Fluorinations of unsymmetrical diaryliodonium salts containing ortho-sidearms; influence of sidearm on selectivity.

Activated aromatics were reacted with two different fluoroidoane reagents 1 and 2 in the presence of triflic acid to prepare only the para-substituted diaryliodonium salts. With fluoroiodane 1 the unsymmetrical diaryliodonium salts contained an ortho-propan-2-ol sidearm, whereas the alcohol sidearm was eliminated to form an ortho-styrene sidearm in the reaction with fluoroiodane 2. Only the diaryliodonium salts containing a styrene sidearm were fluorinated successfully to deliver para-fluorinated aromatics in good yields.

Ligand and solvent control of selectivity in the C-H activation of a pyridylimine-substituted 1-naphthalene; a combined synthetic and computational study.

The pyridylimine-substituted 1-naphthalenes, 2-(1-C10H7)-6-{CR[double bond, length as m-dash]N(2,6-i-Pr2C6H3)}C5H3N (R = Me HLMe, H HLH), react with Na2[PdCl4] in acetic acid at elevated temperature to afford either ortho-C-Hnaphthyl activated (LMe)PdCl (2ortho) or the unactivated adduct (HLH)PdCl2 (1b). Alternatively, 1b and its ketimine analogue (HLMe)PdCl2 (1a), can be prepared by treating (MeCN)2PdCl2 with either HLMe or HLH in chloroform at room temperature. Regio-selective ortho-C-H activation to form 2ortho can also be initiated by the thermolysis of 1a in acetic acid, while no reaction occurs under similar conditions with 1b. Interestingly, the C-H activation of HLMe to give 2ortho is found to be reversible with 100% deuteration of the peri-site occurring on reacting Na2[PdCl4] with HLMe in acetic acid-d4. By contrast, heating 1a in toluene gives a 55 : 45 mixture of 2ortho and its peri-activated isomer 2peri. Pure 2peri can, however, be obtained either from (LMe)PdOAc (3peri) by OAc/Cl exchange or by the sequential reactions of 1a with firstly silver acetate then with aqueous sodium chloride. Intriguingly, a peri to ortho interconversion occurs on heating 2peri in acetic acid to give 2ortho. DFT calculations have been used to investigate the C-H activation steps and it is found that in acetic acid ortho-C-H activation is kinetically and thermodynamically favoured but peri-CH activation is kinetically accessible (ΔΔG‡ = 2.4 kcal mol-1). By contrast in toluene, the reaction appears to be irreversible with the difference in barrier height for ortho- and peri-C-H activation being very small within the error of the method (ΔΔG‡ = 0.7 kcal mol-1), findings that are in agreement with the empirically observed product distribution for 2ortho and 2peri. Single crystal X-ray structures are reported for 1a, 1b, 2ortho and 2peri.

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.

Organo-palladium(II) complexes bearing unsymmetrical N,N,N-pincer ligands: synthesis, structures and oxidatively induced coupling reactions.

The 2-(2'-aniline)-6-imine-pyridines, 2-(C6H4-2'-NH2)-6-(CMe=NAr)C5H3N (Ar = 4-i-PrC6H4 (HL1a), 2,6-i-Pr2C6H3 (HL1b)), have been synthesised via sequential Stille cross-coupling, deprotection and condensation steps from 6-tributylstannyl-2-(2-methyl-1,3-dioxolan-2-yl)pyridine and 2-bromonitrobenzene. The palladium(II) acetate N,N,N-pincer complexes, [{2-(C6H4-2'-NH)-6-(CMe=NAr)C5H3N}Pd(OAc)] (Ar = 4-i-PrC6H4 (1a), 2,6-i-Pr2C6H3 (1b)), can be prepared by reacting HL1 with Pd(OAc)2 or, in the case of 1a, more conveniently by the template reaction of ketone 2-(C6H4-2'-NH2)-6-(CMe=O)C5H3N, Pd(OAc)2 and 4-isopropylaniline; ready conversion of 1 to their chloride analogues, [{2-(C6H4-2'-NH)-6-(CMe=NAr)C5H3N}PdCl] (Ar = 4-i-PrC6H4 (2a), 2,6-i-Pr2C6H3 (2b)), has been demonstrated. The phenyl-containing complexes, [{2-(C6H4-2'-NH)-6-(CMe=NAr)C5H3N}PdPh] (Ar = 4-i-PrC6H4 (3a), 2,6-i-Pr2C6H3 (3b)), can be obtained by treating HL1 with (PPh3)2PdPh(Br) in the presence of NaH or with regard to 3a, by the salt elimination reaction of 2a with phenyllithium. Reaction of 2a with silver tetrafluoroborate or triflate in the presence of acetonitrile allows access to cationic [{2-(C6H4-2'-NH)-6-(CMe=N(4-i-PrC6H4)C5H3N}Pd(NCMe)][X] (X = BF4 (4), X = O3SCF3 (5)), respectively; the pyridine analogue of 5, [{2-(C6H4-2'-NH)-6-(CMe=N(4-i-PrC6H4)C5H3N}Pd(NC5H5)][O3SCF3] (5'), is also reported. Oxidation of phenyl-containing 3a with one equivalent of 1-chloromethyl-4-fluoro-1,4-diazoniabicyclo[2.2.2]octane bis(tetrafluoroborate) (Selectfluor™) in acetonitrile at low temperature leads to a new palladium species that slowly decomposes to give 4 and biphenyl; biphenyl formation is also observed upon reaction of 3a with XeF2. However, no such oxidatively induced coupling occurs when using 3b. Single crystal X-ray diffraction studies have been performed on HL1b, 1a, 1b, 2a, 2b, 3a, 3b and 5'.

