AbstractThe axially dissymmetric diphosphines (−)‐(R)‐ and (+)‐(S)‐(6‐6′‐dimethylbiphenyl‐2,2′‐diyl)bis(diphenyl‐phosphine) ((−)‐(R)‐10and (+)‐(S)‐10; ‘BIPHEMP’) have been synthesized, starting from (R)‐ and (S)‐6,6′‐dimethylbiphenyl‐2,2′‐diamine ((R)‐ and(S)‐16), respectively,via Sandmeyerreaction, liathiation, and phosphinylation. Moreover, racemic 4,4′‐ dimethyl‐ and 4,4′‐bis(dimethylamino)‐substituted analogues11and12respectively, and the 6,6′‐bridged analogues 1,11‐bis(diphenylphosphino)‐5,7‐dihydrodibenz[c,e]oxepin(13)were synthesized and resolved into optically pure (R)‐ and(S)‐enantiomersviacomplexation with di‐μ‐chlorob is {(R)‐2‐[1‐(dimethylamino)ethyl]pheny‐CN}dipalladium(II) ((R)‐18). The molecular structures of the diphosphines (S)‐10and (R)‐13and of two derived cationic Rh(I) complexes,[Rh((S)‐10)(nbd)]BF4and [Rh((R)‐13)(nbd)]BF4were determined by x‐ray analyses. Absolute configurations were established for (+)‐(S)‐10by X‐ray analyses of both the free diphosphine and of the derived Rh(I) complex, and for (−)‐(R)‐13by X‐ray analysis of the derived Rh(I) complex. Configurational assignments for the substituted BIPHEMP analogues1112were achieved by means of1H‐NMR comparisons. The BIPHEMP ligand10and analogues11,12and13are the first examples of optically active bis(triaylphosphines) containing the axially dissymmetric biphenyl moiety. All these new diphosphines proved to be excellent asy