Borane complexes phosphorus-metal

The chemistry of secondary phosphine oxides, R2P(H)0 and their phosphi-nous acid tautomers, R2POH, has continued to attract attention. The study of the phosphinous acid tautomers has been aided by the development of stereoselective procedures for direct conversion of secondary phosphine oxides to the phosphinous acid-boranes (83). Treatment of the secondary phosphine oxide with either a base-borane complex or boron trifluoride and sodium borohyd-ride provides the phosphinous acid-borane with predominant inversion of configuration at phosphorus. The phosphinous acid tautomers are usually trapped as ligands in metal complexes and further examples of this behaviour have been noted. Discrimination of enantiomeric forms of chiral phosphinous acids, Ph(R)OH, coordinated to a chiral rhodium complex, has been studied by NMR. °° Palladium complexes of di(t-butyl)phosphinous acid have found application as homogeneous catalysts.A lithium salt of the tellurophos-phinite Ph2PTeH has been prepared and structurally characterised. ... 

Except for thephosphane adducts of tin(IV) halides, the experimental evidence points towards a positive sign of i/( Sn, P) ( K(" Sn, P) < 0 ) in all tin-phosphorus(III) compounds, a consequence of the dominant influence of the lone pair of electrons at the phosphorus atom. Even for transition metal complexes of stannylphosphanes, or in borane complexes of stannylphosphanes, the coupling sign remains positive. 

As has been the pattern in recent years, there has been considerable interest in the synthesis and characterisation of phosphide reagents derived from metals other than lithium, sodium, and potassium, and also in studies of the structure of metallophosphides in the solid state. A new route to P-chiral phosphine-boranes of high enantiopurity is afforded by treatment of the borane complexes of methyl(phenyl)phosphine with a copper(I) reagent, giving the copper-phosphido intermediate (83), which, on subsequent treatment with an iodoarene in the presence of a palladium(O) catalyst, gives the related chiral t-phosphine-borane (84), with retention of configuration at phosphorus. Organophosphido systems... 

At low temperatures phosphine reacts with perchloric acid to produce crystals of phosphonium perchlorate, PH CIO4, which are explosive and very sensitive to heat, moisture and friction. Phosphine readily forms addition complexes in which a metal-phosphorus bond is present, for example, H3P AICI3, H3P TiCl4, (H3P) Cr(CO)3 and HjP Co(NO)(CO)2 (Chapter 8.11). Borane complexes are also formed (Chapter 9.1). 

Common reducing agents are hydrogen in the presence of metallic or complex catalysts (e.g. Ni, Pd, Pt, Ru, Rh), hydrides (e.g. alanes, boranes, LIAIH, NaBHJ, reducing metals (e.g. Li, Na, Mg, Ca, Zn), and low-valent compounds of nitrogen (e.g. NjHj, NjHJ, phosphorus (e.g. triethyl phosphite, triphenyiphosphine), and sulfur (e.g. HO-CHj-SOjNa = SFS, sodium dithionite = Na S O. ... 

Aminomethylphosphines are convenient objects for a comparison of phosphorus and nitrogen donor ability in complexation reactions. Coordination compounds of heterocyclic aminomethylphosphines with metals are discussed in Section VII. In this section we present reactions of aminomethylphosphines with boranes (BH3). 

A theoretical study of the intermediates involved in the formation of phospha-propyne from pyrolysis of vinylphosphirane has led to a new route to phospha-alkynes. Thus, pyrolysis of trimethylsilyl(l-phosphiranyl)diazomethane has yielded MeaSiC = P, via an intermediate 1-phosphiranylmethylene . Regioselec-tivity in the [3 + 2] cycloaddition reaction between phosphaethyne and diazomethane has been studied by theoretical techniques , and further examples of reactions of this type described . Cycloaddition of phospha-alkynes with silylenes has also been reported. The primary phosphine 324 has been isolated from the addition of diethylphosphite to t-butylphosphaethyne. The chemistry of phospha-alkyne cyclotetramer systems has been reviewed and the first examples of platinum(II) complexes of such cage systems described. Aspects of the reactivity of coordinated phospha-alkynes have received further study, and a remarkable metal-mediated double reduction of t-butylphosphaethyne to the complexed fluorophosphine 325 described Phosphorus-carbon-aluminium cage structures have been isolated from the reactions of kinetically stable phospha-alkynes with trialkylaluminium compounds and new phosphaborane systems have been obtained from the reactions of phospha-alkynes with polyhedral boranes . Further studies of wo-phospha-alkyne coordination chemistry have appeared . The reactivity of the ion 326 has been explored. ... 

The chlorophosphine boranes 97 are efficient starting reagents for the synthesis of various classes of P-chiral phosphorus compounds. Reactions of chlorophosphine boranes 97 with nucleophiles, such as carbanions, phenoxides, phenylthiolates, or amides, leads to the formation of corresponding organophos-phorus compounds 100-103 in yields of 53-99% and with up to 99% ee. This method was also used for the preparation of various classes of symmetric and asymmetric P-chiral ligands useful for asymmetric reactions, catalyzed by complexes of transition metals (Scheme 31) [52, 60, 61]. 

Both deprotection methods are very stereoselective, with complete retention of configuration at the phosphorus atom. Losses of optical purity have been reported very rarely. The reader must be aware that deboronation is not always required since phosphine boranes can be used directly in transition metal homogeneous catalysis. Juge and co-workers " combined the reducing properties of the borane moiety to prepare, in situ, Cu(I), Pd(0) and Rh(I) metal complexes by mixing Cu(II), Pd(II) and Rh(III) salts and phosphine boranes. 

The (-)-enantiomer of sparteine is obtained from natural sources as a commercially available and relatively inexpensive oil. The metallation of 1 with n-BuLi in hexane, in the presence of (-)"Sp, produced the a-carbanion 2 which was subsequently quenched affording the known phosphine oxide 3 in approximately 14% ee. Although it has been suggested that the low stereoselectivity is due to the disruption of the (-)-sp/BuLi complex by complexation of the oxygen atom to the lithium cation, the same reaction with unprotected dimethylphenylphosphine provides completely racemic products. Due to the low enantioselectivity, this method was initially ignored in phosphorus chemistry until a seminal paper of Evans and co-workers in which they described similar reactions with phosphine boranes and sulfides. In this case, the enan-tioselectivities were much higher and the method could be successfully applied... 

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