81408-66-4Relevant academic research and scientific papers
Dissociative and nondissociative pathways in the endo to exo isomerization of tetramethyl-o-xylylene complexes of ruthenium and osmium, ML3{η4o-C6Me4(CH 2)2} (M = Ru, L = PMe3; M = Os, L = PMe3, PMe2Ph).
Bennett, Martin A.,Bown, Mark,Hockless, David C. R.,McGrady, John E.,Schranz, Harold W.,Stranger, Robert,Willis, Anthony C.
, p. 3784 - 3797 (1998)
Treatment of the (η6-hexamethylbenzene)ruthenium(II) and -osmium(II) salts [M(O2-CCF3)L2(η6-C 6Me6)]PF6 (M = Ru, L = PMe3; M = Os, L = PMe3, PMe2Ph) in the presence of L with KO-t-Bu gives exclusively the endo- (tetramethyl-o-xylylene)metal(0) complexes ML3{η4-endo-o-C6Me4(CH 2)2}, endo-1, -2, and -3, respectively, in high yield; these are protonated by an excess of triflic acid (CF3SO3H, TfOH) to give the (η6-hexamethylbenzene)metal(II) salts [ML3(η6-C6Me6)](OTf)2 [M = Ru, L = PMe3 (4); M = Os, L = PMe3 (5); M = Os, L = PMe2Ph (6)). Complexes 4-6 revert to endo-1-3 on treatment with KO-t-Bu, whereas for M=Ru, L=PMe2Ph the complexes [ML3(η6-C6Me6)]2+ and [M(O2CCF3)L2(η6-C 6-Me6)]+/L react with KO-t-Bu to give exclusively the exo isomer, Ru(PMe2Ph)3{η4-exo-o-(CH2) 2C6Me4} (exo-7). The endo complexes 1-3 are converted quantitatively into the corresponding exo isomers in toluene in the temperature range 65-106°C, the process being first order in endo complex. Kinetics studies in the presence of PMe3 (for 1 and 2) or PMe2-Ph (for 3) indicate that two pathways are available: one depends on initial dissociation of L and proceeds through a bis(ligand) intermediate or intermediates, e.g., ML2{endo-o-C6-Me4(CH2)2} and ML2{exo-o-(CH2)2C6Me4}, and the other does not. The dissociative mechanism is predominant for M = Ru, L = PMe3, whereas the nondissociative or direct mechanism plays the dominant, possibly exclusive, role for M = Os, L = PMe3. The osmium(0) compound exo-2 adds PMe3 irreversibly to give the σ-bonded (hexamethylbenzene-1,2-diyl)osmium(II) complex Os(PMe3)4{κ2-o-(CH2) 2C6Me4} (8), whereas the corresponding PMe2Ph derivative 9 is in equilibrium with exo-3 and PMe2Ph and cannot be isolated; the ruthenium(0) compound exo-1 is inert toward PMe3. Density functional calculations on the model compounds ML3-{η4-exo-o-(CH2)2C 6H4} and ML4{κ2-o-(CH2)2C 6H4}(M = Ru, Os; L = PH3) correctly reflect the observed stability order Os > Ru for the diyl complex but predict the latter to be more stable than the η4 complex for both elements. In this case, the usual computational simplification of replacing a tertiary phosphine by PH3 is probably unjustified. The molecular structures of the η4 complexes endo-3, exo-3, and exo-1 and of the diyl complex 8 have been determined by X-ray crystallography. The endo- to exo-o-xylylene isomerizations are compared with the intramolecular migrations that occur in Fe(CO)3(η4-polyene) and Cr(CO)3(η6-substituted-naphthalene) complexes.
Double deprotonation of ruthenium(II) cations containing 1,2-dimethyl-substituted η6-arenes. Protonation of the resulting exo-coordinated (o-xylylene)ruthenium(0) complexes and X-ray crystal structures of the agostic (η3-pentamethylbenzyl)ruthenium(II) complexes [Ru{η3-(HCH2)(CH2)C6Me 4 ...
Bennett, Martin A.,Goh, Lai Yoong,McMahon, Ian J.,Mitchell, Thomas R. B.,Robertson, Glen B.,Turney, Terence W.,Wickramasinghe, Wasantha A.
