127793-86-6Relevant articles and documents
Combinatorial screening of an in situ generated library of tungsten oxyhalide and imido complexes for olefin metathesis
Romer, Duane R.,Sussman, Victor J.,Burdett, Ken,Chen, Yu,Miller, Kami J.
, p. 551 - 557 (2014)
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.
Stable imido amido complexes of tungsten (VI)
Nielson, Alastair J.,Clark, George R.,Rickard, Clifton E.F.
, p. 259 - 265 (2007/10/03)
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.
Further studies of imido alkylidene complexes of tungsten, well-characterized olefin metathesis catalysts with controllable activity
Schrock,DePue,Feldman,Yap,Yang,Davis,Park,DiMare,Schofield,Anhaus,Walborsky,Evitt,Krüger,Betz
, p. 2262 - 2275 (2008/10/08)
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).
