Recent progress in perfluoroalkyl-phosphorus chemistry

Fluoride Abstraction Induced by Tris(pentafluoroethyl)difluorophosphorane: A Convenient Way to Synthesize Cationic N-Heterocyclic Carbene- and Cyclic (Alkyl)(amino)carbene-Ligated Copper Alkyne and Arene Complexes

We herein report the convenient synthesis of different N-heterocyclic carbene (NHC)- and cyclic (alkyl)(amino)carbene (cAAC)-ligated copper cations using the weakly coordinating tris(pentafluoroethyl)trifluorophosphate counterion (FAP anion, [(C2F5)3PF3]-). The reaction of the fluorido complexes [(carbene)CuF] (carbene = NHC, cAACMe) 2a-2f and the tris(pentafluoroethyl)difluorophosphorane (C2F5)3PF2 in the presence of alkynes or arenes led to fluoride transfer from Cu to the phosphorane with formation of the cationic transition metal complexes [(carbene)Cu(L)]+ and the weakly coordinating counteranion [(C2F5)3PF3]- (FAP). Using this method, the complexes [(IDipp)Cu(L)]+FAP- (IDipp = 1,3-bis(2,6-di-iso-propylphenyl)-imidazolin-2-ylidene; L = PhC≡CPh, 4d; PhC≡CMe, 5d), [(cAACMe)Cu(L)]+FAP- (cAACMe = 1-(2,6-di-iso-propylphenyl)-3,3,5,5-tetramethyl-pyrrolidin-2-ylidene; L = PhC≡CPh, 4f; PhC≡CMe, 5f), [(SIDipp)Cu(C6Me6)]+FAP- (6e), (SIDipp = 1,3-bis(2,6-di-iso-propylphenyl)-imidazolidine-2-ylidene), and [(cAACMe)Cu(C6Me6)]+FAP- (6f) have been synthesized and characterized. The complexes [(IDipp)Cu(C6Me6)]+FAP- (6d) and [(cAACMe)Cu(C6Me6)]+FAP- (6f) have been used as catalysts for the copper(I)-catalyzed cycloaddition of benzyl azide to terminal alkynes.

The Field of Main Group Lewis Acids and Lewis Superacids: Important Basics and Recent Developments

New developments in the field of Lewis acidity are highlighted, with the focus of novel Lewis acids and Lewis superacids of group 2, 13, 14, and 15 elements. Several important basics, illustrated by modern examples (classification of Donor-Acceptor (DA) complexes, amphoteric nature of any compound in terms of DA interactions, reorganization energies of main group Lewis acids and the role of the energies of frontier orbitals) are presented and discussed. It is emphasized that the Lewis acidity phenomena are general and play vital role in different areas of chemistry: from weak "atomophilic" interactions to the complexes of Lewis superacids.

Ionic Liquids as Working Fluids for Heat Storage Applications: Decomposition Behavior of N-Butyl-N-methylpyrrolidinium tris(pentafluoroethyl)trifluorophosphate

Ionic liquids (ILs) represent promising working fluids to be used in thermal energy storage (TES) technologies thanks to their peculiar properties, such as low volatility, high chemical stability, and high heat capacity. Here, we studied the thermal stability of the IL N-butyl-N-methylpyrrolidinium tris(pentafluoroethyl)trifluorophosphate ([BmPyrr]FAP), a potential working fluid for TES applications. The IL was heated at 200 °C for up to 168 h either in the absence or in contact with steel, copper, and brass plates to simulate the conditions used in TES plants. High-resolution magic angle spinning nuclear magnetic resonance spectroscopy was found to be useful for the identification of the degradation products of both the cation and the anion, thanks to the acquisition of ¹H, ¹³C, ³¹P, and ¹⁹F-based experiments. In addition, elemental analysis was performed on the thermally degraded samples by inductively coupled plasma optical emission spectroscopy and energy dispersive X-ray spectroscopy. Our analysis shows a significant degradation of the FAP anion upon heating for more than 4 h, even in the absence of the metal/alloy plates; on the other hand, the [BmPyrr] cation displays a remarkable stability also when heated in contact with steel and brass.

