Fluorous Phosphine Research Articles

Phosphorus-Recycling Wittig Reaction: Design and Facile Synthesis of a Fluorous Phosphine and Its Reusable Process in the Wittig Reaction.

This study shows that phosphorus sources can be recycled using the appropriate fluorous phosphine in the Wittig reaction. The designed fluorous phosphine, which has an ethylene spacer between its phosphorus atom and the perfluoroalkyl group, was synthesized from air-stable phosphine reagents. The synthesized phosphine can be used for the Wittig reaction process to obtain various alkenes in adequate yields and stereoselectivity. The concomitantly formed fluorous phosphine oxide was extracted from the reaction mixture using a fluorous biphasic system. The fluorous phosphine was regenerated by reducing the fluorous phosphine oxide with diisobutylaluminum hydride. Finally, a series of gram scale phosphorus recycling processes were performed, which included the Wittig reaction, separation, reduction, and reuse.

ChemInform Abstract: Synthesis and Applications of Fluorous Phosphines

AbstractReview: 63 refs.

Synthesis and applications of fluorous phosphines

The synthesis, some of the properties and the applications of fluorous phosphines in biphasic, organometallic and organo-catalysis were reviewed.

A phase based approach to insulated molecular wires: Diplatinum octatetraynediyl complexes bearing fluorous trialkylphosphine ligands

Reactions of [(tetrahydrothiophene)Pt(C6F5)μ-Cl]2 and fluorous phosphines P((CH2)mRfn)3 (Rfn = (CF2)n−1CF3; m/n = a, 2/8; b, 3/8; c, 3/10) afford the chloride complexes trans-(C6F5)((Rfn(CH2)m)3P)2PtCl (8a-c, 40–74%), which upon treatment with butadiyne and CuI (cat.) in HNEt2/CF3C6H5 give trans-(C6F5)((Rfn(CH2)m)3P)2Pt(CC)2H (9a-c, 44–64%). Subsequent reactions with oxygen and CuCl/TMEDA in acetone yield the title complexes trans,trans-(C6F5)((Rfn(CH2)m)3P)2Pt(CC)4Pt(P((CH2)mRfn)3)2(C6F5) (10a-c, 35–52%). All platinum complexes exhibit CF3C6F11/toluene partition coefficients of >99:<1. The crystal structure of 8b shows that the perfluoroalkyl groups segregate into fluorous domains. It was therefore thought that the perfluoroalkyl groups in 10a-c would aggregate about the polyynediyl chain. However, these adducts could not be crystallized. Electrochemical oxidations of 10a-c give radical cations that are much less stable than trialkyl and triarylphosphine analogs.

Activation of Single-Component Nickel(II) Polyethylene Catalysts via Phase Transfer of Fluorous Phosphine Ligands.

The nickel salicylaldiminato phosphine complexes [1,2,3-C6H3(9-anthracenyl)O(CH═N(2,6-C6H3(iPr)2)]Ni(Me)[P(4-C6H4R)3] (4; R = a, (CH2)2Rf8; b, (CH2)3Rf8; c, H (Rf8 = (CF2)7CF3)) are prepared from the corresponding phosphines 3a-c and nickel NCMe adduct (46-68%). These are applied as catalysts for ethylene polymerization in toluene and fluorous/toluene liquid/liquid biphasic mixtures. Under the latter conditions, the fluorous phosphines 3a,b that must dissociate to generate the active catalyst migrate to the fluorous phase (partition coefficients 97.5:2.5 and 66.6:33.4 vs <0.5:>99.5 for 4a,b). Catalysts 4a,b show marked accelerations under biphasic conditions, but 4c (which has a lipophilic phosphine ligand) does not. Under all conditions, 4a,b are faster catalysts than the Ni(Ph)(PPh3) analogue, a previously reported benchmark.