O,N,N-pincer ligand effects on oxidatively induced carbon-chlorine coupling reactions at palladium.

The syntheses of two families of sterically tuneable O,N,N pro-ligands are reported, namely the 2-(phenyl-2'-ol)-6-imine-pyridines, 2-(C6H4-2'-OH),6-(CMe=NAr)C5H3N [Ar = 4-i-PrC6H4 (HL1(a)), 2,6-i-Pr2C6H3 (HL1(b))] and the 2-(phenyl-2'-ol)-6-(amino-prop-2-yl)pyridines, 2-(C6H4-2'-OH),6-(CMe2NHAr)C5H3N [Ar = 4-i-PrC6H4 (HL2(a)), 2,6-i-Pr2C6H3 (HL2(b))], using straightforward synthetic approaches and in reasonable overall yields. Interaction of HL1(a/c) and HL2(a/b) with palladium(II) acetate affords the O,N,N-pincer complexes, [{2-(C6H4-2'-O)-6-(CMe=NAr)C5H3N}Pd(OAc)] (Ar = 4-i-PrC6H4 (1a), 2,6-i-Pr2C6H3 (1b)) and [{2-(C6H4-2'-O)-6-(CMe2NHAr)C5H3N}Pd(OAc)] (Ar = 4-i-PrC6H4 (2a), 2,6-i-Pr2C6H3 (2b)), which can be readily converted to their chloride derivatives, [{2-(C6H4-2'-O)-6-(CMe=NAr)C5H3N}PdCl] (Ar = 4-i-PrC6H4 (3a), 2,6-i-Pr2C6H3 (3b)) and [{2-(C6H4-2'-O)-6-(CMe2NHAr)C5H3N}PdCl] (Ar = 4-i-PrC6H4 (4a), 2,6-i-Pr2C6H3 (4b)), respectively, on reaction with an aqueous sodium chloride solution. Treating each of 3a, 3b, 4a and 4b with two equivalents of di-p-tolyliodonium triflate at 100 °C in a toluene/acetonitrile mixture affords varying amounts of 4-chlorotoluene along with the 4-iodotoluene by-product with the conversions highly dependent on the steric and backbone properties of the pincer complex employed (viz. 4a > 3a > 4b > 3b); notably, the least sterically bulky and most flexible amine-containing 4a reaches 90% conversion to 4-chlorotoluene in 15 h as opposed to 17% for imine-containing 3b. In the case of 3a, the inorganic palladium species recovered from the reaction has been identified as the Pd(II) salt [{2-(C6H4-2'-O)-6-(CMe=N(4-i-PrC6H4)C5H3N}Pd(NCMe)][O3SCF3] (5a), which was independently prepared by the reaction of 3a with silver triflate in acetonitrile. Single crystal X-ray structures are reported for HL1(a), HL2(a), 1a, 1b, 2a, 2b, 3a and 5a.

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.

From discrete monomeric complexes to hydrogen-bonded dimeric assemblies based on sterically encumbered square planar palladium(II) ONN-pincers.

