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Binding and activation of small molecules by ruthenium complexes containing a chelated aminophosphine ligand

University of British Columbia

Ruthenium(II) and Ru(III) complexes of the type RuC1ɳ(P-N)(PR3) have been prepared, generally by reaction of the appropriate aminophosphine P-N with RuC12(PR3)3 and RuC13(PR3)2(DMA), respectively [n = 2 or 3; P-N = PMA (o-diphenylphosphino-N,N-dimethylaniline), PAN (1-(dimethylanuno)-8-(diphenylphosphino) naphthalene), or (R)-AMPHOS ((R)-(+)-N,N-dimethyl- 1 -[o-(diphenyl phosphino)phenyljethylamine); R = Ph or p-tolyl; DMA N,N-dimethylaceta mide]. [Scientific models] The X-ray crystal structure of RuC1 2 (PMA)(P(p-tolyl)3) reveals a square pyramidal geometry, with trans-chlorides, the N-arm of the PMA chelate and the P(p-tolyl)3 in the basal plane. These structural features are presumed to be shared also by the Ru(II)-(AMPHOS) and Ru(II)-(PAN) complexes. As evidenced by 31P{ 1H} and 1H NMR spectroscopic studies, the Ru(II)-(P-N)complexes retain their solid state structure in solution. The crystallographically characterized RuCI3(PMA)(PPh3) and RuCI3(AMPHOS)(PPh3) complexes show a meridional arrangement of chloride ligands in an octahedral structure, with the N-arm of the P-N chelate trans to the monodentate phosphine. The X-ray structure of (R) AMPHOS was also determined. Chloroform or CH 2 C1 2 solutions of RuCl 2 (PMA)(PR2) react rapidly and reversibly with 1 atm of H2 in the absence of an added base to give in situ formation (85% conversion) of the dihydrogen complex (ɳ2-H2)RuCl2(PMA)-(PR3). The-n2-H2 moiety is characterized by means of 1H NMR spectroscopy; for the R=p-tolyl complex, the short T1 value (T1(min) = 13.4 ± 0.2 ms at 232 K and 300 MHz), and the relatively large H-D coupling for the ɳ2-HD isotopomer (JHD = 30 Hz), support the formulation. The H-H distance for the dihydrogen moiety in (ɳ2-H2)RuCl2(PMA)(P(p-tolyl)3) is estimated to be 0.87 ± 0.03 A by variable temperature T1 measurements. Solution reactions of the Ru(II) and Ru(III) complexes of PMA and AMPHOS with 1 atm ofH2 in the presence of 1,8-bis(dimethylamino) naphthalene [Proton Sponge (PS)] result in the formation of the corresponding Ru(II)-chloro(hydrido) complexes Ru(H)C1(P-N)(PR3). Evidence for formation of the monohydride complexes by an overall heterolytic cleavage of H2 via a molecular hydrogen complex is also presented. Based on kinetic studies of the reaction of RuC13(AMPHOS)(PR3) (R p-tolyl) with H2 in DMA, a mechanism involving a “Ru(H)C12” intermediate en route to the RuC12-(AMPHOS)(PR3) species is proposed within an overall process for the formation of the RuC13(AMPHOS)(PR3) complex. Studies on the catalytic hydrogenation of styrene (1 atm of H2 at 30 °C in DMA) using the RuC13(AMPHOS)(PR3) complexes, where P-N = PMA or AMPHOS and R = Ph or p-tolyl, in the presence of PS reveal that the corresponding monohydride complexes RuC13(AMPHOS)(PR3) are probably the catalytically active species. The catalytic asymmetric hydrogenation of (z)-a-acetamidocinnamic and tiglic acids, carried out in benzene/methanol under 17-68 atm H2, using RuC13(AMPHOS)(PHh3) as catalyst precursor result in complete hydrogenation of the olefinic bond, but with only 6 and 0% e.e., respectively. Reaction of the five-coordinate RuC12(PMA)(PR3) complex in solution with a variety of small molecules results in a range of adducts of the form RuC12(PMA)(PR3)(L) where the chlorides are either cis [L = H2 (see above), ,N2 SO2, and H2S] or trans (L = H2O, MeOH, and CO). With L = EtSH, a mixture of cis- and trans-dichloro adducts was obtained. These adducts were either isolated or studied in situ, and characterized mainly by NMR and IR spectroscopies. Characterization of the RuCl2(PMA)(P(p-tolyl)3)(L) complexes, where L =H20 or H2S, includes single-crystal X-ray structure determinations, which reveal a trans- and cis-dichloro arrangement respectively in the octahedral complexes; the P(p-tolyl)3 group is trans to the N-arm of the aminophosphine in both complexes. The molecular structure of the H2S adduct provides the second example of a structurally characterized transition metal-H2S complex. Of note, the RuCl2(PMA)(P(p-tolyl)3)(SH2) complex could also be obtained by the solid state reaction of the precursor five-coordinate complex with 1 atm H2S at room temperature. The solution reaction of RuC12(PMA)(PR3) with 02 results in formation of a species which is tentatively proposed to be the peroxo-bridged complex [RuC12(PMA)(PR3)]2(µ-O2). The reaction of RuC12(PMA)(PR3) with CO at <-20 °C in solution, or in the solid state at room temperature, results in formation of the mono-CO adduct with trans-chlorides, while the solution reaction carried out at room temperature results in a mixture of cis-trans and cis-cis isomers of the dicarbonyl Ru(CO)2Cl2(PMA); the carbonyl-containing species were characterized mainly by NMR and IR spectroscopies. The five-coordinate RuCl2(PAN)(P(p-tolyl)3) complex shows no reactivity toward the small molecules investigated, presumably because of steric effects. Preliminary studies on the reaction of RuC12(AMPHOS)(P(p-tolyl)3) with SO2 reveal formation of the SO2 adduct.

Thesis/Dissertation

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2009-04-14

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http://hdl.handle.net/2429/7060

Chemistry

University of British Columbia

UBCV

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