Synthesis of Optically Pure Helicene Metallocenes.

Area of Science:

• Organometallic Chemistry
• Chiral Synthesis
• Helicene Chemistry

Background:

• Helicenes are polycyclic aromatic hydrocarbons known for their unique helical structure and chirality.
• Ruthenocenes and ferrocenes are organometallic compounds with diverse applications in catalysis and materials science.
• Synthesizing chiral organometallic complexes with bulky ligands presents synthetic challenges.

Purpose of the Study:

• To synthesize novel mono- and bis-helicene ruthenocenes and a ferrocene analogue.
• To explore the coordination chemistry of a [7]helicene ligand with a cyclopentadienyl moiety.
• To isolate and characterize the chiral properties of the synthesized organometallic complexes.

Main Methods:

• Synthesis of rac-9H-cyclopenta[1,2-c:4,3-c']diphenanthrenyl anion precursor.
• Coordination of the [7]helicene ligand with ruthenium and iron precursors.
• Separation of diastereomers (rac-2 and meso-2) and isolation of enantiomers.
• Characterization using techniques such as NMR spectroscopy, X-ray crystallography, optical rotation, and circular dichroism (CD).

Main Results:

• Successful synthesis of mono-helicene ruthenocene (1), bis-helicene ruthenocene (2), and its iron analogue (1_Fe).
• Isolation of diastereomers rac-2 and meso-2 in a 7:3 ratio from the racemic ligand precursor.
• High racemization barrier of the [7]helicene ligand allowed for the isolation of pure enantiomers.
• The enantiomerically pure complexes displayed large optical rotations and intense circular dichroism (CD) responses.

Conclusions:

• Novel chiral ruthenocene and ferrocene complexes incorporating a [7]helicene ligand were synthesized.
• The high configurational stability of the [7]helicene ligand facilitates the isolation of enantiopure organometallic compounds.
• These chiral complexes exhibit significant chiroptical properties, indicating potential applications in asymmetric catalysis or molecular recognition.