Abstract:Successive O−C and sp3 C−H bond
activation occurs in the reaction of Ru(COD)(COT)
(1)/PMe3
with allyl 2,6-xylyl ether to
(4).
Alternatively, 4 can be obtained by
O−H and sp3 C−H bond activation in 2,6-xylenol
by
1/PMe3. In both cases, an
η3-allyl fragment could be
responsible for the sp3 C−H bond activation.
“…The new compound was unambiguously characterized as the η 3 -cyclooctenyl complex 8c (Scheme ) by one- and two-dimensional multinuclear NMR spectroscopic techniques and X-ray crystal structure analysis. The most salient feature of its structure is a unique terdentate κ 2 P,P‘-(η 3 -allyl) ligand arising from intramolecular cleavage of three adjacent C−H bonds in one of the cyclohexyl rings attached to the phosphorus donor of a chelating bisphosphane. ,, The intermolecular C−H-activation leading to a κ 2 P,P‘-(η 3 -allyl) ligand becomes the predominant pathway even at lower temperatures if the butylene-bridged bisphosphane 1d is reacted with the precursor 4 (Scheme ). After 24 h at 50 °C, complex 8d can be isolated in pure form by fractional crystallization in 32% yield.…”
Complexes of type [{R2P(CH2)
n
PR2}Ru(2-Me-all)2] (2-Me-all = 2-methylpropenyl; R = Cy,
n = 1−3, 5a−c; R = Me, n = 2, 6; R2 = −(CH2)4−, n = 2, 7) have been synthesized from the
reaction of the corresponding electron-rich diphosphines with [(cod)Ru(2-Me-all)2] (4) at 50−70 °C. The new complexes were fully characterized by multinuclear NMR spectroscopy and
mass spectroscopic techniques. Reacting 4 with Cy2P(CH2)
n
PCy2 containing hydrocarbon
bridges with n = 3 (1c) and n = 4 (1d) at 95 and 50 °C, respectively, led to [κ2P,P‘-{(η3-C6H8)CyP(CH2)
n
PCy2}Ru(η3-C8H13)] (n = 3, 4; 8c,d) via intramolecular C−H bond activation
and concomitant hydride transfer to cyclooctadiene. The molecular structure of 8c was
unambiguously assigned by multinuclear 1D and 2D NMR spectroscopy and confirmed by
single-crystal X-ray diffraction. The new complexes were tested as homogeneous catalyst
precursors in thermal intermolecular C−H activation processes. In dehydrogenation of
cyclooctane (coa), an initial turnover frequency of 1.9 h-1 was observed using complex 5a
under refluxing conditions without the need of a hydrogen scavenger. A maximum total
number of 5 catalytic turnovers was achieved after 48 h. Ligand degradation by dehydrogenation was detected under catalytic conditions, presumably initiated via intramolecular
C−H activation as in species of type 8. Attempts to utilize complexes 5 for C−H activation
in scCO2 as the reaction medium resulted in insertion of CO2 into the Ru−allyl moiety,
yielding catalytically inactive ruthenium carboxylates.
