Planar-Chiral Phosphine-Olefin Ligands Exploiting a (Cyclopentadienyl)manganese(I) Scaffold To Achieve High Robustness and High Enantioselectivity

Abstract

A series of 2-methyl-1,3-propenylene-bridged (η-diarylphosphinocyclopentadienyl)(phosphine)manganese(I) dicarbonyl complexes 2 have been developed as a new class of phosphine-olefin ligands based on a planar-chiral transition-metal scaffold, which show better robustness as well as higher enantioselectivity over phosphine-olefin ligands 1 with a planar-chiral (η-arene)chromium(0) framework. The practical enantiospecific and scalable synthesis of 2 has been established. Phosphine-olefin ligands 2 enable construction of an effective chiral environment around a transition-metal center upon coordination, and thus their rhodium(I) complexes exhibit excellent catalytic performance in the various asymmetric addition reactions of arylboron nucleophiles. Complex 2b, which has a bis(3,5-dimethylphenyl)phosphino group on the cyclopentadienyl ring, is found to be a superior chiral ligand in the rhodium-catalyzed asymmetric 1,4-addition reactions of arylboronic acids to various cyclic/acyclic enones giving the corresponding arylation products in over 99% ee. On the other hand, 2c and 2d, which have bis[3,5-bis(trifluoromethyl)phenyl]phosphino and bis(3,5-di-tert-buthyl-4-methoxyphenyl)phosphino groups, respectively, are highly efficient chiral ligands in the rhodium-catalyzed asymmetric 1,2-addition reactions of the arylboron nucleophiles to imines or aldehydes showing up to 99.9% ee. The X-ray crystallographic studies of (R)-2b and [RhCl((S*)-2b)] reveal the absolute configuration of 2b and its phosphine-olefin bidentate coordination to a rhodium(I) cation. Structural comparison with [RhCl((R*)-1b)] postulates the origins of the higher enantioselectivity of newly developed phosphine-olefin ligands 2.

Efficient Synthesis of Polycyclic γ‐Lactams by Catalytic Carbonylation of Ene‐Imines via Nickelacycle Intermediates

“…The chiral phosphoramidite ligand L*1 worked well to give 2 h in 95 % yield and 62 % ee . The chiral MOP ligand L*2 , P‐stereogenic iminophosphorane L*3 , and the planar‐chiral phosphine‐olefin ligand L*4 were also used, as these compounds should act as hemilabile bidentate ligands. However, any improvements on the results were not observed.…”

Efficient Synthesis of Polycyclic γ‐Lactams by Catalytic Carbonylation of Ene‐Imines via Nickelacycle Intermediates

“…Thec hiral phosphoramidite ligand [14] L*1 worked well to give 2h in 95 %y ield and 62 % ee. Thec hiral MOP ligand [15] L*2,P -stereogenic iminophosphorane [16] L*3,a nd the planar-chiral phosphine-olefin ligand [17] L*4 were also used, as these compounds should act as hemilabile bidentate ligands.However,any improvements on the results were not observed. Nevertheless,t he result given by L*1 shows promising reactivity of nickel(0)/chiral monodentate phosphine systems in this first example of an ickel(0)-catalyzed asymmetric carbonylative cycloaddition of ene-imines and CO.F urther studies to attain higher enantioselectivity are currently ongoing.…”

Enantioselective Preparation of Planar‐Chiral Transition Metal Complexes by Asymmetric Olefin‐Metathesis Reactions in Metal Coordination Spheres

“…Diarylphosphino-derivatives 21, which was prepared from (R)or (S)-20 a, were outstanding chiral phosphine-olefin ligands in the various rhodium-catalyzed asymmetric addition reactions of organoboron nucleophiles [28] showing the better robustness (i. e., easier handling) as well as the higher enantioselectivity than phosphine-olefin ligands 15 that were with a planar-chiral (η 6 -arene)chromium(0) framework. [32]…”