Studies on trichloromethyl phosphorus fluorides

J. Inorg. Nucl. Chem., 1965, Vol. 27, pp. 1281 to 1287. PergamonPress Ltd. Printed in Northern Ireland

STUDIES ON TRICHLOROMETHYL FLUORIDES 1

PHOSPHORUS

J. F. NIxoN* University Chemical Laboratory, LensfieldRoad, Cambridge (Received 30 September 1964; in revised form 2 January 1965)

Al~traet--Fluorination of dichlorotrichloromethylphosphine with antimony trifluoride produces only difluorotrichloromethylphosphine, which reacts with 1 mole of chlorine or bromine to form the volatile solid difluorodihalogenophosphoranes CClaPFsX2 (X = C1, Br.). Trichloromethyltetrafluorophosphorane is prepared by the action of arsenic trifluoride on either dichlorodifluorotrichloromethylphosphorane or trichloromethyltetrachlorophosphorane. The sip and 19F nuclear magnetic resonance spectra of these compounds are presented, and the likely stereoehemistry of the pentavalent phosphorus derivatives is discussed. reacts with antimony trifluoride to produce only difluorotrichloromethylphosphine CClsPF~;

DICHLOROTRICHLOROMETHYLPHOSPHINE

3CClaPC12 ÷ 2SbF a ~ 3CCIaPF 2 ÷ 2SbCI 3

(1)

This contrasts with the behaviour of alkyl and aryl dichlorophosphines, which under similar conditions form the pentavalent tetrafluorophosphoranes RPF 4 via a redox reaction :~2) 3RPC12 + 4SbF a ~ 3RPF a + 2SbC13 + 2Sb (2) The inherent instability of alkyl difluorophosphines is evidenced by the ease with which they disproportionate at ambient temperatures to the corresponding tetrafluorophosphoranes and cyclo-polyphosphines, ta) 2nRPF 2 ~ nRPF 4 + (RP),,

(3)

Previous literature reports of the compounds C2HsPF 2 and C2HnPFCI, t4) said to result from the fluorination of C2HsPCla, have recently been shown to be erroneous, and the products have been identified as C2HsPF 4 and C~HsPOF ~ respectively, tSJ The completion of the fluorination at the fluorophosphine stage when a more electronegative group e.g. perfluoroalkyl/a,6) alkoxy, tT) or dialkylaminotS) is attached to phosphorus, suggests that the substituents reduce the availability of the lone pair * Present address: Chemistry Department, St. Salvators College, University of St. Andrews, Fife, Scotland. ~1~For a preliminary report of this work see J. F. NIXON, Chem. & Industr. 1555 (1963). ~2)R. SCHMUTZLER,Inorg. Chem. 3, 410 (1964). is) V. N. KULAKOVA,YU. M. ZINOVEV and L. Z. SOaOROVS~:H,Zh. Obshch. Khim. 29, 3957 (1959). ~4~ F. HOVORKAand E. E. WEAVER,A. C. S. Meeting Buffalo (1952). J. R. VAN WAZER, C. F. CALLIS, J. N. SHOOLERYand R. C. JONES, J. Amer. Chem. Soc. 78, 5715 (1956). i~) R. SCHMUTZLER,J. Chem. Soc. 4551 (1964). ~6~A. B. BURG and G. BRENDEL, J. Amer. Chem. Soc. 80, 3198 (1958). J. F. NtxoN, J. Chem. Soc. 777 (1965). R. N. STERLIN,R. D. YATSENKO, L. N. PINKINA and I. L. KNUNVA~zrs,lZV. Akad. Nauk. SSSR. Odtel Khim. Nauk. 1991 (1960). 17~ R. SCHMUTZLER, Chem. Bet. 96, 2435 (1963). ~s~ R. SCnMUTZLER,Inorg. Chem. 3, 415, (1964), J. F. NtxoN and R. G. CAVELL,J. Chem. Soc. In Press. 1281

