Fluorinated phosphorus compounds: Part 10. Bis(fluoroalkyl) S-alkyl phosphorothiolates and tris(fluoroalkyl) phosphorothionates

Treatment of bis(fluoroalkyl) phosphites (R_FCH₂O)₂P(O)H, where R_F was CF₃ or C₂F₅ with sulfur in pyridine at 80 °C gave salts of structure [(R_FCH₂O)₂P(O)SH]NC₅H₅ in 90 and 88% yield, respectively. The salts reacted with alkyl iodides in acetonitrile at 50 °C to furnish bis(fluoroalkyl) S-alkyl phosphorothiolates (R_FCH₂O)₂P(O)SR, where R was Me, Et, n- and i-Pr (when R_F = CF₃) and Me (when R_F = C₂F₅). Yields ranged from 21 to 57%. Bis(trifluoroethyl) S-methyl phosphorothiolate (CF₃CH₂O)₂P(O)SMe underwent fluorination by silver(I) fluoride in acetonitrile at room temperature to yield the phosphorofluoridate (CF₃CH₂O)₂P(O)F in 75% yield. Tris(fluoroalkyl) phosphorothionates (R_FCH₂O)₃P = S, where R_F was CF₃, C₂F₅ and C₃F₇, were prepared in 30-34% yield by heating the tris(fluoroalkyl) phosphites (R_FCH₂O)₃P and sulfur to 200 °C in a sealed tube for 8 h.     

Fluorinated phosphorus compounds: Part 7. The reactions of bis(fluoroalkyl) phosphorochloridates with nitrogen nucleophiles

Forty bis(fluoroalkyl) phosphoramidates (R_FO)₂P(O)R were prepared in 10-91% yield by treating phosphorochloridates (R_FO)₂P(O)Cl where R_F was HCF₂CH₂, HCF₂CF₂CH₂, HCF₂CF₂CF₂CF₂CH₂, CF₃CH₂, C₂F₅CH₂, C₃F₇CH₂, (CF₃)₂CH, (FCH₂)₂CH and (CH₃)₂CF₃C with nucleophiles HR, where R was NH₂, NHMe, NMe₂, NHEt and NEt₂ in diethyl ether at 0-5 °C. The bulky chloridate [(CH₃)₂CF₃CO]₂P(O)Cl reacted with ammonia, methylamine, dimethylamine and ethylamine, but not with diethylamine—even on heating in the presence of 4-dimethylaminopyridine—due to steric hindrance at phosphorus. Fluorinated phosphoramidates have lower basicity and nucleophilicity than their unfluorinated counterparts: (EtO)₂P(O)NH₂ is more easily hydrolysed by HCl than (CF₃CH₂O)₂P(O)NH₂ and whereas, (EtO)₂P(O)NH₂ is known to react with oxalyl chloride and thionyl chloride to give (EtO)₂P(O)NCO and (EtO)₂P(O)NSO respectively, (CF₃CH₂O)₂P(O)NH₂ reacted only with oxalyl chloride to give (CF₃CH₂O)₂P(O)NCO in 10% yield. Two other new fluorinated species, (CF₃CH₂O)₂P(O)NHOMe and (CF₃CH₂O)₂P(O)N₃, were prepared by nucleophilic substitution of bis(trifluoroethyl) phosphorochloridate with methoxyamine and azide ion.     

Fluorinated phosphorus compounds: Part 8. The reactions of bis(fluoroalkyl) phosphorochloridates with sulfur nucleophiles