Crystal Structure and Computational Investigation of an Analogue of Grubbs’ Second Generation Catalyst with a Fluorous Phosphine

A fluorous phosphine analogue of Grubbs' second generation olefin metathesis catalyst, (H(2)IMes)((R(f8)(CH(2))(2))(3)P)(Cl)(2)Ru(=CHPh) (1; H(2)IMes/R(f8) = 1,3-dimesityl-4,5-dihydroimidazol-2-ylidene/(CF(2))(7)CF(3)) is crystallized and the X-ray structure analyzed in detail. The bond lengths and angles about ruthenium are compared to those of two solvates and five derivatives of Grubbs' second generation catalyst. All exhibit distorted square pyramidal geometries in which the alkylidene ligands occupy apical positions, and geometric trends are interpreted with the help of density functional calculations. The perfluoroalkyl groups (1) exhibit helical conformations, as manifested by various torsional relationships, (2) segregate in the lattice, and (3) align in pairs of opposite helical chiralities.

Phase Transfer Activation of Fluorous Analogs of Grubbs’ Second-Generation Catalyst: Ring-Opening Metathesis Polymerization

Grubbs’ second-generation alkene metathesis catalyst and the fluorous analog (H2IMes)((Rf8(CH2)2)3P)(Cl)2Ru(═CHPh) (1; H2IMes/Rf8 = 1,3-dimesityl-4,5-dihydroimidazol-2-ylidene/(CF2)7CF3) catalyze ring-opening metathesis polymerizations of norbornene at essentially identical rates (CDCl3, RT). However, dramatic accelerations can be observed with 1 in the presence of the fluorous solvent perfluoro(methylcyclohexane) (PFMC). The fluorous phosphine (Rf8(CH2)2)3P must first dissociate from 1 to generate the 14-valence-electron intermediate that begins the catalytic cycle and should be scavenged by the PFMC phase (PFMC/toluene partition coefficient >99.7:<0.3). This would allow alkenes to more effectively compete for active catalyst. However, faster rates are seen only when 1 (partition coefficient 39.6:60.4) is added as a PFMC solution or a PFMC/CDCl3 biphase mixture, as opposed to CDCl3 solution, and possible additional contributing factors are analyzed. Analogous effects are observed with a 7-oxanorbornene-b...

Thermomorphic fluorous phosphines as organocatalysts for Michael addition reactions

The fluorous phosphines P[(CH 2) m R f n ] 3 (R f n = (CF 2) n −1CF 3; m/ n = 2/8, 3/8, 3/10) are efficient nucleophilic catalysts of Michael addition reactions. They can be easily recycled based upon their highly temperature-dependent solubilities (thermomorphism), with recovery by simple liquid/solid phase separation. The phosphonium salt formed by reaction of the nucleophilic phosphine with the α,β-unsaturated system appears to be a significant component of the catalyst rest state.

Fluorous triosmium clusters. Preparation, properties, and reactivity of Os 3(CO) 11{P(CH 2CH 2(CF 2) 5CF 3) 3} and Os 3(CO) 10{P(CH 2CH 2(CF 2) 5CF 3) 3} 2. Crystal structure of Os 3(CO) 9(PPh 3) 2{P(CH 2CH 2(CF 2) 5CF 3) 3}. Ring opening metathesis polymerization of norbornene by (μ-H) 2Os 3(CO) 9{P(C 6H 4-4-CH 2CH 2(CF 2) 7CF 3)

Several fluorous phosphine ligand triosmium carbonyl cluster derivatives, e.g., Os 3(CO) 11{P(CH 2CH 2(CF 2) 5CF 3) 3} ( 1) and Os 3(CO) 10{P(CH 2CH 2(CF 2) 5CF 3) 3} 2 ( 2) have been synthesized in order to assess their properties in fluorocarbon, or fluorous, phases. Cluster 1 reacts with PPh 3 above 100 °C to substitute one or two carbonyl ligands and provide the mixed ligand derivatives Os 3(CO) 10(PPh 3){P(CH 2CH 2(CF 2) 5CF 3) 3}, ( 3) and Os 3(CO) 9(PPh 3) 2{P(CH 2CH 2(CF 2) 5CF 3) 3}, ( 4). The crystal structure of 4 has been determined by single crystal X-ray diffraction. At circa 102 °C and 1 atm H 2, 1 will form the unsaturated compound (μ-H) 2Os 3(CO) 9{P(CH 2CH 2(CF 2) 5CF 3) 3} ( 5) in modest yield. Compound 5 and the related compound (μ-H) 2Os 3(CO) 9{P(C 6H 4-4-CH 2CH 2(CF 2) 7CF 3) 3} ( 6) are obtained more cleanly by treating (μ-H) 2Os 3(CO) 10 with the corresponding fluorous phosphine ligand at room temperature followed by decarbonylation in refluxing hexane. Compounds 1– 6 have been characterized by employment of IR and 1H NMR and 31P NMR spectroscopy. Partition coefficients between fluorous and non-fluorous solvents have been determined. The use of 6 as a ROMP catalyst with norbornene in a variety of organic and universal solvents is described.