The 2-(3-biphenyl-2-ol)-6-iminepyridines, 2-(3-C12H8-2-OH)-6-(CH=NAr)C5H3N (Ar = 2,6-i-Pr2C6H3 (L1a-H), 2,4,6-Me3C6H2 (L1b-H)), have been prepared in high yield via sequential Suzuki coupling, deprotection and condensation reactions from 2-methoxybiphenyl-3-ylboronic acid and 2-bromo-6-formylpyridine. Treatment of L1-H with Pd(OAc)2 or (MeCN)2PdCl2 results in deprotonation of L1-H to afford the discrete square planar ONN-chelates, [{2-(3-C12H8-2-O)-6-(CHNAr)C5H3N}Pd(OAc)] (Ar = 2,6-i-Pr2C6H3 (1a), 2,4,6-Me3C6H2 (1b)) and [{2-(3-C12H8-2-O)-6-(CH=NAr)C5H3N}PdCl] (Ar = 2,6-i-Pr2C6H3 (2a), 2,4,6-Me3C6H2 (2b)), in good yield, respectively; conversion of 1 to 2 using aqueous sodium chloride has been demonstrated. Selective reduction of the imino unit in L1-H with LiAlH4 proceeds smoothly to yield the 2-(3-biphenyl-2-ol)-6-(methylamine)pyridines, 2-(3-C12H8-2-OH)-6-(CH2-NHAr)C5H3N (Ar = 2,6-i-Pr2C6H3 (L2a-H), 2,4,6-Me3C6H2 (L2b-H)), which on reaction with Pd(OAc)2 give [{2-(3-C12H8-2-O)-6-(CH2-NHAr)C5H3N}Pd(OAc)] (Ar = 2,6-i-Pr2C6H3 (3a), 2,4,6-Me3C6H2 (3b)). Depending on the temperature of the reaction, the oxidised aldimine products 1a or 1b can also be observed as a competitive side-product during the formation of 3a or 3b. Similarly, ketimine-containing, [{2-(3-C12H8-2-O)-6-(CMe=N(2,6-i-Pr2C6H3))C5H3N}Pd(OAc)] (5), can be detected during the preparation of chiral [{2-(3-C12H8-2-O)-6-(CMeH-NH(2,6-i-Pr2C6H3))C5H3N}Pd(OAc)] (4) from 2-(3-C12H8-2-OH)-6-(CH2-NH(2,6-i-Pr2C6H3))C5H3N (L3-H) and Pd(OAc)2. Complexes 3a, 3b and 4 all exist as dimeric species in the solid state in which two anti-aligned square planar monomers are held together by two intermolecular NH(amine)···O(phenolate) interactions resulting in palladium­palladium separations of between 3.141­3.284 Å. The structurally related chloride-containing dimeric assemblies, [{2-(3-C12H8-2-O)-6-(CH2-NHAr)C5H3N)}PdCl] (Ar = 2,6-i-Pr2C6H3 (6a), 2,4,6-Me3C6H2 (6b)), can also be isolated on treatment of 3 with aqueous sodium chloride or by reaction of L3-H with (MeCN)2PdCl2. Single crystal X-ray diffraction studies have been performed on L1a-H, L3-H, 1a, 1b, 2a, 2b, 3a, 3b, 4, 6a and 6b.

N,N-Chelate-control on the regioselectivity in acetate-assisted C-H activation.

Bidentate N,N-pyridylimine or N,N-pyridylamine donors are effective chelating ligands for regiospecific C-H activation at the peri-(C(8))-position of a naphthyl ring on reaction with palladium(ii) acetate; DFT calculations show N,N-chelates bias the cyclopalladation towards 6-membered ring products.

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.

Stabilisation of iridium(III) fluoride complexes with NHCs.

The first neutral, [IrClF(2)(NHC)(COD)] and [IrClF(2)(CO)(2)(NHC)] (NHC = IMes, IPr), and cationic, [IrF(2)py(IMes)(COD)][BF(4)] and [IrF(2)L(CO)(2)(NHC)][BF(4)] (NHC = IMes, L = PPh(2)Et, PPh(2)CCPh, py; NHC = IPr, L = py), NHC iridium(III) fluoride complexes, have been synthesised by the xenon difluoride oxidation of iridium(I) substrates. The stereochemistries of these iridium(III) complexes have been confirmed by multinuclear NMR spectroscopy in solution and no examples of fluoride-trans-NHC arrangements were observed. Throughout, CO was found to be a better co-ligand for the stabilisation of the iridium(III) fluoride complexes than COD. Attempts to generate neutral trifluoroiridium(III) complexes, [IrF(3)(CO)(NHC)], via the ligand substitution reaction of [IrF(3)(CO)(3)] with the free NHCs were unsuccessful.

