The high pressure interaction of phosphorus trifluoride with transition metal oxides

J. inorg, nucL Chem., 1973,Vol. 35, pp. 3719-3722. PergamonPress. Printed in Great Britain.

THE HIGH PRESSURE INTERACTION TRIFLUORIDE WITH TRANSITION

OF PHOSPHORUS METAL OXIDES

ARNULF P. HAGEN and EUGENE A. ELPHINGSTONE The University of Oklahoma, Norman, Oklahoma 73069

(Received 26 February 1973) Abstract--The reaction of PF a at 4000 atm and at 300~ with NiO results in the formation of Ni(PF3)4, when combined with NiO, MoO3 and WO3 in the presence of magnesium Ni(PF3)4, Mo(PF3)6 and W(PF3)6 were formed. When Cr203, CrO3, RuO2, Na2WO4, Na2MoO,, ZrO, V20 s, TiO2, Fe203, CoO, OsO,,, TazOs, MnO and RuO2 with magnesium were combined wfth PF3 at 4000 atm and at 300°, OPF3 and [F2P(O)]20 were isolated indicating a reduction of the metal oxide.

INTRODUCTION

A VARIETYof synthetic routes have been used to prepare transition metal complexes including the interaction of the metal and PF3 [ 1, 2], ligand exchange[3, 4] and reductive fluorophosphination[5]. In related papers the high pressure reactions of P F 3 with 02, S, Se and Te[6] and the low pressure syntheses of [F2P(O)]20 and OPF 3 from PF5 and 02 in the presence of magnesium[7] have been described. Since the properties of PF 3 have been compared to the behavior of carbon monoxide it was thought to be desirable to study the reducing properties of PF 3 with respect to transition metal oxides. It has been found in this study that NiO, M o O 3 and WO3 were transformed into Ni(PF3)4, Mo(PF3)6 and W(PF3) 6. In addition several other oxides were found to readily give up their oxygen forming OPF3 and [F2P(O)]20. EXPERIMENTAL

Apparatus All work was carried out in a borosilicate glass vacuum system constructed with Teflon stopcocks (Fisher & Porter Co., Warminster, Pa. No. 795-005-0004). High pressures were generated using a gas pressure booster manufactured by High Pressure Equipment Co., Erie, Pa. The samples were contained in sealed ampules made from 3 mm dia thin walled gold tubing which were placed in a high pressure micro reactor (Autoclave Engineers, Erie, Pa.). Nitrogen gas was used to generate the desired pressure. At the end of a reaction period the micro reactor was cooled to - 19C before releasing the pressure. Then the frozen ampule was placed in an opening device attached to the vacuum line. Water and other condensable materials on the surface of the gold tubing were removed and then the ampule was opened. The substances 1. 2. 3. 4, 5. 6. 7.

T. Kruck and K. Baur, Chem. Ber. 98, 3070 (1965). P. L. Timms, J. chem. Soc. (A), 2526 (1970). T. Kruck, Z. Naturf. 19b, 165 (1964). L. A. Woodward and J. R. Hall, Spectrochim. Acta 16, 654 (1960). T. Kruck, Angew. Chem. inter ed. 6, 53 (1967). A. P. Hagen and E. A. Eiphingstone, lnorg. Chem. 12, 478 (1973). A. P. Hagen and E. A. Elphingstone, Syn. lnorg. Metal-Org. Chem. 2, 335 (1972). 3719

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ARNULF P. HAGEN and EUGENE A. ELPHINGSTONE

which volatilized were then transferred directly into the vacuum line. I.R. spectra were recorded on a Beckman Model I.R.-10 double beam grating spectrophotometer. Volatile materials were confined in a 10-cm cell fitted with KBr or AgC! windows sealed with rubber O-rings at reduced pressure. Mass spectra were taken at 70-eV electron energies on a Hitachi Perkin-Elmer RMU-6E mass spectrometer at 150°.