Triorganylphosphoranides: Realization of an Unusual Structural Motif Utilizing Electron Withdrawing Pentafluoroethyl Groups

Phosphoranides comprising three phosphorus carbon bonds are scarcely represented in the literature. We now utilized tris(pentafluoroethyl)phosphane, P(C₂ F₅ )₃ , and cyanobis(pentafluoroethyl)phosphane, P(C₂ F₅ )₂ (CN), featuring electron withdrawing pentafluoroethyl groups, to synthesize such compounds. Metal fluorides MF (M=Ag, Cs) add to P(C₂ F₅ )₃ yielding respective M[P(C₂ F₅ )₃ F] salts. Those M[P(C₂ F₅ )₃ F] subsequently suffer a loss of C₂ F₄ , furnishing M[P(C₂ F₅ )₂ F₂ ]. The cesium salt decomposes instantaneously when warmed to rt, whereas the silver salt decomposes slowly over several days at rt. Treatment of Ag[P(C₂ F₅ )₃ F] with 2,2'-bipyridine facilitated the isolation and structural characterization of [Ag(bipy){P(C₂ F₅ )₃ F}]. With P(C₂ F₅ )₂ (CN), AgF reacts under substitution of the cyano group yielding P(C₂ F₅ )₂ F, rather than phosphoranide formation. However, [K(18-crown-6)]F adds to P(C₂ F₅ )₂ (CN) furnishing [K(18-crown-6)][P(C₂ F₅ )₂ (CN)F]. Its structural characterization was successful, despite its tendency to undergo an exchange of substituents, yielding [K(18-crown-6)][P(C₂ F₅ )₂ F₂ ] and presumably [K(18-crown-6)][P(C₂ F₅ )₂ (CN)₂ ]. The latter forms an equilibrium with [K(18-crown-6)]CN and P(C₂ F₅ )₂ (CN) which lies well on side of the phosphane and cyanide salt.

Free Difluorobis(pentafluoroethyl)phosphoranide Ion and Its Ligand Properties

In this contribution, we report on the "free" [P(C₂F₅)₂F₂]^- ion and its ligand properties in transition metal complex chemistry. For this purpose, Ag[P(C₂F₅)₂F₂] was treated with [{(Et₂N)₃P═N}₃P═NHC(CH₃)₃]Cl ([EtP₄H]Cl) to yield [EtP₄H][P(C₂F₅)₂F₂], featuring a weakly coordinating phosphazenium cation. Due to the weak interaction between the cation and anion, the [P(C₂F₅)₂F₂]^- ion meets the so-called pseudo-gas-phase conditions. To determine the Tolman electronic parameter, [EtP₄H][Ni(CO)₃{P(C₂F₅)₂F₂}] was prepared from [EtP₄H][P(C₂F₅)₂F₂] and [Ni(CO)₄], facilitating the classification of the P(C₂F₅)₂F₂ moiety as a moderately π-acidic ligand. By treatment of [EtP₄H][P(C₂F₅)₂F₂] with [AuCl(tht)], the neutral tetrahydrothiophene ligand was substituted by the phosphoranide ion, yielding [EtP₄H][AuCl{P(C₂F₅)₂F₂}]. When Ag[P(C₂F₅)₂F₂] was treated with [AuCl(tht)], on the other hand, the chloride was substituted. Transmetalation reactions of this type proved to be an efficient transfer method of the P(C₂F₅)₂F₂ moiety, as further demonstrated by the reactions of Ag[P(C₂F₅)₂F₂] with [FeCl(CO)₂Cp], [FeCl(CO)₂Cp*], and [PdCl₂(NCMe)₂]. Surprisingly, P(C₂F₅)₂F demonstrated fluorinating abilities toward [FeCl(CO)₂Cp], [FeCl(CO)₂Cp*], [AuCl(tht)], and [PdCl₂(NCMe)₂]. Apparently, fluorido transition metal complexes were generated in situ under the formation of P(C₂F₅)₂Cl. The fluorido iron and palladium complexes transfer their fluoride ions onto P(C₂F₅)₂F, yielding the respective phosphoranido complexes, featuring the P(C₂F₅)₂F₂ moiety.

