Cis-dihydroxylation Of Alkenes Research Articles

Oxidizing Ability of a Dioxygen-Activating Nonheme Iron(II)-Benzilate Complex Immobilized on Gold Nanoparticles.

An iron(II)-benzilate complex [(TPASH)FeII(benzilate)]ClO4@C8Au (2) (TPASH = 11-((6-((bis(pyridin-2-ylmethyl)amino)methyl)pyridin-2-yl)methoxy)undecane-1-thiol) immobilized on octanethiol stabilized gold nanoparticles (C8Au) of core diameter less than 5 nm has been prepared to evaluate its reactivity toward O2-dependent oxidations compared to a nonimmobilized complex [(TPA-O-Allyl)FeII(benzilate)]ClO4 (1a) (TPA-O-Allyl = N-((6-(allyloxymethyl)pyridin-2-yl)methyl)(pyridin-2-yl)- N-(pyridin-2-ylmethyl)methanamine). X-ray crystal structure of the nonimmobilized complex 1a reveals a six-coordinate iron(II) center in which the TPA-O-Allyl acts as a pentadentate ligand and the benzilate anion binds in monodentate fashion. Both the complexes (1a and 2) react with dioxygen under ambient conditions to form benzophenone as the sole product through decarboxylation of the coordinated benzilate. Interception studies reveal that a nucleophilic iron-oxygen intermediate is formed in the decarboxylation reaction. The oxidants from both the complexes are able to carry out oxo atom transfer reactions. The immobilized complex 2 not only performs faster decarboxylation but also exhibits enhanced reactivity in oxo atom transfer to sulfides. Importantly, the immobilized complex 2, unlike 1a, displays catalytic turnovers in sulfide oxidation. However, the complexes are not efficient to carry out cis-dihydroxylation of alkenes. Although the immobilized complex yields a slightly higher amount of cis-diol from 1-octene, restricted access of dioxygen and substrates at the coordinatively saturated metal centers of the complexes likely makes the resulting iron-oxygen species less active in oxygen atom transfer to alkenes. The results implicate that surface immobilized nonheme iron complexes containing accessible coordination sites would exhibit better reactivity in O2-dependent oxygenation reactions.

Enzymatic cis-Dihydroxylation of Alkenes

Enzymatic cis-Dihydroxylation of Alkenes

ChemInform Abstract: Practical Iron‐Catalyzed Atom/Group Transfer and Insertion Reactions

AbstractReview: 86 refs.

Practical iron-catalyzed atom/group transfer and insertion reactions

Iron-catalyzed reactions are receiving a surge of interest owing to the natural abundance and biocompatibility of Fe and the urge to develop practically useful sustainable catalysis for fine chemical industries. This article is a brief account of our studies on the C–O and C–N bond formation reactions catalyzed by Fe complexes supported by oligopyridine, macrocyclic tetraaza, and fluorinated porphyrin ligands. The working principle is the in situ generation of reactive Fe=O and Fe=NR intermediates supported by these oxidatively robust N-donor ligands for oxygen atom/nitrogen group transfer and insertion reactions. The catalytic reactions include C–H bond oxidation of saturated hydrocarbons (up to 87 % yield), epoxidation of alkenes (up to 96 % yield), cis-dihydroxylation of alkenes (up to 99 % yield), epoxidation–isomerization (E–I) reaction of aryl alkenes (up to 94 % yield), amination of C–H bonds (up to 95 % yield), aziridination of alkenes (up to 95 % yield), sulfimidation of sulfides (up to 96 % yield), and amide formation from aldehydes (up to 89 % yield). Many of these catalytic reactions feature high regio- and diastereoselectivity and/or high product yields and substrate conversions, and recyclability of the catalyst, demonstrating the applicability of Fe-catalyzed oxidative organic transformation reactions in practical organic synthesis.

The role of salicylic acid, l-ascorbic acid and oxalic acid in promoting the oxidation of alkenes with H2O2 catalysed by [MnIV2(O)3(tmtacn)2]2+

The role played by the additives salicylic acid, L-ascorbic acid and oxalic acid in promoting the catalytic activity of [MnIV2(O)3(tmtacn)2](PF6)2 (1(PF6)2, where tmtacn = N,N',N''-trimethyl-1,4,7-triazacyclononane) in the epoxidation and cis-dihydroxylation of alkenes with H2O2 and in suppressing the catalysed decomposition of H2O2 is examined. Whereas aliphatic and aromatic carboxylic acids effect enhancement of the catalytic activity of 1 through the in situ formation dinuclear carboxylato bridged complexes of the type [MnIII2(mu-O)(mu-RCO2)2(tmtacn)2]2+, for L-ascorbic acid and oxalic acid notable differences in reactivity are observed. Although for L-ascorbic acid key differences in the spectroscopic properties of the reaction mixtures are observed compared with carboxylic acids, the involvement of carboxylic acids formed in situ is apparent. For oxalic acid the situation is more complex with two distinct catalyst systems in operation; the first, which engages in epoxidation only, is dominant until the oxalic acid additive is consumed completely at which point carboxylic acids formed in situ take on the role of additives to form a second distinct catalyst system, i.e. that which was observed for alkyl and aromatic carboxylic acids, which yield both cis-diol and epoxide products.

Homogeneous [RuIII(Me3tacn)Cl3]‐Catalyzed Alkene cis‐Dihydroxylation with Aqueous Hydrogen Peroxide

A simple and green method that uses [Ru(Me3tacn)Cl3] (1; Me3tacn = N,N',N''-trimethyl-1,4,7-triazacyclononane) as catalyst, aqueous H2O2 as the terminal oxidant, and Al2O3 and NaCl as additives is effective in the cis-dihydroxylation of alkenes in aqueous tert-butanol. Unfunctionalized alkenes, including cycloalkenes, aliphatic alkenes, and styrenes (14 examples) were selectively oxidized to their corresponding cis-diols in good to excellent yield (70-96%) based on substrate conversions of up to 100%. The preparation of cis-1,2-cycloheptanediol (119 g, 91% yield) and cis-1,2-cyclooctanediol (128 g, 92% yield) from cycloheptene and cyclooctene, respectively, on the 1-mol scale can be achieved by scaling up the reaction without modification. Results from Hammett correlation studies on the competitive oxidation of para-substituted styrenes (rho = -0.97, R = 0.988) and the detection of the cycloadduct [(Me3tacn)ClRuHO2(C8H14)]+ by ESI-MS for the 1-catalyzed oxidation of cyclooctene to cis-1,2-cyclooctanediol are similar to those of the stoichiometric oxidation of alkenes by cis-[(Me3tacn)(CF3CO2)Ru(VI)O2]+ through [3+2] cycloaddition (W.-P. Yip, W.-Y. Yu, N. Zhu, C.-M. Che, J. Am. Chem. Soc. 2005, 127, 14239).

Vicinal Dihydroxylation of Alkenes with Tetradecyltrimethylammonium permanganate and potassium hydroxide in a two phase Solvent System

Vicinal cis-dihydroxylation of alkenes has been carried out in good yields using tetradecyltrimethylammonium permanganate in a two phase solvent system with an inorganic base present from the beginning of the reaction. With benzyltrimethylammonium hydroxide as an organic base in nonaqueous solvent system reasonably good yields of diols are realised.