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92 Science of Synthesis 2.6 Complexes of Cr, Mo, and W without CO Ligands CH 2CH 2CH 3]; 13 C NMR (benzene-d 6, ä): 272 [d, WC(Pr)H, 1 J CW = 180 Hz, 1 J CH = 142 Hz], 41.6 (WCCH 2CH 2CH 3), 29.5 (WCCH 2CH 2CH 3), 14.5 (WCCH 2CH 2CH 3). 2.6.1.1.2 Variation 2: Ligand Addition When di- or polyalkyl complexes do not spontaneously give rise to Æ-hydrogen elimination, this process may often be accomplished by addition of two-electron ligands (e.g., phosphines). [14,15] Thus, the tris(2,2-dimethylpropyl)(2,2-dimethylpropylidyne)tungsten complex 5 transforms into the (2,2-dimethylpropyl)(2,2-dimethylpropylidene)(2,2-dimethylpropylidyne) product 6 upon addition of trimethylphosphine (Scheme 2). The conditions required to induce this process depend on the system, from –788C for dibromotetrakis[(trimethylsilyl)methyl]dimolybdenum(III)(Mo”Mo) [15] to room temperature for cyclopentadienylbis(2,2-dimethylpropyl)nitrosylmolybdenum(II). [16] In the synthesis of compound 7, substitution of two alkoxide ligands with the less sterically encumbering (and also poorer ð-donor) chlorides opens up the coordination sphere to the coordination of a bidentate 1,2-dimethoxyethane molecule, inducing carbene formation. The dialkoxo precursor, albeit five coordinate, does not spontaneously undergo the alkane elimination process. [17] The increase of the coordination sphere can also be achieved by replacement of a monodentate ligand (e.g., chloride) with a polyfunctional ligand, e.g. hydrotris(pyrazolyl)borate [18] or 2-[(dimethylamino)methyl]phenyl (see synthesis of 8) (Scheme 2). [19] This strategy has also been utilized in other cases via replacement of a bulky alkyl with chloride by protonation with LH + Cl – in the presence of excess ligand L. [10] Scheme 2 Æ-Hydrogen Elimination Induced by Ligand Addition [14,17,19] ButH2C W CBut But Bu H2C tH2C 5 OBu W N t OBut ButH2C But Pr H2C i Pri CH2TMS NPh Cl W CH2TMS CH2TMS Me3P (neat) 100 oC, 5 min quant PCl5, DME −35 oC 90% 2-Me 2NCH 2C 6H 4Li Et 2O, −78 o C 70% But Me3P t CBu H2C W CHBu Me3P t 6 Pr i Cl N W Cl CHBut O O Pri Me Me 8 7 NMe2 NPh W CHTMS CH2TMS Dichloro[(2,6-diisopropylphenyl)imido](1,2-dimethoxyethane-O,O¢)(2,2-dimethylpropylidene)tungsten(VI) (7); Typical Procedure: [17] Finely ground PCl 5 (2.25 g, 10.8 mmol) was added to a chilled (–358C) soln of [W(CH 2t- Bu) 2(Ot-Bu 2) 2(=NC 6H 3-2,6-iPr 2) (7.0 g, 10.8 mmol) in DME (120 mL). The mixture was warmed to rt and stirred for an additional 1 h after all the solids had disappeared. The mixture was then concentrated in vacuo until an orange powder formed. This material was washed with cold pentane to give the product as a yellow-orange powder. This synthesis can fail virtually completely if the DME is not scrupulously dried and the PCl 5 not
2.6.1 Metal–Carbene Complexes 93 rigorously purified; yield: 5.75 g (90%); 1 H NMR (benzene-d 6, ä): 9.97 (s, J HW = 7.3 Hz, CHt- Bu); 13 C NMR (benzene-d 6, ä): 283.8 (d, W=C, 1 J CH = 114 Hz, 1 J CW = 163 Hz). 2.6.1.1.3 Variation 3: Replacement of an Oxo or Imido Ligand Replacement of an oxo [20–22] or imido [23] ligand with two singly bonded heteroelement ligands has often proven to be an efficient method for inducing the Æ-elimination process from dialkyl compounds. Examples of syntheses of these types are shown in Scheme 3. The interaction between a dialkoxodialkyloxo complex of tungsten(VI) and a Lewis acid (AX n, viz. aluminum trichloride, tin(IV) chloride, magnesium bromide, etc.) proceeds via an isolable adduct containing the W=O-AX n moiety when conducted in hexane, which then yields the dialkoxodihalocarbene product. [24] Although this procedure is not general, subsequent ligand exchange or stoichiometric alkene metathesis (see Section 2.6.1.2) allows the preparation of a much broader series of derivatives. [21,22] Lewis base adducts such as compound 9 easily undergo exchange of the Lewis base, or can be converted into the base-free material. The reaction yielding 10 is the most convenient entry into the catalytically active dialkoxo(alkylidene)imido complexes of molybdenum and tungsten, since the trifluoromethanesulfonate ligands can be easily replaced with a variety of alkoxide groups, and the dialkyldiimido precursor complex is readily available in two high-yield steps from commercially available dichlorodioxotungsten(VI) or ammonium