Difluorobis(pentafluoroethyl)phosphoranide: A Promising Building Block for Phosphoranidometal Complexes

Despite the fact that different metal tetrafluorophosphoranides, M[PF₄] (M = Cs, Ag, K), decompose readily, we successfully enhanced the stability of such species by the replacement of two fluorine atoms with electron withdrawing pentafluoroethyl groups. Thus, AgF adds to P(C₂F₅)₂F, yielding Ag[P(C₂F₅)₂F₂], which served as a starting material for the synthesis of mono-, bis-, and tris[difluorobis(pentafluoroethyl)phosphoranido]silver complexes. Addition of 2,2'-bipyridine allowed for the isolation of stable [Ag(bipy){P(C₂F₅)₂F₂}], whereas the reaction with the chlorides [NMe₄]Cl and CoCl₂ afforded the bis- and trisphosphoranidoargentates [NMe₄][Ag{P(C₂F₅)₂F₂}₂(OEt₂)] and [Co(NCMe)₆][Ag{P(C₂F₅)₂F₂}₃]·2MeCN, respectively. Altogether, the difluorobis(pentafluoroethyl)phosphoranido moiety serves as a novel, small, noncyclic phosphoranido ligand. It provided access to the first homoleptic phosphoranidometal complex, [Co(NCMe)₆][Ag{P(C₂F₅)₂F₂}₃]·2MeCN, which itself features the unusual structural motif of an [AgX₃]^2- ion.

Tris(pentafluoroethyl)difluorophosphorane: A Versatile Fluoride Acceptor for Transition Metal Chemistry

Fluoride abstraction from different types of transition metal fluoride complexes [Ln MF] (M=Ti, Ni, Cu) by the Lewis acid tris(pentafluoroethyl)difluorophosphorane (C2 F5 )3 PF2 to yield cationic transition metal complexes with the tris(pentafluoroethyl)trifluorophosphate counterion (FAP anion, [(C2 F5 )3 PF3 ]- ) is reported. (C2 F5 )3 PF2 reacted with trans-[Ni(iPr2 Im)2 (ArF )F] (iPr2 Im=1,3-diisopropylimidazolin-2-ylidene; ArF =C6 F5 , 1 a; 4-CF3 -C6 F4 , 1 b; 4-C6 F5 -C6 F4 , 1 c) through fluoride transfer to form the complex salts trans-[Ni(iPr2 Im)2 (solv)(ArF )]FAP (2 a-c[solv]; solv=Et2 O, CH2 Cl2 , THF) depending on the reaction medium. In the presence of stronger Lewis bases such as carbenes or PPh3 , solvent coordination was suppressed and the complexes trans-[Ni(iPr2 Im)2 (PPh3 )(C6 F5 )]FAP (trans-2 a[PPh3 ]) and cis-[Ni(iPr2 Im)2 (Dipp2 Im)(C6 F5 )]FAP (cis-2 a[Dipp2 Im]) (Dipp2 Im=1,3-bis(2,6-diisopropylphenyl)imidazolin-2-ylidene) were isolated. Fluoride abstraction from [(Dipp2 Im)CuF] (3) in CH2 Cl2 or 1,2-difluorobenzene led to the isolation of [{(Dipp2 Im)Cu}2 ]2+ 2 FAP- (4). Subsequent reaction of 4 with PPh3 and different carbenes resulted in the complexes [(Dipp2 Im)Cu(LB)]FAP (5 a-e, LB=Lewis base). In the presence of C6 Me6 , fluoride transfer afforded [(Dipp2 Im)Cu(C6 Me6 )]FAP (5 f), which serves as a source of [(Dipp2 Im)Cu)]+ . Fluoride abstraction of [Cp2 TiF2 ] (7) resulted in the formation of dinuclear [FCp2 Ti(μ-F)TiCp2 F]FAP (8) (Cp=η5 -C5 H5 ) with one terminal fluoride ligand at each titanium atom and an additional bridging fluoride ligand.

