The reactivity of the hydroperoxo complex [Co(CN)(5)OOH](3)(-) has been studied in aqueous solution. The complex undergoes acid-catalyzed aquation (k = 1.89(5) x 10(-)(2) s(-)(1), pK(a) = 5.21(4), T = 20 degrees C, I = 0.1 M). Assuming an I(d) mechanism, this allows the relative affinity for Co(III) to be deduced as H(2)O(2) < H(2)O < HO(2)(-) and implies H(2)O(2) to be a very weak ligand. At neutral pH the hydroperoxo complex effects efficient oxygen atom transfer to L-methionine to give an intermediate identified as [Co(CN)(5)(L-methionine S-oxide)](2)(-), which then dissociates to [Co(CN)(5)OH(2)](2)(-) and L-methionine S-oxide. The reaction is acid catalyzed and is proposed to take place via nucleophilic attack of sulfur on the proximal oxygen of the hydroperoxo ligand with concerted loss of water. The significance of these results for the interaction of hydrogen peroxide with labile metal ions is discussed.

No abstract

No abstract

No abstract

Abstract:The reaction of acetophenone with tetrabutylammonium hydroxide affords the tetrabutylammonium enolate of phenyl (2-hydroxy-2-pheny1)propyl ketone. The crystal structure of this chiral enolate shows intramolecular hydrogen bonding between the hydroxyl group and the enolate oxygen atom. Furthermore, the a-methylene units of the ammonium counterion form hydrogen bonds to the basic enolate C and 0 atoms and to the 0 atom of the hydroxy group. This three-point bonding occurs selectively on the Re,Re side, a phenomenon which may be responsible for the direction of diastereoselectivity in the epoxide-forming reaction of the enolate with N-bromosuccinimide. Kasymmetric synthmis * chirality * enolatcs hydrogen bonds structure eiucidationEnolates constitute a synthetically important class of reagents used in aldol, Michael, alkylation, bromination and amination reactions.['] The vast amount of research that has been invested in the development of stereoselective variations of such reactions ['] has stimulated interest in the structure and aggregation state of the compounds.[31 The nature of the metal (or counterion) is known to play a crucial role. For example, X-ray structural studies show that lithium enolates exist as dimers or higher aggregates, depending upon the carbonyl precursor, solvent and a d d i t i~e .~~.~] Of theoretical and practical interest is the propensity of certain lithium enolates to form hydrogen bonds with secondary amines R,NH in which the enolate carbon atom rather than the oxygen atom is involved.13b, 51 A rare case of an alcohol-solvated lithium enolate has recently been documented.16] Accordingly, the lithium enolate derived from 1,3-cyclohexanedione undergoes hydrogen bonding to methanol, as shown by X-ray crystallography. Although several X-ray structural studies of chiral functionalized organolithium reagents have been reported,r71 the crystal structure of a chiral lithium enolate has not appeared in the literature thus far.Ketone and ester enolates having tetraalkylammonium counterions as used in phase-transfer catalysis were long believed to be "naked" monomeric species.[81 However, we recently showed that the tetraalkylammonium salts of such CH-acidic compounds as malonic acid diesters ['] as well as phenylacetic and propionic acid esters"'] are in fact species in which anion and cation interact through hydrogen bonds, ["] It is therefore to be expected that in homologs such as (nBu),N+ the positive charge is delocalized on the a-methylene entities, which also means that these positions are somewhat acidified. In this paper we describe the synthesis, X-ray structural analysis, aggregation state and stereoselective bromination of a chiral metal-free ketone enolate having (nBu),N+ as the counterion. It is stabilized by a novel intramolecular hydrogen bond and by hydrogen bonds between anion and cation. Results and DiscussionSynthesis and Crystal Structure : Upon treating a toluene solution of acetophenone (1) with tetrabutylammonium hydroxide and removing the water azeotr~pical...