Direct Resolutions with Cyclometallated Pd Complexes

Given the high tendency of trivalent phosphorus compounds towards coordination to transition metal ions, is not surprising that enantiopure complexes 

This types of resolution were originally described in 1971 by Otsuka and coworkers with 15 (R = R = Me) and since then they have been applied to numerous racemic P-stereogenic phosphines. In spite of an early use of complex 17 (R = R = Me), 15 or 16 are more typically used. A limitation of the method is that the optimum complex for the resolution depends on the exact phosphine being resolved. Naphthyl complex 16 is frequently a better resolving agent than 15, but also more expensive.  

Most of the monodentate phosphines resolved to date by means of cyclo-metallated palladacycles are listed in Table 2.3. 

The palladacycles discussed here are very effective for the resolution of bidentate mono- and diphosphines. For C2-symmetric diphosphines, a single pair of cationic complexes is formed but for Ci-bidentates two isomers can be formed. For the resolution of these complexes the chloride counterion is usually exchanged by hexafluorophosphate for solubility reasons.  

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