Oligophosphan-Liganden

Dahlenburg, Lutz; Kerstan, S.; Werner, Detlef

doi:10.1016/0022-328x(91)83050-e

Cited by 18 publications

(7 citation statements)

References 27 publications

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“…Dahlenburg et al have studied the reduction of a variety of related MP 4 Cl 2 (M = Ru, Os) complexes in which the phosphines have methyl rather than phenyl substituents …”

Section: Discussionmentioning

confidence: 99%

Photochemistry of M(PP₃)H₂ (M = Ru, Os; PP₃ = P(CH₂CH₂PPh₂)₃): Preparative, NMR, and Time-Resolved Studies

et al. 1997

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Photochemical reaction of Ru(PP3)H2 (PP3 = P(CH2CH2PPh2)3) in THF under a rigorously inert atmosphere yields the cyclometalated complex Ru[(Ph2PCH2CH2)2P(CH2CH2PPhC6H4)]H. The latter is converted back to Ru(PP3)H2 under H2 and reacts even with traces of N2 to yield Ru(PP3)(N2). The dinitrogen complex may be synthesized directly by a number of methods. NMR spectroscopy shows that photolysis of Ru(PP3)H2 under C2H4 and CO yields Ru(PP3)(C2H4) and Ru(PP3)(CO), respectively. Photolysis of Ru(PP3)H2 with HSiEt3 in THF yields Ru(PP3)(SiEt3)H, while photolysis in mixtures of THF and benzene at low temperature yields Ru(PP3)(Ph)H. The latter is also generated by reduction of Ru(PP3)Cl2 in the presence of benzene. Os(PP3)(Ph)H is formed either by photolysis of Os(PP3)H2 or by reduction of Os(PP3)Cl2 in the presence of benzene. Irradiation of Os(PP3)H2 in THF or THF/hexane mixtures initially yields the THF C−H activation product, Os(PP3)(2-C4H7O)H. This complex is also generated by reduction of Os(PP3)Cl2 with sodium naphthalenide under N2 in the presence of THF. Os(PP3)(2-C4H7O)H is converted to the cyclometalated complex, Os[(Ph2PCH2CH2)2P(CH2CH2PPhC6H4)]H, on irradiation in THF and to Os(PP3)(Ph)H on irradiation in benzene. Reaction of Os(PP3)H2 with CH3OTf (Tf = triflate) yields Os(PP3)(OTf)H, which is converted to the labile Os(PP3)(CH3)H on reaction with methyllithium. Laser flash photolysis of Ru(PP3)H2 in cyclohexane (laser wavelength 308 nm) yields transient Ru(PP3) with an absorption maximum at 395 nm. The transient reacts with H2, C6H6, HSiEt3, CO, N2, C2H4, and THF with little discrimination; the second-order rate constants for these reactions lie in the range 5 × 105−2 × 106 dm3 mol-1 s-1 at 295 K. Kinetic isotope effects have been determined for the reaction with benzene and THF, as 1.5 (0.2) and 1.1 (0.2), respectively. Activation parameters for reaction of Ru(PP3) are as follows: with HSiEt3 ΔH ⧧ = 35 (2) kJ mol-1, ΔS ⧧ = −18 (6) J K-1 mol-1; with C6H6 ΔH ⧧ = 39 (4) kJ mol-1, ΔS ⧧ ≈ 0 J K-1 mol-1. The reaction with THF yields a short-lived adduct, probably bound through oxygen, which is rapidly converted to the cyclometalated product. Laser flash photolysis of Os(PP3)H2 generates transient Os(PP3) (λmax = 390 nm). The transient kinetics of Os(PP3) are substantially different from its ruthenium analogue. It reacts with alkanes and shows different behavior toward THF but is unaffected by addition of H2. Rate constants in the range 6 × 104−6 × 105 dm3 mol-1 s-1 (295 K) are presented for reaction with C6H6, THF, HSiEt3, CO, C2H4, N2, and several alkanes. Kinetic isotope effects have been determined for the reactions with methylcyclohexane and benzene as 5.6 (1.5) and 0.6 (0.1), respectively. The rate constants for reaction with alkanes rise in the order, methylcyclohexane < pentane < heptane < methane. The rate constants for reaction with methane and benzene are insignificantly different. Following reaction of Os(PP3) with THF to form Os(PP3)(THF), C−H insertion occurs with a first-order rate constant of 4.2 (...

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“…Dahlenburg et al have studied the reduction of a variety of related MP 4 Cl 2 (M = Ru, Os) complexes in which the phosphines have methyl rather than phenyl substituents …”

Section: Discussionmentioning

confidence: 99%

Photochemistry of M(PP₃)H₂ (M = Ru, Os; PP₃ = P(CH₂CH₂PPh₂)₃): Preparative, NMR, and Time-Resolved Studies

et al. 1997

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“…Neopentyl chloride (Aldrich) and 3-bromo-2-methylpropene (Aldrich) were dried over P 2 O 5 prior to use. Me 3 CCD 2 MgBr was prepared according to literature procedures. , (SiP 3 )(PMe 3 )RuCl 2 (3) was prepared by the method of Dahlenburg …”

Section: Methodsmentioning

confidence: 99%

C−C and C−H Bond Activation at Ruthenium(II): The Stepwise Degradation of a Neopentyl Ligand to a Trimethylenemethane Ligand