Binuclear ruthenium complexes of fluorous phosphine ligands: Synthesis, properties, and biphasic catalytic activity. Crystal structure of [Ru(μ-O 2CMe)(CO) 2P(CH 2CH 2(CF 2) 5CF 3) 3] 2

The fluorocarbon soluble, binuclear ruthenium(I) complexes [Ru(μ-O 2CMe)(CO) 2L F] 2, where L F is the perfluoroalkyl substituted tertiary phosphine, P(C 6H 4-4-CH 2CH 2(CF 2) 7CF 3) 3, or P(CH 2CH 2(CF 2) 5CF 3) 3, were synthesized and partition coefficients for the complexes in fluorocarbon/hydrocarbon biphases were determined. Catalytic hydrogenation of acetophenone to 1-phenylethanol in benzotrifluoride at 105 °C occured in the presence of either [Ru(μ-O 2CMe)(CO) 2P(C 6H 4-4-CH 2CH 2(CF 2) 7CF 3) 3] 2 ( 1) or [Ru(μ-O 2CMe)(CO) 2P(CH 2CH 2(CF 2) 5CF 3) 3] 2 ( 2). The X-ray crystal structure of [Ru(μ-O 2CMe)(CO) 2P(CH 2CH 2(CF 2) 5CF 3) 3] 2 was determined. The compound exhibited discrete regions of fluorous and non-fluorous packing.

Comparative properties of fluorous phosphine ligand complexes: W(CO) 5L F. Crystal structure of W(CO) 5P(C 6H 4-4-CH 2CH 2(CF 2) 7CF 3) 3

The compounds W(CO) 5P(C 6H 4-4-CH 2CH 2(CF 2) 7CF 3) 3 ( 1) and W(CO) 5P(CH 2CH 2(CF 2) 5CF 3) 3 ( 2) were synthesized in order to probe the electronic and physical effects of ligation by perfluorocarbon substituted tertiary phosphine ligands in a W(CO) 5L complex. The π-accepting ability of the fluorous phosphines was found to rank with non-fluorous comparators as P(CH 2CH 2(CF 2) 5CF 3) 3 > P(C 6H 4-4-CH 2CH 2(CF 2) 7CF 3) 3 > PPh 3 > P( p-tolyl) 3 > P( n-octyl) 3. The X-ray crystal structure of W(CO) 5P(C 6H 4-4-CH 2CH 2(CF 2) 7CF 3) 3 shows strong intermolecular association of fluorous components but confirms that the para fluorocarbon subtituents have an insignificant effect on the tungsten coordination environment. Partition coefficients (toluene/perfluoromethylcyclohexane) were measured for compounds 1 and 2.

Catalysis of Intramolecular Morita–Baylis–Hillman and Rauhut–Currier Reactions by Fluorous Phosphines; Facile Recovery by Liquid/Solid Organic/Fluorous Biphase Protocols Involving Precipitation, Teflon® Tape, and Gore‐Rastex® Fiber

AbstractThe fluorous phosphine P[(CH2)3Rf8]3 [1, Rf8=(CF2)7CF3; 10 mol%] catalyzes intramolecular Morita–Baylis–Hillman reactions of O=CH(CH2)nCHCH(CO)R [n/R=2/Ph (2a), 2/S‐i‐Pr, 3/p‐tol] in acetonitrile at 60–72 °C. Upon cooling, 1 precipitates and is recycled. The products HOCH(CH2)nCHC(CO)R are isolated from the supernatant (78–96%). The educt i‐PrS(CO)CHCH(CH2)2CHCH(CO)S‐i‐Pr similarly undergoes a Rauhut–Currier reaction to give i‐PrS(CO)CH2CH(CH2)2CHC(CO)S‐i‐Pr (71–73%). In the case of 2a, reactions are also conducted in the presence of Teflon® tape or Gore‐Rastex® fiber. The catalyst now precipitates onto the fluoropolymer support, mechanically facilitating recycling. For each reaction, three to five cycles are conducted. HPLC or GC monitoring of the rates show low activity losses, with Gore‐Rastex® fiber giving better results than Teflon® tape, presumably due to a higher surface area.