The reactivity of bis(fluoroalkyl) phosphorochloridates to nucleophiles is summarised. Previous data and the results described here indicate that reactivities decrease in the order: amines>alcohols>thiols. The synthesis of CF₃CH₂OP(O)(SEt)₂ in 30% yield was accomplished by treating CF₃CH₂OP(O)Cl₂ with two molar equivalents of EtSH and Et₃N in ether. The chloridates (CF₃CH₂O)₂P(O)Cl and (C₂F₅CH₂O)₂P(O)Cl did not react with MeSH in ether at −78 °C or when heated with Pb(SMe)₂ in benzene. Ethanethiol and propanethiol reacted with fluorinated chloridates in the presence of triethylamine to give thiolates (R_FO)₂P(O)SR in 13-41% yield where R_F was CF₃CH₂, C₂F₅CH₂, C₃F₇CH₂ or (CF₃)₂CH and R was Et or n-Pr. Similarly, reaction of phosphorobromidates (R_FCH₂O)₂P(O)Br, made by brominating the corresponding bis(fluoroalkyl) H-phosphonates, with benzenethiol gave derivatives (R_FCH₂O)₂P(O)SPh in 43 and 46% yield where R_F was CF₃ and C₂F₅, respectively. Treatment of the chloridothiolate Cl(EtO)P(O)SMe, prepared in two steps from triethyl phosphite, with fluoroalcohols and triethylamine in ether gave species R_FO(EtO)P(O)SMe in 62-74% yield where R_F was CF₃CH₂, C₂F₅CH₂, C₃F₇CH₂ or (CF₃)₂CH. The reactions of bis(trifluoroethyl) phosphorochloridate with 2-mercaptoethanol, 3-mercaptopropanol and ethane-1,2-dithiol gave several unexpected products whose structures were tentatively assigned.     

Fluorinated phosphorus compounds: Part 9. The reactions of bis(fluoroalkyl) phosphorochloridates with oxygen nucleophiles

Twenty nine bis(fluoroalkyl) phosphates (R_FO)₂P(O)OR were prepared in 18-75% yield by treating phosphorochloridates (R_FO)₂P(O)Cl, where R_F was HCF₂CH₂, HCF₂CF₂CH₂, H(CF₂)₄CH₂, C₂F₅CH₂, C₃F₇CH₂, (CF₃)₂CH, (FCH₂)₂CH and (CH₃)₂CF₃C with methanol, ethanol, propanol and isopropanol in diethyl ether in the presence of triethylamine. The bulky chloridate [(CH₃)₂CF₃CO]₂P(O)Cl reacted with methanol, ethanol and propanol, but not with isopropanol - even on heating in the presence of the catalyst 4-dimethylaminopyridine - due to steric hindrance at phosphorus. The relative reactivities of three of the chloridates decreased in the order [(CF₃)₂CHO]₂P(O)Cl > [(FCH₂)₂CHO]₂P(O)Cl > [(CH₃)₂CF₃CO]₂P(O)Cl. Also described is the synthesis of phosphates (CF₃CH₂O)₂P(O)OCH₂R, where R = CH₂Br, CH₂Cl, CH₂F and CHF₂, and diphosphates [H(CF₂)_nCH₂O]₂P(O)OCH₂(CF₂)₂CH₂OP(O)[OCH₂(CF₂)_nH]₂, where n = 1, 2 and 4.     

Fluorinated phosphorus compounds: Part 11. The reactions of some fluorinated amines with dialkyl and bis(fluoroalkyl) phosphorochloridates

Dimethyl phosphorochloridate reacted with R_FCH₂NH₂ in ether in the presence of Et₃N to afford (MeO)₂P(O)NHCH₂R_F, where R_F = CF₃ and C₂F₅, in 39 and 47% yield, respectively. Similar reactions with di-n-propyl and diisopropyl phosphorochloridates could be effected only with H₂NCH₂CF₃ when 4-dimethylaminopyridine catalyst was added and (n-PrO)₂P(O)NHCH₂CF₃ and (i-PrO)₂P(O)NHCH₂CF₃ were isolated in 49 and 25% yield, respectively. Treatment of POCl₃ with one molar equivalent each of H₂NCH₂CF₃ and Et₃N permitted the synthesis of Cl₂P(O)NHCH₂CF₃ in 43% yield. Bis(fluoroalkyl) phosphorochloridates (R_FO)₂P(O)Cl, where R_F = C₂F₅CH₂, C₃F₇CH₂ and (CF₃)₂CH, reacted with 2,2,2-trifluoroethylamine and 2,2,3,3,3-pentafluoropropylamine to furnish phosphoramidates (R_FO)₂P(O)NHCH₂R, where R = CF₃ or C₂F₅, in yields of 32-67%.     

