J. A. Van Doorn

Metal-catalyzed epoxidation of olefins with organic hydroperoxides: I. A comparison of various metal catalysts

Cyclohexene and 1-octene have been epoxidized in the liquid phase with tert-butyl hydroperoxide in the presence of a wide variety of transition-metal catalysts. The reactions occurring in these systems involve competing metal-catalyzed epoxidation and metal-catalyzed homolytic decomposition of the hydroperoxide. Subsequent reactions of the radicals produced in the latter reaction are responsible for the formation of many of the by-products observed. It is concluded that an active epoxidation catalyst should be both a weak oxidant and a fairly strong Lewis acid. These requirements are best met by compounds of certain metals in high oxidation states [Mo(VI), W(VI), Ti(IV)]. Many of the epoxidations described are subject to autoretardation by the co-product tert-butanol, the extent of which increases in the order W < Mo < Ti < V.

Metal-catalyzed epoxidation of olefins with organic hydroperoxides: II. The effect of solvent and hydroperoxide structure

The relatively unreactive olefins 1-octene and allyl chloride have been epoxidized with tert-butyl hydroperoxide in the presence of Mo(CO)6 or TiO2-on-SiO2, in a variety of solvents. The rates and selectivities are highest in polychlorinated hydrocarbons, slightly lower in hydrocarbon solvents, and very poor in coordinating solvents such as alcohols, ethers, etc. In addition, the selectivities to epichlorohydrin obtained in the epoxidation of allyl chloride with several organic hydroperoxides have been compared. The low selectivities observed with alkylaromatic hydroperoxides are due to their facile heterolytic decomposition under the reaction conditions. Competition from this reaction is diminished when the hydroperoxide contains electron-attracting groups. A further complication in the epoxidation with alkylaromatic hydroperoxides is the metal-catalyzed dehydration of the co-product alcohol.

Cycloaddition of group VIII metal-dioxygen complexes to electrophilic olefins

Abstract The dioxygen complexes (Ph 3 P) 2 MO 2 (M  Pd, Pt) readily add to electrophilic olefins, such as 1,1-dicyano-olefins, at room temperature, to give cyclic peroxy-adducts in high yield. The adducts undergo thermal decomposition in solution to carbonyl compounds, the reaction proceeding via carboncarbon bond cleavage.

Boron hydride reduction of transition metal—acetyl complexes

Abstract Acetyl complexes of iron(II) and ruthenium(II) of the type (π-C 5 H 5 )(CO)LM(COCH 3 ), where L = PPh 3 , P(OPh) 3 , P(cyclohexyl) 3 , PMe 2 Ph or CO for M = Fe, and PPh 3 for M = Ru, are rapidly reduced to the corresponding ethyl complexes by BH 3 · THF or B 2 H 6 /C 6 H 6 . In some cases hydrido complexes of the type (π-C 5 H 5 )(CO)LMH are also formed. The reaction has been studied by use of 1 H NMR and the spectrum of (π-C 5 H 5 )(CO)(PPh 3 )FeC 2 H 5 , which shows several unusual features, is discussed in detail. It is suggested that the rate of reduction increases with increasing electron density at the metal centre. Acetyl complexes of other transition metals, i.e. Ir, Pt, Pd, Co and Mo, are also reduced to the corresponding ethyl compounds by B 2 H 6 /C 6 H 6 .

SYNTHESIS OF SOME FUNCTIONALIZED PHOSPHINOCARBOXYLIC ACIDS

Abstract Various functionalized phosphinocarboxylic acids have been prepared by a number of complementary methods. Reactions of relatively electron-poor secondary phosphides with electron-rich halocarboxylates in liquid ammonia give high yields of phosphinocarboxylates. The substitution reaction may proceed by a classical SN 2 mechanism or by an SN rad mechanism. Reduction of the carboxylate can be a deleterious side reaction in the preparation of phosphinoacetic acids. Several phosphinopropionic acids are prepared by the Michael addition of diphenylphosphine to unsaturated esters. A valuable method proved to be the reaction of dichlorophosphinoacetic ester with functionalized organometallic reagents.

