RESOLUTIONS USING METAL-COMPLEXES - SYNTHESIS, SEPARATION INTO DIASTEREOISOMERS, AND RESOLUTION OF ORTHO-PHENYLENEBIS(METHYLPHENYLPHOSPHINE) USING PALLADIUM COMPLEXES CONTAINING OPTICALLY-ACTIVE ORTHO-METALLATED DIMETHYL(ALPHA-METHYLBENZYL)AMINES

The new chelating di(tertiary phosphine) o-phenylenebis(methylphenylphosphine) has been prepared in 68% yield from o-dichlorobenzene by reaction with sodium methylphenylphosphide in tetrahydrofuran solution. The racemic and meso forms of the ligand, (RR;SS)-diphos and (RS)-diphos, respectively, were separated by a combination of direct fractional crystallization of the mixture of diastereoisomers, and by selective precipitation of the sparingly soluble complex [Ni(SCN)((RS)-diphos)2]SCN. The diastereoisomeric di(tertiary phosphines) were subsequently identified by analyzing the 1H NMR spectra of their respective substituted 1H-1,3-benzodiphospholenium salts. Optimized conditions are described for the large-scale resolution of (RR;SS)-diphos by a method which involves the separation of internally diastereoisomeric palladium complexes containing the dissymmetric di(tertiary phosphine) and an optically active ortho-metalated dimethyl(a-methylbenzyl)amine. The optically pure enantiomers, [α]D ± 81.5° (CH2Cl2), are air-stable, crystalline solids, mp 112-113°C, whose absolute configurations have been determined by X-ray analysis. The optically active di(tertiary phosphines) epimerize rapidly upon heating, although they can be recovered unchanged from concentrated hydrochloric acid solution. Indeed, optically active monoprotonated phosphonium salts can be isolated from these solutions. © 1979, American Chemical Society. All rights reserved.