Bis(fluoroalkyl)acrylic and methacrylic phosphate monomers, their polymers and some of their properties

Ten fluoromonomers of structure (R_FO)₂P(O)OCH₂CH₂OC(O)CRCH₂ were made in 30-64% yield by treating the chloridates (R_FO)₂P(O)Cl with HOCH₂CH₂OC(O)CRCH₂ in chloroform in the presence of triethylamine [R_F=CF₃CH₂, C₂F₅CH₂, C₃F₇CH₂, C₄F₉CH₂, C₄F₉CH₂CH₂ or C₆F₁₃CH₂CH₂; R  H or Me]. The chloromonomer (CCl₃CH₂O)₂P(O)OCH₂CH₂OC(O)CHCH₂ was obtained analogously in 29% yield. Polymerisation of the acrylate monomers, but not the methacrylate monomers, could be effected using α-azoisobutyronitrile as a radical initiator. Acrylic polymers having CF₃CH₂O, CCl₃CH₂O and C₆F₁₃CH₂CH₂O side-chains were obtained as translucent rubbers. Specimens of cotton fabric were treated with solutions of the polymers, and average water and oil repellency ratings measured. Fabric coated with the polymer with the C₆F₁₃CH₂CH₂O side-chain afforded protection from penetration of the test liquids. Treated fabrics were subjected to the limiting oxygen index (LOI) test according to BS EN ISO 4589-2 (1999): this test determines the point at which a material just burns in a volumetric flow of oxygen and nitrogen. The treated fabrics were more fire-resistant (LOI 22-29%) than the untreated fabric (LOI 18%). Fabric coated with the CCl₃CH₂O-based polymer can be considered fire-retardant (LOI 29%). The fluoromonomers were tested for anti-acetylcholinesterase activity and were found to be poor enzyme inhibitors; they are predicted to possess low acute toxicity.     

First examples of stable polyfluorinated bis- and tris-(alkoxy)methyl cations

Stable polyfluorinated bis- and tris-(alkoxy)methyl cations were prepared by the reaction of the corresponding difluoroformals (R_fO)₂CF₂ (R_f = -CH₂CF₃, -CH(CF₃)₂, -CH₂CF₂Cl) with an excess of SbF₅. Although the cation (CF₃CH₂O)₂CF⁺ (1a) is stable at ambient temperature, the chlorinated analog (ClCF₂CH₂O)₂CF⁺ (3a) can be generated only at low temperature in SO₂ClF solvent and rapidly decomposes at ambient temperature. Although the salt [(CF₃)₂CHO]₂CF⁺Sb_nF_5n+1⁻ (2a) is slightly more stable than the salt of cation 3a, at ambient temperature it undergoes rapid disproportionation with formation of equal amounts of [(CF₃)₂CHO]₃C⁺Sb_nF_5n+1⁻ (2b) and CF₃OCH(CF₃)₂ (2c). Stable solid salt 2b (n = 2) was isolated and fully characterized by ¹H, ¹⁹F and ¹³C NMR spectroscopy and its structure was confirmed by single crystal X-ray diffraction.     

New types of asymmetrical bromonium salts [RF(RF′)Br]Y where RF and/or RF′ represent perfluorinated aryl, alkenyl, and alkynyl groups

A series of previously unknown asymmetrical fluorinated bis(aryl)bromonium, alkenyl(aryl)bromonium, and alkynyl(aryl)bromonium salts was prepared by reactions of C₆F₅BrF₂ or 4-CF₃C₆H₄BrF₂ with aryl group transfer reagents Ar′SiF₃ (Ar′ = C₆F₅, 4-FC₆H₄, C₆H₅) or perfluoroorganyl group transfer reagents R_F′BF₂ (R_F = C₆F₅, trans-CF₃CFCF, C₃F₇C≡C) preferentially in weakly coordinating solvents (CCl₃F, CCl₂FCClF₂, CH₂Cl₂, CF₃CH₂CHF₂ (PFP), CF₃CH₂CF₂CH₃ (PFB)). The presence of the base MeCN and the influence of the adducts R_F′BF₂·NCMe (R_F = C₆F₅, CF₃C≡C) on reactions aside to bromonium salt formation are discussed. Reactions of C₆F₅BrF₂ with Alk_F′BF₂ in PFP gave mainly C₆F₅Br and Alk_F′F (Alk_F′ = C₆F₁₃, C₆F₁₃CH₂CH₂), presumably, deriving from the unstable salts [C₆F₅(Alk_F′)Br]Y (Y = [Alk_F′BF₃]⁻). Prototypical reactivities of selected bromonium salts were investigated with the nucleophile I^-and the electrophile H⁺. [4-CF₃C₆H₄(C₆F₅)Br][BF₄] showed the conversion into 4-CF₃C₆H₄Br and C₆F₅I when reacted with [Bu₄N]I in MeCN. Perfluoroalkynylbromonium salts [C_nF_2n+1C≡C(R_F)Br][BF₄] slowly added HF when dissolved in aHF and formed [Z-C_nF_2n+1CFCH(R_F)Br][BF₄].     

