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1.
Dehydrogenation of alcohols into aldehydes and ketones by Ru3(CO)12/PPh3 based homogeneous catalysis has been investigated as an alternative for the classical Oppenauer oxidation. Several catalytic systems have been screened in the Oppenauer-like oxidation of alcohols. A systematic study of various combinations of Ru3(CO)12, mono- and bidentate ligands and hydride acceptors was performed to enable dehydrogenation of primary alcohols to stop at the aldehyde stage. Among many H-acceptors screened, diphenylacetylene (tolane) proved the most suitable judged from its smooth reduction. Electron rich and deficient analogues of tolane have been synthesized and, based on competition experiments between these H-acceptors, a tentative catalytic cycle for the Ru3(CO)12/PPh3-catalyzed dehydrogenations has been proposed. 相似文献
2.
Y. Adachi K. Aoki 《Colloids and surfaces. A, Physicochemical and engineering aspects》2003,230(1-3):37-44
Standardized mixing procedure was applied to the analysis of flocculation of polystyrene latex (PSL) particles with polyelectrolytes. After confirming the initial enhancement of flocculation rate in the very beginning followed by abrupt stop with excess dosage, attention was shifted to the system of moderate dosage. In the former, effects of ionic strength were further analyzed to find the consistency with adsorption isotherm. In the latter, flocculation started slowly in the beginning, sometime slower than salt-induced rapid coagulation, however, the rate gradually increases in the middle stage. Often, the increased rate exceeds that of salt-induced rapid coagulation. This behavior emerged more clearly in the case of lower ionic strength. This is the indication that the rate of relaxation of polymer on the colloidal surface is a function of surface coverage and ionic strength. The ultimate degree of flocculation is usually higher than that observed for excess dosage. The size distribution of flocs was also examined, however, no clear difference between different experimental conditions was confirmed for the same degree of flocculation. 相似文献
3.
Polyol Metal Complexes. 27. Bis-Diolato Antimonates(III ) with Guanosine as the Diol The complex anions of K3[SbIII(Guo1,2′,3′H?3)2] · 10 H2O ( 1 ) and [Co(NH3)6][SbIII(Guo1,2′,3′H?3)2] · 9 H2O ( 2 ) are four-coordinate homoleptic bis(diolato)antimonate(III ) species. The guanosine trianions act as carbohydrate ligands through their cis-furanoidic ribosyl moiety, thus forming no nucleobase–metal bonds. 相似文献
4.
Guido Kickelbick Dieter Rutzinger Thomas Gallauner 《Monatshefte für Chemie / Chemical Monthly》2002,133(8):1157-1164
Summary. Hexadentate ligands were formed by the reaction of primary dimethylaminoethyl- or methoxyethylamines with formaldehyde. The
resulting N, N′, N″-functionalized hexahydro-1,3,5-triazines contain pending amino or ether functionalities which are able to coordinate to
metals in addition to the ring nitrogen atoms. Both ligands were reacted with CuBr, and novel tricopper clusters were isolated
and characterized by X-ray structure analysis. In these compounds a ring nitrogen atom, the pending amino or ether functionality,
and two bridging bromine atoms coordinate each of the copper atoms.
Received January 22, 2002; accepted (revised) March 22, 2002 相似文献
5.
Heterobimetallic Complexes with Chelate Ligands from Multidentate Amines and 1,1-Bis(diphenylphosphine)ethene By an addition reaction of bidentate amines Me2N(CH2)nNH2 (n = 2, as-4C2N; 3, as-5C2N) and vinylidene derivatives with an activated double bond CH2 = C(PPh2)2M(CO)4 (M = Cr, Mo, W) were synthesized in dichlormethane unsymmetrical chelate ligands of the type as-4C2N (or as-5C2N)PPM(CO)4. They gave with divalent salts M′Y2 (Y = ac, M′ = Cu, Ni. Y = Cl, M′ = Zn, Cd, Hg) the coloured bimetallic complexes M′Y(as-4C2N) (or as-5C2N)PPM(CO)4 which were characterized by means of IR-, UV/VIS spectroscopic and 1H, 13C and 31P NMR measurements. The molecular structures of the complexes Cuac2(as-5C2N)PPCr(CO)4, I and that of CdCl2(as-4C2N)PPCr(CO)4, II , were acertained by results of single crystal X-ray determinations. In the crystals of I—II , the coordination polyhedron of each chromium(0) central atom containing two phosphorous donor atoms in a four-membered chelate ring and four terminal CO ligands is octahedrally distorted. This coordination sphere is connected at the carbon ring atom via a methylen chain group (spacer) with the bidentate amine ligand, which has a secondary and a tertiary nitrogen donor atom. Both nitrogen atoms are coordinated with the Cuac2 under formation of a new kind of [4 + 2]-coordination in a trischelate complex. The six-membered diamine chelat ring in I has a chair-like conformation. The chromium-cadmium complex II is dimer from which the Cd central atoms obtain the rare coordination number of five. The related five-membered diamine chelate ring has δ conformation. 相似文献
6.
Three new rigid bridging ligands for metal complexation (7=bmb, 8=bqb and 11=btb) were prepared from a rigid triptycene spacer connected to two bipyridine ligands using a Horner–Emmons type reaction. The triptycene spacer is substituted by methoxy groups in the case of bmb and in the case of bqb by a benzoquinone substituent. The corresponding metal complexes (ruthenium and/or osmium) were synthesised and the different luminescence behaviour was tested. They show great potential for the investigation of intramolecular electron and energy transfer reactions. The dinuclear metal complex Ru---bqb---Os is an interesting system in which the bridging ligand bqb acts as a redox switch, able to tune the conductivity for energy or electrons across the bridge. 相似文献
7.
