Synthesis of epimer of Taniaphos ligand

• Epimer of Taniaphos ligand was synthesized by step-wise lithiation.
• The structure of the ligands was unambiguously determined by X-ray crystallography.
• Diastereoselectivity of lithiation was elucidated by quantum-chemical calculations.

The spatial arrangement of groups within a chiral ligand is essential for its catalytic performance. This work describes convenient synthesis of (R,Sp)-1-(2-(diphenylphosphano)ferrocenyl)-1-(2-diphenylphosphanophenyl)-N,N-dimethylmethanamine, a diastereomer of the well known (R,Rp)-Taniaphos ligand. The compound was prepared from the same homochiral amine as Taniaphos by sequential twofold lithiation followed by trapping with diphenyphosphane chloride. Sequential twofold lithiation, in contrast to simultaneous dilithiation, leads to the opposite configuration of the stereogenic plane. The structure and configuration of the (R,Sp)-diastereomer along with its CuBr-complex were confirmed by X-ray structural analysis. DFT calculations elucidated underlying effects controlling the stereochemical outcome of the lithiation.

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