, p. 3069 - 3085 (2008/10/08)
Full title: Double deprotonation of ruthenium(II) cations containing 1,2-dimethyl-substituted η6-arenes. Protonation of the resulting exo-coordinated (o-xylylene)ruthenium(0) complexes and X-ray crystal structures of the agostic (η3-pentamethylbenzyl)ruthenium(II) complexes [Ru{η3-(HCH2)(CH2)C6Me 4}{(Z)-Ph2PCH=CHPPh2}(PMe 2Ph)]PF6 and [Ru{η3-(HCH2)(CH2)C6Me 4}(PMe2Ph)3]PF6. Treatment of the various ruthenium(II) salts [Ru(ONO2)(η6-1,2-dimethylarene)L2]NO 3 and [Ru-(O2CCF3)(η6-1,2-dimethylarene)L 2]PF6 with KO-t-Bu or (Me3Si)2NNa in the presence of a ligand L′ gives o-xylylene (o-quinodimethane) complexes of zerovalent ruthenium, i.e. Ru{η4-(CH2)2C6Me 4}L2L′ (L = L′ = PMe2Ph, P(CD3)2Ph, PMePh2, P(OMe)3, P(OCH2)3CMe; L2 = Ph2PCH2CH2PPh2, L′ = PMe2Ph; L2 = (Z)-Ph2PCH=CHPPh2, L′ = PMe2Ph, P(CD3)2Ph), Ru{η4-(CH2)2H2Me 2}L2L′ (L = L′ = PMe2Ph, PMePh2), and Ru{η4-(CH2)2C6H 4}(PMe2Ph)3, in good to moderate yields. In all cases the o-xylylene group is coordinated through its exo pair of double bonds. The reactions are proposed to proceed via the undetected intermediates Ru(o-xylylene)L2 (L = monodentate P-donor ligand, L2 = bidentate P-donor ligand) in which the ruthenium atom can migrate from the endo to the exo pair of double bonds before ligand L′ attacks. On treatment with HPF6, Ru{η4-(CH2)2C6Me 4}L2L′ and Ru{η4-(CH2)2C6H 4}(PMe2Ph)3 give (η3-benzyl)ruthenium(II) salts [Ru{η3-(HCH2)(CH2)C6Me 4)L2L′]PF6 (L = Ph2PCH2CH2PPh2, L′ = PMe2Ph (1); L = (Z)-Ph2PCH=CHPPh2, L′ = PMe2Ph (2), P(CD3)2Ph (2a); L = L′ = PMe2Ph (3), P(CD3)2Ph (3a)) and [Ru{η3-(HCH2)-(CH2)C6H 4)(PMe2Ph)3]PF6 (4) in which the added proton bridges the metal atom and a terminal methylene group. Crystals of 2 are monoclinic, space group P21/n, with a = 18.884 (3) A?, b = 18.612 (3) A?, c = 12.361 (1) A?, β = 90.40 (1)°, and Z = 4; those of 3 are monoclinic, space group C2/c, with a = 21.220 (8) A?, b = 23.412 (10) A?, c = 18.580 (7) A?, β = 126.05 (1)°, and Z = 8. The structures were solved by heavy-atom methods and refined by least-squares analysis to R = 0.042 and Rw = 0.053 for 5787 independent reflections (I ≥ 3σ) (2) and R = 0.053 and Rw = 0.076 for 5832 independent reflections (I > 3σ) (3). Both cations contain a ruthenium atom coordinated in a distorted-octahedral arrangement by a η3-pentamethylbenzyl group, which occupies two sites, three phosphorus atoms, and an agostic methyl hydrogen atom that has been directly located in 2 but not 3. The η3-benzyl interaction in 2 shows the usual asymmetry, the shortest Ru-C bond being to the terminal CH2 group (Ru-C(22) = 2.164 (5) A?, Ru-C(2) = 2.342 (4) A?, Ru-C(1) = 2.358 (4) A?). The metrical parameters defining the agostic Ru-H-CH2 interaction in 2 are r(Ru-C) = 2.416 (5) A?, r(Ru-H) = 1.92 (4) A?, r(C-H) = 1.01 (5) A?, and ∠C-H-Ru = 107 (3)°. The distances from ruthenium to the terminal carbon atoms in 3 (Ru-C(11) = 2.333 (9) A?, Ru-C(22) = 2.283 (10) A?) are almost equal within experimental error, in contrast with the corresponding distances in 2, and indicate that the solid-state structure of 3 is an average in which either C(11) or C(22) is protonated. Variable-temperature NMR (1H, 31P) spectra of complexes 1, 2, 2a, 3, 3a, and 4 show these molecules to be fluxional as a consequence of three processes: (1) reversible Ru-H (agostic) bond breaking, which cannot be frozen out, even at -100°C; (2) reversible η3 ? η1 interconversions of the benzyl group, for which the estimated ΔG≠ values are ca. 13 kcal/mol at 303 K for 2 and ca 10 kcal/mol at 243 K for 3; (3) reversible C-H bond breaking in the Ru-H-CH2 bond, for which limiting high-temperature spectra cannot be reached owing to sample decomposition. For complexes 1-3, a combination of these processes enables the RuL3 fragment to circumnavigate the six-membered ring.
