Chelate ring size effects of Ir(P,N,N) complexes: Chemoselectivity switch in the asymmetric hydrogenation of alpha,beta-unsaturated ketones

摘要

A novel, highly modular approach has been developed for the synthesis of new chiral P,N,N ligands with the general formula Ph2P(CH3)CH(CH2)mCH(CH3)NHCH2CH2(CH2)nN(CH3)(2) and Ph2P(CH3)CHCH2CH(CH3)NHCH2(CH2)(n)-2-Py (m, n = 0, 1). The systematic variation of their P-N and N-N backbone led to the conclusion that the activity, chemoand enantioselectivity in the hydrogenation of alpha,beta-unsaturated ketones are highly dependent on the combination of the two bridge lengths. It has been found that a minor change in the ligand's structure, i. e. varying the value of m from 1 to 0, can switch the chemoselectivity of the reaction, from 80% C=O to 97% C=C selectivity.