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on phosphorus to participate in further bonding. Replacement of one proton by chlorine in methyldichlorophosphine is sufficient to result in exclusive formation of chloromethyldifluorophosphine as the fluorination product, ~z) although a nuclear magnetic resonance study ~9) now indicates that this compound slowly disporportionates at room temperature in accordance with Equation (3). The trichloromethyl group is more strongly electron withdrawing, having an estimated electronegativity of 2.76 ~1°) which is comparable with bromine, and as a result difluorotrichloromethylphosphine shows no such tendency to disproportionate. Difluorotrichloromethylphosphine is a colourless liquid melting at 15.8-16.4 ° and boiling at 73.1 ° (est), whose identity is confirmed by its phosphorus nuclear magnetic resonance spectrum, which consists of a very low field 1-2-1 triplet (relative to 85 700 H3PO4 as standard). This low field shift is known from other work to be diagnostic of all trivalent phosphorus fluorides/n) The triplet structure arises from spin-spin coupling with the two fluorine nuclei:. The fluorine nuclear magnetic resonance spectrum consists of a sharp 1-1 doublet. Values of chemical shifts and Jp_~ coupling constants are listed in the Table, and the internal consistency of the values from the two spectra confirms the assignments made. An unusual amine substitution reaction of difluorotrichloromethylphosphine has been the subject of a recent paper. ~12~ The stability of difluorotrichloromethylphosphine enables a study of its reaction with halogens to be undertaken; thus slow warming of a mixture of chlorine (or bromine) and the fluorophosphine leads to the nearly quantitative formation of the colourless, crystalline solid difluorodihalogenotrichloromethylphosphoranes CClzPF2X2 (X = C1, Br). The identity of these compounds was confirmed by 19F and zip n.m.r. spectroscopy (vide infra), and by the closeness of the combining ratios to the expected 1 : 1 value. Both compounds are sufficiently volatile at room temperature to be handled satisfactorily in the high vacuum system, and thus exist in a molecular form which is most likely based on a trigonal bipyramid structure. The analogous addition of chlorine or bromine to phosphorus trifluoride ~13) is known to lead initially to the liquid products PFsC12 and PFzBr 2 which revert to ionic forms on standing: 2PFzC12 ~ (PC14)+ (PF6)Other mixed P(V) chlorofluorides of the type PFs_,C1 n have been discussed recently,~14) but the only related compounds which also contain a phosphorus-carbon linkage are the unstable solids ArPFzC1 (Ar = aryl) formed by chlorination of ArPFzH. ~15~ The dihalogenodifluorotrichloromethylphosphoranes are readily hydrolysed in moist air, and easily decompose on heating. When stored in sealed glass tubes at room temperature, the dibromo-compound readily produces liquid products, but the dichloro-compound appears much more stable, attacking the glass only slowly, and can be recovered unchanged from a fluorotrichloromethane solution which has t~ j. F. NIXON and R. SCHMUTZLER,unpublished observations. ,10~ R. E. KAGARISE, J. Amer. Chem. Soc. 77, 1377 (1955). (lt~ j. F. NIXON and R. SCHMUTZLER,Spectrochim. Acta 20, 1835 (1964). t12~j. F. NIXON, J. Chem. Soc. 2469 (1964). txa} T. KENNEDY and D. S. PAYNE, J. Chem. Soc. 1228 (1959); E. L. MUETTERTIES, T. A. BITHER, i . W. FARLOW and D. D. COFFMANN,J. Inorff. Nucl. Chem. 16, 52 (1961); L. KOLDITZ and A. FELTZ, Z. anorff. Chem. 293, 155 (1957); R. R. HOLMES, J. Chem. Educ. 40, 125 (1963). t141 R. R. HOLMES and W. P. GALLAGHER, Inorff. Chem. 2, 433 (1963). ~'~ M. IVANOVAand A. B. KIRSANOV,Zh. Obshch. Khim. 32, 2592 (1962).

