Alison M. Stuart

FLUOROUS BIPHASE CATALYSIS

Abstract The evolution and future prospects for the fluorous biphase approach to homogeneous catalysis are discussed.

Hydroformylation in perfluorinated solvents; improved selectivity, catalyst retention and product separation

Abstract The hydroformylation of linear terminal alkenes using rhodium based catalysts under fluorous biphasic conditions in the presence and absence of toluene is reported. Using fluorinated ponytails to modify triarylphosphites and triarylphosphines, good selectivities and reactivities can be obtained, along with good retention of the catalyst and ligand within the fluorous phase. Using P(O–4-C 6 H 4 C 6 F 13 ) 3 (P/Rh=3:1) as the ligand in toluene/perfluoro-1,3-dimethylcyclohexane, good results are obtained at 60°C, but decomposition of the catalyst and/or ligand occurs on increasing the temperature. More impressive results are obtained by omitting the toluene, with higher rates, better l/b ratios, and better retention of the catalyst and the phosphite within the perfluorocarbon solvent. Competing isomerisation restricts linear aldehyde selectivities to 6 H 4 C 6 F 13 ) 3 is used as the ligand in the absence of toluene, even more impressive results can be obtained, with linear aldehyde selectivities up to 80.9%, high rates, and the retention of up to 99.95% of the rhodium and up to 96.7% of the phosphine within the fluorous phase. These results are compared with those of commercial systems for propene hydroformylation and with those previously reported in the literature for hydroformylation under fluorous biphasic conditions. Phase behaviour studies show that 1-octene is completely miscible with the fluorous solvent under the conditions used for the hydroformylation experiments, but that the product nonanal, phase separates.

Synthesis of fluoroalkyl-derivatised BINAP ligands

Abstract Fluoroalkyl-derivatised R-BINAP ligands have been prepared, characterised and applied in the ruthenium-catalysed asymmetric hydrogenation of dimethyl itaconate.

Electrophilic fluorination using a hypervalent iodine reagent derived from fluoride

The air and moisture stable fluoroiodane 8, readily prepared on a 6 g scale by nucleophilic fluorination of the hydroxyiodane 7 with TREAT-HF, has been used as an electrophilic fluorinating reagent for the first time to monofluorinate 1,3-ketoesters and difluorinate 1,3-diketones in good isolated yields.

Phosphorus(III) ligands in fluorous biphase catalysis

Abstract The synthesis, coordination chemistry and catalytic applications of a series of perfluoroalkyl-substituted phosphorus(III) ligands is illustrated.

A convenient access to triarylphosphines with fluorous phase affinity

Abstract Perfluorocarbon-soluble triarylphosphines with electronic properties similar to those of tris( p -methoxyphenyl)phosphine can be easily prepared through O -alkylation of tris( p -hydroxyphenyl)phosphine oxide and subsequent reduction with trichlorosilane.

The rhodium catalysed hydrogenation of styrene in the fluorous biphase

Abstract Using the rhodium-catalysed hydrogenation of styrene as a model system, the influence of the perfluorocarbon and organic solvents and the perfluoroalkyl-ponytails on an application of the fluorous biphase approach to homogeneous catalysis is illustrated, including a preliminary study into the effects of intersolvent mixing.

Intramolecular Fluorocyclizations of Unsaturated Carboxylic Acids with a Stable Hypervalent Fluoroiodane Reagent

A new class of fluorinated lactones was prepared by the intramolecular fluorocyclizations of unsaturated carboxylic acids by using the stable fluoroiodane reagent in combination with AgBF4. This unique reaction incorporates a cyclization, an aryl migration, and a fluorination all in one step. The fluoroiodane reagent, prepared easily from fluoride, can also be used without a metal catalyst to give moderate yields within just 1 hour, thus demonstrating that it is a suitable reagent for developing new (18)F-labelled radiotracers for PET imaging.

Preparation of iodonium ylides: probing the fluorination of 1,3-dicarbonyl compounds with a fluoroiodane

The isolation of iodonium ylide 8, from the reaction of fluoroiodane 1 with ethyl 3-oxo-3-phenylpropanoate 5 in the presence of potassium fluoride, provides strong evidence that 1,3-dicarbonyl compounds undergo an addition reaction with fluoroiodane 1 to form an iodonium intermediate which can be deprotonated to generate an iodonium ylide. In the presence of TREAT-HF, however, the iodonium intermediate reacts to form the 2-fluoro-1,3-dicarbonyl product and we propose that fluoroiodane 1 simulates electrophilic fluorination via an addition/substitution mechanism. Further evidence to support this mechanism was obtained by successfully reacting the isolated iodonium ylide 8 with TREAT-HF, hydrochloric acid, acetic acid and p-toluenesulfonic acid to form the 2-fluoro-, 2-chloro-, 2-acetyl- and 2-tosyl-1,3-ketoesters respectively.

A recyclable perfluoroalkylated PCP pincer palladium complex.

A new fluorous PCP pincer ligand has been coordinated to Ni(II), Pd(II) and Pt(II). The air stable palladium complex, which promotes Heck reactions between methyl acrylate and either aryl bromides or iodides, can be recovered intact by fluorous solid-phase extraction and was reused four times in the Heck reaction between methyl acrylate and 4-bromoacetophenone without loss in catalytic activity.