Materials All of the oxides were commercial reagents and were used without any purification except for dying. Phosphorus trifluoride was purified by distilling the sample through a trap cooled to - 9 5 ° to remove impurities of low volatility and then retaining the material which stopped in a trap cooled to - 134° mol. wt: caled. 87-9: found 87-8: confirmed by i.r.[8] and mass spectral9]).

Synthesis of Ni(PFa) 4 Phosphorus trifluoride (195 mg, 2.21 m-mole) was condensed into a gold tube which had been charged with NiO (20'0 mg, 0.267 m-mole). The tube was sealed and held at 4000 atm and 300° for 12 hr. The ampule was opened and the volatile material passed through a trap cooled to - 6 4 ° into a trap at - 196°. The former trap contained Ni(PFa)4 (33.3 mg, 0"081 m-mole; identified by i.r.[10] and confirmed by mass spectra). The latter trap contained a mixture o f P F a (150 mg, 1.70 m-mole) and OPF s (10 mg, 0"10 m-mole).

Synthesis of Ni(PFa) 4 (with Mg) Phosphorus trifluoride (128 mg, 1.46 m-mole) was condensed into a gold tube containing NiO (20'0 mg, 0"267 m-mole) and Mg (24 mg, 1 m-mole). The tube was sealed and held at 4000 atm and 300° for 12 hr. The ampule was opened and the volatile material passed through a trap cooled to - 6 4 ° into a trap at 196°. The former trap contained Ni(PF3)4 (33.3 mg, 1"081 m-mole) contaminated with a small amount of [F2P(O)]20. The latter fraction contained a mixture of PF3 (93'3 mg, 1.06 m-mole) and OPF a (10 mg, 0.10 m-mole). Additional experiments are summarized in Tables 1 and 2. In all cases the reaction time was 12 hr. The volatile products were identified and confirmed by i.r. and mass spectroscopy. -

Table 1. Reactions of PFa with metal oxides at 4000 atm and 300°* Reactants Metal oxide

PF 3

OPF 3

Cr20 3 CrOa RuO 2 Na2WO4 Na2MoO 4 ZrO V205 TiO 2 Fe20 a CoO OsO4t TaO5 MnO RuO2~"

1"08 1"16 1'41 1'35 1.44 1"26 1"08 0'97 1.18 0.97 1'24 1"24 1.03 1.41

0.04 0-13 0-09 0"07 0"07 0"04 0-06 0"08 0-07 0"02 0.08 0"06 0"02 0.04

Products PF3 0.39 0"70 0"79 0-62 0'63 0'87 0'57 0"75 0-63 0"65 0"76 0"53 0-77 0.84

P2OaF4 0"32 0.17 0"26 0'33 0.37 ff18 0-22 0"07 0-24 0.15 0"20 0-32 0"12 0-30

* Each tube contained ~ 0.20 m-mole of the oxide and ~ 1 m-mole of Mg, quantities are given in m-mole. t 2OO°. 8. H. S. Gutowsky and A. D. Liehr, J. chem. Phys. 20, 1652 (1932). 9. E. E. Saalfeld and M. V. McDowell, (U.S.) Naval Res. Lab. Report 6639, 1967. 10. T. Kruck, K. Baur and W. Lang, Chem. Ber. 101, 138 (1968).

Interaction of PF 3 with metal oxides

3721

Table 2. Formation* of M(PF3)x at 300° Metal oxide NiO NiO NiO MoO 3 MoO a MoO 3 WO 3 WO3 WO3

0'267 0.267t 0'267t 0"13 0"12"I" 0"13t 0.15 0' 15t 0"15t

PF 3

Pressure

M(PF3) x

OPF 3

PF 3

2'21 1.46 0.93 1-24 1.23 1.10 1.14 0'90 1"14

4000 4000 100 4000 4000 100 4000 4000 100

0"08 0.06 0.08 0'05

0-10 0.10:~ 0' 10:~ 0-30 0'30~

0'04

0-30 0"24:~

1'79 1.06 0"50 0"65 0.77 0-95 0'61 0"33 0"96

* Quantities in m-mole, pressure in atm. t With ~ 1 m-mole of magnesium. :~ Small amounts of [F2P(O)]20 also present.