Studies on trichloromethylphosphorus fluorides

1283

stood for several weeks at room temperature. In neither case is there any evidence for an isomeric ionic form. The synthesis of trichloromethyltetrafluorophosphorane, CCI3PFa, from dichlorotrichloromethylphosphine can be accomplished in the two independent routes summarized in the following reaction sequence:

I///

;,CClsPF 2

1I

CCI3PCI2

~- CClsPF2CI2 i I[I

~CC13PC14

v

-~ CCI3PF4

(I : S b F 3,II : C I 2 - IV, III : A s F 3 - V ) . An attemped fluorination of trichloromethyl tetrachlorophosphorane using the solid fluorinating agent antimony trifluoride at 70°, produced only small amounts of the desired compound together with much more volatile products containing POF 3 and C-F material. Under these conditions it appears that the trichloromethyl tetrachlorophosphorane decomposes before the fluorination can be effected. This was confirmed in a subsequent experiment in which trichloromethyl tetrachlorophosphorane produced phosphorus trichloride and carbon tetrachloride when heated alone. When liquid arsenic trifluoride is employed however, the fluorination reaction occurs readily at room temperature producing good yields of trichloromethyltetrafluorophosphorane. 3CClaPCI4 + 4AsF3 --~ 3CCI3PF4 + 4AsCI3 Likewise arsenic trifluoride reacts easily with dichlorodifluorotrichloromethylphosphorane at room temperature to form trichloromethyltetrafluorophosphorane. 3CCIsPF~C12 -- 2AsF 3 --~ 3CClsPF 4 + 2AsCls Vapour pressure measurements on the product of these reactions leads to a normal boiling point of 70°, in good agreement with the only previous literature report/16~ in which the compound was synthesized by the action of hydrogen fluoride on the adduct CCI3PC13+A1C1c.

Nuclear magnetic resonance spectra and stereochemistry of the P(V) fluorides The 31p and 19F chemical shift and JP-v spin-spin coupling constant data for all the trichloromethyl phosphorus compounds studied are listed in Table 1. The triplet structure of the alp n.m.r, spectra of the difluorodihalogenophosphoranes arises from spin coupling with two spectroscopically equivalent fluorine nuclei. Similarly the 19F n.m.r, spectra show a 1-1 doublet, arising from coupling with the 31p nucleus, which also indicates one type of fluorine in these molecules. These observations are consistent with either (a) both fluorine atoms occupying apical positions, or (b) both fluorines occupying equatorial positions, in a trigonal bipyramid model. The observed equivalence could arise from an intramolecular exchange process, but this is thought unlikely in view of the size of the other groups ~1~I. P. KOMKOV,S. Z. IVIN, K. W. KARAWANOVand L. E. SMIRNOV,Zh. Obshch.Khim. 32, 301 (1962).

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J.F. NIXON

attached to phosphorus.* Similar reasoning for the related RaPF 2 and R~PF3 systems, (17) led to internal consistency of the observed ~gF chemical shifts. However it is also worth noting that an intramolecular exchange of fluorine atoms does occur in the PF3C12 system, taT) in which there is apparent equivalence of fluorine atoms at room temperature, but at --80 ° the tgF n.m.r, spectrum shows the typical R2PF 3 TABLE1 alp spectra Compound

~v*

Jv-v(c/s)

Comments

CCI3PF2 CCI3PF~Clz CC13PFzBr2 CClsPF4 CClsPC14 CClsPCI~

--131.0 +7"4 +26"0 +67.0 + 19 -- 147

1290 1090 1100 1120 ---

1-2-1 Triplet 1-2-1 Triplet 1-2-1 Triplet 1--4-6-4-1 Quintet

Compound

¢Ft

Jr-l¢ (c/s)

