Privileged Chiral Bisphosphine Ligands: From DIPAMP to BINAPINE
Chiral bisphosphine ligands are the cornerstone of asymmetric hydrogenation. The evolution from DIPAMP (1970s) through CHIRAPHOS, PROPHOS, and SEGPHOS to modern variants like BINAPINE represents five decades of ligand design aimed at expanding substrate scope, improving enantioselectivity, and lowering catalyst loading. Each ligand in this lineage occupies a distinct niche in the modern catalytic toolkit.
The Lineage
DIPAMP (1970s, Monsanto)
DIPAMP (1,2-bis[(o-methoxyphenyl)phenylphosphino]ethane) was the first chiral ligand used in an industrial asymmetric hydrogenation — the Monsanto L-DOPA process. DIPAMP-Rh catalyzes the hydrogenation of α-acylaminoacrylic acids to give α-amino acids. Its historical importance and documented regulatory acceptance keep it on the shelf for legacy amino acid routes.
CHIRAPHOS (1970s)
CHIRAPHOS (2,3-bis(diphenylphosphino)butane) is a C₂-symmetric diphosphine derived from chiral 2,3-butanediol. CHIRAPHOS-Rh is used for enamide hydrogenation and offers complementary selectivity to DIPAMP for certain substrates.
PROPHOS (1980s)
PROPHOS (1,2-bis(diphenylphosphino)propane) is the simplest chiral diphosphine, with a single methyl stereocenter. PROPHOS-Rh is used for dehydroamino acid hydrogenation and serves as a benchmark for comparing new ligand designs.
SEGPHOS (1990s, Takasago)
SEGPHOS (5,5’-bis(diphenylphosphino)-4,4’-bi-1,3-benzodioxole) is a biaryl diphosphine with a narrower dihedral angle than BINAP. SEGPHOS-Ru and SEGPHOS-Rh deliver higher enantioselectivity than BINAP for sterically demanding ketones and olefins, particularly in β-keto ester and enamide hydrogenation.
BINAPINE (2000s, Zhang)
BINAPINE is a tunable P-chiral bisphosphine with superior performance for asymmetric hydrogenation of (E)- and (Z)-β-aryl-β-dehydroamino acid derivatives. BINAPINE-Rh delivers >99% ee on substrates where BINAP underperforms, making it the ligand of choice for challenging amino acid syntheses.
Choosing Among the Lineage
| Ligand | Best Substrate | Typical Metal |
|---|---|---|
| DIPAMP | α-Acylaminoacrylic acids | Rh |
| CHIRAPHOS | Enamides, dehydroamino acids | Rh |
| PROPHOS | Dehydroamino acids | Rh |
| SEGPHOS | β-Keto esters, aryl ketones | Ru, Rh |
| BINAPINE | β-Aryl dehydroamino acids | Rh |
Recommended Products
- (S)-DIPAMP / (R)-DIPAMP — legacy amino acid hydrogenation
- (S)-CHIRAPHOS / (R)-CHIRAPHOS — enamide hydrogenation
- (S)-PROPHOS / (R)-PROPHOS — benchmark diphosphine
- (S)-SEGPHOS / (R)-SEGPHOS — high-selectivity biaryl
- (S)-BINAPINE — P-chiral for β-aryl amino acids
The Screening Deck
Modern process chemistry groups maintain a screening deck of 20–50 chiral bisphosphines. The five ligands above — DIPAMP, CHIRAPHOS, PROPHOS, SEGPHOS, BINAPINE — represent the historical core of that deck and remain the first screen for any new asymmetric hydrogenation campaign.