Reactions between 8-quinolinol (and related ligands) and triruthenium dodecacarbonyl; x-ray crystal structure determination of Ru3(CO)8(C9H6NO)2

Abstract 8-Quinolinol reacts with Ru3(CO)12 to give Ru3(CO)8(C9H6NO)2 and Ru- (CO)2(C9H6NO)2. A single-crystal X-ray study of the cluster compound shows that the three ruthenium atoms define an isosceles triangle, with two distances of 2.77 A and one of 3.04 A. Since both metalated oxygens act as three-electron donors (RuO distances 2.12 and 2.18 A), the cluster is a fifty-electron species with a formal zero bond order for the elongated RuRu bond. Four other hydroxyhydrocarbylpyridine compounds also give complexes of composition Ru3(CO)8(L)2 which probably have analogous structures.

Boron-catalyzed epoxidation of olefins with tert-butyl hydroperoxide

Abstract Cyclohexene and 1-octene have been epoxidized with tert -butyl hydroperoxide at 80 °C, in the presence of several boron esters. The catalytic activities of the boron compounds are markedly dependent on their structures and are enhanced by the presence of electron-attracting substituents, which increase the electrophilicity of the boron atom. Alkyl and aryl metaborates catalyze the epoxidation but are rapidly deactivated via alcoholysis to give the corresponding orthoborates, which are inactive. Orthoborate esters containing sufficiently strong electron-withdrawing groups (such as acetylacetonate or hexafluoroacetylacetonate) are, on the other hand, active catalysts. They are also deactivated during the reaction via alcoholysis and/or oxidative destruction of the ligands by hydroperoxide.

ADDITION OF DIPHENYLPHOSPHINE TO MALEIC ANHYDRIDE AND RELATED COMPOUNDS

Abstract A Michael addition of secondary phosphines to activated olefins containing the ethenedione moiety such as maleic anhydride, maleic ester and dibenzoylethene leads to functionalised tertiary phosphines. Reactions of activated olefins which contain a carboxylic group do not lead to the expected adducts; instead, phosphonium salts are formed by a sequence of reactions. A hydrogen shift plays a crucial role both in the reaction that leads to the adduct and in the reaction that leads to the phosphonium salt. Phosphinosuccinic anhydrides and phosphinosuccinic esters can be transformed into the corresponding succinic acids. Decarboxylation of phosphinosuccinic acids leads to phosphinopropionic acids.

Oxidative addition of some geminal halonitroalkanes to iridium(I) and platinum(0) compounds

Abstract Oxidative addition of 1-chloro-1-nitroethane to trans-IrCl(CO)-[P(CH3)2C6H5]2 followed by treatment of the initial product with pyridine yields a new iridium(III) complex IrCl(py)[COC(NO2)CH3][P(CH3)2C6H5]2, whose structure has been confirmed by X-rays crystallography. Two intermediate products have been observed by NMR spectroscopy; their structures have been tentatively assigned. The reaction of the corresponding bromine derivatives yields two isomers of the composition IrBr2(CO)[CH(NO2)CH3][P(CH3)2C6H5]2, and these are not affected by pyridine. The reaction of 1-chloro-1-nitroethane with Pt[P(C6H5)3]4 takes a completely different course in that yields nitrorethane and cis-PtCl2[P(C6H5)3]2 as the main products, with no detectable formation of the products of oxidation addition. A brief mechanistic investigation points towards the participation of radicals and radical anions as transient intermediates and a mechanism is proposed which explains most of the experimental results.

On the direct metalation of tertiary phenylphosphines

Abstract We have envisaged a route towards ortho-phosphinobenzoic acids via direct ortho-metalation of tertiary phenylphosphines. The direct metalation of tertiary phenylphosphines with BuLi/KOt-Bu or BuLi/TMEDA proves to be an a-selective process. After carbonation mixtures of carboxylic acids are obtained. With BuLi/KOt-Bu/THF the reaction occurs preferably at the meta and para positions. With BuLi/TMEDA/hexane all three possible positions are metalated. Introduction of an auxiliary methoxy group leads to a higher selectivity. Blocking of all meta and para positions with methoxy groups leads to metalation in the ortho position. The rate of metalation at the ortho position is relatively slow. Observed side reactions are: substitution of phenyl groups, α-metalation, and substitution of a methoxy group.