Development of an axially chiral sp 3 P/sp 3 NH/sp 2 N-combined linear tridentate ligand— fac -selective formation of Ru(II) complexes and application to ketone hydrogenation

A newly developed chiral linear tridentate ligand, R-PN(H)N (R=H or Ph), possesses Ph2P and PyCH2NH groups at C(2) and C(2′) positions of the 1,1′-binaphthyl skeleton without or with a C(3)-Ph substituent. The steric effect of C(3)-Ph and the electronic effect of the DMSO co-ligand realize the facial selective generation of fac-RuCl2(Ph-PN(H)N)(dmso) and fac-[Ru(H-PN(H)N)(dmso)3](BF4)2, respectively. Both an H–Ru⋯sp3N–H reaction site responsible for the donor–acceptor bifunctional catalyst (DACat) and a fence/plane chiral context were constructed by means of the following advantageous points: i) the sp3P, sp3N, and sp2N ligating atoms have different electronic properties; ii) DMSO trans to sp3N strongly coordinates to Ru and is fixed by a PyC(6)H⋯OS hydrogen bond; and iii) the single NH function simplifies the DACat reaction site. The synergistic effect has led to success in the asymmetric hydrogenation of sterically demanding ketones. Structural characteristics of first-row transition metal complexes of R-PN(H)N have been also investigated.