Synthesis, characterization and coordination chemistry of a new phosphite–ether ligand: The effects of alkali metal salts and the ligand/Rh molar ratio on the catalytic activity and regioselectivity of a Rh(I) complex of this ligand in the hydroformylation of styrene

Abstract

We have recently reported that the addition of alkali metal salts to styrene hydroformylation reactions catalyzed by Rh(I) complexes of bis(phosphite) ligands can significantly improve the iso/ n regioselectivity. To better understand the effects of the alkali metal salts on these styrene hydroformylation reactions, a monodentate phosphite–ether ligand, (2,2′-C 12H 8O 2)POCH 2CH 2OCH 3, 1 has been prepared, and its Rh(I) complex has been evaluated as a catalyst for the hydroformylation of styrene. Both the activity and regioselectivity of the catalyst are sensitive to the ligand:Rh molar ratio and to the presence of salts such as LiBPh 4·3dme, NaBPh 4 and HgCl 2. The most active catalyst has a 1:2.5 Rh:1 molar ratio and a 1:8 Rh:Li + molar ratio, but the most regioselective catalyst has a 1:8.2 Rh:1 ratio and a 1:4 Rh:Li + ratio. Model complexes for various steps in the catalytic cycle, cis-Mo(CO) 4( 1) 2, 6, cis-PtCl 2( 1) 2, 7, and PdCl 2( 1) 2, 8, have been synthesized and characterized by multinuclear NMR spectroscopy and X-ray crystallography to provide insight into the factors that may affect the rates and regioselectivities of the hydroformylation catalysts. The cis– trans isomerization of 6 in the presence of catalytic amount HgCl 2 has been carried out to determine the cis– trans preference of 1 in the octahedral coordination geometry.