Eric G. Hope

Coordination chemistry of higher oxidation states. Part 21. Platinum-195 NMR studies of platinum(II) and platinum(IV) complexes of bi- and multi-dentate phosphorus, arsenic and sulphur ligands

Abstract 195-Platinum NMR spectra are reported for a series of complexes of bidentate ligands [Pt(LL)X4] (X=Cl, Br; LL=diphosphine, diarsine, dithioether, diselenoether), [Pt(Me2PCH2CH2PMe2)2X2]X2, [Pt(o-C6H4(AsMe2)2)2X2]X2, and for the Pt(II) analogues. The trends in chemical shifts δ(Pt) and 1J(PtP), 1J(PtSe) coupling constants are discussed, and used to establish the nature of the solution species obtained by oxidation of Pt(II) complexes of some multidentate phosphorus and arsenic ligands. The [Pt(LL)I4] materials are shown to exist as [PtII(LL)I2] in dimethylsulphoxide solution, but [Pt(o-C6H4(AsMe2)2)2I2]2+ is a genuine Pt(IV) iodo-complex.

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.

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.

Carbon–fluorine and –hydrogen bond activation and carbon–carbon bond formation in η5-pentamethylcyclopentadienyl-rhodium and -iridium phosphine complexes; crystal structures of [M(η5-C5Me5)Cl{(C6F5)2PCH2CH2P(C6F5)2}]+BF4–(M = Rh or Ir)

The reaction between [{M(η5-C5Me5)Cl(µ-Cl)}2](M = Rh or Ir) and (C6F5)2PCH2CH2P(C6F5)2(dfppe) in refluxing benzene yielded the cationic species [M{η5-C5Me3[CH2C6F4P(C6F5)CH2]2-1,3}Cl]+ in which two C–F and two C–H bonds have been cleaved and two C–C bonds formed; HF is also produced. The complexes [M(η5-C5Me5)Cl(dfppe)]+BF4–(M = Rh or Ir), which have not undergone C–F bond activation, were formed by treatment of [{M(η5-C5Me5)Cl(µ-Cl)}2] with NH4BF4 and dfppe, and have been structurally characterized by X-ray crystallography. Activation of the C–F bonds in these complexes is induced by thermolysis in refluxing ethanol. The reaction between [{M(η5-C5Me5)Cl(µ-Cl)}2](M = Rh or Ir) and dfppe in refluxing ethanol yielded a mixture of the cations [M(η5-C5Me5)Cl(dfppe)]+, [M{η5-C5Me3[CH2C6F4P(C6F5)CH2]2-1,3}Cl]+ and, where M = Rh, the singly C–F bond-activated species [Rh{η5-C5Me4CH2C6F4P(C6F5)CH2CH2P(C6F5)2}Cl]+.

Halogen and interhalogen reactions with [60]fullerene: Preparation and characterization of C60Cl24 and C60Cl18F14

Abstract U.V. irradiation of a solution of [60]fullerene in carbon tetrachloride saturated with chlorine gave a yellow solid, the negative ion FAB mass spectrum of which is consistent with the presence of C60Cl24 When a solution of [60]fullerene in CCl4was mixed with IF5, a yellow solid was deposited in the denser IF5 layer. The negative ion FAB mass spectrum of this material indicated it to be C60C18F14 This result provides the first confirmation that halogenation of Merenes is a radical process. Fluorination of C60Br8 gave a range of fluorinated products, having a maximum fluorine content of ca. 36 fluorines per cage, and with either C60F18 or its mono-oxide as major species. EI mass spectrometry of the products at various temperatures indicates that the more highly fluorinated fiiilerenes are either less stable to heat, or are more volatile.

Fluorination of buckminsterfullerene

Fluorination of solid C60 with fluorine gas proceeds in a stepwise manner to give, after twelve days (10 mg scale), a colourless derivative indicated by a single line 19F NMR spectrum to be C60F60; reaction time is quantity dependent.

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.