Fluoroalkenyl, fluoroalkynyl and fluoroalkyl phosphines

A review of the methods available for the preparation of monodentate P(III) compounds containing fluoroalkenyl, fluoroalkynyl and fluoroalkyl groups is given. The synthesis, properties and coordination chemistry of some fluoroalkenyl- and fluoroalkynyl-containing phosphines derived from HFC-134a (CF₃CH₂F) and HFC-245fa (CF₃CH₂CH₂F) is summarised. The development of the reaction between trimethylsilyl-containing phosphines and R_fI which provides a general method by which bulky fluoroalkyl groups, such as i-C₃F₇, t-C₄F₉, c-C₆F₁₁, can be readily introduced into phosphorus(III) centres is reported. Together these methods provide a way of generating P(III) systems of the type R_3−nP(R_f)_n capable of possessing a wide range of steric and electronic properties.     

Kristall- und Molekülstruktur von Bis(pyridin)bis(trifluoromethyl)zink

Crystal and Molecular Structure of Bis(pyridine)bis(trifluoromethyl)zinc Bis(pyridin)bis(trifluoromethyl)zinc 1 has been isolated and characterized by means of single-crystal X-ray diffraction techniques. The title compound represents the first structure determination of a fully fluorinated alkylzinc compound (monoclinic, space group P2₁/c, Z = 4, a = 8.856(3), b = 18.158(3), c = 8.979(3) Å, β = 98.14(2)°, R = 0.054, R_w = 0.035). The zinc atom is in a distorted tetrahedral environment. The molecular structure of [ClZn(CCl₂CF₃) η₂O]₂ 2 was solved, but is not included in a structural comparison due to crystallographic disorder.     

Bis(perfluoroorganyl)bromonium salts [(RF)2Br]Y (RF = aryl, alkenyl, and alkynyl)

Bromonium salts [(R_F)₂Br]Y with perfluorinated groups R_FC₆F₅, CF₃CFCF, C₂F₅CFCF, and CF₃C≡C were isolated from reactions of BrF₃ with R_FBF₂ in weakly coordinating solvents (wcs) like CF₃CH₂CHF₂ (PFP) or CF₃CH₂CF₂CH₃ (PFB) in 30-90% yields. C₆F₅BF₂ formed independent of the stoichiometry only [(C₆F₅)₂Br][BF₄]. 1:2 reactions of BrF₃ and silanes C₆F₅SiY₃ (Y = F, Me) ended with different products - C₆F₅BrF₂ or [(C₆F₅)₂Br][SiF₅] - as pure individuals, depending on Y and on the reaction temperature (Y = F). With C₆F₅SiF₃ at ≥−30 °C [(C₆F₅)₂Br][SiF₅] resulted in 92% yield whereas the reaction with less Lewis acidic C₆F₅SiMe₃ only led to C₆F₅BrF₂ (58%). The interaction of K[C₆F₅BF₃] with BrF₃ or [BrF₂][SbF₆] in anhydrous HF gave [(C₆F₅)₂Br][SbF₆]. Attempts to obtain a bis(perfluoroalkyl)bromonium salt by reactions of C₆F₁₃BF₂ with BrF₃ or of K[C₆F₁₃BF₃] with [BrF₂][SbF₆] failed. The 3:2 reactions of BrF₃ with (C₆F₅)₃B in CH₂Cl₂ gave [(C₆F₅)₂Br][(C₆F₅)_nBF_4−n] salts (n = 0-3). The mixture of anions could be converted to pure [BF₄]⁻ salts by treatment with BF₃·base.     

