Asymmetric Rh Research Articles

Dinuclear Rh(I) complex with 2,7-bis(diphenylphosphino)-1,8-naphthyridine: Synthesis, structure, and dynamic property

Reaction of [RhCl(cod)] 2 with 2,7-bis(diphenylphosphino)-1,8-naphthyridine (dpnapy) and 2,6-xylyl isocyanide (XylNC) in the presence of NH 4PF 6 afforded the dirhodium(I) complex, [Rh 2(μ-dpnapy) 2(XylNC) 4](PF 6) 2 ( 5), and similar procedures using [MCl 2(cod)] (M = Pt, Pd) resulted in the formation of [Pt 2(μ-dpnapy) 2(XylNC) 4](PF 6) 4 ( 6) and [Pd 2Cl 2(μ-dpnapy) 2(XylNC) 2](PF 6) 2 ( 7). Complexes 5– 7 were characterized by elemental analysis, IR, UV–Vis, 1H and 31P{ 1H} NMR, and ESI mass spectroscopic techniques, to involve a small and rigid d 8 {M 2(μ-dpnapy) 2} metallomacrocycle. Complex 5 readily incorporated a silver(I) ion into the macrocycle to afford [Rh 2Ag(μ-dpnapy) 2(XylNC) 4](PF 6) 3 ( 8) which was characterized by X-ray crystallography. The Ag(I) ion is trapped by two trans N atoms of dpnapy ligands, resulting in an asymmetric Rh–Ag⋯Rh structure, determined as a disordered model in the crystal structure, and however, in a CH 2Cl 2 solution, a dynamic interconversion of the two Ag-trapped sites was observed with low-temperature NMR studies, which was further supported by DFT molecular orbital calculations. When an acetonitrile solution of complex 5 was treated over a droplet of mercury(0), the polymeric compound formulated as {[Rh(μ-dpnapy)(XylNC) 2](PF 6)} n ( 9) was isolated as yellow single crystals, which were revealed by X-ray crystallography to consist of C 6 helical rods along c axis with a pitch of 33.5 Å (rise of unit = 5.6 Å) and a diameter of 20.64 Å.

Extending the Concept of Mixtures of Chiral Monodentate P-Ligands in Asymmetric Rh- catalyzed Olefin-Hydrogenation: Use of Oxazaphospholidines

The previously described combinatorial concept of using mixtures of monodentate BINOL-derived phosphites, phosphonites or phosphoramidites as superior ligand systems in Rh-catalyzed asymmetric olefin-hydrogenation has been extended to include chiral oxazaphospholidines. Specifically, the latter were prepared from ephedrine and pseudo-ephedrine according to literature procedures. Mixtures of these P-ligands among themselves or in combination with a BINOL-derived phosphonite lead to enhanced enantioselectivity in the Rh-catalyzed hydrogenation of itaconic acid dimethyl ester (ee up to 89%).

Expedient asymmetric synthesis of all four isomers of N,N'-protected 2,3-diaminobutanoic acid.

2,3-Diaminobutanoic acid (DAB) is found in several peptide antibiotics, toxins, and biologically active molecules. This paper describes the practical and highly enantioselective synthesis of all four N,N'-protected DAB stereoisomers using an asymmetric Rh(I)-phosphine-catalyzed hydrogenation of isomeric enamides as the key step. Thermal and photochemical isomerization of the enamide hydrogenation substrates coupled with catalyst-geometric isomer pairing allows targeted synthesis of single DAB isomers in maximum yield.

On the asymmetric rh(I) catalyzed [4+2] cycloisomerization reaction. Electronic and torsional ligand control of absolute stereoselection.

The use of bisphosphine ligands related to DIOP as chiral modifiers in the Rh(I) catalyzed [4+2] cycloisomerization reaction results in moderate to goo

Infrared spectroscopy at high pressure: Interaction of CO with oxidized Rh/Al 2O 3

Infrared spectroscopy was used to study the interaction of CO with preoxidized Rh/Al 2O 3 catalyst films in a high-pressure cell reactor. An infrared band near 2125 cm −1, which had previously been assigned to a Rh 2+CO species and to one band component of an asymmetric Rh(CO) 3 species by two different laboratories, is now assigned to Rh 2+CO. This work demonstrates that gas-phase contributions from infrared-active species with high extinction coefficients can be eliminated from surface contributions, even at high pressures of the gas.

Formation of an asymmetric RhHgRh bridged complex

Reaction of HgCl 2 with [Rh 2(μ-Cl)(CO) 2(μ-CO)(μ-dppm) 2]Cl (dppm = bis(diphenylphosphino)methane) gives [Rh 2Cl 3(μ-HgCl)(CO) 2(μ-dppm) 2] in which only one Rh is oxidised by insertion into a HgCl bond, and which consequently contains an unusual asymmetric RhHgRh bridge.