Pentakis(trimethylphoshine)osmium(0)

Ermer, Susan; Shinomoto, Ronald S.; Deming, Mark A.; Flood, Thomas C.

doi:10.1021/om00107a040

Cited by 17 publications

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“…The kinetic selectivity of Os(PP 3 ) for methane over cyclohexane is at least 520 times greater than for Tp‘Rh(CNR), where reaction with methane was not observed at atmospheric pressure. Reactions of osmium complexes with alkanes, including methane, have been recorded previously in arene half-sandwich complexes 6 and in other phosphine complexes …”

Section: Discussionmentioning

confidence: 82%

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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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Section: Discussionmentioning

confidence: 82%

“…For comparison, Flood et al have studied the thermolysis of Os(PMe 3 ) 4 (CH 2 CMe 3 )H with hydrocarbons, isolating C−H activation products, Os(PMe 3 ) 4 (R)H, from benzene, Me 4 Si, mesitylene, and methane . In the absence of these substrates a cyclometalation product is formed.…”

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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“…An ion pair mechanism would be expected to show a dependence on solvent polarity, so several other solvents were investigated. Treatment of L 4 Os(H)(OC 6 H 4 CN) ( 6e ) with excess L in propylene carbonate (PPC, ε = 64.4), DMSO- d 6 (ε = 46.7), DMF (ε = 36.7), and CD 3 NO 2 (ε = 35.9) over a period of hours at 80 °C all resulted in high-yield conversions to [L 5 OsH][OAr], with 31 P{ 1 H} NMR resonances at approximately δ −56 (d, 4P, J PP = 17 Hz) and −61 (pent, 1P) . Solvent effects on the chemical shifts were small.…”

Section: Resultsmentioning

confidence: 99%

Phosphine Ligand Exchange in Tetrakis(trimethylphosphine)(hydrido)osmium Anilides, Phenoxides, and Thiophenoxides. Examples of Anion Dissociation and of Labilization by Ligand π-Base Effects

et al. 2000

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The series of phenoxide complexes cis-L 4 Os(H)OC 6 H 4 Z (L ) PMe 3 ; Z ) H, OMe, CF 3 , NH 2 , CN), anilides cis-L 4 Os(H)NHC 6 H 4 Z (Z ) H, OMe, CF 3 ), and thiophenoxides cis-L 4 Os(H)-SC 6 H 4 Z (Z ) H, OMe) have been prepared by treatment of fac-L 3 Os(H)(η 2 -CH 2 PMe 2 ) with the corresponding neutral arene. 1 H NMR spectra of coordinated phenoxides and thiophenoxides show rapid phenyl group rotation, while that of the anilides is slow. Rates and stereochemistry of substitution of P(CH 3 ) 3 (L) by P(CD 3 ) 3 (L′) were determined by 31 P NMR in benzene at 80°C. Anilides substitute first only in the mutually trans sites (a sites) with cleanly first-order kinetics and subsequently into the site trans to the anilide (site c). The latter shows non-first-order behavior that is accurately modeled by iterative kinetics calculations using a mechanism of L dissociation only from the a sites presumably to give a quasi-trigonal-bipyramidal intermediate stabilized by π-electron donation from the anilide lone pair. A three-point Hammett plot against σ p yielding F ) -1.8 is consistent with transition state stabilization by π-donation. Association of L′ occurs only into site a, but subsequent substitution allows the resident L′ to move into site c. Thiophenoxides exhibit substitution rates and stereochemical patterns very similar to those of the anilides and are believed to proceed by the same mechanism. Phenoxide complexes incorporate L′ into all sites, with each site incorporating phosphine independently of the others since exchange rates at all sites are first order. A Hammett plot of exchange rates against sigma minus (σ -) is somewhat scattered (R 2 ) 0.96) but exhibits a positive slope F -) +0.36. Phenoxide dissociation is postulated, but the fact that substantial concentrations of intermediates partially substituted in all positions is seen during the reaction is inconsistent with ratedetermining phenoxide dissociation. An ionization preequilibrium followed by slower phosphine exchange steps in the ion pair is postulated. Treatment of L 4 Os(H)(OC 6 H 4 CN) with excess L in propylene carbonate, DMSO-d 6 , DMF, or CD 3 NO 2 at 80°C all resulted in conversions to [L 5 OsH][OAr]. These results suggest that low steady-state concentrations of [L 5 OsH][OAr] ion pairs in benzene are possible, consistent with an ion pair mechanism for ligand exchange.

