- Combinatorial screening of an in situ generated library of tungsten oxyhalide and imido complexes for olefin metathesis
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A series of substituted tungsten(VI) halides with general formula WECl4 (E = O or 'NR (imido)) were screened via a high throughput study to identify potential new olefin metathesis catalysts. The tungsten species were treated with a series of aluminum alkyl activators and modifier ligands to generate active catalyst species in situ. Ring-opening metathesis polymerization (ROMP) of cyclooctene was used as a primary screen to identify potential metathesis catalysts and active catalysts were subjected to a secondary screen to evaluate tolerance toward polar functional groups. Several combinations from the high throughput campaign yielded active metathesis catalysts for the ROMP of cyclooctene. However, none of the catalysts examined in this study exhibited any evidence of significant polar functional group tolerance as determined by the results of the secondary cyclooctene/butyl acetate screen.
- Romer, Duane R.,Sussman, Victor J.,Burdett, Ken,Chen, Yu,Miller, Kami J.
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- TUNGSTEN CATALYSTS
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Novel Tungsten-containing compounds of formula I defined herein are disclosed, as well as catalytic compositions comprising the compounds. Also disclosed are uses of the compounds and compositions in alkene oligomerisation reactions.
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Paragraph 00161
(2016/11/14)
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- Stable imido amido complexes of tungsten (VI)
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Reaction of Me3SiNHC6H3Pr2i-2,6 with [WCl4(NC6H3Pr2i-2,6)] in thf gives [WCl3(NC6H3Pr2 i-2,6)(NHC6H3Pr2 i-2,6)(thf)] (1), and reaction in CH2Cl2 in the presence of py gives [WCl3(NC6H3Pr2 i-2,6)(NHC6H3Pr2 i-2,6)(py)] (2). Addition of 1 equiv. of NH2C6H3Pr2i-2,6 to [WCl4(NC6H3Pr2i-2,6)] in CH2Cl2 gives the 1:1 adduct [WCl4(NC6H3Pr2 i-2,6)(NH2C6H3Pr2 i2,6)] (3) which when reacted with 1 equiv. of Me3SiNHC6H3Pr2i-2,6 gives rise to [WCl3(NC6H3Pr2 i-2,6)(NHC6H3Pri-2,6)(NH 2C6H3Pr2i-2,6)] (4) and also the tris amido complex [WCl3(NHC6H3Pr2 i-2,6)3] (5). Complex (4) converts into complex (5), and after long reaction periods only complex (5) is isolated. Addition of 1 equiv. of Me3SiNHC6H3Pr2i-2,6 to [WCl5(NC6H3Pr2 i-2,6)NEt4 in CH2Cl2 gives rise to [WCl4(NC6H3Pr2 i-2,6)(NHC6H3Pr2i-2,6)] NEt4 (6), and if Me3SiNHC6H3Me2-2,6 is used, instead, [WCl4(NC6H3Pr2 i-2,6)(NHC6H3Me2-2,6)] NEt4 (7) results. Me3SiNHC6H5 gives unidentified mixtures of products. Reaction of NH2C6H3Pr2i-2,6 with [WCl4(O)] leads to the complex [WCl4(NC6H3Pr2 i-2,6)(NHC6H3Pr2i-2,6)] NH3C6H3Pr2i-2,6 (8) which was characterized by X-ray crystallography. The structure shows an octahedral array with cis-oriented imido and amido ligands. For the imido ligand the W-N bond length is 1·67(2) A and W-N-C bond angle 174(2)°; for the amido ligand, the corresponding values are 1·87(2) A and 144(2)°. The amido ligand orientates so that any NH contacts with nearby chlorine ligands are minimized. Complexes (1)-(8) give insight into an intramolecular NH proton transfer process leading to an organoimido ligand.
- Nielson, Alastair J.,Clark, George R.,Rickard, Clifton E.F.
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p. 259 - 265
(2007/10/03)
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- Synthesis of tungsten vinyl alkylidene complexes via the reactions of WCl2(NAr)(PX3)3 (X = R, OMe) precursors with 3,3-disubstituted cyclopropenes
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Several WCl2(NAr)(PX3)3 complexes were synthesized, including WCl2(N-2,6-C6H3Me2)(PEt 2Ph)3 (1), WCl2(NPh)[P(OMe)3]3 (2), WCl2(N-2,6-C6H3Me2) [P(OMe)3]3 (3), and WCl2[N-2,6-C6H3(i-Pr)2] [P(OMe)3]3 (4). NMR spectroscopic data for these complexes and a single-crystal X-ray diffraction study of 4 supported a meridional arrangement of the three PX3 ligands, all lying cis to the apical imido ligand. The lability of one PX3 ligand in complexes 1-4 was demonstrated by reactions with ethylene and phenyl- and diphenylacetylene to give the corresponding π-acceptor (L) complex WCl2(L)(NAr)(PX3]2. In solution, some of the WCl2(L)(NAr)(PX3)2 complexes, especially those with P(OMe)3 ligands, were in equilibrium with WCl2(L)(NAr)(PX3) and free PX3; complete removal of 1 equiv of PX3 was achieved upon addition of CuCl. Complexes 1-4 and also WCl2(NPh)(PMePh2)3 reacted with 3,3-diphenylcyclopropene and 4,8-dioxaspiro[2.5]oct-1-ene (referred to subsequently as diphenyl- and ketalcyclopropene) to give a number of η2-cyclopropene complexes and/or vinyl alkylidene complexes. Concentrated diethyl ether solutions of the reactants and use of the sterically smaller tungsten precursors enabled the clean formation of the η2-cyclopropene complexes W(η2-cyclopropene)Cl2(NAr)(PX3) 2. Spectroscopic data and a single-crystal X-ray diffraction study of W(η2-diphenylcyclopropene)Cl2(NPh) [P(OMe)3]2 indicated an octahedral geometry in which the two mutually trans PX3 ligands and the cyclopropene occupy equatorial positions cis to the apical imido ligand and the substituents of the cyclopropene lie syn to the imido ligand. The η2-cyclopropene complexes were converted to the corresponding vinyl alkylidene complexes W(=CHCH=CR2)Cl2(NAr)(PX3)2 thermally, photochemically, and chemically (catalysis by HgCl2). For the reactions of the sterically more bulky tungsten precursors with cyclopropenes, direct isolation of the vinyl alkylidene complexes was possible. A crystal structure of an alkoxide derivative W(=CHCH=CPh2) [N-2,6-C6H3-(i-Pr)2] [OCMe(CF3)2]2[P(OMe)3] confirmed the formation of a diphenylvinyl alkylidene ligand with an s-trans arrangement of the double bonds. In addition to an s-trans isomer, the ketalvinyl alkylidene ligand also formed two different s-cis isomers with one oxygen atom of the ketal ring chelating to tungsten. A crystal structure showed that, in one of these isomers, the ketal ring has been opened by a chloride ligand from tungsten, and a mechanism is proposed for this rearrangement.