dimolybdate. [17,25] Scheme 3 Æ-Hydrogen Elimination Induced by Substitution of Oxo or Imido Ligands [8,17,23,29] ButN Mo But CH2Bu N t CH2But Pr i Pri N M Pr N i CH2R1 CH2R1 Pr i M = Mo, W R1 = t-Bu, CMe2Ph (CF3) 2CHOH (2 equiv) pentane, rt 80% TfOH (3 equiv) DME, −30 oC 65−78% OCH(CF3) 2 Mo NH2Bu OCH(CF3) 2 t ButN ButHC 9 M R1 Pr N OTf O HC O OTf i Pri Me Me [(2,6-Diisopropylphenyl)imido](1,2-dimethoxyethane-O,O¢)(2,2-dimethylpropylidene)bis(trifluoromethanesulfonato-O)molybdenum(VI) (10,M=Mo;R 1 = t-Bu); Typical Procedure: [8] A prechilled soln of TfOH (3.15 mL, 35.5 mmol, 3 equiv) in DME (20 mL) was added in a dropwise manner to an orange soln of Mo(CH 2t-Bu) 2(=NC 6H 3-2,6-iPr 2) 2 (7.00 g, 11.8 mmol) in DME (200 mL) at –308C over a period of 10 min. [It is important in this step that the soln be homogeneous and cold. It is best to grind the crystals of the molybdenum starting complex to a fine powder to aid dissolution; the addition of some pentane (15–30 mL) may facilitate this step.] The soln was allowed to warm up to rt and stirred for 3 h. During this period the color changed from orange to dark yellow. The solvent was evaporated in vacuo to yield a yellow solid, which was then extracted with cold toluene (100–150 mL). The 10 for references see p 135
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Science of Synthesis Houben-Weyl Me
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Science of Synthesis Houben-Weyl Me
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8 Science of Synthesis Category 1:
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Volume 1: Compounds withTransition
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Table of Contents Volume 2 13 Volum
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Table of Contents 15 Volume 4: Comp
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Table of Contents 17 4.4.27 Product
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2001 Georg Thieme Verlag Rüdigerst
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1.1 Product Class 1: Organometallic
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1.1 Product Class 1: Organometallic
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1.1.1 Nickel Complexes of 1,3-Diene
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1.1.1 Nickel Complexes of 1,3-Diene
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1.1.2 Nickel-Allyl Complexes 37 tra
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1.1.2 Nickel-Allyl Complexes 39 Bis
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Page 79 and 80: References 79 References [1] Chetcu
Page 81 and 82: References 81 [98] Tsuda, T.; Mizun
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Page 86 and 87: 86 Biographical Sketches Rinaldo Po
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2002 Georg Thieme Verlag Rüdigerst
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4.4.27 Product Subclass 27: Æ-Halo
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4.4.27 Æ-Haloalkylsilanes 147 Sche
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4.4.27 Æ-Haloalkylsilanes 149 dros
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4.4.27 Æ-Haloalkylsilanes 151 4.4.
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4.4.27 Æ-Haloalkylsilanes 153 In g
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4.4.27 Æ-Haloalkylsilanes 155 4.4.
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4.4.27 Æ-Haloalkylsilanes 157 Æ-H
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References 159 References [1] Haman
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References 161 [93] Bruno, J. W.; S
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164
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166 Biographical Sketches Alan Spiv
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168 5.1.22 Product Subclass 22: Ary
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170 Science of Synthesis 5.1 German
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176 References [43] Eaborn, C.; Var
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178 Abbreviations Chemical (cont.)
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180 Abbreviations Ligands (cont.) 2
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182 Abbreviations General (cont.) q
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