Homogeneous Coordination Catalysis with Molybdenum Complexes
About: This article is published in Studies in Inorganic Chemistry.The article was published on 1994-01-01. It has received 2 citations till now. The article focuses on the topics: Molybdenum & Catalysis.
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01 Mar 1980
TL;DR: Complexes of the types M(CHCR/sub 3/)L/sub 2/X/Sub 3/M/LX, WO(WO(L/Sub 2/Cl/sub2/X)/sub 3), M( CHCR/ sub 3/)R/R/L/X, X, and Cl/Br showed good activities in metathesis of terminal olefins, including ethylene, propylene, styrene, 1-butene, and cis-2-pentene, at 25/sup 0/
Abstract: Complexes of the types M(CHCR/sub 3/)L/sub 2/X/sub 3/, M(CHCR/sub 3/)(OCR/sub 3/)/sub 2/LX, and WO(CHCR/sub 3/)L/sub 2/Cl/sub 2/, where M is Nb or Ta, R is methyl, L is a tertiary phosphine, and X is Cl or Br, showed good activities in metathesis of terminal olefins, including ethylene, propylene, styrene, 1-butene, and cis-2-pentene, at 25/sup 0/C in the presence of traces of AlCl/sub 3/.
3 citations
TL;DR: In this article, a Schiff-base complex was synthesized for oxomolybdenum-VI co-ordination using spectroscopic and X-ray diffraction analysis.
Abstract: Oxomolybdenum compounds are of great interest because of their function in several enzymes 1 and in many catalytic systems. 2 The presence of the cis-dioxomolybdenum(VI) fragment in the oxidative form of certain molybdoenzymes has stimulated search for new structures in which this moiety is co-ordinated to ligands containing nitrogen, oxygen and/or sulfur donors. Molybdenum(VI) Schiff-base complexes represent an important and interesting class of that kind of coordination compound. 3 The cis-dioxo moiety, cis-Mo(O) 2 ,i s the most commonly encountered structural form in Mo(VI) co-ordination chemistry. 4 cis-Mo(O) 2 complexes of dianionic tridentate Schiff base ligands can exist as monomers, Mo(O) 2 (L)(D) ‐ where: L = Schiff base, D = monodentate neutral ligand, which is dominant, 3 dimers, [Mo(O)(μ-O)(L)] 2 ‐ with asymmetric double oxygen bridge, 5 or oligomers with a postulated ······Mo=O·······Mo=O····· interaction. 6 This type of complex has a distinct advantage as models for oxo-transfer processes due to the presence of a labile (monomeric form) or easy accessible vacant co-ordination site (dimers and/or oligomers) for potential binding and/or activating of substrates. In this paper we present the syntheses of a Schiff-base complex, [Mo(O) 2 (3,5-di-tert-Busap)(EtOH)] (1), and its characterisation by spectroscopic and X-ray diffraction analysis. The complex is stable in the solid state (no changes were observed during 10 months storage) whereas the analogue [Mo(O) 2 (sap)(EtOH)] loses the co-ordinated ethanol slowly with simultaneous disappearance of its orange colour. The brown product formed from [Mo(O) 2 (sap)(EtOH)] is probably an oxo-bridged oligomer 6 or dimer 5 , revertible to its original mononuclear form when treated with ethanol. Thermogravimetric analysis shows that both complexes lose the co-ordinated ethanol in the ranges 413‐433 and 363‐373 K, respectively for [Mo(O) 2 (3,5-di-tert-Busap)(EtOH)] and [Mo(O) 2 (sap)(EtOH)]. The IR spectral data of the complex are typical for a co-ordinated anionic Schiff base and oxygen donor. The complex does not show a phenolic ν(O‐H) band and the δ(C‐O) band at 1258 and 1284 cm ‐1 has shifted to higher wavenumber compared to the free ligand (1170 and 1202 cm ‐1 ), both suggestive of coordination of the phenolic C‐O groups. The characteristic frequency ν(C=N) of the free ligand observed at 1616 cm ‐1 displays a shift to lower frequency at 1611 cm ‐1 , indicating coordination of the azomethine nitrogen to molybdenum. A broad band at 3269 cm ‐1 and medium one at 1047 cm ‐1 are characteristic of co-ordinated ethanol. An additional δ(Mo‐O) band at 575 cm ‐1 appears after complexation. The complex exhibits strong infrared absorptions at 933 and 916 cm ‐1 (Figure 1), which are characteristic of the cis-Mo(O) 2 group. 3 The complex free of ethanol (bands at 3269 and 1047 cm ‐1 disappear) as well as absorption within the 940‐900 cm ‐1 range, shows a very intensive absorptions at 862 and 836 cm ‐1 (Figure 1). The changes in the IR spectrum of both compounds are very similar to those observed for [Mo(O) 2 (sae)(H 2 O)] and [Mo(O)(μ-O)(sae)] 2 complexes. 5
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TL;DR: In this article, a metal alkoxide is used as a catalyst, where the metal has a coordination number of at least four, and at least one, usually two, of the alkoxide groups bonded to the metal are bonded to asymmetric carbon atoms.