- Johnson, Lynda K.,Grubbs, Robert H.,Ziller, Joseph W.
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p. 8130 - 8145
(2007/10/02)
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- Further studies of imido alkylidene complexes of tungsten, well-characterized olefin metathesis catalysts with controllable activity
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An alternative synthesis of W(CH-t-Bu)(NAr)(dme)Cl2 (Ar = 2,6-C6-H3-i-Pr2) consists of the five steps WCl6 → W(O)Cl4 → W(NAr)Cl4 → W(NAr)(O-t-Bu)2Cl2(THF) → W(NAr)(O-t-Bu)2(CH2-t-Bu)2 → W-(CH-t-Bu)(NAr)(dme)Cl2, in which tert-butoxide "protecting groups" are replaced by chlorides in the last step upon addition of PCl5. The easiest synthesis to a catalyst precursor consists of the three steps WO2Cl2 → W(NAr)2Cl2(dme) → W(NAr)2(CH2R)2 → W(CHR)(NAr)(OTf)2(dme) (R = t-Bu, CMe2Ph; OTf = OSO2CF3), in which an imido ligand protecting group is ultimately replaced by two triflate ligands upon addition of triflic acid in the last step. An X-ray study of W(CH-t-Bu)(NAr)(O-t-Bu)2 shows it to be a pseudotetrahedral complex in which the tert-butyl group points toward the imido ligand (syn conformation; space group P1, a = 14.050 (5) ?, b = 18.885 (5) ?, c = 11.123 (5) ?, α = 92.22 (3)°, β = 108.30 (3)°, γ = 79.25 (2)°, V = 2752 (2) ?3, Z = 4, Mr 572.46, ρ = 1.381 g cm-3, μ = 43.03 cm-1; R = 0.039, Rw = 0.043). Complexes of the type W(CH-t-Bu)(NAr′)(OR)2 (NAr′ = N-2,6-C6H3Me2; OR = O-t-Bu, OCMe2(CF3), OCMe(CF3)2, OC(CF3)2(CF2CF2CF3)) were prepared by methods analogous to those used originally to prepare NAr complexes. Reactions between NAr′ complexes and olefins in general yield less stable organometallic products than when the NAr ligand is present. In one case (addition of internal olefins to W(CH-t-Bu)(NAr′)[OCMe(CF3)2]2) a product was isolated that was consistent with the formation {W(NAr′)-[OCMe(CF3)2]2}2. Some of the W(CH-t-Bu)(NAr)X2 variations that were prepared include X = OAr, OCEt3, OCMe2Ph, SAr, and CH2-t-Bu. Other variations include W(CHEt)(NAr)X2 complexes (X = OCEt3, NPh2), W(CHSiMe3)(NAr)X2 complexes (X = OAr, OCMe2(CF3), OCMe(CF3)2), and W[CHSi(OMe)3](NAr)X2 complexes (X = OAr, OCMe2(CF3), OCMe(CF3)2). Syn and anti rotamers of W(CHSiMe3)(NAr)(OAr)2 were observed and found to interconvert on the NMR time scale (ΔG?298 = 15.0 (1) kcal mol-1). None of the variations have any obvious advantage over known alkoxide/NAr complexes for metathesis of ordinary or strained cyclic olefins. An attempt to prepare a derivative containing the OC(CF3)2(tolyl) ligand yielded W[OC(C6H3Me)(CF3)2](NAr)[OC(CF 3)2(tolyl)](CH2-t-Bu), formed by addition of an ortho CH bond to the W=C bond (space group P21/c, a = 16.821 (2) ?, b = 11.951 (1) ?, c = 19.455 (4) ?, β = 93.852 (8)°, V = 3920.5 ?3, Z = 4, Mr 943.6, ρ(calcd) = 1.606 g cm-3, μ = 31.09 cm-1; R = 0.038, Rw = 0.043).
- Schrock,DePue,Feldman,Yap,Yang,Davis,Park,DiMare,Schofield,Anhaus,Walborsky,Evitt,Krüger,Betz
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p. 2262 - 2275
(2008/10/08)
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