“…The new compound was unambiguously characterized as the η 3 -cyclooctenyl complex 8c (Scheme ) by one- and two-dimensional multinuclear NMR spectroscopic techniques and X-ray crystal structure analysis. The most salient feature of its structure is a unique terdentate κ 2 P,P‘-(η 3 -allyl) ligand arising from intramolecular cleavage of three adjacent C−H bonds in one of the cyclohexyl rings attached to the phosphorus donor of a chelating bisphosphane. ,, The intermolecular C−H-activation leading to a κ 2 P,P‘-(η 3 -allyl) ligand becomes the predominant pathway even at lower temperatures if the butylene-bridged bisphosphane 1d is reacted with the precursor 4 (Scheme ). After 24 h at 50 °C, complex 8d can be isolated in pure form by fractional crystallization in 32% yield.…”
Complexes of type [{R2P(CH2)
n
PR2}Ru(2-Me-all)2] (2-Me-all = 2-methylpropenyl; R = Cy,
n = 1−3, 5a−c; R = Me, n = 2, 6; R2 = −(CH2)4−, n = 2, 7) have been synthesized from the
reaction of the corresponding electron-rich diphosphines with [(cod)Ru(2-Me-all)2] (4) at 50−70 °C. The new complexes were fully characterized by multinuclear NMR spectroscopy and
mass spectroscopic techniques. Reacting 4 with Cy2P(CH2)
n
PCy2 containing hydrocarbon
bridges with n = 3 (1c) and n = 4 (1d) at 95 and 50 °C, respectively, led to [κ2P,P‘-{(η3-C6H8)CyP(CH2)
n
PCy2}Ru(η3-C8H13)] (n = 3, 4; 8c,d) via intramolecular C−H bond activation
and concomitant hydride transfer to cyclooctadiene. The molecular structure of 8c was
unambiguously assigned by multinuclear 1D and 2D NMR spectroscopy and confirmed by
single-crystal X-ray diffraction. The new complexes were tested as homogeneous catalyst
precursors in thermal intermolecular C−H activation processes. In dehydrogenation of
cyclooctane (coa), an initial turnover frequency of 1.9 h-1 was observed using complex 5a
under refluxing conditions without the need of a hydrogen scavenger. A maximum total
number of 5 catalytic turnovers was achieved after 48 h. Ligand degradation by dehydrogenation was detected under catalytic conditions, presumably initiated via intramolecular
C−H activation as in species of type 8. Attempts to utilize complexes 5 for C−H activation
in scCO2 as the reaction medium resulted in insertion of CO2 into the Ru−allyl moiety,
yielding catalytically inactive ruthenium carboxylates.
“…An interesting feature of the ( η 4 -cyclooctatriene)ruthenium(0) complex 4c is its high reactivity toward the C−O bond oxidative addition of vinyl propionate giving ( η 1 -vinyl)(carboxylato)ruthenium(II) complex, whereas a similar reaction of 3a , b did not take place at all (Scheme ). These present results are of special relevance in the ruthenium-promoted C−O bond cleavage reactions. − Whereas the cyclooctatriene ligand in the zerovalent complex 4c can be displaced by the vinylic substrate affording eventually the oxidative addition product Ru( η 1 -C 2 H 3 )(OCOEt)(PEt 3 ) 3 , the η 1 : η 3 -C 8 H 10 ligand in the divalent complexes 3a , b is strongly bonded to ruthenium so that neither displacement reaction nor oxidative addition of the vinyl-oxygen bond is observed. 2 …”
Reaction of Ru(η 4 -C 8 H 12 )(η 6 -C 8 H 10 ) (1) or Ru(η 4 -C 8 H 11 ) 2 (2) with tertiary phosphines gives Ru(η 4 -C 8 H 10 )L 3 [L ) PMe 3 (4a), PMe 2 Ph (4b), PEt 3 (4c), PEt 2 Ph (4d), P(n-Bu) 3 (4e)]. The cyclooctatriene moiety in 4a oxidatively adds to the ruthenium, giving Ru(6-η 1 :1-3-η 3 -C 8 H 10 )-L 3 [L ) PMe 3 (3a), PMe 2 Ph (3b)]. Complexes 4c-e dissociate one phosphine ligand in solution, affording the (hydrido)ruthenium complexes RuH(η 5 -C 8 H 9 )L 2 [L ) PEt 3 (5c), PEt 2 -Ph (5d), P(n-Bu) 3 (5e)]. Whereas prolonged heating of 4c at 70 °C caused disproportionation of the η 4 -C 8 H 10 moiety giving a mixture of the cyclooctatetraene complex Ru(η 4 -C 8 H 8 )(PEt 3 ) 3 (6) and RuH(η 5 -C 8 H 11 )(PEt 3 ) 2 ( 7), heating of 1 with PEt 3 , 4c, or 4d in the presence of 1,5-C 8 H 12 at 70 °C gave Ru(η 4 -bicyclo[4.The molecular structures of 3b, 4c, 6, and 8b have been established by X-ray structure analysis.
“…We have reported allylic CO bond oxidative additions of carboxylates [9] and ethers [10] to [Ru( 4 -1,5-COD)( 6 -1,3,5-COT)] (1) in the presence of tertiary phosphine [11] (Scheme 2). While similar vinylic CO oxidative addition of carboxylates took place to give a 4 (carboxylato)(vinyl)ruthenium(II) [12], no CO bond oxidative addition occurred when vinyl ether was used for the reaction [13].…”
Section: Scheme 1 C-o Bond Cleavage Reactions Of Alkenyl Ethersmentioning
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