic growth of bacteria to different extents. In general, the binuclear palladium(II) complex was the most active one.     

Mechanism of the catalytic action of the mechanoactivated salt K2PTCL4 in the gas-phase hydrochlorination of acetylene

A heterogeneous catalyst for the hydrochlorination of acetylene by gaseous HCl is formed as a result of mechanical treatment of the solid salt K₂PtCl₄ in an atmosphere of acetylene, ethylene, or propylene by the formation of π complexes of platinum(II) as active centers in the surface layer under these conditions. The controlling stage of the catalytic reaction is chloroplatination of the π-coordinated acetylene by the HCl molecule. The reaction takes place as a concerted process, in which an intermediate β-chlorovinyl derivative of platinum(II), a complex of platinum with a coordination vacancy[PtCl ₃ ^* ]⁻, and a new molecule of HCl are formed simultaneously with cleavage of the H—Cl and Pt—Cl bonds in the metal complex adjacent to the π-acetylene complex. The catalytic cycle closes with rapid dissociation of the organoplatinum intermediate by the action of HCl, giving the final product and the initial complex [PtCl₄]²⁻. __________ Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 42, No. 5, pp. 306–311, September–October, 2006.     

Preparation of High-alloying Pt-Ru/CMK-3 Catalysts in THF-H2O-EtOH Ternary Solution System

The Pt-Ru particles of the Pt-Ru/CMK-3 catalyst were found to possess high degree of alloying, small average size, and low relative crystallinity when the Pt-Ru/CMK-3 catalyst was prepared using the general chemical reduction method in the ternary solution system containing tetrahydrofuran (THF), H₂O, and ethanol. The Pt-Ru/CMK-3 catalyst showed high electrocatalytic activity for methanol oxidation. It indicated that the alloying of Pt-Ru could significantly affect the electrocatalytic activity for methanol oxidation. The Pt-Ru/CMK-3 catalyst with high alloying degree can be obtained because THF and H₂PtCl₆ can form a complex leading to the reduction potentials of H₂PtCl₆ and RuCl₃, which are close to each other in the aqueous solution with THF.