Synthesis and resolution of 2,2'-bis-diphenylphosphino [3,3']biindolyl ; a new atropisomeric ligand for transition metal catalysis

A synthesis of the title ligand is described in which the key step is the dilithiation of 1,1'-bis(dimethylaminomethyl)-3,3'-biindolyl and electrophilic trapping with ClPPh2. Concomitant N-deprotection and resolution with bis[(R)-dimethyl(1-(1-naphthyl) ethylaminato-C2,N)palladium chloride] led to selective recovery of the S-enantiomer. The N-dimethylaminomethyl-substituted biindolyl, but not the parent compound, showed strongly second-order behaviour for 13C NMR peaks in the region of the phosphorus atom due to a desymmetrising 13C-induced isotope shift of the 31P resonance.