CH activation of pendant alkoxides by tungsten imide complexes

Jordan, Amy; Meyer, Tara Y.

doi:10.1016/s0022-328x(99)00423-4

Cited by 15 publications

(9 citation statements)

References 19 publications

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“…Similar decomposition reactions were also acting in a recently attempted synthesis of dialkoxo-bridged cyclopentadienylsiloxo titanium cationic complexes. , Surprisingly, the lowest stability for complexes of this type was noticed for the expected [Cp*Ti(O t Bu)(Me)] (+) [MeB(C 6 F 5 ) 3 ] (−) complex, which decomposed immediately after mixing its precursors . The complete elimination of isobutene however indicated a different decomposition pathway …”

Section: Introductionsupporting

confidence: 52%

Pentamethylcyclopentadienylmethyltitanium Silsesquioxanes and Their Zwitterionic Complexes with Tris(pentafluorophenyl)borane

et al. 2009

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Reaction of [(η5-C5Me5)TiMe3] with [(c-C5H9)7Si8O12(OH)] (SIPOSS) or [(c-C5H9)7Si7O9(OSiMe3)(OH)2)] (DIPOSS′) affords stoichiometrically the half-sandwich titanium-disiloxy-methyl complexes [(η5-C5Me5){(c-C5H9)7Si8O12O}2TiMe] (1) and [(η5-C5Me5){(c-C5H9)7Si7O9(OSiMe3)O2}TiMe] (2), respectively. Compound 2 consists of the two stereoisomers possessing the (η5-C5Me5) ligand and OSiMe3 group in syn- (2a) and anti-position (2b). The more abundant 2a (2a/2b ≈ 2:1) was isolated by fractional crystallization. Compounds 1 and 2a reacted rapidly with B(C6F5)3 to give zwitterionic complexes [(η5-C5Me5){(c-C5H9)7Si8O12O}2Ti](+)[(μ-Me)B(C6F5)3](−) (3) and syn-[(η5-C5Me5){(c-C5H9)7Si7O9(OSiMe3)O2}Ti](+)[(μ-Me)B(C6F5)3](−) (4a), respectively. Infrared spectra proved that 3 and 4a were thermally stable in the solid state, and the structure of 4a was determined by X-ray single-crystal analysis. In contrast, 1H, 13C, and 19F NMR spectra of 3 in toluene C7D8 revealed that it was completely dissociated into initial components at 25 °C; however, the features of 3 were dominating already at −35 °C. On the other hand, 4a was dissociated only slightly at 25 °C. Stable ionic complexes 7 and 8 were prepared by reacting [PhNHMe2]+[B(C6F5)4]− with 1 and 2, respectively. Both 7 and 8 contained the molecule PhNMe2 coordinated to the titanium cation, and 8 consisted of the syn- and anti-isomers 8a and 8b in abundances found for 2a/2b. Analogous reaction of 1 and 2 with [Ph3C]+[B(C6F5)4]− afforded impure ionic complexes 9 and 10. When dissolved in the presence of PhNMe2, the amine coordinated to the titanium cations, thus reproducing complexes 7 and 8a/8b, identified by 1H NMR spectra. All compounds 1−10 were inactive in polymerization of styrene to syndiotactic polymer. A low activity was achieved by adding of 2 equiv of AlMe3 to 3 or 4.

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Section: Introductionsupporting

confidence: 52%

Pentamethylcyclopentadienylmethyltitanium Silsesquioxanes and Their Zwitterionic Complexes with Tris(pentafluorophenyl)borane

et al. 2009

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“…Although there have, thus far, been several reported examples of μ 3 -imido complexes, little is known about their reactivity. Hydrogenation of the μ 3 -imido complex that generates ammonia seems to be crucial for success in the catalytic hydrogenation of hydrazine by the use of a polyhydride complex as a catalyst.…”

Section: Resultsmentioning

confidence: 99%

Reductive Cleavage of the N−N Bond of Hydrazine Induced by a Cationic Trinuclear Ruthenium Hexahydride Complex, [(Cp‘Ru)₃(μ-H)₆]X (Cp‘ = η⁵-C₅Me₅; X = ¹/₂ SO₄, BF₄, PF₆, BPh₄) and Dihydrogen

2004

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The reaction of the monocationic triruthenium hexahydride [(Cp‘Ru)3(μ-H)6]X (1; X = 1/2 SO4, BF4, PF6, BPh4) with hydrazine leads to the formation of the mono(μ3-imido) complex (Cp‘Ru)3(μ3-NH)(μ-H)3 (3) and the triruthenium pentahydride complex (Cp‘Ru)3(μ3-H)2(μ-H)3 (2). Complex 1 is in equilibrium with 2 in the presence of NH4X or N2H5X, and complex 1 is regenerated upon treatment of 2 with such a protic salt. Complex 3 further reacts with hydrazine to yield the bis(μ3-imido) complex (Cp‘Ru)3(μ3-NH)2(μ-H) (4) as a result of cleavage of the nitrogen−nitrogen bond, which is formally catalyzed by a proton. Both 3 and 4 undergo hydrogenation to generate 2 together with ammonia. Thus, reductive cleavage of the nitrogen−nitrogen bond of hydrazine leading to ammonia is achieved by the use of the monocationic trinuclear hexahydride complex 1 and dihydrogen under conditions without any added proton source and a reducing agent.

