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A detailed mechanistic study on the M ukaiyam a epoxidation of lim onene with dioxygen as oxidant, bis(acetylacetonato)nickel(II) as catalyst, and an aldehyde as co-reagent is reported.All m ajor products of the reaction have been quantitatively identified, both with i-butyraldehyde and 2-methylundecanal as co-reacting aldehydes. Lim onene epoxide is form ed in good yield. The main products evolving from the aldehyde are carboxylic acid, CO2, C O , and low er m olecular w eight ketone and alcohol (K+A). A m echanism is proposed in which an acylperoxy radical form ed by the autoxidation of the aldehyde is the epoxidizing species. The observation of carbon dioxide and (K+A) in a 1:1 m olar ratio supports this mechanism. CO 2 and (K+A) are form ed in m olar amounts of 50-60% with respect to the am ount of epoxide produced, indicating that epoxidation not only takes place via acylperoxy radicals, but also via a peracid route.Cyclohexene epoxidation was also investigated with a num ber of different metal com plexes as catalysts. Cyclohexene is very sensitive for allylic oxidation, which provides inform ation about the action of the catalyst, e.g. metals which form strongly oxidizing stable high valence com plexes are more likely to induce allylic oxidation. Color changes in the reaction m ixture indicate the presence of such high valence species. In the case of nickel, it was found that high valence com plexes are absent during the reaction which is in line with the fact that this metal displays the highest selectivity for epoxide. A mechanism which accounts for the observations is presented.

The scope, mechanism and kinetics of the aerobic epoxidation of alkenes with an aldehyde and substituted β-diketonate-transition metal complexes as catalysts were studied. β-Diketonate complexes of nickel() proved to be among the best catalysts for this reaction. The epoxidation is not dependent on substrate concentration and is first order in aldehyde, catalyst concentration and oxygen partial pressure. It was shown by reactivity studies and EPR experiments that the reaction is radical in nature. Additional evidence for this was obtained from stereochemical investigations. The metal catalyst is not only an efficient initiator of the reaction, but is also believed to enhance the reactivity of intermediate species in the oxidation process by allowing these to co-ordinate to the metal center. A mechanism is proposed for the catalytic reaction.Molecular oxygen as a cheap, clean and readily available oxidant has received much attention in recent years. 1 Mukaiyama and co-workers 2-7 and others 8-11 have reported that molecular oxygen can be used as the terminal oxidant in the epoxidation of alkenes with an aldehyde or primary alcohol as coreactant and a metal β-diketonate as a catalyst (Scheme 1). There has been discussion in the literature about the mechanism of the 'Mukaiyama' catalytic system and the role of the transitionmetal catalyst in it, which can be omitted as was shown by Kaneda et al. 12 Since peroxyacids, which are formed in the autoxidation of aldehydes, are powerful epoxidizing reagents, the reaction in Scheme 1 might proceed through the peroxyacid as the actual epoxidizing agent. The only role of the transitionmetal catalyst in this scenario is to catalyse the formation of the peracid as shown in Scheme 2.Another possible mechanism proposed in the literature 10 is the formation of a metal-oxygen complex which reacts to form an oxometal species, similar to species described for manganese or vanadium. 13,14 In Scheme 3 this mechanism is outlined for a transition-metal()-β-diketonate complex.A combination of the mechanisms in Schemes 2 and 3 was considered by Nam et al. 15 They investigated the 'Mukaiyama' system using cyclam-type transition-metal complexes and concluded from indirect evidence that the epoxidation reaction in their system is radical in nature. The peroxyacid and the oxometal mechanisms in Schemes 2 and 3 were believed to play no role. An acylperoxy radical, rather than a peroxyacid, was proposed to react with the alkene to form an epoxide. Alternatively, the acylperoxy radical could co-ordinate to the metal first, and this complex subsequently epoxidizes the alkene. The same authors reported shortly after 16 that cyclam complexes of Ni II are inhibitors of this radical reaction. These complexes were believed to be sufficiently good reducing agents to react with an acylperoxy radical and form an unreactive acylperoxy anion and a nickel() complex.In the present paper we further explore the scope, kinetics and mechanism of the epoxidation of alkenes by the 'Mukaiyama' system. The mos...

The amorphous polyester 1 a prepared by melt condensation of 1,5-bis-(9-hydroxy-l,4,7-trioxanonyl)naphthalene (2 a) and adipoylchloride (3 a), which contains bis-1,4,7-trioxanonyl (triethyleneglycol) segments in its main chain, represents a matrix for ion-conducting materials. Despite the fact that only triethyleneglycol segments are present, which are shorter than the minimum required for full solvation of Li+ cations, ion-conductivities of 0 = 3.3 x S cm-' at 368 K are found for Li+/l a 0.25 (cations per polymer repeat unit). Hence, more than one bis-l,4,7-trioxanonyl segment (either intra-or interchain) has to be involved in Li+ complexation. The 0 value compares favorably with previous data for more complex polymer matrices. Acta Polymer., 48, 314-318 0 VCH Verlagsgesellschaft mbH, D-69451 Weinheim 1997 0323-7648/97/0808-03 14$17.50+.50/0 S cm-' at 368 K is comparable with values determined for PEO derived polymer electrolytes: LiC104/PE0 (6 x 10" S cm-' at 312 K) [14], NaI/PEO (lo4 S cm-' at 298 K) [15], LiC104/oxymethylene linked PEO (5 x S cm-' at 298 K) [ 161, LiC104/PE0 blends ( lop5 S cm-' at 298 K) [ 171 and LiC104/hyperbranched poly(ethyleneglyco1s) Nonetheless, the high temperature value o = 3.3 x S cm-' at 303 K) [8].

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