DISCUSSION

The reduction of a metal oxide with PF3 should follow the path given by the equation MOy+yPF 3~M

+ y O P F 3.

(1)

If the metal is capable of forming a complex with PF 3 then the overall equation includes the formation of the complex M O y + (x + y ) P F 3 ~ M ( P F 3 ) x + y O P F 3.

(2)

The latter reaction would be thermodynamically pressure favored since the stoichiometry of the reaction indicates a reduction in the total volume of the system since x moles of PF3 are consumed. The former reaction may also take place with a reduction in volume if the density of the reduced substance is greater than that of the metal oxide[11]. This decrease in volume will shift the equilibrium to favor the formation of products as the pressure is increased. The rates of chemical reactions are also influenced by an increase in pressure [11-15]. The most easily identifiable changes would be an increase in the concentration of the gaseous reactant as compared to the same reaction at atmospheric pressure and in the value of the rate constant. The rate constant would be expected to increase if the partial molar volume of the activated state is less than the volume of the reactants as given by the expression (c3In k / ~ P ) r = - A V * / R T . No rate studies have been carried out in this study since the apparent half-life of reaction at 4000 atm appears to be E. Whalley, Ann. Rev. Phys. Chem. 18, 205 (1967). R. C. Neuman, Jr., J. org. Chem. 37, 495 (1972). W. J. leNoble, Prog. Phys. Org. Chem. 5, 207 (1967). S. D. Hamann, In High Pressure Physics and Chemistry (Edited by R. S. Bradley) Vol 2, Chapter 8. Academic Press, New York (1963). 15. C. Walling and T. A. Augurt, J. Am. chem. Soc. 88, 4163 (1966), i 1. 12. 13. 14.

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ARNULF P. HAGEN and EUGENE A. ELPHINGSTONE

less than or close to the physical time lag which results from heating and quenching the microreactor. The half-life would therefore be 90 min or less as determined by running experiments for varying times. Table 2 describes the results when a transition metal complex was formed. The reactions of MoO3 and WO3 required a pressure in excess of 100 atm, however the reaction of NiO readily took place at 100 atm. The reaction of NiO with PF3 at 4000 atm and at 300° proceeded according to the equation NiO + 5 P F 3 ~ Ni(PF3)4 + OPF3.

(3)

This reaction was found to also take place at pressures as low as 100 atm in the presence of metallic magnesium, however, the product mixture also contained [F2P(O)]20. This product most likely formed from the reaction of MgO with O P F 3 according to the equation MgO + 2OPF 3 --*MgF 2 + [F2P(O)]20

(4)

since this reaction was found to take place readily when O P F 3 and MgO were combined at 1 atm and at 300* [7]. The reaction forming Ni(PF3) 4 in the absence of magnesium was not found to take place at 100 arm and at 300°. This observation demonstrates the need for the higher pressure. Of the metal oxides studied at 4000 atm and at 300° no other was found to form a P F 3 complex in the absence of magnesium even though in several cases the complex has been prepared by another route[5]. MoO3 and WOa were found to form Mo(PF3)6 and W ( P F a ) 6 when the reduction was carried out at 4000 atm and at 300° in the presence of magnesium. When combined with PF 3 and metallic magnesium at 300° and 4000 atm pressure C r 2 0 3 , C r O 3, R u O 2, Na2WO4, Na2MoO4, ZrO, V20 5, TiO2, Fe203, CoO, OsO4, Ta2Os, MnO and RuO2 were reduced. Table 1 summarizes the experiments which led only to the formation of OPF3 and EF2P(O)]20. Corresponding experiments were carried out without the magnesium, in these experiments the only volatile product in addition to unreacted P F 3 was OPF3. The magnesium which in itself could have served as the reducing agent was not necessary for the reduction, but for M o O 3 and WO3 was necessary for the formation of the P F 3 complex. Acknowledgement--This research was supported by the National Science Foundation under Grant GP-19873.