Comments

CCI3PF2 CC1sPF~CI~ CCI2PFsBra CC13PF~

+88"0 --2"4 --22'8 +67.1

I'F Spectra

1285 1106 1109 1124

1-1 Doublet 1-1 Doublet 1-1 Doublet 1-1 Doublet

* In p.p.m, relative to 85 % HsPO4 as external standard. i" In p.p.m, relative to CCIsF as internal standard. pattern in which two fluorines occupy apical positions of a trigonal bipyramid. The C~ symmetry of PFaC12 has recently been confirmed by an infra-red and Raman studyJ is) From stereochemical considerations, the two fluorine atoms in the CCI3PF~X ~ systems would be expected to occupy apical positions in the trigonal bipyramid model in order to minimize ligand repulsions. Support for this structure comes from the observed 19F chemical shift values which are much closer to the values found for apical fluorines in the 1L2PF3and R3PF2 series than for the corresponding equatorial substituents/17) Indeed the presence of the halogen atoms enhances the downfield shift, and also increases the magnitude of the Jl,-r spin coupling constant. Similar observations have been made on the PFs_,~C1n series of compounds. (m HOLMES(19) has suggested that if the bonding orbitals of the phosphorus atom are considered to be mainly sp2 hybrids in the equatorial plane, and dp hybridized in the apex positions, then because fluorine can participate in p~ -- d, bonding with phosphorus to a greater extent than the other halogens, apical fluorine substitution should partially compensate for the large s to d promotional energy required to form the dp hybrid. The 3tp n.m.r, spectrum of trichloromethyltetrafluorophosphorane shows a 1-4-6 4 1 quintet of lines arising from spin coupling with four apparently equivalent * Intermolecular exchange is ruled out by the presence of spin coupling between the fluorine and phosphorus nuclei. E. L. MUETTERTIES,W. MAHLERand R. SCHMUTZLER, Inorg. Chem. 2, 613 (1963). (is) j. E. GRIFFITHS, R. P. CARTER and R. R. HOLMES, J. Chem. Phys. 41, 863 (1964). (~7~

c18)R. R. HOLMES,Abstracts Paper 13A. 1, 8th International Conference on Coordination Chemistry, Vienna, Sept. 1964.

Studies on trichloromethyl phosphorus fluorides

1285

fluorine atoms. The observed chemical shift value is known from previous work {11) to be indicative of a perhalogenalkyl fluorophosphorane. Similarly the equivalence of fluorine atoms is apparent in the 19F n.m.r, spectrum which exhibits a 1-1 doublet. Other work on RPF 4 systems t~71 favours a trigonal bipyramid structure in which the R- group is in an equatorial position, rather than the tetragonal pyramid with the Rgroup at its apex. Fast positional exchange of fluorine atoms, first suggested by BERRYt2°~ for PFs, thus leads to their observed n.m.r, equivalence. Similar spectroscopic equivalence of ligands is known for Fe(CO)5, t21) PFs, t22~ SOF4, ~3~ and AsFs, t2~) even though the five bonding orbitals in a trigonal bipyramid structure cannot be made equivalent, t2~ It is interesting to note also that although the structure of solid pentaphenyl antimony is a tetragonal pyramid, tz~ the analogous phosphorus compound has recently been shown to be based on a trigonal bipyramid model. {27~ EXPERIMENTAL All the compounds were extremely sensitive to air and moisture, and manipulations were carried out in the high vacuum system. Stopcocks were lubricated with Halocarbon grease when handling the halogens, but usuallly Apiezon grease sufficed. Molecular weight and vapour pressure measurements were made using an immersible tensimeter in conjunction with mercury manometers. Dichlorotrichloromethylphosphine was made by heating white phosphorus and carbon tetrachloride in a sealed tube. t2a~ Antimony trifluoride was resublimed before use, and arsenic trifluoride was carefully fractionated in the vacuum line and stored in sealed ampoules until required. The nuclear magnetic resonance spectra were recorded on a Varian Associates 4300 B spectrometer equipped with a 12 in. magnet with flux stabilization and a Varian 4356 field homogeneity control unit. The fluorine resonance measurements were made at 40 Mc/s, using CCIsF as solvent and internal standard. The samples were sealed in 5 mm o.d. Pyrex tubes which were spun in the magnetic field. Phosphorus spectra were recorded at 16.2 Mc/s with the sample contained in a 10 m m o.d. tube enclosing a 2 m m dia. capillary of 85 ~ H3PO4 as external standard. Calibration of the spectra was done by the normal sideband technique of the resonance of either the compound or the standard. The values quoted are the average of several determinations.

