128951-56-4Relevant articles and documents
Reactions of M(N-2,6-i Pr2C6H3)(CHR) (CH2R′)2 (M = Mo, W) complexes with alcohols to give olefin metathesis catalysts of the type M(N-2,6-i-Pr2C 6H3)(CHR)(CH2R′)(OR″)
Sinha, Amritanshu,Lopez, Lourdes Pia H.,Schrock, Richard R.,Hock, Adam S.,Mueller, Peter
, p. 1412 - 1423 (2006)
The reaction between M(NAr)(CH-t-Bu)(CH2-t-Bu)2 (M = Mo, W, Ar = 2,6-i-Pr2C6H3) and various alcohols (1-adamantyl-OH, t-BuOH, ArOH, (CF3)2CHOH, (CF 3)2MeCOH, CF3Me2COH, (CF 3)3COH, C6F5OH) in pentane or toluene yields either complexes of the type M(NAr)(CH-t-Bu)(CH 2-t-Bu)(OR), through direct addition of ROH across a Mo-C bond, or complexes of the type M(NAr)(CH2-t-Bu)3-(OR), through direct addition of ROH across a Mo=C bond. The trineopentyl species appear to be formed when the alcohol has a relatively low pKa value. The outcome also can depend on whether the alcohol is employed neat or in benzene, and mixtures are observed in some circumstances. The conversion of M(NAr)(CH 2-t-Bu)3(OR) into M(NAr)(CH-t-Bu)(CH2-t-Bu)(OR) was shown to be unimolecular in several examples. Preliminary experiments have shown that M(NAr)(CH-t-Bu)(CH2-t-Bu)(OR) complexes are surprisingly active catalysts for various metathesis reactions, although conversion is sometimes limited by decomposition of intermediate alkylidenes to yield dimeric species that contain M=M bonds. In contrast, M(NAr)(CH-t-Bu)(CH 2-t-Bu)2 species are virtually inactive for metathesis. X-ray structures are reported for Mo(NAr)(CH2-t-Bu) 3(OC6F5), Mo(NAr)(CH-t-Bu)(CH 2-t-Bu)[OSi(O-t-Bu)3], [Mo(NAr)(CH-t-Bu)-(CH 2-t-Bu)(OC6F5)]2, and Mo(NAr)(CH-t-Bu)(CH2-t-Bu)(OC6F5)(PMe 3).
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).