Thomas Kauffmann 《Angewandte Chemie (International ed. in English)》1997,36(12):1258-1275
Hitherto there was no reaction known that permits transformations of R1R2-CO → 0.5 R1R2R3C–CR1R2R3 in one step. This type of additive–reductive carbonyl dimerization is now possible using alkoxy(alkyl)tungsten(v) complexes with aromatic, heteroaromatic or α,β-unsaturated aldehydes and ketones. When a corresponding phenyl complex was employed in a test experiment, it was revealed that an aliphatic ketone could be used as the substrate in this reaction. A second interesting type of reaction is the transformation of CH3 ligands into μ-CH2 ligands, which occurs during the treatment of MeLi or Me3Al with molybdenum or tungsten chlorides (oxidation states VI and V, for Mo additionally IV) at low temperatures with liberation of CH4. Here, the question arises as to whether the intermediate involved has a terminal CH2 ligand (Schrock carbene complex) or a μ-CH3 ligand (CH3 bound by a two-electron three-center bond to two metal atoms). Of all the μ-CH2 complexes obtained, those which were synthesized by the action of MeLi on molybdenum chlorides can be recommended as reagents for carbonylmethylenation of aldehydes and ketones. They display high selectivity, very low basicity, a surprising resistance to protons, they are readily available, can be easily modified and, as regards their selective behavior, they have been investigated more thoroughly than other readily accessible carbonylmethylenation reagents of comparable selectivity. The results of NMR spectroscopic investigations on the structure of the μ-CH2 complexes, and associated reaction mechanisms are discussed. A survey of carbonylmethylenation reagents, which have been reported in the literature, permits comparisons to be made with carbonylmethylenating molybdenum and tungsten complexes. 相似文献
8.
Gold-gold interactions in small polynuclear complexes are analysed using extended Hückel calculations. They are influenced by the nature of the ligand donor atoms, by the bridging ligands, but most by the formal oxidation state of the metal. Au---Au bonds are much stronger in complexes of Au(II) and Au(III), but a weak interaction between two d10 centres exists for Au(I) complexes, owing to mixing of the s and p orbitals with the d orbitals. Phosphines induce stronger metal-metal bonds when coordinated trans to the Au---Au bond in [Au(II)[(CH2)2PPh2]L]2 (Ph = phenyl), but have the opposite effect when bonded orthogonally to the metal-metal axis in Au(I) binuclear species. When two gold atoms are bridged by a single carbon atom, belonging either to mesityl (Mes = 2,4,6-Me3C6H2) or CR2, the former produces stronger Au(I)---Au(I) interactions, reflected in shorter distances. Formal oxidation states are proposed for the gold atoms in two mixed-valence clusters, [Au4(C6F5)2((PPh3)2CH})2(PPh3)2](ClO4)2 and [{(2,4,6-C6F3H2)Au(CH2PPh2CH2)2Au{in2-Au(CH2PPh2CH2)2Au](ClO4)2. The results suggest a higher oxidation state for the outer gold atoms, in both the T-shaped tetranuclear cluster and the Au6 linear chain. 相似文献
9.
Reactivity of Monophosphine Platinum(0) Complexes with SO2 . The addition reaction of (PPh3)Pt(ViSi) (ViSi = {η2-H2C?CHSiMe2}2O) ( 1 ) with SO2 gives within 30 min the red SO2 complex (PPh3)Pt(η2-H2C?CHSiMe2- OSiMe2CH?CH2)(SO2) ( 2 ). A reaction time of 24 h with SO2 leads to the elimination of the ViSi ligand, and the unstable monomeric intermediate (PPh3)Pt(SO2) cyclo- trimerizes to the stable cluster [Pt(PPh3)(SO2)]3 ( 3 ). 3 is also obtained within 30 min by the reaction of (PPh3)Pt(C2H4)2 ( 4 ) with SO2. The crystal structure of 3 has been determined; space group P21/n, Z = 4, a = 1 606.1(3), b = 1 019.3(1), c = 3 624.6(5) pm, β = 93.67°, R/Rw = 0.102/0.121. 相似文献
10.
Istvan Bakk Dietrich Gudat Stefan Hp Martin Nieger Lszl Nyulaszi Lszl Szarvas 《无机化学与普通化学杂志》2005,631(1):47-54
Reactions of the phosphonio‐benzophospholide π‐complexes 3a, b[Cr] with [M(CO)5(olefin)] or of the σ‐complexes 2a, b[M] (M = Cr, Mo, W) with [M(CO)3(aren)] lead to the first binuclear complexes 4a, b[CrM] featuring phosphonoio‐benzophospholides as μ‐bridging 8e‐donor ligands to two group 6 metal atoms. The constitution of the products was determined by spectroscopic and X‐ray diffraction studies. Mixed complexes with both group 6 and 7 metals were not accessible. Mechanistic studies showed that the reactions follow a complicated mechanism whose single steps may involve transfer of either M(CO)n fragments or single CO ligands between complexes; the latter are associated with a σ/π‐coordination isomerization of the benzophospholide unit. Competition between both reaction channels can lead to the formation of product mixtures whose composition is controlled by the relative thermodynamic stabilities of the products. Computational studies suggest that in the more stable isomer of heterobimetallic complexes 4a, b[MM′] end‐on coordination to the heavier and side‐on coordination to the lighter metal atom is preferred. 相似文献