Abstract: OF THE DISCLOSURE Methods and compositions are provided for asymecrically donating an oxygen atom to a pair of electrons to produce an asymmetric product. Specifically, a metal alkoxide is used as a catalyst, where the metal has a coordination number of at least four, and at least one, usually two, of the alkoxide groups bonded to the metal are bonded to asymmetric carbon atoms. The metal catalyst is employed in conjunction with a hydroperoxide and an alkanol having a functionality with a pair of electrons capable of accepting an oxygen atom. The resulting product is enriched in one enantiomer due to the enantioselective introduction of an asymmetric center or an enhanced rate of reaction of one of the enantiomers of a chiral alkanol. Greatly enhanced yields of enantiomers are achieved as compared to prior enantioselective introduction of oxygen. This invention was made at least in part in the course of a grant from the U.S. National Institutes of Health (GM24551).
2,306 citations
931 citations
TL;DR: In this paper, a precursor to imido alkylidene complexes that is related to 2 has been prepared by the sequence MoO{sub 2} {yields} MoO(NAr)Cl{sub 3} (dme = 1,2-dimethoxyethane) and Me{ sub 3}SiNHAr (Ar = 2,6-diisopropylphenyl) yields Mo(C-t-Bu)(NHAr), which upon treatment with a catalytic amount of NEt-sub 3] is transformed into
Abstract: The reaction between Mo(C-t-Bu)(dme)Cl{sub 3} (dme = 1,2-dimethoxyethane) and Me{sub 3}SiNHAr (Ar = 2,6-diisopropylphenyl) yields Mo(C-t-Bu)(NHAr)Cl{sub 2}(dme) (1), which upon treatment with a catalytic amount of NEt{sub 3} is transformed into Mo(CH-t-Bu)(NAr)Cl{sub 2}(dme) (2). Complexes of the type Mo(CH-t-Bu)(NAr)(OR){sub 2} (OR = OCMe(CF{sub 3}){sub 2}, OCMe{sub 2}(CF{sub 3}), O-t-Bu, or OAr) have been prepared from 2. Complexes of the type Mo(C-t-Bu)(NHAr)(OR){sub 2} (OR = OCMe(CF{sub 3}){sub 2} or OAr) have been prepared from 1, but they cannot be transformed into Mo(CH-t-Bu)(NAr)(OR){sub 2} complexes. A precursor to imido alkylidene complexes that is related to 2 has been prepared by the sequence MoO{sub 2} {yields} MoO{sub 2}Cl{sub 2} {yields} Mo(NAr){sub 2}Cl{sub 2} {yields} Mo(NAr){sub 2}(CH{sub 2}R{prime}){sub 2} {yields} Mo(CHR{prime})(NAr)(OTf){sub 2}(dme) (R{prime} = t-Bu or CMe{sub 2}Ph; OTf = OSO{sub 2}CF{sub 3}). Mo(CH-t-Bu)(NAr)(OTf){sub 2}(dme) crystallizes in the space group P{anti 1} with a = 17.543 {angstrom}, b = 19.008 {angstrom}, c = 9.711 {angstrom}, {alpha} = 91.91{degree}, {beta} = 99.30{degree}, {gamma} = 87.27{degree}, Z = 4, M{sub r} = 729.60, V = 3,191.1 {angstrom}{sup 3}, {rho}(calcd) = 1.518 g cm{sup {minus}3}.
928 citations
TL;DR: In this article, the authors defined heteropoly acids as polymeric oxoanions which are formed by the condensation of more than two different oxo-oanions [Eq. (1)l.
Abstract: Heteropolyanions are polymeric oxoanions which are formed by the condensation of more than two different oxoanions [Eq. (1)l. Polyanions consisting of one kind of oxoanion are called isopolyanions [Eq. (2)]. Acidic elements such as Mo, W, V, Nb, and Ta are present as oxoanions in aqueous solutions and polymerize to form polyanions at low pH. Free acids (or acid forms) of these species are called heteropoly and isopoly acids, respectively. Here, the term “heteropoly compounds” is used for heteropoly acids and their salts.
918 citations
TL;DR: On propose un schema reactionnel en accord avec les faits observes dans la reaction de disproportion des olefines acycliques, la polymerisation des ollines cycliques, the telomerisation of l'olefine cyclique, and the polymerisation of olline cycliques by les olefine acyCLiques as discussed by the authors.
Abstract: La co-reaction des olefines cycliques avec les olefines acycliques en presence des systemes WOCl4/Al(C2H5)2Cl et WOCl4/Sn(C4H9)4 conduit a une telomerisation de l'olefine cyclique; aux extremites des molecules de telomere sont fixes deux groupements, identiques ou differents, issus de l'olefine acyclique par une reaction non consecutive.
Ont ete plus particulierement etudies: le cyclopentene et le cyclooctene d'une part, le pentene-2, le pentene-1, le butene-2 et le propylene d'autre part.
Le cyclooctadiene-1.5 et le cyclododecatriene-1.5.9 reagissent avec le pentene-2, par reaction non consecutive, en tant que reste CHCH2CH2CH.
La repartition des telomeres obeit a une loi statistique.
On propose un schema reactionnel en accord avec les faits observes dans la reaction de disproportion des olefines acycliques, la polymerisation des olefines cycliques et la telomerisation des olefines cycliques par les olefines acycliques.
882 citations