Synthesis of a new type of P,N-ligand with a spiro skeleton for Ir-catalyzed asymmetric hydrogenations

A new type of chiral phosphine–quinoline ligand bearing a spiro[4,4]-1,6-nonadiene scaffold was designed and synthesized. Its cationic iridium complex has been characterized by X-ray diffraction analysis and evaluated in the catalytic asymmetric hydrogenation of alkene and imine derivatives, giving the corresponding hydrogenation products with high activity albeit moderate enantioselecitivity.

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(S)-2-Diphenylphosphinylspiro[2-cyclopentene-1,3′-[3H]cyclopenta[b]quinoline], 2′,3′-dihydroC28H24NOPEe >99%[α]D20=+32.4 (c 0.53, CHCl3)Source of chirality: chiral HPLC resolutionAbsoluted configuration: (S)

(S)-2-Diphenylphosphinospiro[2-cyclopentene-1,3′-[3H]cyclopenta[b] quinoline], 2′,3′-dihydroC28H24NP[α]D20=-88.9 (c 0.65, CHCl3)Source of chirality: chiral HPLC resolutionAbsoluted configuration: (S)

(S)-2-Diphenylphosphinylspiro[2-cyclopentene-1,3′-[3H]cyclopenta[b]quinoline], 2′,3′-dihydro-(η4-1,5-cyclooctadiene)-iridium(I)tetrakis[3,5-bis(trifluoromethyl)phenyl]borateC68H48BF24IrNP[α]D20=+1.3 (c 0.50, CHCl3)Source of chirality: chiral HPLC resolutionAbsoluted configuration: (S)