Synthesis of dichloro-sulphoxide complexes of ruthenium (II) and their use as catalysts for homogeneous asymmetric hydrogenation
Creators: name: McMillan, Roderick Stewart
Publisher: name: University of British Columbia
Year: 2010

description: Syntheses of a number of chiral and non-chiral sulphoxides and corresponding Ru(II) sulphoxide compounds are described, as well as significant reactions of some of these complexes with molecular hydrogen, olefins, and carbon monoxide. The new sulphoxides presented are: (S,R;S,S)-(+)-2-methylbutyl methyl sulphoxide, (MBMSO), (2R,3R)-(-)-2,3-0-isopropylidene-2,3-dihydroxy-1,4-bis(methyl sulphinyl)butane‧H₂0, (Dios), and (2R,3R)-(-)-2,3-0-isopropylidene-2,3-dihydroxy-l,4-bis(benzyl sulphinyl)butane‧H₂0, (BDios). These sulphoxides are prepared as mixtures of diastereomers. Other sulphoxides discussed are: dimethyl (DMSO), methyl n-propyl, (MeⁿprS0), methyl phenyl, (MPSO), and R-(+)-methyl p-tolyl sulphoxide, (MPTSO) and (2R,3R)-2,3-dihydroxy-l,4-bis(methyl sulphinyl)butane, (DDios). The previously unknown complexes, [NH₂Me₂][RuCl₃(DMSO)₃], [NH₂Me₂][RuCl₃(MeⁿprS0)₃], [RuCl₂(MBMSO)₂]₃, [RuCl₂(MPTSO)₂]₃, [RuCl₂(MPS0)₂]n, RuCl₂(DDios)₂‧2H₂0, RuCl₂(Dios)(DDios) and RuC1₂(DDios)(DMSO)(MeOH) have been prepared using newly developed synthetic routes. The previously prepared compounds, RuCl₂(DMS0)₄ and RuBr₂(DMSO)₄ are more fully described and in collaboration with A. Mercer and J. Trotter of this department the structures of the chloro-complex and the [NH₂Me₂][RuC1₃(DMSO)₃] compound were determined by x-ray crystallography. Both [NH₂Me₂][RuCl₃(DMSO ₃] and RuC1₂(DMSO)₄ react readily with molecular hydrogen in N,N'-dimethylacetamide (DMA) in the presence of a strong base, proton sponge R . The net heterolytic cleavage of H₂ results in hydride species which although not well characterized have anomalously high *H n.m.r. hydride chemical shifts at least for Ru(II). The anionic DMSO complex catalyses the hydrogen reduction of activated olefins in DMA at 60°C under 1 atm and kinetic and spectral studies indicate the following mechanism: [equation omitted] Activation of H₂ is thought to occur by net heterolytic cleavage of molecular hydrogen and this and an olefin insertion step are considered to be rate determining, (k₃ and k₄). Reduction proceeds by two pathways, one olefin-dependent and the other olefin-independent; the final step involves protonolysis of a σ-alkyl complex. Catalytic hydrogenation of acrylamide in DMA at 70°C using [RuCl₂(MBMSO)₂]₃ is described and the postulated mechanism is summarized below [equation omitted]. As with the anion system a two-path reduction occurs, one olefin-dependent and one olefin-independent, with the H₂-activation steps rate determining, (k₁ and k₄); however, H₂ activation is this time via oxidative addition. Asymmetric hydrogenation studies using the catalysts [RuCl₂(MBMSO)₂]₃, [RuCl₂ (MPTSO) ₂]₃, RuCl₂ (DDios) ₂•2H₂0, RuCl₂ (Dios)(DDios), and RuCl₂(DDios)(DMSO)(MeOH) are presented. The largest optical purities obtained are 25 and 15%, for the RuCl₂(Dios)(DDios)-itaconic acid and [RuCl₂(MBMSO)₂]₃-itaconic acid systems, respectively. The preparation of carbonyl derivatives of [RuCl₂(MBMSO)₂]₃ and [RuCl₂ (MPTS0) ₂]₃ are described; these derivatives have anomalously high v(C0) values.