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“…The 'non-innocent' nature of alkoxide ancillary ligands has been highlighted by Mayer, 19 and several studies have shown c-H abstraction to be a dominant mechanism in the vapour phase decomposition of group 4 metal alkoxides at >300 • C. [20][21][22] It has also been proposed that solution decomposition of W(NAr)(O t Bu) 2 Cl 2 (THF) and W(NAr)(O t Bu) 4 to give oxo compounds and isobutene, where Ar = 2,6-diisopropylphenyl, similarly proceeds via c-H abstraction. 23 In contrast, Wolczanski attributed the thermal instability of Zr(tritox)Cl 2 (tritox = OC t Bu 3 ) to the generation of tri-tert-butylcarbonium ion, 24 whilst Cummins has utilised radical C-O bond cleavage in molybdenum tert-butoxo complexes for the synthesis of heterometallic complexes. 25 Gibson has shown that protonation of Mo=O in MoO 2 (O t Bu) 2 provides a low energy decomposition pathway via heterolytic C-O cleavage compared to the higher energy c-H abstraction mechanism in the nonprotonated molecule.…”

Section: Discussionmentioning

confidence: 99%

Non-aqueous synthetic methodology for TiW5 polyoxometalates: protonolysis of [(MeO)TiW5O18]3– with alcohols, water and phenols

et al. 2007

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The tetra-n-butylammonium (TBA) salt of [(MeO)TiW(5)O(18)](3-) 1 was reacted with alcohols ROH to give primary, secondary and tertiary alkoxide derivatives [(RO)TiW(5)O(18)](3-) (R = Et 2, (i)Pr 3 and (t)Bu 4), whilst hydrolysis afforded [(mu-O)(TiW(5)O(18))(2)](6-) 5 rather than the hydroxo derivative (R = H). In reactions with (i)PrOH and (t)BuOH, impurity peaks observed at 1015 and 1020 ppm in the (17)O NMR spectra indicate alkoxide degradation and Ti=O bond formation via reactions analogous to those occurring at the surfaces of solid heteropolyacids. Aryloxides [(ArO)TiW(5)O(18)](3-) were prepared by reacting 1 with phenols ArOH (Ar = C(6)H(5) 6, C(6)H(4)Me-4 7, C(6)H(4)(t)Bu-4 8, C(6)H(4)OH-4 9, C(6)H(4)OH-3 10, C(6)H(3)(OH)(2)-3,5 11 and C(6)H(4)CHO-2 13). TiW(5)O(18) units were linked by reacting 1 with 9 to give [(mu-1,4-OC(6)H(4)O)(TiW(5)O(18))(2)](6-) 12. (17)O and (183)W NMR spectra are reported and X-ray crystal structures were obtained for TBA salts of anions 3-10 and 13, which showed that the titanium is six-coordinate in all cases. Reactions were monitored by (1)H NMR, including a 2D-EXSY study of methoxo exchange, and the slow rates observed are probably associated with the reluctance of titanium in these anions to achieve seven-coordination.

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CH activation of pendant alkoxides by tungsten imide complexes

Cited by 15 publications

References 19 publications

Pentamethylcyclopentadienylmethyltitanium Silsesquioxanes and Their Zwitterionic Complexes with Tris(pentafluorophenyl)borane

Pentamethylcyclopentadienylmethyltitanium Silsesquioxanes and Their Zwitterionic Complexes with Tris(pentafluorophenyl)borane

Reductive Cleavage of the N−N Bond of Hydrazine Induced by a Cationic Trinuclear Ruthenium Hexahydride Complex, [(Cp‘Ru)₃(μ-H)₆]X (Cp‘ = η⁵-C₅Me₅; X = ¹/₂ SO₄, BF₄, PF₆, BPh₄) and Dihydrogen

Non-aqueous synthetic methodology for TiW5 polyoxometalates: protonolysis of [(MeO)TiW5O18]3– with alcohols, water and phenols

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CH activation of pendant alkoxides by tungsten imide complexes

Cited by 15 publications

References 19 publications

Pentamethylcyclopentadienylmethyltitanium Silsesquioxanes and Their Zwitterionic Complexes with Tris(pentafluorophenyl)borane

Pentamethylcyclopentadienylmethyltitanium Silsesquioxanes and Their Zwitterionic Complexes with Tris(pentafluorophenyl)borane

Reductive Cleavage of the N−N Bond of Hydrazine Induced by a Cationic Trinuclear Ruthenium Hexahydride Complex, [(Cp‘Ru)3(μ-H)6]X (Cp‘ = η5-C5Me5; X = 1/2 SO4, BF4, PF6, BPh4) and Dihydrogen

Non-aqueous synthetic methodology for TiW5 polyoxometalates: protonolysis of [(MeO)TiW5O18]3– with alcohols, water and phenols

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Reductive Cleavage of the N−N Bond of Hydrazine Induced by a Cationic Trinuclear Ruthenium Hexahydride Complex, [(Cp‘Ru)₃(μ-H)₆]X (Cp‘ = η⁵-C₅Me₅; X = ¹/₂ SO₄, BF₄, PF₆, BPh₄) and Dihydrogen