Preparation of Metal Phosphides

Metal phosphides can, in general, be made by direct union of the elements, in vacuo or protective atmosphere nnder conditions which prevent loss of phosphorus, as, for example. 

In specified cases they may be made by reaction of phosphine with an alkali metal (Equation 8.3), an oxide (Equation 8.4) or a metal chloride (Equation 8.5). Alternatively, the reduction, under correct conditions, of a phosphate with carbon (Equation 8.6) or hydrogen (Equation 8.7) may be used. 

BajPj Ba4P3 Ba3P4 Ba5P4 BaP3 Ba3Pi4 BaPj BaPio BejPj BePj 

CsP Cs4Pe CS3P7 CS3P, CSP7 CsPi, CsPij 

K3P K4P3 K3P4 KP K3P4 K3P7 K4PJ KPis 

---

There are several different preparations of metal phosphides. Secondary phosphines can be metallated by strong bases such as butyl-lithium or alkali metals (Scheme 5). Primary phosphines can be doubly lithiated using LDA or BuLi.11 Both the anion and dianion metal phosphides can be generated in situ before adding the electrophile into the same pot.12,13 Phosphorus halides can be metallated using lithium metal. 

Early preparation of metallic phosphides Named the mineral apatite Prepared PCI3 and PCI3 Lecithin isolated from brain fat Alkyl phosphates prepared... 

Up to now, metal phosphides have mainly been obtained either by solid-state synthetic techniques, under extreme conditions with long reaction times, or via the molecular phase to enable their use in the preparation of new materials. However, the renaissance and subsequent development of the chemistry of catenated oligophosphanide anions and their metal complexes may open up novel routes for the preparation of metal phosphides by thermal treatment of phosphorus-rich metal complexes. 

Inspired by previous work of Baudler, Issleib and Fritz, we set out to develop targeted syntheses for transition metal cat fza-oligophosphanediides as potential precursors for the preparation of metal phosphides [57, 58]. 

Potential Application of Metal Oligophosphanides as Precursors in the Preparation of Metal Phosphides... 

Alternative routes that seem feasible are decomposition of the corresponding phosphorus-rich metal oligophosphanide complexes under mild conditions, and reactions of metal salts and neutral phosphorus-rich phosphanes under solvothermal conditions. These studies may lead to the preparation of novel phosphorus-rich metal phosphides whose potential as anode materials for lithium-ion batteries [134-136, 141-146] and thermoelectric materials may be studied [139, 140]. One of the principal processes for the preparations of metal phosphides starting from phosphorus-rich metal ohgophosphanide complexes is removal of the R group, which should be possible by thermal decomposition of the compounds, to give organyl-free species such as M Py. These species have already been observed in the mass spectra of several of these complexes. 

The various techniques for the synthesis of transition metal phosphides have been summarized in the monograph by Aronsson, Lundstrom, and Rundqvist.1 The most common method used for the preparation of the phosphides is the direct combination of the elements. However, in general, the products are not pure or... 

Isslieb and Boettcher described a general procedure for the preparation of cyclic molecules containing the P—E—P functionality. The preparation involves reaction of metal phosphides with appropriate electrophiles, such as N,N-dichloroethylamine, to give 79 (76MI2). 

The most general method for the preparation of solid phosphides is from the elements however, there are several problems to overcome in that highly electropositive metals are often air- and moisture-sensitive, so that the educts and often the products must be handled under inert conditions (glove box or Schlenk technique). A well described example for the synthesis of the air- and moisture-sensitive phosphides Na3 7 and Na3Pii has been described. ... 

Our research on supported transition-metal phosphides started with the preparation of nickel phosphides supported on an amorphous Si02 carrier. Si02 was preferred to AI2O3 as it interacts to a lesser extent with phosphates, which are known to form aluminum phosphates in the presence of AI2O3 [21]. The latter was already used as a support for MoP [22], but the authors had to introduce high loadings of molydenum and phosphorus... 

