title: Osmium(0)-Catalyzed C-C Coupling of Ethylene and α-Olefins with Diols, Ketols, or Hydroxy Esters via Transfer Hydrogenation.
abstract: Osmium(0) complexes derived from Os3(CO)12 and XPhos (2-dicyclohexylphosphino-2',4',6'-triisopropylbiphenyl) catalyze the C-C coupling of α-hydroxy esters 1a-1i, α-ketols 1j-1o, or 1,2-diols dihydro-1j-1o with ethylene 2a to form ethylated tertiary alcohols 3a-3o. As illustrated in couplings of 1-octene 2b with vicinally dioxygenated reactants 1a, 1b, 1i, 1j, 1k, 1m, higher α-olefins are converted to adducts 4a, 4b, 4i, 4j, 4k, 4m with complete levels of branched regioselectivity. Oxidation level independent C-C coupling is demonstrated by the reaction of 1-octene 2b with diol dihydro-1k, α-ketol 1k, and dione dehydro-1k. Functionalized olefins 2c-2f react with ethyl mandelate 1a to furnish adducts 5a-8a as single regioisomers. The collective data, including deuterium labeling studies, are consistent with a catalytic mechanism involving olefin-dione oxidative coupling to form an oxa-osmacyclopentane, which upon reductive cleavage via hydrogen transfer from the secondary alcohol reactant releases the product of carbinol C-alkylation with regeneration of the ketone. Single-crystal X-ray diffraction data of the dinuclear complex Os2(CO)4(O2CR)2(XPhos)2 and the trinuclear complex Os3(CO)11(XPhos) are reported. These studies suggest increased π-backbonding at the stage of the metal-olefin π-complex plays a critical role in facilitating alkene-carbonyl oxidative coupling, as isostructural ruthenium(0) complexes, which are weaker π-donors, do not catalyze the transformations reported herein.
authors: Department of Chemistry, University of Texas at Austin , Austin, Texas 78712, United States.
authors: Boyoung Y
authors: BY
authors: Park
authors: Department of Chemistry, University of Texas at Austin , Austin, Texas 78712, United States.
authors: Tom
authors: T
authors: Luong
authors: Department of Chemistry, University of Texas at Austin , Austin, Texas 78712, United States.
authors: Hiroki
authors: H
authors: Sato
authors: Department of Chemistry, University of Texas at Austin , Austin, Texas 78712, United States.
authors: Michael J
authors: MJ
authors: Krische
mesh_terms: D000475:Alkenes / Q000737:chemistry*; D002384:Catalysis; D018360:Crystallography, X-Ray; D004952:Esters / Q000737:chemistry; D005030:Ethylenes / Q000737:chemistry*; D006865:Hydrogenation; D009992:Osmium / Q000737:chemistry*; D013057:Spectrum Analysis / Q000379:methods
chemical_list: D000475:Alkenes; D004952:Esters; D005030:Ethylenes; D009992:Osmium; C036216:ethylene