(+)-1,2-Bis((2S,5S)-2,5-dimethylphospholano)benzene(1,5-cyclooctadiene)rhodium(I) tetrafluoroborate
[CAS# 205064-10-4]

Identification

• Classification: Organic raw materials >> Organometallic compound >> Organic rhodium
• Name: (+)-1,2-Bis((2S,5S)-2,5-dimethylphospholano)benzene(1,5-cyclooctadiene)rhodium(I) tetrafluoroborate
• Synonyms: Cycloocta-1,5-diene (2S,5S)-1-[2-[(2S,5S)-2,5-dimethylphospholan-1-yl]phenyl]-2,5-dimethylphospholane rhodium;tetrafluoroborate
• Molecular Formula: C₂₆H₃₈BF₄P₂Rh
• Molecular Weight: 602.24
• CAS Registry Number: 205064-10-4
• SMILES: [F-][B+3]([F-])([F-])[F-].C[C@@H]1P2([C@@H](C)CC1)[Rh+]345(P6([C@H](CC[C@@H]6C)C)C7=CC=CC=C27)C8=C3CCC4=C5CC8

Safety Data

• Hazard Symbols: GHS05 Danger
• Hazard Statements: H314
• Precautionary Statements: P501-P260-P264-P280-P303+P361+P353-P301+P330+P331-P363-P304+P340+P310-P305+P351+P338+P310-P405
• Transport Information: UN 1759

Discovory and Applicatios

(+)-1,2-Bis((2S,5S)-2,5-dimethylphospholano)benzene(1,5-cyclooctadiene)rhodium(I) tetrafluoroborate is a chiral organometallic complex used primarily as a catalyst in asymmetric hydrogenation reactions. The complex consists of a rhodium(I) center coordinated to three ligands: (1) 1,5-cyclooctadiene (COD), which acts as a stabilizing diene ligand; (2) a bidentate chiral diphosphine ligand, (+)-1,2-bis((2S,5S)-2,5-dimethylphospholano)benzene, commonly known as (S,S)-Me₂BoPhoz; and (3) a counterion, tetrafluoroborate (BF₄⁻), which balances the positive charge on the metal complex.

This compound belongs to a family of highly enantioselective rhodium-based catalysts that have been developed to promote homogeneous asymmetric hydrogenation of prochiral olefins, enamides, and dehydroamino acid derivatives. The chiral diphosphine ligand imparts stereoselectivity, enabling the selective formation of one enantiomer of the hydrogenated product over the other. The (2S,5S)-2,5-dimethylphospholane groups are crucial for creating a well-defined chiral environment around the rhodium center.

The development of this catalyst is part of ongoing advances in enantioselective catalysis, particularly those reported in the 1990s and 2000s. The BoPhoz ligand family, from which the diphosphine component is derived, was designed to combine both steric and electronic properties conducive to high enantioselectivity. The incorporation of phospholane rings into a biphenyl backbone enhances both rigidity and asymmetry in the ligand geometry.

The rhodium(I) center coordinated with COD and the chiral diphosphine ligand forms a highly active catalyst precursor. Upon activation, typically under hydrogen gas, the COD ligand is displaced, allowing the formation of a catalytically active species that binds the substrate. Hydrogenation proceeds via oxidative addition of H₂, migratory insertion into the coordinated alkene or imine substrate, and reductive elimination to release the chiral hydrogenated product.

Applications of this catalyst include the synthesis of chiral amines, amino acids, and pharmaceutical intermediates. It has been used in academic and industrial settings to produce enantiomerically enriched compounds with high yields and optical purities. Due to its predictable selectivity and efficiency, it is particularly useful in the synthesis of compounds where the absolute configuration of the product is critical for biological activity.

The catalyst is usually handled under inert atmosphere conditions (argon or nitrogen) to avoid oxidation or hydrolysis of the metal center. It is typically used in solvents such as dichloromethane, ethanol, or methanol, depending on the substrate and desired reaction conditions. Catalytic loadings are often in the range of 0.1–1 mol%, with reaction temperatures ranging from 0 °C to 50 °C, and pressures of hydrogen between 1 and 10 atm.

Stability of the complex is generally good under dry and inert conditions, but it may degrade in the presence of moisture, oxygen, or strong acids and bases. The tetrafluoroborate counterion is non-coordinating and helps maintain the complex in solution while having minimal influence on the catalytic cycle.

In summary, (+)-1,2-bis((2S,5S)-2,5-dimethylphospholano)benzene(1,5-cyclooctadiene)rhodium(I) tetrafluoroborate is a highly selective chiral rhodium complex used as a homogeneous catalyst in asymmetric hydrogenation. Its effectiveness arises from the precise chiral environment provided by the BoPhoz-type ligand, enabling the synthesis of enantiomerically enriched compounds critical to modern pharmaceutical and fine chemical production.