Borane complexes phosphorus-transition metal

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]. 

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. 

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. 

---