F-alkylation of bis(allyl) polyoxyethylene ethers

Bis(3-F-alkylallyl) polyoxyethylene ethers were obtained via radical addition of F-alkyl iodides on bis(allyl) ethers CH₂CH(CH₂OCH₂)_nCHCH₂ followed by 1,8-diazabicyclo[5.4.0]undec-7-ne (DBU) dehydrohalogenation.     

Synthesen und Eigenschaften von Tetrakis(perfluoralkyl)tellur Te(Rf)4 (Rf = CF3, C2F5, C2F5, C3F7, C4F9)

Synthesis and Properties of Tetrakis(Perfluoroalkyl)Tellurium Te(R_f)₄ (R_f = CF₃, C₂F₅, C₃F₇, C₄F₉) Te(CF₃)₄ is obtained from the reaction of Te(CF₃)Cl₂ with Cd(CF₃)₂ complexes as a complex with e. g. CH₃CN, DMF. It is a light and temperature sensitive hydrolysable liquid. The reaction with fluorides yields the complex anion [Te(CF₃)₄F]^?, with fluoride ion acceptors the complex cation [Te(CF₃)₃]⁺. With traces of water an acidic solution is formed. Te(CF₃)₄ acts as a trifluoromethylation reagent. The reaction with XeF₂ gives hints for the formation of Ye(CF₃)₄F₂. Properties and NMR spectra are discussed. The much more stable complexes of Te(R_f)₄ (R_f = C₂F₅, C₃F₇, C₄F₉) are formed from the reaction of TeCl₄ with the corresponding Cd(R_f)₂ complexes.     

The gas-phase structure of bis(fluorosulfonyl)difluoromethane, (SO2F)2CF2

New synthetic pathways and the infrared spectrum of bis(fluorosulfonyl)difluoromethane, (SO₂F)₂CF₂, are reported. The geometric structure and conformational properties of the title compound have been studied by gas electron diffraction. Depending on the rotational position of the two SO₂F groups, four conformers with different symmetries can occur in this compound: C_2v symmetry, if both S? F bonds stagger the CF₂ group. C₂ or C_s symmetry, if one S?O bond of each group staggers the CF₂ group. The experimental electron diffraction intensities can be fitted equally well with a C₁ conformer or with a mixture of C_2v, C₂ and C_s conformers, in a ratio of 3:2:5. The following geometric parameters (r_a distances, ∠_α angles with 3σ uncertainties) were derived: C? F = 1.340(6) Å, S?O = 1.412(2) Å, S? F = 1.550(3) Å, C? S = 1.848(4) Å, S? C? S = 113.6(7)°, F? C? F = 110.0(10)°, O?S?O = 124.6(18)°, C? S? F = 96.5(16)° and C? S?O = 108.4(14)°.     

A novel simple synthesis of bis(diorganoselenophosphoryl)selenides (R2PSe)2Se from secondary phosphines and elemental selenium

Secondary phosphines R₂PH [R = Ph(CH₂)₂, 4-t-BuC₆H₄(CH₂)₂, 4-MeOC₆H₄(CH₂)₂, 2-Naphth(CH₂)₂] react with two equivalents of elemental selenium under mild conditions (85 °C, 3 h, toluene) to afford bis(diorganoselenophosphoryl)selenides (R₂PSe)₂Se in high yields (75-92%).     

