Douglas F. Foster

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.

Phosphine-containing carbosilane dendrimers based on polyhedral silsesquioxane cores as ligands for hydroformylation reaction of oct-1-ene

Radical additions of diethyl- and diphenylphosphine have been used to prepare 1st and 2nd generation dendrimers based on polyhedral oligosilsesquioxane cores by a divergent synthetic method. The 1st generation dendrimer is built on either 16 and 24 vinyl or allyl arms formed by successive hydrosilation and vinylation or allylation of vinyl-functionalised polyhedral silsesquioxanes. Successive hydrosilation/allylation followed by hydrosilation/vinylation and addition of phosphine produce the 2nd generation dendrimer. The dendrimers have been used as ligands for the hydroformylation of oct-1-ene catalysed by [Rh(acac)(CO) 2 ]. Using the alkylphosphine-containing dendrimers as ligands, alcohols (nonan-1-ol and 2-methyloctanol) are obtained, whilst the diphenylphosphine counterparts lead to the formation of aldehydes (nonan-1-al and 2-methyloctanal). Linear to branched ratios of 3/1 are obtained for the diethylphosphine compounds while ratios of 12 to 14/1 are given by the diphenylphosphine dendritic molecules.

Dendrimer-bound tertiary phosphines for alkene hydroformylation

Abstract Dendrimer-based phosphines with 8, 24 and 72 PR2 arms (R=Me, Et, hexyl, Cy or Ph) based on polyhedral oligomeric silsesquioxane (POSS) cores have been synthesized and shown to catalyse hydroformylation reactions, in some cases with higher linear:branched product ratio (1:b) than their monomeric analogues.

Increased selectivity in hydroformylation reactions using dendrimer based catalysts; a positive dendrimer effect

Dendrimers based on polyhedral oligomeric silsesquioxanes (POSS) cores with 16 PPh2 arms give much higher linear selectivities (14∶1) than their small molecule analogues (3–4∶1) in the hydroformylation of oct-1-ene.

Highly selective formation of linear esters from terminal and internal alkenes catalysed by palladium complexes of bis-(di-tert-butylphosphinomethyl)benzene

The methoxycarbonylation of terminal or internal alkenes catalysed by palladium complexes of bis-(di-tert-butylphosphinomethyl)benzene under mild conditions leads to linear esters in 99% selectivity via a hydride mechanism.

Hydroformylation in fluorous solventsElectronic supplementary information (ESI) available: typical experimental details. See http://www.rsc.org/suppdata/cc/b1/b110061k/

Triaryl-phosphines and -phosphites bearing fluorous ponytails give high rates, good linear selectivity and good retention of catalyst in the fluorous phase during hydroformylation of alkenes in fluorous solvents.

Alkene epoxidation catalysed by camphor-derived β-ketophosphonate complexes of molybdenum(VI)

New β-ketophosphonates (L) have been prepared from (R)- or (S)-camphor with various substituents on the phosphorus atom [EtO, (R)- or (S)-BusO, Ph or binaphthoxy] and reacted with [MoO2CI2] to form complexes [MoO2CI2L]. These complexes have been used to give highly active catalysts for epoxidation of alkenes by ButOOH. Very fast initial rates (ca. 400 catalyst turnovers in the first minute) gave way to much slower rates because the hemi-labile β-ketophosphonate is displaced by a diol ligand. In the presence of molecular sieves, the fast initial stage of the reaction is extended and for styrene, which gives low conversions followed by degradation in the absence of molecular sieves, styrene oxide can be formed with 98% conversion and 94% selectivity. It is demonstrated that both the ButOOH and the catalyst bind to the molecular sieves, the latter with loss of the β-ketophosphonate ligand.

Gas-phase formation of zinc/cadmium chalcogenide cluster complexes and their solid-state thermal decomposition to form II-VI nanoparticulate material

Gas-phase reactions between R 2 Zn (R=Me and Et) and t BuSH produce cluster complexes of the type [RZnS t Bu] n . These clusters, along with [MeZnS t Bu(py)] 2 (py=pyridine), have been characterised by 13 C{ 1 H} solid-state NMR. On heating to 100°C in the solid-state, the complexes [MeZnS t Bu] 5 and [MeZnS t Bu(py)] 2 release dimethylzinc (Me 2 Zn) to form the zinc bis(thiolate) compound, [Zn(S t Bu) 2 ] n , with further heating (>200°C) leading to the formation of ZnS. The ethyl analogue, [EtZnS t Bu] 5 , does not lose Et 2 Zn on heating and thermogravimetric analysis (TGA) suggests a different decomposition pathway, one which mainly involves loss of the organic moieties without the concurrent loss of volatile Zn or S compounds, although ZnS is again the final thermal decomposition product. The decomposition of the involatile pentamers, [MeZnS t Bu] 5 and [EtZnS t Bu] 5 , and the dimer, [MeZnS t Bu(py)] 2 , proceeds at higher temperature (200-350°C) to give agglomerates of ME nanoparticulate material, with the individual particles having diameters of 2-20 nm in all cases. The mechanistic pathway by which these clusters decompose appears to be highly dependent upon the R group (Me or Et) present within the cluster. Preliminary results suggest that complexes of the type [RME t Bu] n are also produced from the gas-phase reactions of Me 2 Zn with t BuSeH and from Me 2 Cd with t BuSH.

Effect of pyridine upon gas-phase reactions between H2S and Me2Cd; control of nanoparticle growth

The effect of pyridine upon the gas-phase reaction of dimethyl-cadmium (Me2Cd) with hydrogen sulfide (H2S) has been investigated. Analysis of the solid reaction product by powder X-ray diffraction (PXRD), elemental analysis (EA) and transmission electron microscopy (TEM) reveals the deposit to consist of crystalline CdS particles in the nanometre size range of the Greenockite (hexagonal) phase, with pyridine molecules bound to surface cadmium atoms. The average particle size within the deposit is dependent upon both the concentration of pyridine in the gas phase and the temperature at which the gas-phase reactants are mixed.

Gas-phase synthesis of nanoparticles of group 12chalcogenides

The effect of pyridine addition upon the gas-phase reactions of hydrogen sulfide (H 2 S) or hydrogen selenide (H 2 Se) with either dimethylcadmium (Me 2 Cd) or dimethylzinc (Me 2 Zn) has been investigated. The deposits of CdS, CdSe, ZnSe or ZnS which form have been analysed by powder X-ray diffraction (PXRD), elemental analysis and transmission electron microscopy (TEM). At ambient temperatures the deposits consist of particles in the nanocrystalline size range of the hexagonal phase. The average particle size within the deposits is dependent upon the concentration of pyridine in the gas phase, the temperature at which the reactants are mixed and, in the case of ZnSe, whether an inert (He) or reducing (H 2 ) carrier gas is used. At ambient temperatures in an inert carrier gas, the control of particle size exerted by pyridine decreases in the order ZnS > CdS > CdSe > ZnSe, although in hydrogen, the prereaction between Me 2 Zn and H 2 Se could be almost completely eliminated by raising the temperature. Further investigation of CdS deposits have been carried out by photoacoustic spectroscopy (PAS) to access the band-gap, and solid-state 13 C and 113 Cd NMR to probe the surface state of the particles. Elemental analysis and the NMR studies suggest that pyridine binds through the lone pair of the nitrogen to surface metal atoms on growing particles, inhibiting further particle growth. The particle size is greatly dependent upon the strength of the pyridine–surface metal atom interaction, the acidity of the EH bond (E=S or Se) and the polarity of the MMe bond (M=Zn or Cd). In hydrogen, it is proposed that amide species may form and be responsible for growth inhibition.