Rhodium-catalyzed asymmetric olefin hydrogenation by easily accessible aniline- and pyridine-derived chiral phosphites

Comparative Study of Novel Phosphordiamidite and Phosphite Ligands Used in Alkene Hydroformylation; Synthesis, Characterization, Metalation, and Catalytic Evaluation

“…As expected, ligands L1 and L3 predominantly formed cis disubstituted tetracarbonylmolybdenum(0) complexes with a bidentate κ 2 ‐ P , N chelating ligand when a 1:1 stoichiometry was used. The coordination mode is confirmed by the 13 C NMR spectra that display three doublet carbonyl resonances characteristic of P,N coordination . The magnitudes of | 2 J P,C | coupling constants are consistent with whether the carbonyl is cis or trans to the phosphorus ( cis , approximately 11 Hz; trans , approximately 56 Hz).…”

“…This also is consistent with the Δ δ for L3 in 3 being 10 ppm greater than that of the closely related L5 , (2,2′‐C 12 H 8 O 2 )POCH 2 CH 2 OCH 3 in cis ‐[Mo(CO) 4 (L5) 2 ], suggesting the increased Δ δ arises from ring strain. This phenomenon is observed in [RhCOD(L)]BF 4 complexes where a κ 2 ‐ P , N chelated [(2,2′‐binaphthoxy)P(oxymethyl)]pyridine ligand has a 31 P NMR chemical shift of δ = 134.0 ppm, whereas the complex in with a κ 2 ‐ P , N chelated [(2,2′‐binaphthoxy)P(oxyethyl)]pyridine has a 31 P NMR chemical shift of 124.2 ppm due to the less strained seven‐membered chelate ring in the latter complex …”

“…The cis ‐[Mo(CO) 4 L n ] complexes were prepared by the reaction of [Mo(CO) 4 (nbd)] (nbd = norbornadiene) with the appropriate ligand in hexanes (Scheme and Scheme ). Because ligands similar to L1 and L3 exhibit multiple coordination modes: (1) bidentate κ 2 ‐ P , N chelation, (2) monodentate P‐donation or (3) bidentate P,N bridging,, the coordination reactions were carried out at multiple stoichiometries. As expected, ligands L1 and L3 predominantly formed cis disubstituted tetracarbonylmolybdenum(0) complexes with a bidentate κ 2 ‐ P , N chelating ligand when a 1:1 stoichiometry was used.…”

“…As a whole, these reactions have substantially lower yields compared to the molybdenum complexes (43–83 %). Like the molybdenum complexes, monomer/dimer/oligomer and multiple coordination modes ( cis/trans ) and sites (P/N) are available for the labile metal centers , , , , , , . However, due to the relatively limited bite angles of L1 and L3 , in combination with the chelate effect, the primary isolable products were the mononuclear cis ‐[PdCl 2 (κ 2 ‐ P , N ‐ L )] complexes ( 4 and 6 ).…”

“…To expand upon this research, it is of interest to incorporate other donating groups that can act as hemilabile ligands such as pyridyl groups . Similar heterodonor P,N ligand have been used successfully in Pd‐catalyzd Suzuiki–Miyayra coupling, asymmetric Pd‐catalyzed allylic alkylation reactions, Cu‐catalyzed asymmetric conjugate 1,4‐additions, and Ir‐ or Rh‐catalyzed alkene hydrogenations,, , but very few have been studied in Rh‐catalyzed hydroformylation reactions . These catalysts are more complicated than the mixed P‐donor/ether ligands that we previously studied because the pyridyl group is more likely to competitively bind to the catalytically active Rh I metal centers .…”