Mono and Bisphosphonates from Perfluoro Olefins and Polyfunctional Fluoro Ketones. Syntheses,Molecular Structure and Derivatives

Perfluoroalkenyl phosphonates were formed along with Me₃SiF using CF₃CF=CF₂, CF₃CH=CF₂, F₅SCF=CF₂ or F₅SCH=CF₂ and silylated phosphites, (R¹O)₂POSiMe₃ (R¹=Et, SiMe₃). This straightforward method could be extended to perfluorobutadienes CF₂=C(R^F)C(R^F)=CF₂ (R^F F=F, CF₃). The formation of CF₃C(=O)P(=O)(OSiMe₃)₂ and further reactions to yield bisphosphonates will be described. Acetylphosphonates, R²C(=O)P(=O)(OSiMe₃)₂ (R²=CH₃, CF₃) reacted with the ketimine, CH₃C(=NiPr)Ph to give α-hydroxy-γ-imino phosphonates. Trifluoroacetylphenol and 2,6-bis(trifluoracetyl)-4-methyl-phenol have been proven to be versatile precursors for α-and γ-hydroxy phosphonates. Intermediates in these reactions were found to be cyclic λ⁵σ⁵P species.     

Metallacrown ethers with a symmetric bis(phosphite) ligand derived from 1,2-bis-(2-hydroxyethoxy)benzene: Synthesis, characterization and hydroformylation of styrene

To better understand the effects of ligand configuration on hydroformylation reactions carried out in the presence of LiBPh₄·3dme (dme = 1,2-dimethoxyethane), a conformationally restrained bis(phosphite) ligand derived from 1,2-bis-(2-hydroxyethoxy)benzene, {[(2,2′-O₂C₁₂H₈)P(C₂H₄O₂)]₂C₆H₄}, 1, has been prepared and its Rh(I) metallacrown ether complex has been evaluated as a catalyst for the hydroformylation of styrene. Both the activity and regioselectivity of the catalyst are sensitive to the amount of the LiBPh₄·3dme added with the activity decreasing by 16% and the regioselectivity for the iso increasing by 9% at a 8:1 LiBPh₄:Rh ratio.Model complexes for the octahedral, cis-Mo(CO)₄(1), 2, and square planar, cis-PtCl₂(1), 3, and cis-PdCl₂(1), 4, complexes in the catalytic cycle has been have been studied using multinuclear NMR spectroscopy and X-ray crystallography. Although the X-ray crystal structure of 2 suggests that the metallacrown ether ring could adopt a configuration capable of binding alkali metal cations, this does not appear to occur in a dichloromethane-d₂ solution of 2 because no shift in the ³¹P NMR resonance 2 is observed upon the addition of an excess of LiBPh₄·3dme. The ³¹P{¹H} NMR spectra of chloroform-d solutions of 2 (in the presence of a catalytic amount of HgCl₂) and of 4 and the X-ray crystal structures of the complexes indicate that the bis(phosphite) ligands are cis coordinated in these complexes in both the solution and in the solid state. This is particularly surprising for 4 because related PdCl₂{Ph₂P(CH₂CH₂O)_nCH₂CH₂PPh₂} (n = 3-5) complexes exhibit both cis-trans and monomer-oligomer equilibria in solution.     

Synthesen und Eigenschaften von Tris(perfluoralkyl)arsen- und -antimon(III,V)-Verbindungen

Preparations and Properties of Tris(perfluoroalkyl) Arsenic and Antimony(III, V) Compounds As(R_f)₃ and Sb(R_f)₃ (R_f?C₂F₅, C₄F₉, C₆F₁₃) are prepared in good yields by the polar reactions of AsCl₃ and SbCl₃ with bis(perfluoroalkyl) cadmium compounds as colourless liquids or solids. The oxidation of As(C₂F₅)₃ and Sb(C₂F₅)₃ with XeF₂ gives the difluorides M(C₂F₅)₃F₂ (M?As, Sb). As(C₂F₅)₃Cl₂ is prepared by chlorination of As(C₂F₅)₃ in the presence of AlCl₃, while Sb(C₂F₅)₃Cl₂ is formed in the reaction of Sb(C₂F₅)₃F₂ with (CH₃)₃SiCl. During the reaction of M(C₂F₅)₃F₂ with (CH₃)₃SiBr ¹⁹F-NMR spectroscopic evidence is found for M(C₂F₅)₃ Br₂. The thermal decompositions of M(C₂F₅)₃F₂ mainly yield C₄F₁₀ and M(C₂F₅)F₂, while the thermal decompositions of M(C₂F₅)₃Cl₂ yield M(C₂F₅)₂Cl and C₂F₅Cl. The properties and spectroscopic data of the new compounds are described.     

