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.
Keywords: BINOL, diphosphite, ditopic, hydroformylation, rhodium, regioselectivity, Lithium ion.
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