1997

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Ruthenacyclobutane complexes (SiP3)(PMe3)Ru(CH2EMe2CH2) (SiP3 = MeSi(CH2PMe2)3; 1, E = C; 2, E = Si) were synthesized from (SiP3)(PMe3)RuCl2 (3) and 2 equiv of the Grignard reagents, Me3ECH2MgCl. Metallacycle 1 was found to reversibly interconvert with the allyl complex (SiP3)Ru(Me)(η3-CH2CMeCH2) (4) and PMe3 when heated above 75 °C. From the results of kinetic studies and thermolysis of labeled material, the interconversion is proposed to take place by reversible β-methyl elimination/insertion. Conversion of 1 to 4 is an endothermic process (ΔH° = 14.3 ± 1.1 kcal mol-1), but it is entropically favorable (ΔS° = 40.9 ± 2.8 cal K-1 mol-1) due to the loss of the PMe3 ligand. Activation parameters for the β-insertion were determined to be ΔH ⧧ = 26.0 ± 1.2 kcal mol-1 and ΔS ⧧ = −10.5 ± 0.9 cal K-1 mol-1. Allyl complex 4 has been isolated as a mixture of isomers (7:1 endo:exo). The mechanism of interconversion of 4 endo and 4 exo was determined by 1H{31P} NMR spectroscopy (EXSY) to be a process involving a stereochemically rigid, square-pyramidal η1-intermediate. Thermolysis of 4 leads to loss of CH4 and the production of the trimethylenemethane complex (SiP3)Ru(η4-C(CH2)3) (7). The solid state structures of 1 and 7 were determined by X-ray diffraction.

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“…Dimer formation from unsaturated pincer intermediates has been reported by Spasyuk et al 35 P−C bond cleavage at phosphine ligands is known to occur (albeit not under such mild conditions) in the coordination sphere of ruthenium and other transition metals. 36,37 Scheme 2. Reaction of Complex 1 with Strong Bases A separately crystallized sample yielded another dimeric structure, the product of N−C cleavage at the ligand, with one ruthenium atom bearing only a monophosphine ligand: Ph 2 (CH 2 ) 2 NH (complex 4; Figure 3).…”

Section: ■ Introductionmentioning

confidence: 99%

Study of Precatalyst Degradation Leading to the Discovery of a New Ru⁰ Precatalyst for Hydrogenation and Dehydrogenation

Anaby¹,

Schelwies

Schwaben

et al. 2018

Organometallics

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The complex Ru-MACHO ( 1) is a widely used precatalyst for hydrogenation and dehydrogenation reactions under basic conditions. In an attempt to identify the active catalyst form, 1 was reacted with a strong base. The formation of previously unreported species was observed by NMR and mass spectrometry. This observation indicated that complex 1 quickly degraded under basic conditions when no substrate was present. X-ray crystallography enabled the identification of three complexes as products of this degradation of complex 1. These complexes suggested degradation pathways which included ligand cleavage and reassembly, along with reduction of the ruthenium atom. One of the decomposition products, the Ru 0 complex [Ru(N(CH 2 CH 2 PPh 2 ) 3 )CO] (5), was prepared independently and studied. 5 was found to be active, entirely additivefree, in the acceptorless dehydrogenation of aliphatic alcohols to esters. The hydrogenation of esters catalyzed by 5 was also demonstrated under base-free conditions with methanol as an additive. Protic substrates were shown to add reversibly to complex 5, generating Ru II −hydrido species, thus presenting a rare example of reversible oxidative addition from Ru 0 to Ru II and reductive elimination from Ru II to Ru 0 .

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Oligophosphan-Liganden

Cited by 18 publications

References 27 publications

Photochemistry of M(PP₃)H₂ (M = Ru, Os; PP₃ = P(CH₂CH₂PPh₂)₃): Preparative, NMR, and Time-Resolved Studies

Photochemistry of M(PP₃)H₂ (M = Ru, Os; PP₃ = P(CH₂CH₂PPh₂)₃): Preparative, NMR, and Time-Resolved Studies

C−C and C−H Bond Activation at Ruthenium(II): The Stepwise Degradation of a Neopentyl Ligand to a Trimethylenemethane Ligand

Study of Precatalyst Degradation Leading to the Discovery of a New Ru⁰ Precatalyst for Hydrogenation and Dehydrogenation

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Oligophosphan-Liganden

Cited by 18 publications

References 27 publications

Photochemistry of M(PP3)H2 (M = Ru, Os; PP3 = P(CH2CH2PPh2)3): Preparative, NMR, and Time-Resolved Studies

Photochemistry of M(PP3)H2 (M = Ru, Os; PP3 = P(CH2CH2PPh2)3): Preparative, NMR, and Time-Resolved Studies

C−C and C−H Bond Activation at Ruthenium(II): The Stepwise Degradation of a Neopentyl Ligand to a Trimethylenemethane Ligand

Study of Precatalyst Degradation Leading to the Discovery of a New Ru0 Precatalyst for Hydrogenation and Dehydrogenation

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Photochemistry of M(PP₃)H₂ (M = Ru, Os; PP₃ = P(CH₂CH₂PPh₂)₃): Preparative, NMR, and Time-Resolved Studies

Photochemistry of M(PP₃)H₂ (M = Ru, Os; PP₃ = P(CH₂CH₂PPh₂)₃): Preparative, NMR, and Time-Resolved Studies

Study of Precatalyst Degradation Leading to the Discovery of a New Ru⁰ Precatalyst for Hydrogenation and Dehydrogenation