Synthesis and characterisation of some iridium-carbonyl-fluoride complexes. Crystal structures of [IrF(CO){P(C6H4-2-CH3)3}2] and [IrF2(COD)py2][BF4].

Two routes to iridium(III) fluorocomplexes are described. The direct reaction of tetrairidium dodecacarbonyl with elemental fluorine in aHF offers a clean, convenient, large scale route to [IrF(3)(CO)(3)]; addition of phosphines to [IrF(3)(CO)(3)] in THF affords mer-[IrF(3)(CO)L(2)] or [IrF(CO)L(2)]. Alternatively, cationic [IrF(2)(COD)L(2)](+) and [IrF(2)(CO)(2)L(2)](+) (L = phosphine, pyridine; L(2) = alpha-diimine) are accessible via the oxidation of the iridium(I) precursors with xenon difluoride.

N-Heterocyclic carbene-containing ruthenium difluoro complexes and their reactivity towards BF(3).

Treatment of tetranuclear [RuF(-F)(CO)3]4 (1) with the free N-heterocyclic carbenes (NHCs), IMes (1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene) and IPr (1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene), followed by work-up in carbon tetrachloride leads to fluoride-bridge cleavage in 1 and the formation of the mononuclear octahedral complexes cis,cis,trans-[RuF2(CO)2(NHC)2] [NHC = IMes (2a), IPr (2b)], respectively. Complexes 2a and 2b can also be obtained by interaction of 1 with the corresponding imidazolium chloride, [-N(Ar)CHN(Ar)CHCH-]Cl (Ar = 2,4,6-Me3C6H2, 2,6-i-Pr2C6H3), in the presence of KOtBu. However, extension of this latter base-assisted approach to [-N(Ar)CHN(Ar)CHCH-]Cl (Ar = 2,6-Me2C6H3, 2,4,6-i-Pr3C6H2) results in halide exchange with the work-up solvent (CCl4) to generate cis,cis,trans-[RuCl2(CO)2(IMe)2] (3) and dinuclear [RuCl(mu-Cl)(CO)2(ITPr)]2 (4), respectively. Reaction of 2a with gaseous BF3 in dichloromethane and subsequent carbonylation affords in high yield monocationic [Ru(FBF3)(CO)3(IMes)2](BF4) (5), while with 2b, BF3 addition alone results in solvent exchange to yield dinuclear monocationic [Ru2(mu-Cl)3(CO)4(IPr)2](BF4)/(F) (6). Conversely, interaction of 2a and 2b with BF3.OEt2 in acetonitrile furnishes dicationic cis,cis,trans-[Ru(CO)2(NCMe)2(NHC)2](BF4)2 [NHC = IMes (7a), IPr (7b)]; in the case of 7a carbonylation gives [Ru(CO)4(IMes)2](B2F7)2 (8). Single crystal X-ray structures are presented for 3, 4, 5, 6 and 8.

Bis[1,2-bis(diphenylphosphino)ethane-kappa2P,P']difluoridoruthenium(II) trichloromethane disolvate.

In the crystal structure of the title compound, [RuF(2)(C(26)H(24)P(2))(2)].2CHCl(3), the Ru atom lies on a centre of symmetry with a trans arrangement of the F atoms. A H...F contact (2.249 A) suggests weak intramolecular hydrogen bonding. The solvent molecules exhibit hydrogen bonding with the F atoms (H...F = 1.91 A).

cis-Dicarbonyl-cis-dichlorido-trans-bis(triphenylphosphine-kappaP)iridium(III) tetrafluoridoborate, formed by reaction of (cycloocta-1,5-diene)bis(triphenylphosphine)iridium tetrafluoridoborate with carbonyl fluoride in dichloromethane solution.

