137769-97-2Relevant academic research and scientific papers
Catalytic asymmetric hydrogenation of imines. Use of rhodium(I)/phosphine complexes and characterization of rhodium(I)/imine complexes
Becalski, Adam G.,Cullen, William R.,Fryzuk, Michael D.,James, Brian R.,Kang, Guo-J.,Rettig, Steven J.
, p. 5002 - 5008 (2008/10/08)
An in situ Rh1(P-P) catalyst formed from [Rh(NBD)Cl]2 and cycphos (P-P = 1,2-bis(diphenylphosphino)-1-cyclohexylethane) effects asymmetric hydrogenation of some commercially important and model imines in 1:1 benzene/methanol under 1000-1500 psig H2 from -25 to +25°C; a maximum of 91% ee is obtained for ArC(Me)=NCH2Ph (Ar = 4-MeOC6H4) in the presence of iodide cocatalyst at -25°C. Two [Rh(diphos)(imine)2]BF4 complexes have been isolated (diphos = 1,2-bis(diphenylphosphino)ethane): imine 8 = 6,7-dimethoxy-1-methyl-3,4-dihydroisoquinoline (complex 11) or imine 4 with Ar = 2-MeOC6H4 (complex 16). Complex 11 crystallizes in the triclinic system, space group P1, with a = 12.564 (1) A?, b = 21.446 (2) A?, c = 10.521 (1) A?, α = 100.655 (9)°, β = 110.539 (8)°, γ = 79.102 (7)°, and Z = 2, the structure refining to R = 6.8% and Rw = 8.2% for 5881 reflections; the η1-imines bind via nitrogen in a syn arrangement at the essentially square-planar Rh, while in solution an anti isomer is also evident. Other species [Rh(diphos)(η1-imine)(MeOH)]+ and Rh(P-P)Cl(η1-imine), where P-P = diphos or chiral bis(tertiary phosphines), have been characterized in solution, and Rh(diop)(Cl) (8) has been isolated (diop = 2,3-o-isopropylidene-2,3-dihydroxy-1,4-bis(diphenylphosphino)butane). Complexes [Rh(diphos)(imine)]+ containing a chelated imine (via the nitrogen lone pair and oxygen of a methoxy functionality) exist, but chelation is not essential for effective asymmetric induction. The catalytic hydrogenations appear to occur via an unsaturate route; a plausible intermediate is Rh(P-P)(X)-(MeOH)(imine), where X = halide and the alcohol facilitates η2-(C=N) binding.
