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120 Science of Synthesis 2.6 Complexes of Cr, Mo, and W without CO Ligands ing dichloro dimers with lithium or Grignard reagents and they are not isolated in view of their extreme thermolability. A large variety of alkyl groups, (trimethylsilyl)methyl, and phenyl have been used as R 3 , including ones where the â-hydrogen elimination process is possible. [60] The procedure consists of the addition of the carbonyl substrate to 75 in tetrahydrofuran at –788C, followed by warming to reflux and room-temperature base hydrolysis. Various substituents (e.g., methoxy, dimethylamino, fluoro, chloro, and hydroxy) on phenyl groups are tolerated (e.g., see synthesis of 76), but the nitro and ethoxycarbonyl groups are not. [135] For R 3 = Me, the carbonyl group must be conjugated with an unsaturated group, otherwise the monomeric carbinol is obtained. With R 3 = Ph, however, even saturated ketones yield the additive–reductive carbonyl dimerization product. Rearrangement products can also be obtained, depending on the substituents linked to the carbonyl group; see, for example, the reaction of 2-furaldehyde (77). [60] Scheme 31 Additive–Reductive Carbonyl Dimerization [60,135] 2 Me 2N O R 1 R 2 O 77 73 CHO 2 [R3 + M] O H R1 2(PrO) 2W W(OPr) 2R O 1 Pr O 2 Pr 75 R 1 = Me 82% Pr O Me2(PrO) 2W W(OPr) 2Me2 O Pr 75 R 1 = Me R 1 R 1 R 74 2 R3 R2 R3 O Me2N 43% O + 76 O O 1,2-Bis[4-(dimethylamino)phenyl]-1,2-dimethylethane (76); Typical Procedure: [135] [W 2Cl 4(ì-OPr) 4(OPr) 4] (2.2 g, 2.50 mmol) was dissolved in THF (100 mL) at –788C, followed by treatment with 1.5 M MeLi in Et 2O (4 equiv), resulting in a color change to dark green. After 30 min, the Gilman test indicated the absence of MeLi. To this soln was added a THF soln (25 mL) of 4-(dimethylamino)benzaldehyde (2.50 mmol). After stirring for 15 min at –78 8C, the mixture was slowly warmed and refluxed for 3 h. The mixture was then hydrolyzed with 2 M NaOH (100 mL) at 20 8C. Et 2O (50 mL) and petroleum ether were added and the mixture was stirred until dissolution of the amorphous hydrolysis product occurred. The organic phase was removed and the aqueous phase was extracted with Et 2O (2 ” 100 mL). The combined organic phases were washed with H 2O and dried (Na 2SO 4). The solvents were removed by rotary evaporation, leaving a crude material which was identified (by GC in comparison with authentic samples) as a mixture of the title compound 76; yield: 82% and 1-[4-(dimethylamino)phenyl]ethanol; yield: 4%. 2.6.5 Product Subclass 5: Metallacyclic Complexes In many respects, the synthetic methods and reactivity of metallacyclic complexes parallel those of analogous dialkyl complexes. Metallacyclobutanes and metallacyclopentanes, on the other hand, display unique features. They may easily transform into, or be pre- 30% NMe2 Et
2.6.5 Metallacyclic Complexes 121 pared from, carbene–alkene and dialkene isomers, respectively (Scheme 32). The cyclic forms tend to be more stable for the heavier metal, with differences in stability of three orders of magnitude being reported for congeneric molybdenum and tungsten compounds. [8] Scheme 32 Transformations of Metallacyclobutanes and Metallacyclopentanes M M M M Metallacyclobutane complexes are involved as intermediates in alkene metathesis reactions catalyzed by alkylidene complexes and their use is equivalent to that of the carbene complexes in this particular organic application (see Section 2.6.1). Chromacyclopentane complexes are invoked as intermediates in the catalytic trimerization of ethene to hex-1ene. [136] This catalytic process takes place with good selectivity (74%), but has not yet found application for the oligomerization of other alkenes nor for cross-oligomerization processes. Synthesis of Product Subclass 5 2.6.5.1 Method 1: By Transmetalation This method is not as common as those described below for the preparation of group 6 metallacyclic derivatives. Dilithium and di-Grignard reagents have been used, as exemplified by the syntheses of 78, 79, and 80 (see Scheme 33). [104,137] The synthesis of metallacycles with large ring sizes suffers from the competitive formation of oligomers and from âhydrogen elimination processes. Scheme 33 Metallacycles by Transmetalation [104,137] Bu Cr N tN But Br N Br N Me2 Cr Cl Cl Et 2O, −30 o C Li CH(TMS)Li(TMEDA) CH(TMS)Li(TMEDA) 64% THF, −20 o C 77% Li Bu Cr tN ButN N Me 2 TMS TMS 78 Cr 79 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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1.1.2 Nickel-Allyl Complexes 41 App
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1.1.2 Nickel-Allyl Complexes 43 NiC
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1.1.2 Nickel-Allyl Complexes 45 Sch
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1.1.2 Nickel-Allyl Complexes 47 Sch
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1.1.3 Nickel-Alkyne Complexes 49 Ca
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1.1.3 Nickel-Alkyne Complexes 51 (2
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1.1.3 Nickel-Alkyne Complexes 53 Sc
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1.1.3 Nickel-Alkyne Complexes 55 at
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1.1.3 Nickel-Alkyne Complexes 57 Sc
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1.1.3 Nickel-Alkyne Complexes 59 en
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1.1.3 Nickel-Alkyne Complexes 61 of
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1.1.4 Nickel-Alkene Complexes 63 Bi
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1.1.4 Nickel-Alkene Complexes 65 Sc
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1.1.4 Nickel-Alkene Complexes 67 1.
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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
Page 88 and 89: 88 2.6.4.2.2 Variation 2: Two-Elect
Page 90 and 91: 90 2.6 Product Class 6: Organometal
Page 92 and 93: 92 Science of Synthesis 2.6 Complex
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Page 141 and 142: 141 Science of Synthesis Houben-Wey
Page 143 and 144: 2002 Georg Thieme Verlag Rüdigerst
Page 145 and 146: 4.4.27 Product Subclass 27: Æ-Halo
Page 147 and 148: 4.4.27 Æ-Haloalkylsilanes 147 Sche
Page 149 and 150: 4.4.27 Æ-Haloalkylsilanes 149 dros
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Page 159 and 160: References 159 References [1] Haman
Page 161: References 161 [93] Bruno, J. W.; S
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Page 166 and 167: 166 Biographical Sketches Alan Spiv
Page 168 and 169: 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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