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 coligand 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-sp 3 N-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 sp 3 P, sp 3 N, and sp 2 N ligating atoms have different electronic properties; ii) DMSO trans to sp 3 N strongly coordinates to Ru and is fixed by a PyC(6)H-O=S 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.

No abstract

The linear tridentate sp 3 P/sp 3 NH/sp 2 N ligand PN(H)N ((R)-2′-(diphenylphosphino)-N-(pyridin-2ylmethyl)[1,1′-binaphthalen]-2-amine) exclusively forms fac-[Ru(PN(H)N)(dmso) 3 ](BF 4 ) 2 over the mer isomer with the help of the three strongly π-accepting DMSO ligands. The three different ligating atoms exert a divergent effect on the trans-DMSORu bond strengths, enabling the stereoselective generation of fac-RuH(CH 3 O)(PN(H)N)(dmso) (RuNH). RuNH efficiently hydrogenates both nonchelatable t-butyl methyl ketone (BMK) and chelatable t-butyl methoxycarbonylmethyl ketone (BMCK) in the presence of a catalytic amount of CH 3 OK. The reaction proceeds at the Hsp 3 NRuH bifunctional reaction site of fac-RuH 2 (PN(H)N)(dmso), and high enantioselectivity is attained in a chiral 3D cavity constructed by the sp 3 N trans DMSO, the conformation of which is fixed by a PyC(6)HOS hydrogen bond. We determined the structures of RuNH, the K amide RuNK, Ru dihydride, and Ru amido species by detailed NMR analysis using 15 N-labeled PN(H)N and C(3)-Ph-substituted PN(H)N. The rate of BMK hydrogenation is significantly affected by [CH 3 OK] 0 , showing a characteristic curve with a peak followed by a pseudo-minus-first-order decay. The RuNH is easily deprotonated by CH 3 OK to generate RuNK, which is less reactive but has the same enantioface discrimination ability. Increased contribution of the slow RuNK cycle decreases the rate at higher [CH 3 OK] 0 . The RuNH-and RuNK-involved dual catalytic cycle is supported by curve-fitting analyses and K + trapping experiments. In hydrogenation of BMCK, only the RuNH cycle operates because BMCK is preferentially deprotonated over RuNH.

A versatile method has been found to catalyze the dehydrogenative N-((triisopropylsilyl)oxy)carbonyl (Tsoc) protection of amines using Pd/C, volatile iPr3SiH and CO2 gas without the liberation of any salts. A simple filtration/evaporation process facilitates the easy isolation of the product, thereby enhancing the utility of Tsoc as an amine-protecting group in organic synthesis.