Andreia F. Peixoto, Artur R. Abreu, Ana R. Almeida, Angela Neves, Paulo E. Abreu, Maria J.S.M. Moreno, Juan C. Bayon, Alberto A.C.C. Pais and Mariette M. Pereira Pages 301 - 309 ( 9 )
BINOL-based diphosphite ligands containing oxygen or nitrogen heteroatoms are currently a new class of promising ligands for homogeneous catalysis. Herein we present a useful strategy to synthesize ditopic (R)-BINOL-based diphosphites, containing pyridyl or propyl ether bridges between BINOL fragments in high isolated yields (50-92 %). Their rhodium complexes were evaluated in styrene hydroformylation, in which a moderate regioselectivity for the branched aldehyde was observed. The addition of a lithium salt led to a significant increase in the regioselectivity (25 %) for the branched aldehyde. This interesting observation has been rationalized based on a full two-level factorial design with 3 factors, including pressure, temperature and the Li/Rh ratio, using Rh/10 as model catalyst. The improvement of the regioselectivity in the presence of lithium salts has been interpreted through31PNMR spectroscopy and semiempirical PM6 computational studies.
BINOL, diphosphite, ditopic, hydroformylation, rhodium, regioselectivity, Lithium ion.
Centro de Química de Coimbra, Departmento de Química, Universidade de Coimbra, Rua Larga, 3030-535 Coimbra, Portugal.