Initiation reactivity of anionic polymerization of fluorinated acrylates and methacrylates with diethyl(ethyl cyanoacetato)aluminum

Pseudo first‐order rate constants of the reaction of diethyl(ethyl cyanoacetato)aluminum [(C₂H₅)₂Al(NCCHCOOC₂H₅)] with 17 fluorinated acrylates and methacrylates and five hydrocarbon analogs for references were investigated to examine the initiation reactivities of the anionic polymerization of fluorinated vinyl monomers to afford the reactivity order: CH₂?C(CF₃)COOC₂H₅ > CH₂?C(CF₃)COOCH(CH₃)₂ > CH₂?CHCOOCH₂C₆F₅ > CH₂?C(CF₃)COOC(CH₃)₃ > CH₂?C(CF₃)COOCH₂C₆F₅ > CH₂?C(CF₃)COOCH(CF₃)₂ ≥ CH₂?CHCOOCH₃ > CH₂?CHCOOCH₂C₆H₅ ≥ CH₂?C(CF₃)COOCH₂CF₃ > CH₂?C(CH₃)COOCH₂C₆F₅ > CH₂?CHCOOCH₂CF₃ > CH₂?CHCOOCH₂C₂F₅ > CH₂?CHCOOCH(CF₃)₂ > CH₂?C(CH₃)COOCH₃ > CH₂?C(CH₃)COOCH₂C₆H₅ ≥ CH₂?C(CH₃)COOCH₂CH₂C₈F₁₇ > CH₂?C(CH₃)COOCH(CH₃)₂ > CH₂?C(CH₃)COOCH₂C₂F₅ ≥ CH₂?C(CH₃)COOCH₂CF₃. No rate constants for CH₂?C(CH₃)COOCH(CF₃)₂, CH₂?CFCOOC(CH₃)₃, and CH₂?CFCOOCH₂C₂F₅ were obtained because of too fast polymerization. The incorporation of a trifluoromethyl group into the vinyl group enhanced the reactivity toward the delocalized carbanion. The reactivity of other fluorinated acrylates and methacrylates was concluded to approximately be controlled by the fluorine contents and the bulkiness of substituents of monomers. The reactivity was generally decreased by increasing fluorine contents of fluoroalkyl substituents in ester groups. © Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 7011–7021, 2008     

Molybdenum(VI) Bis(imido) Complexes: From Frustrated Lewis Pairs to Weakly Coordinating Cations

Molybdenum(VI) bis(imido) complexes [Mo(NtBu)₂(L^R)₂] (R=H 1 a ; R=CF₃ 1 b ) combined with B(C₆F₅)₃ ( 1 a /B(C₆F₅)₃, 1 b /B(C₆F₅)₃) exhibit a frustrated Lewis pair (FLP) character that can heterolytically split H−H, Si−H and O−H bonds. Cleavage of H₂ and Et₃SiH affords ion pairs [Mo(NtBu)(NHtBu)(L^R)₂][HB(C₆F₅)₃] (R=H 2 a ; R=CF₃ 2 b ) composed of a Mo(VI) amido imido cation and a hydridoborate anion, while reaction with H₂O leads to [Mo(NtBu)(NHtBu)(L^R)₂][(HO)B(C₆F₅)₃] (R=H 3 a ; R=CF₃ 3 b ). Ion pairs 2 a and 2 b are catalysts for the hydrosilylation of aldehydes with triethylsilane, with 2 b being more active than 2 a . Mechanistic elucidation revealed insertion of the aldehyde into the B−H bond of [HB(C₆F₅)₃]⁻. We were able to isolate and fully characterize, including by single-crystal X-ray diffraction analysis, the inserted products Mo(NtBu)(NHtBu)(L^R)₂][{PhCH₂O}B(C₆F₅)₃] (R=H 4 a ; R=CF₃ 4 b ). Catalysis occurs at [HB(C₆F₅)₃]⁻ while [Mo(NtBu)(NHtBu)(L^R)₂]⁺ (R=H or CF₃) act as the cationic counterions. However, the striking difference in reactivity gives ample evidence that molybdenum cations behave as weakly coordinating cations (WCC).