Nickel, trifluorophosphine complexes

Trifluorophosphine complexes of nickel, palladium, and platinum have been obtained by direct reaction of PF3 with the metal at elevated temperatures and pressures (172). Similarly several fluorophosphine complexes of zero-valent nickel can be made under very mild conditions (60°C) using metallic nickel formed by decarboxylation of nickel oxalate... 

When manganese vapour and a mixture of nitric oxide, trifluorophosphine and boron trifluoride are co-condensed the compound Mn(PF3)(NO)3 is produced [280]. Co-condensation of nickel and carbon dioxide results in the formation of some nickel tetracarbonyl [280]. Burdett and Turner [298] showed that co-condensation of nickel and nitrogen at 20°K resulted in a nickel—nitrogen complex. Moskovits and Ozin [299] have recently repeated the experiment and have shown from the infrared spectrum of the matrix that the major product is NiN2, with the nickel atom bonded to the end of the nitrogen molecule. 

Trifluorophosphine is a very convenient ligand in metal atom chemistry to use along with other ligands, e.g., in the stabilization of metal arene complexes (Section III,B). Reaction of a mixture of PF3 and PH3 with nickel vapor yields Ni(PF3)3PH3 and Ni(PF3)2(PH3)2 but no Ni(PH3)4. Attempts to make Ni(PH3)4 lead to hydrogen evolution from the ligand during or after condensation with the nickel vapor (128). 

In our study of the fluorination of coordinated chlorophosphine ligands (23), we started out with tetrakis(trichlorophosphine)nickel-(0), which could previously be converted into tetrakis(trifluorophosphine)nickel-(0) by displacement of the coordinated phosphorus trichloride with excess phosphorus trifluoride in a sealed tube (32). The limitations of this method, requiring the use of phosphorus trifluoride, a low boiling gas, under pressure, and involving the mechanical separation of the fluorophosphine complex from phosphorus trichloride, are obvious, and the yield was low. A straightforward method for the synthesis of this interesting compound was found in the fluorination of the coordinated phosphorus trichloride with potassium fluorosulfinate ... 

The comparatively simple method of preparation of tetrakis (trifluorophos-phine)nickel-(0) encouraged some scouting experiments on its still unexplored chemistry. Whereas the compound is hydrolytically remarkably stable, it was found to react readily with amines and ammonia with complete aminolysis of the phosphorus-fluorine bonds. Very typical of tetrakis(trifluorophosphine) nickel-(0) and similar fluorophosphine and chlorophosphine complexes of zerovalent nickel is the rapid decomposition with precipitation of elemental nickel by aqueous alkali hydroxide. 

It was decided to study the system tetrakis (trifluorophosphine) nickel- (0) -ammonia (23) in some detail a smooth reaction was observed when the complex, condensed on excess ammonia at liquid air temperature, was allowed to warm up gradually. Precipitation of colorless crystals, identified as ammonium fluoride in almost stoichiometric amount, based on complete ammonolysis of the phosphorus-fluorine bonds, was observed at temperatures as low as —90° to —80°. Removal of the ammonium fluoride by filtration at temperatures not higher than —50°, and subsequent slow evaporation of the ammonia from the filtrate invariably led to a brown-yellow solid, although a colorless, crystalline material was formed initially. The product was decomposed almost instantaneously by water with precipitation of elemental nickel. Analysis of the hydrolyzate obtained in aqueous hydrochloric acid revealed a nickel-phosphorus-nitrogen atom ratio close to 1 4 4, corresponding to an apparently polymeric condensation product. 

The chemical and thermal stability of the fluorophosphine complexes is markedly increased in every case over the chlorophosphine complexes, none of the latter being volatile. The stability of the fluorophophine complexes as compared with the parent carbonyl is also noteworthy. While nickel carbonyl is distillable only with considerable decomposition, tetrakis(trifluorophosphine)nickel-(0) is far more stable on distillation at atmospheric pressure, and can also conveniently be handled in a high-vacuum system. 

A number of transition metals have been shown to react with trifluoro-phosphine [280]. Chromium, cobalt, nickel, palladium and iron all produced stable complexes. Manganese and copper also reacted at —196°C, but the products were unstable, and decomposed on warming. Nickel vapour has also been reacted with difluorochlorophosphine, yielding Ni(PF2Cl)2. Complexes produced by reaction with phosphine itself were unstable, decomposing on warming, although when a mixture of phosphine and trifluorophosphine was co-condensed with nickel vapour some mixed complexes were isolated. 

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