New synthetic routes toward enantiopure nitrogen donor ligands.
New polypyridylic chiral ligands, having either C3 or lower symmetry, have been prepared via a de novo construction of the pyridine nucleus by means of Kröhnke methodology in the key step. The chiral moieties of these ligands originate from the monoterpen chiral pool, namely (-)-alpha-pinene ((-)-14, (-)-15) and (-)-myrtenal ((-)-9, (-)-10). Extension of the above-mentioned asymmetric synthesis procedure to the preparation of enantiopure derivatives of some commonly used polypyridylic ligands has been achieved through a new aldehyde building block ((-)-16). As an example, the synthesis of a chiral derivative of N,N-bis(2-pyridylmethyl)ethylamine (bpea) ligand, (-)-19, has been performed to illustrate the viability of the method. The coordinative ability of the ligands has been tested through the synthesis and characterization of complexes [Mn((-)-19)Br2], (-)-20, and [RuCl((-)-10)(bpy)](BF4), (-)-21. Some preliminary results related to the enantioselective catalytic epoxidation of styrene with the ruthenium complex are also presented.
Sala
Xavier
X
Departament de Química, Universitat de Girona, Campus Montilivi s /n, E-17071 Girona, Spain.
Rodríguez
Anna M
AM
Rodríguez
Montserrat
M
Romero
Isabel
I
Parella
Teodor
T
von Zelewsky
Alexander
A
Llobet
Antoni
A
Benet-Buchholz
Jordi
J