The hydrides phosphine PH3, arsine AsH3 and stibine SbH3 can be prepared by hydrolysis of metal phosphides, or by reduction of molecular compounds such as PC13. The molecules have a pyramidal (C3 ) structure but with bond angles less than in NH3 (see Topic C6). They are very toxic gases,... 

The interrelation between structure and hydrolytic behavior of metal phosphides is reviewed in [1]. Of the numerous phosphides that release PH3 when hydrolyzed, Ca3P2 and AlP have been predominantly used to prepare the compound on a laboratory scale. 

Simple triarylphosphines linked covalently to PS can be prepared from bro-mopolystyrene via lithiation and subsequent reaction with ClPhAr2 (Scheme 2.41) [144]. A serious side reaction may be the attack of alkyl Uthium on the resin, which causes eventually poor swelling properties or undesired contamination in the product. This problem can be overcome by reaction of metal phosphides with chloromethylated resins. Both lithiated and brominated PS can be prepared from PS. Phosphine ligands of this type have been tested in rhodium-catalyzed hydro-formylation [145]. 

Synthetic methods for the preparation of metal-rich metal phosphides and monophosphides are very different depending on the morphology and the conditions of use of the final products. For example, metal phosphides can be obtained as bulk materials from high-temperamre elemental reactions, as films by chemical deposition techniques and as nanoparticles by molecular solvothermal reactions [14, 15, 94, 102-126]. 

The most general preparative route to phosphides (Faraday s method) is to heat the metal with the appropriate amount of red P at high temperature in an inert atmosphere or an evacuated sealed tube ... 

Reactions of alkyl halides with alkaU metal phosphides [39-41], addition reactions of olefins with PHj [42] or the pyrolytic cleavage of P-0 bonds in RPO2H2 [43] are also reported for the preparation of alkyl/aryl functionalized primary... 

Preparation of Phosphines from Metallated Phosphines.- It has been shown that phosphide anions may be generated from primary and secondary phosphines under aqueous conditions using concentrated aqueous alkali in DMSO or other dipolar aprotic solvents. 

Phosphides and amides are closely related, as a synthetic route is based on metathesis of metal amides, especially the respective trimethylsilyl amides, with the appropriate free acidic phosphine or an anion derived therefrom. Reaction of metal halides and trisilylphosphines is an alternative for preparing metal phosphides. 

In the review by Kanatzidis et al. (2005), the preparation by the tin-flux method is mentioned also for several ternary phosphides and polyphosphides of rare-earth and transition metals. Typically the components (R metal, T metal, P and Sn in an atomic ratio of about 1 4 20 50) in sealed silica tubes were slowly heated, to avoid violent reactions, up to 800°C, annealed at that temperature for 1 week and slowly (2 K/h) cooled to ambient temperature. The tin-rich matrix was dissolved in diluted hydrochloric acid. The authors described the preparation of compounds corresponding for instance to the formula MeT4P12 (Me = heavy rare-earth metals and Th and U, T = Fe, Ru, etc.) and to the series of phases MeT2P2 (Me is a lanthanide or an actinide and T a late transition metal) having a structure related to the BaAl4 or ThCr2Si2 types. 

The reaction of alkali metal phosphides with appropriate halides, sultones or cyclic sulfates is a generd method for preparation of a variety of tertiary phosphines useful in aqueous organometallic catalysis. These... 

Sultones are useful starting materials for the preparation of various sulfoalkyl- (18, 20) or sulfoarylphosphines (7) when reacted with the appropriate alkali metal phosphide [20]. Reaction of the homologous alkyl-1,2-sultones (C3 to Cu) with tris(2-pyridylphosphine) afforded highly water soluble betains (30) [21]. 

By far the most ubiquitous intermediates in synthesis of this class of phosphines are the alkali metal phosphides which can be prepared by either the KOH/DMSO method, by reaction of tertiary phosphines or chlorophosphines with alkali metals, or in the reaction of BuLi with appropriate secondary or tertiary phosphines. A number of the ligands in Figures 6 and 7 were prepared this way (60-69,72-74). 

---