Nature of catalytic effect of Ni(O)- and BF3OEt2-based systems in propene dimerization

¹H NMR, EPR and IR spectroscopic studies of the products of the interaction between components of the Ni[PPh₃]₄+EtOH+BF₃.OEt₂ and Ni(PPh₃)₄+BF₃OEt₂ systems suggest the formation of two types of complexes [HNi(PP₃)₃L]⁺[BF₃OEt]^– and [Ni(PPh₃)₃L]⁺BF ₄ ^– , which are catalytically active in propene dimerization.

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¹H, , - Ni(PPh₃)₄+ EtOH+BF₃OEt₂ Ni(PPh₃)₄+BF₃·OEt₂ [HNi (PPh₃)₃L]⁺ [BF₃OEt]^– [Ni (PPh₃)L₂]⁺BF ₄ ^– .

     

Tribromogermyl monochelates — derivatives of N,N-disubstituted 2-hydroxycarboxylic amides

Reactions of GeBr₄ with N,N-dimethyl-2-trimethylsiloxypropionamide (2a), (S)-2-trime-thylsiloxypropionpyrrolidide ((S)-2b), and N,N-dimethyl-O-(trimethylsilyl)mandelamide (2c) afforded pentacoordinated neutral (O,O)-monochelates, viz., N,N-dimethyl-2-tribromoger-myloxypropionamide (3a), (S)-2-tribromogermyloxypropionpyrrolidide ((S)-3b), and N,N-dimethyl-O-(tribromogermyl)mandelamide (3c), respectively. X-ray diffraction study was performed for tribromides 3a, (S)-3b, and 3c, as well as for the N,N-dimethylmandelamide (1c) described earlier. According to the X-ray diffraction data, the Ge atom in tribromides 3a, (S)-3b, and 3c is pentacoordinated and has trigonal bipyramidal configuration with two halogen atoms and oxygen atom of the ether group in the equatorial positions and the halogen atom and the amide oxygen atom in the axial fragment, the bonds in which are somewhat longer as compared to the analogous bonds in tetracoordinated Ge compounds.     

Synthesis, molecular and crystal structure, and features of the electronic structure of bis(O’i)-chelated bis(2,2-dimethylbenzo-[2H]-4-oxo-1,3-oxazino-3-methyl)difluorosilane

A method has been developed for the synthesis of a bis(O→Si)-chelated bis(2,2-dimethylbenzo[2H]-4-oxo-1,3-oxazino-3-methyl)difluorosilane from 2,2-dimethyl-3-trimethylsilylbenzo[2H]-1,3-oxazin-4-one and bis(chloromethyl)dichlorosilane via the intermediate formation of the corresponding unstable bis-chelated dichloride, subsequent hydrolysis with NaHCO₃ and, without separation, treatment of the hydrolysis product with boron trifluoride etherate. Analysis of the electron density distribution showed the presence of dative bonding in both O→Si-F fragments. Dedicated to Prof. Edmunds Lukevics on the occasion of his 70th birthday __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 12, pp. 1866–1879, December, 2006.     

Characteristics of copper sulfide nanoparticles obtained in the copper sulfate–sodium thiosulfate system

Stable hydrosols of copper sulfide nanoparticles are synthesized by heating aqueous solutions with different ratios of sodium thiosulfate and copper sulfate in the presence of polyvinylpyrrolidone and studied by a number of physicochemical methods in situ (optical spectroscopy, dynamic light scattering) and ex situ (transmission electron microscopy, powder X-ray diffraction, X-ray photoelectron spectroscopy). The main product is CuS covellite nanoparticles with some impurities of other phases (Cu₂S, Cu_1,8S, Cu₇S₄). With an increase in the initial molar ratio S₂O ^2?₃ / Cu from 0.2 to 5 the nanoparticle size increases from 1-5 nm to 30-50 nm and then decreases to 4 nm at a ratio of 10. A substantial increase in the intensity of plasmon absorption within 800-1500 nm is observed during the formation of planar nanoparticles with a lateral size of about 30 nm at S₂O ^2?₃:Cu = 5. A band gap obtained from both direct and indirect optical absorption spectra of sulfides (2.6 eV and 1.7 eV respectively) remains constant for all particles.     

Formation mechanism and structure of compounds catalytically active in propylene dimerization and formed in Pd(acac)2?PR3?BF3OEt2 systems

The interaction between the components of catalytic Pd(acac)₂–PR₃–BF₃OEt₂ systems dimerizing propylene to linear hexenes with 59 % selectivity, has been studied by UV and¹H NMR spectroscopy methods. Formation mechanism of catalytically active [R₃P–Pd–H]⁺BF ₄ ^– compounds is suggested.

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, ¹ Pd(acac)₂–PR₃–BF₃OEt₂, 59%, [R₃P–Pd–H]⁺BF ₄ ^– .

