Triphenylphosphine catalysis

The basic catalysis of the epoxide-phenol reaction has been studied by a variety of authors (12,13). In general, the conclusion has been that basic catalysis gives selectivity for the phenol-epoxide reaction over the secondary alcohol-epoxide reaction (the secondary alcohol being formed from the opening of an epoxide). Although the base catalyzed reaction has been studied, the specific mechanism for triphenylphosphine Catalysis has not been determined. We propose the mechanism shown in Reaction Scheme 3 which is consistent with our experimental results. 

Another highly selective polyaddition is based on the reaction between phenols and oxazolines, which was applied for the synthesis of hb poly(etheramide)s (3-10). The AB2-monomer 2-(3,5-dihydroxyphenyl)-l,3-oxazoline was polymerized thermally at 190 °C in N-methylcaprolactam solution and randomly branched products with a DB of 50% were obtained.Kakodawa et al. used monomer 3-14, namely 2,2-bis(hydroxymethyl) propyl acrylate, for the synthesis of poly(ether ester)s via triphenylphosphine catalysis. The polymers had only low molecular weight, but as they contain phosphonium ions they can be applied in flame-retardant coatings, which can be cured by UV. These materials can also be synthesized via an A2+Bs-approach [vide infra) of tri(acryloy-loxyethyl) phosphate in the presence of piperidine." ... 

In contrast to triphenylphosphine-modified rhodium catalysis, a high aldehyde product isomer ratio via cobalt-catalyzed hydroformylation requires high CO partial pressures, eg, 9 MPa (1305 psi) and 110°C. Under such conditions alkyl isomerization is almost completely suppressed, and the 4.4 1 isomer ratio reflects the precursor mixture which contains principally the kinetically favored -butyryl to isobutyryl cobalt tetracarbonyl. At lower CO partial pressures, eg, 0.25 MPa (36.25 psi) and 110°C, the rate of isomerization of the -butyryl cobalt intermediate is competitive with butyryl reductive elimination to aldehyde. The product n/iso ratio of 1.6 1 obtained under these conditions reflects the equihbrium isomer ratio of the precursor butyryl cobalt tetracarbonyls (11). 

The hberated iodine, as the complex triiodide ion, may be titrated with standard thiosulfate solution. A general iodometric assay method for organic peroxides has been pubUshed (253). Some peroxyesters may be determined by ferric ion-catalyzed iodometric analysis or by cupric ion catalysis. The latter has become an ASTM Standard procedure (254). Other reducing agents are ferrous, titanous, chromous, staimous, and arsenite ions triphenylphosphine diphenyl sulfide and triphenjiarsine (255,256). 

The Suzuki-Miyaura synthesis is one of the most commonly used methods for the formation of carbon-to-carbon bonds [7]. As a palladium catalyst typically tetrakis(triphenylphosphine)palladium(0) has been used, giving yields of44—78%. Recently, Suzuki coupling between aryl halides and phenylboronic acid with efficient catalysis by palladacycles was reported to give yields of 83%. 

The C-C coupling through aqueous two-phase catalysis, is exemplified by reaction (17), which is carried out industrially in France. Here Ru with triphenylphosphine trisulphonate (TPPT) is used. 

Miscellaneous Reactions of Phosphines.- The role of chiral phosphines as ligands in the catalysis of reactions leading to the formation of chiral products has been reviewed.1111 A procedure for the determination of the enantiomeric excess in chiral phosphines has been developed, based on 13C n.m.r. studies of the diastereoisomeric complexes formed by phosphines with the chiral pinenyl nickel bromide complex. 111 Studies of the sulphonation of triphenylphosphine and of chiral arylphosphines have been reported in attempts to prepare water soluble ligands which aid... 

No catalyst has an infinite lifetime. The accepted view of a catalytic cycle is that it proceeds via a series of reactive species, be they transient transition state type structures or relatively more stable intermediates. Reaction of such intermediates with either excess ligand or substrate can give rise to very stable complexes that are kinetically incompetent of sustaining catalysis. The textbook example of this is triphenylphosphine modified rhodium hydroformylation, where a plot of activity versus ligand metal ratio shows the classical volcano plot whereby activity reaches a peak at a certain ratio but then falls off rapidly in the presence of excess phosphine, see Figure... 

A set of core-functionalized dendrimers was synthesized by Van Leeuwen et al. and one compound was applied in continuous catalysis. [45] The dendritic dppf, Xantphos and triphenylphosphine derivatives (Figures 4.22, 4.30 and 4.31) were active in rhodium-catalyzed hydroformylation and hydrogenation reactions (performed batch-wise). Dendritic effects were observed which are discussed in paragraph 4.5. The dendritic rhodium-dppf complex was applied in a continuous hydrogenation reaction of dimethyl itaconate. 

Scheme 6.3 Amphiphilic poly(2-oxazoline) block copolymers bearing triphenylphosphine and bipyridine moieties respectively as polymeric macroligands for micellar catalysis.

Scheme 6.6 Heck coupling of iodobenzene and styrene as a model reaction for micellar catalysis using triphenylphosphine-functionalized poly(2-oxazoline)s as macroligands...

---