All-carbon phosphoranes via difluorocarbene trapping

A reaction of intramolecularly disposed phosphonium and phenoxide (or thiophenoxide) fragments with difluorocarbene affording all-carbon λ⁵-phosphoranes is described.

Activation of Acetonitrile with (C2 F5 )3 PF2 and Amines

Acetonitrile is deprotonated by a combination of the strong Lewis acid (C₂ F₅ )₃ PF₂ and triethylamine. The resulting cyanomethyl function is bound to the phosphorus moiety, affording the highly stable salt [HNEt₃ ][P(C₂ F₅ )₃ F₂ (CH₂ CN)]. Salt metathesis reactions furnished the corresponding [Cu(MeCN)₂ ]⁺ and [Ag(MeCN)]⁺ derivatives in which the CH₂ CN substituent of the anion [P(C₂ F₅ )₃ F₂ (CH₂ CN)]^- coordinates to the metal. An investigation of the gas separation capability of the silver salt [Ag(MeCN)][P(C₂ F₅ )₃ F₂ (CH₂ CN)] shows an uptake of 1.7 equivalents of isobutene from a propane/isobutene mixture. The reaction of (C₂ F₅ )₃ PF₂ with acetonitrile and diethylamine furnishes [P(C₂ F₅ )₃ F₂ {NHC(CH₃ )NEt₂ }]-a phosphate featuring an amidine ligand which formally results from hydroamination of acetonitrile by HNEt₂ . Exchange of HNEt₂ with the primary amines H₂ NPh and H₂ NBu leads to comparable amidine salts that exhibit a solvent-dependent conformational isomerism.

Tandem dihetero-Diels–Alder and Huisgen cycloaddition reactions. Synthesis, crystal structure and hydrolysis of the novel cage phosphoranes

The reaction of 2-(1-phenylvinyloxy)benzo-1,3,2-dioxaphosphole with activated carbonyl compounds leads to the stereoselective formation of cage phosphoranes.

Synthesis of Functional Bis(pentafluoroethyl)silanes (C2 F5 )2 SiX2 , with X=H, F, Cl, Br, OPh, and O2 CCF3

As recently shown, the introduction of pentafluoroethyl functionalities into silicon compounds is of general interest due to an enhanced Lewis acidity of the resulting species. By this means, the synthesis of previously inaccessible hypervalent silicon derivatives is enabled. While an easy access to tris(pentafluoroethyl)silanes has already been published, synthetic strategies for the selective preparation of bis derivatives are yet unknown. In this contribution, a convenient protocol for the synthesis of functional bis(pentafluoroethyl)silicon compounds is presented. These compounds represent precursors for the synthesis of pentafluoroethylated polysiloxanes. Furthermore, they prove to be resistant to oxonium cations, which is a key feature for the preparation of stable pentafluoroethylsilic acids. Treatment of dichlorodiphenoxysilane with in situ generated pentafluoroethyl lithium leads to the corresponding bis(pentafluoroethyl)silane in high yields. (C₂ F₅ )₂ Si(OPh)₂ serves as a starting material for further functionalized bis(pentafluoroethyl)silanes. These silanes have been isolated and their reactivity towards N bases studied. The pronounced Lewis acidity of the obtained compounds has been documented by the formation of octahedral adducts with nitrogen donors such as 1,10-phenanthroline and acetonitrile.