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“…After 1.5 h at 70 °C the 31 P NMR spectrum revealed complete transformation of [Os(CH 3 )(PMe 3 ) 5 ] + to Os(H) 2 (PMe 3 ) 4 , while a small amount of the [Os(H)(PMe 3 ) 5 ] + cation remained unreacted. This reduction presumably involves formation of the neutral complex Os(PMe 3 ) 5 , which can lose one phosphine to give Os(H)(CH 2 PMe 2 )(PMe 3 ) 3 8a…”

Section: Synthesis Of M(h)2l4 and [Mh3l4]+ Complexes (M = Fe Ru Os; L...mentioning

confidence: 99%

Synthesis, Structural Diversity, Dynamics, and Acidity of the M(II) and M(IV) Complexes [MH₃(PR₃)₄]⁺ (M = Fe, Ru, Os; R = Me, Et)

et al. 1997

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The syntheses of complexes MH2L4 and their protonated analogues [MH3L4]+ (M = Fe (1), Ru (2), Os (3); R = Me (a), Et (b)) are described. The structures of 1a, 1b, and 3a were determined in X-ray diffraction studies. The solution structures of complexes 1−3 were established by detailed NMR investigations. 1a, 2b, and 3a form equilibrium mixtures of two isomers in solution. The iron (1a) and ruthenium (2b) complexes isomerize between six-coordinate M(II) dihydrogen cis-[MH(H2)L4]+ and seven-coordinate M(IV) trihydride [M(H)3L4]+ molecular geometries: the first is a distorted octahedron and the second can be viewed as a hydride-capped M(PR3)4 tetrahedron. Complex 3a is a pentagonal bipyramidal trihydride cis-[Os(H)3(PMe3)4]+ in equilibrium with the hydride-capped tetrahedral structural form. Trihydrides 1b and 3b are exclusively represented by the latter structural type. The cationic molecule 2a corresponds to a dihydrogen complex cis-[RuH(H2)(PMe3)4]+. The metal fragment [MH(PR3)4]+ is thus most reactive toward oxidative addition of H2 for osmium and iron, with a notably lower ability to reduce H2 for ruthenium. This trend and related properties are due to electronic rather than steric factors. All [MH3(PR3)4]+ species (1−3) are fluxional in solution. The intramolecular hydride exchanges and isomerizations were studied between 20 and −140 °C and quantitatively described in terms of their activation parameters. On the basis of these, mechanistic interpretations are provided. Finally the acid/base properties of the [MH3(PR3)4]+/M(H)2(PR3)4 systems were established in a series of NMR experiments in THF-d 8. The pK a values range from 10.3 to 12.9 units and increase in the following order: 1a (10.3) < 2b (10.7) < 2a (10.9) < 3a (11.2) < 3b (12.9). This series demonstrates a higher acidity than that of the related [MH(H2)(PP)2]+ molecules with bidentate ligands. The complexes with monodentate phosphine ligands [MH3(PR3)4]+ (1−3) represent a new and distinguished family with structural, dynamic, and acid/base properties remarkably different from most of the other known [MH3L4]+ representatives.

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Pentakis(trimethylphoshine)osmium(0)

Cited by 17 publications

References 0 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

Phosphine Ligand Exchange in Tetrakis(trimethylphosphine)(hydrido)osmium Anilides, Phenoxides, and Thiophenoxides. Examples of Anion Dissociation and of Labilization by Ligand π-Base Effects

Synthesis, Structural Diversity, Dynamics, and Acidity of the M(II) and M(IV) Complexes [MH₃(PR₃)₄]⁺ (M = Fe, Ru, Os; R = Me, Et)

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Pentakis(trimethylphoshine)osmium(0)

Cited by 17 publications

References 0 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

Phosphine Ligand Exchange in Tetrakis(trimethylphosphine)(hydrido)osmium Anilides, Phenoxides, and Thiophenoxides. Examples of Anion Dissociation and of Labilization by Ligand π-Base Effects

Synthesis, Structural Diversity, Dynamics, and Acidity of the M(II) and M(IV) Complexes [MH3(PR3)4]+ (M = Fe, Ru, Os; R = Me, Et)

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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

Synthesis, Structural Diversity, Dynamics, and Acidity of the M(II) and M(IV) Complexes [MH₃(PR₃)₄]⁺ (M = Fe, Ru, Os; R = Me, Et)