     

Phase formation of BICUVOX solid solutions

Phase formation of Bi₄(V_{1 ? x} Cu _x )₂O_{11 ? z} solid solutions (BICUVOX) with x = 0.00–0.20 and Δx = 0.02 was studied. The concentration stability ranges were determined for the α, β, and γ polymorphs of BICUVOX solid solutions at room temperature, and their unit cell parameters were revised. The following was found to occur as x rises: the α ai β phase transition temperature between the monoclinic and orthorhombic phases shifts down, the β ai γ phase transition temperature to the high-temperature tetragonal phase shifts down, and the order-disorder phase transition temperature between γ′ ai γ tetragonal phases shifts up.     

Trichloro- and methyldichlorogermyl monochelates and dibromo- and dichlorogermyl bischelates derived from N,N-disubstituted amides of 2-hydroxycarboxylic acids

The reactions of GeCl₄, GeBr₄, and MeGeCl₃ with O-trimethylsilyl derivatives of N,N-disubstituted amides of 2-hydroxycarboxylic acids afforded pentacoordinate and hexacoordinate neutral (O,O)-mono- and (O,O)-bischelates. The reactions of glycolic acid derivatives with GeX₄ produced bischelates X₂Ge[OCH₂C(O)NR²R³]₂ 7a,c,d (X = Cl, R² = R³ = Me (a), (CH₂)₅ (c), (CH₂CH₂)₂O (d)) and 8a (X = Br). By contrast, the reactions of lactic and mandelic acid derivatives with GeCl₄ and MeGeCl₃ gave monochelates Cl₃Ge[OCH(R¹)C(O)NR²R³] (S)-9a–c (R¹ = Me) and Cl₂MeGe[OCH(R¹)C(O)NR²R³] 10a (R¹ = H), (S)-11a,b (R¹ = Me), and (S)-12a (R¹ = Ph) (R²R³ = (CH₂)₄ (b)), respectively. According to the X-ray diffraction data, the Ge atom in bischelates 7c,d and 8a has a coordination number 6, and its coordination polyhedron can be described as a slightly distorted octahedron. In monochelates (S)-9a-c, 10a, (S)-11a,b, and (S)-12a, the Ge atom has a coordination number 5, and its coordination polyhedron can be described as a trigonal bipyramid with two halogen atoms or one halogen atom and one ethereal oxygen atom in equatorial positions and the halogen atom and the amide oxygen atom in the axial positions. The bonds in the axial positions are somewhat longer than the corresponding bonds in tetracoordinate Ge compounds.     

Donor-stabilized five-coordinate cationic chelate silicon compounds with two (O→Si)-coordinating ligands

Cationic O→Si-coordinated bis-C,O-chelate silicon complexes [(LCH₂)₂Si(F)]BF₄, containing monoanionic AcN(Me)CH₂, 2-oxoperhydroazepinomethyl, 2,2-dimethyl-4-oxobenzo[1,3]oxazin-3-ylmethyl, and 4-methyl-2-oxoquinolinomethyl C,O-coordinating ligands were synthesized by the reaction of trimethylsilyl derivatives of amides, lactams, and related compounds with (ClCH₂)₂SiCl₂ in a 2:1 ratio. The synthesized complexes were reacted with KF to obtain six-coordinate bis-C,O-chelates [(LCH₂)₂SiF₂] which were then converted into the starting tetrafluoroborates by treatment with BF₃·Et₂O. First representatives of cationic bis-O,O′-chelate silicon complexes with a 2-hydroxyacid amide fragment {XSi[OCH(R)C(O)NMe₂]₂}Y (X = Cl, Me, t-Bu, Ph, BrCH₂; R = H, Me; Y - Cl^?, ClHCl^?, HgBr ₃ ^? ) were synthesized by the reaction of XSiCl₃ with O→SiMe₃ derivatives of dimethylamides of (S)-lactic and glycolic acids in a 1:2 ratio or by transesterification of XSi(OMe)₃ with glycolic acid dimethylamide followed by addition of acetyl bromide (ratio 1:3:1). The structure of the resulting chelates was proved by X-ray diffraction analysis.     

Scheme of hydrolysis of five-coordinate chlorosilanes by X-ray diffraction data

Hydrolysis of monochelate five-coordinate chlorosilanes MeC(O)N(Me)CH₂SiMe₂Cl (Ia), L⁷CH₂SiMe₂Cl (Ib), L⁸CH₂SiMe₂Cl (Ic), PhtImCH₂SiMe₂Cl (Id), MeC(O)N(Me)CH₂SiMePhCl (IIa), and Im₅CH₂SiMePhCl (IIe), containing a monoanionic C,O-chelating ligand LCH₂ [L is an amide, n-membered lactam (L ⁿ ), imide (Im ⁿ ), or phthalimide (PhtIm) residue]. The structures of the starting chlorides and their hydrolysis products were established by means of X-ray diffraction analysis. Based on experimental and published data, a general scheme of hydrolysis of mono-C,O-chelate chlorosilanes was suggested, including initial formation of silyloxonium chlorides III and subsequent formation of disiloxane dihydrochlorides IV.