Direct, facile synthesis of acyl azides and nitriles from carboxylic acids using bis(2-methoxyethyl)aminosulfur trifluoride

A mild, efficient, and practical method for the one-step synthesis of acyl azides from carboxylic acids using bis(2-methoxyethyl)aminosulfur trifluoride is described. The reaction was easily extended to the synthesis of the corresponding nitriles by the inclusion of phosphorous reagents. The method can be applied to the synthesis of optically active nitriles in high yields, and is compatible with fluorous phosphines.

Syntheses and Reactivity of Analogues of Grubbs’ Second Generation Metathesis Catalyst with Fluorous Phosphines: A New Phase‐Transfer Strategy for Catalyst Activation

AbstractReactions of the bis(pyridine) complex (H2IMes)(Py)2(Cl)2Ru(=CHPh), (H2IMes=1,3‐dimesityl‐4,5‐dihydroimidazol‐2‐ylidene) and the highly fluorophilic phosphines [Rfn(CH2)m]3P [1; m/n=a, 2/6; b, 2/8; c, 2/10; d, 3/8; Rfn=CF3(CF2)n−1] give (H2IMes){[Rfn(CH2)m]3P}(Cl)2Ru(=CHPh) (4a–d, 64–78 %), which are analogues of Grubbs’ second generation alkene metathesis catalyst. Complexes 4a,b are effective catalysts for conversions of 1,6‐dienes to cyclopentenes under monophasic and biphasic conditions in CH2Cl2 and CH2Cl2/fluorous solvent mixtures. The latter generally exhibit rate accelerations, which are believed to arise from phase transfer of the dissociated fluorous phosphine, allowing the substrate to better compete for the fourteen valence‐electron intermediate. Only modest effects are observed when Grubbs’ second generation catalyst is similarly reacted. The most fluorophilic catalyst, 4c, can be recycled by extracting the reaction mixtures with perfluoro(methylcyclohexane).

Crystal structure of an unusual bis(fluorous phosphine) ruthenium(III) complex derived from a fluorous Grubbs’ catalyst

Attempted crystallization of (H 2IMes)RuCl 2(P(CH 2CH 2R f8) 3)( CHPh) (H 2IMes = 1,3-dimesityl-4,5-dihydroimidazol-2-ylidene; R f8 = (CF 2) 7CF 3) in air affords dark red needles of the octahedral ruthenium(III) salt [H 3IMes] + trans-[RuCl 4(P(CH 2CH 2R f8) 3) 2] −, which is structurally characterized. Only crystal structures of square planar adducts of fluorous alkylphosphines have been determined to date. The bond lengths and angles associated with the cation and RuCl 4L 2 core are similar to those in related compounds. The lattice exhibits fluorous domains unlike those in square planar complexes, and the ponytail conformations are analyzed in detail. The NC HN proton of the cation is hydrogen bonded to two chloride ligands of the anion, and the CH 2CH 2 “backside” is directed at two chloride ligands of another anion, leading to non-fluorous channels in the lattice.

Fluorous phase-transfer activation of catalysts: application of a new rate-enhancement strategy to alkene metathesis

Reactions of the bis(pyridine) complex (H2IMes)(Py)2(Cl)2Ru(=CHPh) and fluorous phosphines P(CH2CH2R(fn))3 (n = a, 6; b, 8; c, 10; R(fn) = (CF2)(n-1)CF3) give (H2IMes)(P(CH2CH2R(fn))3)(Cl)2Ru(=CHPh) (2a-c, 64-73%), which are analogs of Grubbs' second generation catalyst and effective alkene metathesis catalysts under organic monophasic and fluorous/organic biphasic conditions. The latter give rate accelerations, which are believed to arise from phase transfer of the dissociated fluorous phosphine.

