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Solution structures and behavior of trans-RuH(eta(1)-BH(4)) (binap)(1,2-diamine) complexes
Christian A Sandoval1, Yoshiki Yamaguchi, Takeshi Ohkuma
1Department of Chemistry and Research Center for Materials Science, Nagoya University, Chikusa, Nagoya 464-8602, Japan.
Magnetic Resonance in Chemistry : MRC
|December 6, 2005
Summary
Ruthenium precatalysts featuring a borohydride ligand activate without a base due to acidic amine protons. This enables efficient generation of catalytically active species for various applications.
Area of Science:
- Organometallic Chemistry
- Catalysis
- Coordination Chemistry
Background:
- Ruthenium complexes are vital precatalysts in various chemical transformations.
- Understanding precatalyst activation mechanisms is crucial for developing efficient catalytic systems.
- Traditional ruthenium precatalysts often require strong bases for activation.
Purpose of the Study:
- To determine the solution structures of trans-RuH(eta(1)-BH(4))[(S)-tolbinap](1,2-diamine) precatalysts.
- To investigate the activation mechanism of these novel precatalysts.
- To compare their activation pathway with existing ruthenium chloride precatalysts.
Main Methods:
- 2D NMR spectroscopy (COSY, HMQC, HSQC) was employed to elucidate solution structures.
- Nuclear Overhauser Effect (NOE) experiments using DPFGSE were utilized for structural determination.
- H/D exchange studies in deuterated solvents were performed to assess proton acidity.
Main Results:
- The octahedral Ru complexes adopt a trans configuration with hydride and borohydride ligands.
- Amine protons of the precatalysts exhibit high acidity, undergoing facile H/D exchange.
- The BH(4) ligand's lability and proton acidity facilitate base-free activation.
Conclusions:
- trans-RuH(eta(1)-BH(4))[(S)-tolbinap](1,2-diamine) precatalysts activate efficiently without external bases.
- This activation pathway contrasts with the base requirement for trans-RuCl(2)[(S)-tolbinap](1,2-diamine) precatalysts.
- The precatalysts convert to catalytically active cationic ruthenium species in solution.