Preparation of difluorotrichloromethylphosphine In a typical experiment, dichlorotrichloromethylphosphine (0"4752 g, 2'157 mmoles), and resublimed antimony trifluoride (0'559 g), were heated at 60 ° for 8 hr in an evacuated sealed tube. Fractional condensation of the volatile products in the vacuum system, led to the recovery of a very small amount of unreacted dichlorotrichloromethylphosphine, and 0"324 g, (1"725 mmoles), of colourless liquid difluorotrichloromethylphosphine, m.p. 15.8-16-4 °, b.p. 73'1 ° (est). Found M = 186"8, P = 16"4 ~ , F = 22-5 ~ ; CC13PF2 requires M = 187.3, P = 16.5 ~ , F = 20.3 ~ . The vapour tension data for both liquid and solid phases and the I.R. spectrum have been published elsewhereJ TM

Reaction between difluorotrichloromethylphosphine and chlorine Difluorotrichloromethylphosphine (0.4331 g, 2"310mmoles), and chlorine (0.2475g, 3.490 mmoles), reacted together in a sealed tube on slow warming from - 1 9 6 ° to room temperature, ~0~ S. BERRY, J. Chem. Phys. 32, 936 (1960). ~1} F. A. COTTON, A. DANTI, J. S. WAUGrt and R. W. FESSENDEN, J. Chem. Phys. 29, 1427 (1958); R. BRAMLEY, B. N. FIGGIS and R. S. NYnOLM, Trans. Faraday Soc. 58, 1893 (1962). ~2~ H. W. GtrrowsKY, D. W. McCALL and C. P. SLICHTER, J. Chem. Phys. 21, 279 (1953). ~2s~F. B. DUDLEY, J. N. SHOOLERY and G. H. CADY, J. Amer. Chem. Soc. 78, 568 (1956). ~4~ E. L. MUETrERTIES and W. D. PHILI_n's, J. Amer. Chem. Soc. 81, 1084 (1959). ~zs~F. A. COTTON, J. Chem. Phys. 35, 228 (1961). ~e~ p. j. WHEATLEY, Proc. Chem. Soc. 251 (1962). t~7~ p. j. WHEATLEY, J. Chem. Soc. 2206 (1964). ~a~ D. PERNER and A. HENGLEIN, Z. Naturforsch. 17b, 703 (1962).

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J . F . NIXON

producing a white solid. The reaction products were separated in the vacuum system into chlorine (0.079 g, 1.119 mmoles), and dichlorodifluorotrichloromethylphosphorane which was trapped out at --45 ° as a crystalline white solid. Found: P = 11-9 ~ , Hydrolysable CI = 27.6~, CCI3PF2CI~ requires P = 12.0 Y/oo,CI = 27.5 ~ . The combining ratios of CI~:CC13PF2 were thus 1:0-98, adding further confirmation to the formulation.

Reaction between difluorotrichloromethylphosphine and bromine Difluorotrichloromethylphosphine (0"5446 g, 2'908 mmoles) and bromine (0"2237 g, 1"400 mmoles) (previously dried over calcium bromide,) reacted together in a sealed tube on warming slowly from --196 ° to room temperature. The bromine colour faded and a white solid appeared on the tube walls. The tube was then cooled to --24 ° and excess difluorotrichloromethylphosphine (0-2847 g, 1"520 mmoles) was pumped away. Thus the combining ratios CC13PF2:Br2 were 1:1'01. The white crystalline solid dibromodifluorotrichloromethylphosphorane moves slowly into the vacuum line at room temperature, and is completely trapped out at --24 °. Found P = 8.68 ~ , Br = 44.9 Y/o; CCI3PF2Br2 requires P = 8.93 ~ , Br = 46.0 ~ .

Reaction between arsenic trifluoride and dichlorodifluorotrichloromethylphosphorane Difluorotrichloromethylphosphine (0.8854 g, 4.728 mmoles) and chlorine (0"3597 g, 5.073 mmoles) reacted together to produce dichlorodifluorotrichloromethylphosphorane (1.1938 g, 4.620 mmoles). This was then sealed off in vacuo with arsenic trifluoride (0"388 g, 2-942 mmoles), and on warming to room temperature the solid dissolved easily from the tube walls. The reaction mixture was left overnight, and then vacuum fractionation of the volatiles produced arsenic trichloride (0.5350 g, 2.950 mmotes), and trichloromethyl tetrafluorophosphorane (0.8922 g, 3"960 mmoles) as the main products, together with a small amount of unreacted dichlorodifluorotrichloromethylphosphorane and traces of silicon tetrafluoride. Found M = 224, P = 1 3 . 4 ~ ; CClsPF4 requires M = 225, P = 13.7~. Vapour tension measurements in the range --16 to 27 ° are well represented by the equation: log10p (mm) = 7"668 -- 1643/T, which leads to a normal boiling point of 70 °, and a Trouton Constant of 21.9 cal/deg, mole, in good agreement with the literature value of 68-690. ~16~ The infra-red spectrum was recorded in the gas phase, using a Perkin-Elmer Infracord spectrometer and KBr optics, and showed the following major bands: 1380 w, 993 vs (P-F) str.), 960 w, 924 vs ( P - F str.), 896 w, 840 (sh), 810 vs (C-C1 str.), 759 w, 712 m, 663 w, 626 m, 573 s(sh), 568 s, 563 s(sh), 552 m and 494 w cm -1.