Light, Medium, and Heavy Fluorous Triarylphosphines Exhibit Comparable Reactivities to Triphenylphosphine in Typical Reactions of Triarylphosphines

[reaction: see text] The relative reactivities of triphenylphosphine (PPh(3)) and three fluorous triarylphosphines [(p-R(F)(CH(2))(2)C(6)H(4))(n)PPh(3)(-)(n), where n = 1-3] have been compared in internal competition experiments. Product ratios were determined by (31)P NMR spectroscopy. The four phosphines have about the same reactivities in oxidation, alkylation, and Staudinger reactions and give comparable yields in a preparative Mitsunobu reaction. Previously observed rate and yield differences in Staudinger reactions of the fluorous phosphines are attributed to solubility effects, not reactivity differences. A light fluorous phosphine [(p-C(8)F(17)(CH(2))(2)C(6)H(4))PPh(2)] outperforms a commercially available resin-bound phosphine in a competitive benzylation experiment by a factor of about 4.

Parallel synthesis and study of fluorous biphasic partition coefficients of 1H,1H,2H,2H-perfluoroalkylsilyl derivatives of triphenylphosphine: a statistical approach.

A library of fluorous, (1H,1H,2H,2H-perfluoroalkyl)silyl-substituted derivatives of triphenylphosphine, Ph(3-a)P[C(6)H(5-y)[SiMe(3-b)(CH(2)CH(2)C(x)F(2x+1))(b)](y)-pos](a) [a = 1-3; b = 1-3; x = 4, 6, 8, or 10; pos = 3, 4 (y = 1) or 3,5 (y = 2)], was prepared using parallel synthetic techniques. Upon variation of these four parameters, a total of 108 different fluorous phosphines can be synthesized. Using factorial design, 37 phosphines were selected and their partition coefficients in the typical fluorous biphasic solvent system PFMCH/toluene (PFMCH = perfluoromethylcyclohexane) determined. By fitting of the partition coefficient data to linear functions of the parameters a, b, and x, the partition coefficients of the remaining 71 fluorous phosphines, which were not prepared, could be predicted. Using this approach, some unexpected trends in the dependence of the partition coefficient on variations of the four parameters became clear, resulting in a better understanding of the optimum fluorous substitution pattern for obtaining the highest partition coefficient (P). In this way, the partition coefficient was increased by 2 orders of magnitude, i.e., from the initial value P = 7.8 for 1(3, 2, 6, C4) to P > 238 for 1(2, 3, 6, C3C5). Para- and 3,5-substituted phosphines showed irregular behavior in the sense that elongation or increase of the number of perfluoroalkyl tails did not necessarily lead to higher partition coefficients. Particularly high values were found for phosphines containing a total of 72 fluorinated carbon atoms on the meta position(s) of the aryl rings. Linear relationships were found between the predicted log P of 1(a, b, x, C4) and the experimentally determined log P values of fluorous diphosphines [CH(2)P[C(6)H(4)(SiMe(3-b)(CH(2)CH(2)C(6)F(13))(b))-4](2)](2) and monophosphines Ph(3-a)P(C(6)H(4)(CH(2)CH(2)C(6)F(13))-4)(a). One of the most fluorophilic phosphines, i.e., 1(3, 1, 8, C3C5), was applied and efficiently recycled in rhodium-catalyzed, fluorous hydrosilylation of 1-hexene by HSiMe(2)Ph using PFMCH as the fluorous phase and the substrates as the organic phase. It was demonstrated that a higher partition coefficient of the ligand in PFMCH/toluene at 0 degrees C indeed resulted in less leaching of both the catalyst and the free ligand during phase separation.

Synthesis and Properties of Fluorous Arenes and Triaryl Phosphorus Compounds with Branched Fluoroalkyl Moieties (“Split Pony Tails”).

AbstractFor Abstract see ChemInform Abstract in Full Text.

Direct Microwave Synthesis ofN,N′-Diacylhydrazines and Boc-Protected Hydrazides by in situ Carbonylations under Air

Palladium-catalyzed hydrazidocarbonylations of aryl iodides and bromides were performed by controlled microwave irradiation, employing Mo(CO)6 as a convenient CO source. A fluorous phosphine ligand was succesfully used to recycle the catalytic system. Finally, dehydration of a diacylhydrazine to the corresponding 1,3,4-oxadiazole was achieved with POCl3 in a one-pot procedure.