Tris(trialkylsilyl)phosphines have been considered for use in the manufacture of semiconductors and display-related products. Tris(trimethylsilyl)phosphine (hereinafter, also referred to as “TMSP”), which is most widely known among tris(trialkylsilyl)phosphines, is increasingly used as a precursor for providing phosphine.
Known methods for producing TMSP generally employ solvents for uniformity of the reaction and high yield and purity of the product. Typical methods for producing TMSP are as follows: (1) introducing white phosphorus and a Na/K alloy to diglyme solvent through a dropping funnel, and adding chlorotrimethylsilane thereto (G. Beeker, W. Holderch, Chem. Ber. 108, 2484, 1975); (2) introducing red phosphorus and a Na/K alloy to 1,2-dimethylethane (DME) solvent through a dropping funnel, and adding chlorotrimethylsilane thereto (Synthetic Methods of Organometallic and Inorganic Chemistry, Herrmann/Brauer, Vol. 3, 1996, Georg Thieme Verlag Stuttgart New York); (3) reacting phosphorus trichloride and chlorotrimethylsilane with magnesium in hexamethylphosphoric acid triamide (HMPT) or tetrahydrofurane (THF) solvent (H. Schumann, L. Rosch, Chem. Ber. 107, 854, 1974); (4) reacting sodium with white phosphorus in THF solvent to produce sodium phosphide, and adding to sodium phosphide chlorotrimethylsilane in DME solvent to react them (F. R. Askham, G. G. Stanley, E. C. Marques, J. Am. Chem. Soc. 107, 7423, 1985); and (5) reacting phosphine with trimethylsilane triflate (TMSOTf) and triethylamine in dimethyl ether solvent (W. Uhlig, A. Tzschach, Z. Anorg, Allgem. Chem. 576, 281, 1988).
The above conventional methods, however, use an excess of metals such as sodium and potassium, which readily react with oxygen in the air to cause spontaneous ignition. The methods also employ organic solvents such as THF, ethers, DME, diglyme, etc., which are in essence inflammable or generate explosive by-products such as peroxides during the process. Accordingly, they may involve disadvantages that entrainment of oxygen into the process would not only decrease the purity of products but also increase the risk of fire and explosion. Especially, the method in which phosphine is reacted with TMSOTf and triethylamine in dimethyl ether solvent generates solid salts during the reaction, which should be removed by follow-up processes such as filtration, distillation, etc., to increase the purity of the product. Filtration is the most dangerous process in the manufacture of combustible materials, since filtration under positive pressures has a risk of fire due to release of combustible materials into the air, and filtration under negative pressures may give rise to explosion or fire in case of entrainment of external air.
Furthermore, a tris(trialkylsilyl)phosphine by itself readily reacts with oxygen in the air to cause strongly spontaneous ignition. Accordingly, it should be handled in an atmosphere of an inert gas such as nitrogen and helium with oxygen blocked. Entrainment of oxygen during the manufacture, storage, or transportation thereof may not only deteriorate the quality of products, but also cause spontaneous ignition and fire. Furthermore, since organic solvents may aggravate the possibilities of fire and explosion, special care is necessary in the process design and operation, as well as handling of the solvents. For the above reasons, these conventional methods for preparing tris(trialkylsilyl)phosphines have disadvantages of high investment and operation costs.