Reaction between dichlorotrichloromethylphosphine and chlorine A mixture of dichlorotrichloromethylphosphine (0.4487 g, 2.036 mmoles), and chlorine (0.2295 g, 3"236 mmoles) were sealed together in a glass tube and warmed slowly from - 196 ° to room temperature, with formation of a white solid. The tube was opened in the vacuum system, and chlorine (0'0845 g, 1'192 mmoles) was recovered. Thus the combining ratios of CI~:CC18PCI2 are 1:1.004, thus establishing the formula of the involatile trichloromethyltetrachlorophosphoraneJ ~

Reaction of trichloromethyltetrachlorophosphorane

with arsenic trifluoride

Dichlorotrichloromethylphosphine (2'1139g, 9.596mmoles) and chlorine (0.9768g, 13"77 mmoles), reacted smoothly in a glass tube containing three constrictions. After 24 hr the tube was opened in vacuo, and excess chlorine (0.3382 g, 4.670 mmoles) was pumped away. Then arsenic trifluoride (1.5735 g, 11.91 mmoles) (a deliberate deficiency in order to avoid separation difficulties), was condensed on to the residue, and the tube resealed. On warming the mixture from --196 ° to room temperature, the solid tetrachlorophosphorane easily dissolves from the tube walls, and subsequent vacuum fractional condensation of the products showed that all the arsenic trifluoride was consumed. The volatile products were identified as arsenic trichloride (2.1707 g, 11.96 mmoles), which was trapped out at --45 °, and a more volatile fraction stopping at --78 °, which was identified as trichloromethyltetrafluorophosphorane (1.750 g, 7.770 mmoles) by its molecular weight, infrared and IgF n.m.r, spectra, which were identical with the sample obtained from the fluorination of dichl°r°diflu°r°trichl°r°methylph°sph°rane" ~9~ L. D. QuIN and C. H. ROLSTON, J. Org. Chem. 1693 (1958).

Studies on trichloromethyl phosphorus fluorides

1287

Action of Heat on Trichloromethyltetrachlorophosphorane Tricbloromethyltetrachlorophosphorane (1.130 mmoles) was heated in a sealed tube at 140° for 19 hr, and produced 0.2525 g of liquid products which were identified by i.r. spectroscopy as a mixture of carbon tetrachloride and phosphorus trichloride. Mol. Wt. found = 147"5, CC14requires 154.0, and PC13requires 137.4. The two components could not be separated by fraction condensation in the vacuum system, and so the mixture was hydrolysed and the HC1 produced was estimated with standard silver nitrate solution, indicating the presence of 0.69 mmoles of PC13 and 1-02 mmoles of CC14. In addition a small amount (31"8 mg) of a volatile solid was collected at --24 °, but was not investigated further. ANALYSES Because of the instability of the c o m p o u n d s in air, the analyses were carried out by sealing off a weighed a m o u n t of the sample in an evacuated glass tube which was then opened under a solution o f sodium hydroxide to effect hydrolysis. P h o s p h o r u s was determined by the Microanalytical Department o f the chemistry department by the method o f ALLEN,{3°) while fluorine was estimated as lead ehlorofluoride. The accuracy of these determinations is limited by slight loss of material by absorption in the stopcock grease during transfer in the v a c u u m system. Acknowledgements--The author wishes to thank Imperial Chemical Industries Limited for the award of a Research Fellowship, and Mr. E. LIDDELLfor recording the nuclear magnetic resonance spectra. tsgl R. J. L. ALLEN,Biochem. J. 34, 858 (1940).