Formation and hydrolysis of osmate(VI) esters

Abstract

3-Cyclohexenecarboxylic acid reacts with osmium tetraoxide in aqueous buffer solutions in the presence of a variety of pyridines to form osmate(V1) esters of the general formtda (RO)ZOSOZLZ, where L represents the monodentate ligand. The compounds appear to be octahedral osmyl complexes with a trans O=Os=O group. The general kinetic equation describing the formation of the esters is rate = ko[Os04] [SI + klPl[Os04] [SI [L] + kzpz[Os04] [SI [LIZ where S is the substrate,3-cyclohexenecarboxylic acid, and 61 and PZ are the overall stability constants for the osmium tetraoxide-ligand system.

Osmium Tetroxide Complexes as Versatile Tools for Structure Probing and Electrochemical Analysis of Biopolymers

“…The process involves [3+2] addition of osmium tetroxide across the C=C double bond giving rise to an osmic acid diester (glycolate), that is subsequently hydrolyzed to release the glycol moiety and osmate [10,11]. Analogous reactions are given by various compounds possessing the C=C double bonds, including pyrimidine nucleobases (at C5=C6) [1,11] and indole moiety featuring side group of amino acid tryptophan (at C2=C3) [3,[12][13][14][15].…”

“…The process involves [3+2] addition of osmium tetroxide across the C=C double bond giving rise to an osmic acid diester (glycolate), that is subsequently hydrolyzed to release the glycol moiety and osmate [10,11]. Analogous reactions are given by various compounds possessing the C=C double bonds, including pyrimidine nucleobases (at C5=C6) [1,11] and indole moiety featuring side group of amino acid tryptophan (at C2=C3) [3,[12][13][14][15]. It has been established that tertiary amines, such as pyridine (py), 2,2'-bipyridine (bipy), 1,10-phenanthroline (phen) derivatives or N,N,N',N'-tetramethyl ethylenediamine (TEMED), stabilize the osmium(VI) glycolates upon coordination of the central osmium atom by the nitrogenous ligands [1,11,16,17].…”

Kinetic role of tert-amines in the osmium tetroxide catalyzed trimethylamine N-oxide dihydroxylation of cyclohexene

“…Sharpless' group have shown that is formed from OsO 4 .L and alkene in the osmylation step 13 [10 -13]. All tert-amine ligands are known to accelerate the osmylation step [2,4,5,9,10,12,13]. However, if they bind too strongly to the resulting osmium(VI) esters, to form , they cause resistance to oxidation.…”

“…Certain tert-amines [2,4,5,8] and chiral alkaloids [9,10,12 -14] are reported as ligand accelerated catalysts [15] in the stoichiometric and catalytic OsO 4 dihydroxylation of alkenes. Stoichiometric OsO 4 dihydroxylation [2 -5,9,10,12 -14] and catalytic OsO 4 dihydroxylation using perchlorate [6] and N-methylmorpholine-N-oxide [10] as oxidant were found typically first-order in alkene and first-order in OsO 4 .…”

“…Stoichiometric OsO 4 dihydroxylation [2 -5,9,10,12 -14] and catalytic OsO 4 dihydroxylation using perchlorate [6] and N-methylmorpholine-N-oxide [10] as oxidant were found typically first-order in alkene and first-order in OsO 4 . In the stoichiometric OsO 4 plain dihydroxylation catalyzed by tert-amines, rate laws with additional terms which are first-order [2,4,5] and second-order in the tert-amine [4,5], were reported. Sharpless' group reported that the rate determining step is the same in stoichiometric [9,10,12,13] and catalytic [9,10] dihydroxylation of alkenes using Nmethylmorpholine-N-oxide in tert-butyl alcohol at 25°C in the presence of chiral alkaloids [9,10,12,13] or some tert-amines [9,10,12] and consists of the initial addition reaction forming dioxomonoglycolato osmium(VI) esters, and their monoamine adducts, (Scheme I, step a and step b).…”