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.

Metal-catalyzed reductive coupling of olefin-derived nucleophiles: Reinventing carbonyl addition

“…The concept of transfer hydrogenative carbonyl addition introduced by our laboratory (8-10) provides an important inroad to this problem. Using ruthenium(0) catalysts, vicinally oxygenated secondary alcohols serve dually as reductants and carbonyl precursors (11, 12) (Figure 2). Ethylene, propylene, 1-octene, styrene and a host of other terminal olefins were found to engage in highly regio- and diastereoselective C-C coupling with 3-hydroxy-2-oxindoles to form the corresponding tertiary alcohols (11).…”

“…Ethylene, propylene, 1-octene, styrene and a host of other terminal olefins were found to engage in highly regio- and diastereoselective C-C coupling with 3-hydroxy-2-oxindoles to form the corresponding tertiary alcohols (11). The scope of this process was extended through the use of related osmium(0) catalysts (12), which promote the C-C couplings of ethylene and 1-octene with diols, α-ketols or α-hydroxy esters by way of vicinal dicarbonyl intermediates. The collective data corroborate a catalytic mechanism involving oxametalacyclopentane formation via olefin-carbonyl oxidative coupling.…”

Undecacarbonyl[(4-methylsulfanylphenyl)diphenylphosphane]triruthenium(0): crystal structure and Hirshfeld surface analysis

“…Tertiary phosphanes (PR 3 ) have played a major role in the formation and subsequent chemistry of metal carbonyl clusters, often relating to the promising catalytic activity of the products (Bruce et al, 2005;Shawkataly et al, 2013;Park et al, 2016). In general, the thermal reaction of Ru 3 (CO) 12 with PR 3 leads to Ru 3 (CO) 12 -n (PR 3 ) n , n = 1-4, cluster compounds (Bruce et al, 1988(Bruce et al, , 1989.…”

Diols as Dienophiles: Bridged Carbocycles via Ruthenium(0)‐Catalyzed Transfer Hydrogenative Cycloadditions of Cyclohexadiene or Norbornadiene

“…The carboxylic acid cocatalyst is postulated to accelerate transfer hydrogenolysis of the sterically congested metallacycle IIIA via protonolytic cleavage of a ruthenium–oxygen bond to form a more accessible and substitutionally labile ruthenium carboxylate (not shown) . It should be noted that although ethylene and α‐olefins engage in diol‐mediated C−C coupling under the conditions of ruthenium(0) or osmium(0), catalysis, the more highly substituted mono‐olefins cyclohexene and norbornene do not engage in C−C coupling in the presence or absence of a carboxylic acid cocatalyst, likely due to unfavorable equilibria associated with the reversible nature of the oxidative coupling event . Indeed, we have shown that such unfavorable equilibria can be overcome upon use of enol carboxylates as coupling partners, which deliver transient β‐acyloxy‐oxametallacycles that are “captured” through the elimination of carboxylate .…”