Comparative assessment of the environmental hazards of and exposure to perfluoroalkyl phosphonic and phosphinic acids (PFPAs and PFPiAs): Current knowledge, gaps, challenges and research needs

Perfluoroalkyl phosphonic and phosphinic acids (PFPAs and PFPiAs) are sub-groups of per- and polyfluoroalkyl substances (PFASs) that have been commercialized since the 1970s, particularly as defoamers in pesticide formulations and wetting agents in consumer products. Recently, C4/C4 PFPiA and its derivatives have been presented as alternatives to long-chain PFASs in certain applications. In this study, we systematically assess the publicly available information on the hazardous properties, occurrence, and exposure routes of PFPAs and PFPiAs, and make comparisons to the corresponding properties of their better-known carboxylic and sulfonic acid analogs (i.e. PFCAs and PFSAs). This comparative assessment indicates that [i] PFPAs likely have high persistence and long-range transport potential; [ii] PFPiAs may transform to PFPAs (and possibly PFCAs) in the environment and biota; [iii] certain PFPAs and PFPiAs can only be slowly eliminated from rainbow trout and rats, similarly to long-chain PFCAs and PFSAs; [iv] PFPAs and PFPiAs have modes-of-action that are both similar to, and different from, those of PFCAs and PFSAs; and [v] the measured levels of PFPAs/PFPiAs in the global environment and biota appear to be low in comparison to PFCAs and PFSAs, suggesting, for the time being, low risks from PFPAs and PFPiAs alone. Although risks from individual PFPAs/PFPiAs are currently low, their ongoing production and use and high persistence will lead to increasing exposure and risks over time. Furthermore, simultaneous exposure to PFPAs, PFPiAs and other PFASs may result in additive effects necessitating cumulative risk assessments. To facilitate effective future research, we highlight possible strategies to overcome sampling and analytical challenges.

Synthesis, crystal structure and hydrolysis of novel isomeric cage (P–C/P–O)-phosphoranes on the basis of 4,4,5,5-tetramethyl-2-(2-oxo-1,2-diphenylethoxy)-1,3,2-dioxaphospholane and hexafluoroacetone

New rearrangement of P–C-isomer to P–O-isomer in cage phosphoranes series with a high stereoselectivity (>96%) is revealed.

Perfluoropropenyl-containing phosphines from HFC replacements

A series of new perfluoropropenyl-containing phosphines of the type R3-nP(E-CF[double bond, length as m-dash]CFCF3)n (R = Ph, iPr, n = 1, 2; R = tBu, n = 2) have been prepared from the reaction of the hydrofluoroolefin Z-CF3CF[double bond, length as m-dash]CFH (HFO-1225ye) with base and the appropriate chlorophosphine, while reaction with Cl2PCH2CH2PCl2 gave (CF3CF[double bond, length as m-dash]CF)2PCH2CH2P(CF[double bond, length as m-dash]CFCF3)2, the first example of a bidentate perfluoroalkenyl-containing phosphine. An alternative route to these phosphines based on the room- or low-temperature deprotonation of CF3CF2CH2F (HFC-236ea) gives mainly the E-isomer, but also a small amount of the Z-isomer, the ratio of which depends on the reaction temperature. All of the phosphines could be readily oxidised with either H2O2 or urea·H2O2, and the phosphine selenides R3-nP(Se)(E-CF[double bond, length as m-dash]CFCF3)n (R = Ph, n = 1,2; R = iPr, n = 1; R = tBu, n = 2) were also prepared. The steric and electronic properties of these ligands were determined based on their platinum(ii), palladium(ii) and molybdenum carbonyl complexes. The crystal structures of (CF3CF[double bond, length as m-dash]CF)2PCH2CH2P(CF[double bond, length as m-dash]CFCF3)2, (CF3CF[double bond, length as m-dash]CF)2P(O)CH2CH2P(O)(CF[double bond, length as m-dash]CFCF3)2, iPr2P(Se)(CF[double bond, length as m-dash]CFCF3)2, trans-[PtCl2{Ph(3-n)P(E-CF[double bond, length as m-dash]CFCF3)n}2] (n = 1 or 2), trans-[PdCl2{R2P(E-CF[double bond, length as m-dash]CFCF3)}2] (R = Ph, iPr) and [Mo(CO)4{(CF3CF[double bond, length as m-dash]CF)2PCH2CH2P(CF[double bond, length as m-dash]CFCF3)2}] are reported.