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)C6Me4}{(Z)-Ph2PCH=CHPPh2}(PMe2Ph)]PF6 and [Ru{η3-(HCH2)(CH2)C6Me4}(PMe2Ph)3]PF6

Martin A. Bennett, Lai Yoong Goh, Ian J. McMahon, Thomas R.B. Mitchell, Glen B. Robertson, Terence W. Turney, Wasantha A. Wickramasinghe

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Treatment of the various ruthenium(II) salts [Ru(ONO2)(η6-1,2-dimethylarene)L2]NO3 and [Ru-(O2CCF3)(η6-1,2-dimethylarene)L2]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)2C6Me4}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)2C6H2Me2}L2L′ (L = L′ = PMe2Ph, PMePh2), and Ru{η4-(CH2)2C6H4)(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)2C6Me4}L2L′ and Ru{η4-(CH2)2C6H4)(PMe2Ph)3 give (η3-benzyl)ruthenium(II) salts [Ru{η3-(HCH2)(CH2)C6Me4}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)C6H4}(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) Å,b = 18.612 (3) Å,c = 12.361 (1) Å, β = 90.40 (1)°, and Z = 4; those of 3 are monoclinic, space group C2/c, with a = 21.220 (8) Å,b = 23.412 (10) Å, c = 18.580 (7) Å, 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) Å, Ru-C(2) = 2.342 (4) Å, Ru-C(1) = 2.358 (4) Å). The metrical parameters defining the agostic Ru-H-CH2 interaction in 2 are r(Ru-C) = 2.416 (5) Å, r(Ru-H) = 1.92 (4) Å, r(C-H) = 1.01 (5) Å, and ∠C-H-Ru = 107 (3)°. The distances from ruthenium to the terminal carbon atoms in 3 (Ru-C(11) = 2.333 (9) Å, Ru-C(22) = 2.283 (10) Å) 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.

Original languageEnglish
Pages (from-to)3069-3085
Number of pages17
Issue number9
Publication statusPublished - 1 Sept 1992
Externally publishedYes

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