The reaction between carbonyl fluoride and [Ir(COD)(PPh(3))(2)]BF(4) (COD is cycloocta-1,5-diene) in dichloromethane solution affords the novel title iridium salt, [IrCl(2)(C(18)H(15)P)(2)(CO)(2)]BF(4). The cation lies across a twofold rotation axis in the space group P2(1)2(1)2 and its structure confirms the presence in a cis relationship of two metal-bound chlorides, while the phosphine ligands occupy a trans pair of sites. The anion also lies across a twofold rotation axis, and the F atoms are disordered over two sets of sites.

Effect of solutes on the viscosity of supercritical solutions.

This study shows that solutes can impart significant structure to supercritical solutions, resulting in unexpectedly high solution viscosity at pressures close to the critical value. The viscosity passes through a minimum as the pressure is increased, and this is accounted for by a solvation of the solutes leading to a decrease in solute-solute interactions. At high pressure, the solution viscosity is similar to that of the pure solvent as solvent-solvent interactions dominate. The increase in relative viscosity is modeled using a modified Dole-Jones equation, and it is shown that the change in relative viscosity is related to the volume fraction occupied by the solute. A general model is presented for simple solutes whereby the viscosity of a supercritical solution can be calculated from the molecular volume of the solute and the viscosity of the pure fluid. The higher than expected viscosity observed at low pressures is used to explain the variation of reaction rate constant with pressure.

Probing solute clustering in supercritical solutions using solvatochromic parameters.

Kamlet and Taft polarity parameters are presented for three supercritical solutions containing solutes of different polarities at two concentrations. It is shown that the polarizability and hydrogen-bond-donating ability change significantly with pressure. In the lower pressure regime, naphthalene and salicylic acid cause a decrease in the polarity parameters compared with the pure fluid, whereas toluic acid causes an increase. These differences can be explained in terms of solute-solute and solute-indicator clustering. It is shown that there is, however, a direct correlation between the change in the hydrogen-bond-donating ability and polarizability for all solutes and all pressures and concentrations, which is thought to result from changes in the amount of solvent required to solvate the solute.

Rhodium catalysed hydroformylation of alkenes using highly fluorophilic phosphines.

Highly fluorophilic phosphines incorporating at least one aromatic ring containing two directly attached perfluoroalkyl groups have been synthesised, their partition coefficients (organic phase : fluorous phase) measured and their electronic properties probed using (1)J(PtP) data for their trans-[PtCl(2)L(2)] complexes. These phosphines have been used as modifying ligands for the rhodium catalysed hydroformylation of 1-octene in perfluorocarbon solvents. Catalyst activity, regioselectivity and the levels of rhodium leaching to the product phase vary with the substitution patterns of the modifying ligands that do not correlate with the electronic properties or partition coefficients of these ligands, but can be interpreted in terms of differences in the resting states of the catalysts.

Effect of electrolyte concentration on the viscosity and voltammetry of supercritical solutions.

The viscosity of a supercritical electrolyte solution is measured for the first time using a modified quartz crystal microbalance, and it is shown that ionic solvation leads to a significant structuring of the solvent and an appreciable increase in solution viscosity. Voltammetric investigations in the electrolyte solutions are used to confirm the magnitude of the viscosity changes, and these account for the appreciably lower than expected peak currents.

Pressure effects on Friedel-Crafts alkylation reactions in supercritical difluoromethane.

Dielectrometry is used as a novel technique for following the rate of a Friedel-Crafts alkylation reaction in supercritical (sc) difluoromethane. Although the process was not optimized, good product yields were obtained and reaction rates were found to be larger than in CO2 at comparable conditions. The reaction order is determined using the initial rate method and the reaction is shown to be first-order with respect to both anisole and t-butyl chloride. The reaction rate constant is unaffected by pressures above 120 bar but close to the critical pressure the value decreases with increasing pressure. It is also shown that the product distribution for the alkylation of anisole shows significant pressure dependence with substitution at the ortho-position being favored at lower pressures, which is ascribed to hydrogen bonding. This pressure dependency is not observed in sc CO2 or using toluene as a substrate, which supports the idea that hydrogen bonding may be important in the reaction mechanism. The effect of the different reagents and temperature on the rate of the alkylation reaction was also determined.

The design of a continuous reactor for fluorous biphasic reactions under pressure and its use in alkene hydroformylation.

A reactor, into which all reagents can be fed continuously and from which the reaction mixture can be continuously removed to a gravity separator, where product can be continuously removed and the catalyst phase recycled to the reactor, has been constructed and used for the hydroformylation of alkenes in fluorocarbon solvents.