Studies of Homogeneous Dirhodium Catalyst System
Hydroformylation studies were conducted to investigate the effects of various H&sub2;/CO ratios on rac-[Rh&sub2;H&sub2;(μ-CO)&sub2;(et,ph-P4)]²+;, a dirhodium tetraphosphine catalyst system. Similar experiments were also conducted with monometallic catalysts based on BISBI, NAPHOS, and Xantphos, some of the best bisphosphine ligands for hydroformylation catalysis. This was due to the lack of information in literature on the effects of variable ratios and pressures on activities and selectivities of catalysts that contain bisphosphine ligands, and these studies were also used as a basis of comparison for the dirhodium system. Results indicate that the dirhodium system is more efficient with higher H&sub2;/CO ratios (2:1, 90 psig total pressure appears to be near optimum) with good turnover frequencies, high regioselectivities, and lower catalyst fragmentation reactions in comparison to standard 1:1 H&sub2;/CO conditions. The dirhodium catalyst appears to be extremely sensitive to CO induced loss of Rh to deactivate the catalyst. The monometallic systems show that higher H&sub2;/CO ratios increase catalytic activity and yield higher aldehyde regioselectivities, but also increase the percentage of olefin isomerization. The monometallic systems also demonstrate Rh-induced phosphine fragmentation reactions and catalyst decomposition due to the lower CO partial pressures.
Due to the increased activity and selectivity obtained when using a 2:1 H&sub2;/CO ratio, in situ high pressure IR studies were conducted to determine if there were any structural differences between the dirhodium catalyst generated at a 1:1 H&sub2;/CO ratio and a 2:1 H&sub2;/CO ratio. Also due to the increased activity and selectivity in 30% water/acetone (by volume) in comparison to acetone, solvent effect studies were conducted to compare structural differences in acetone and 30% water/acetone. Preliminary IR studies suggest that there are not any structural differences in the 2:1 H&sub2;/CO ratio and 30% water/acetone studies in comparison to standard hydroformylation conditions.
Advisor:Stanley, George G.; Chan, Juilia Y.; Maverick, Andrew W.; Zhang, Donghui; Dokka, Roy K
School:Louisiana State University in Shreveport
School Location:USA - Louisiana
Source Type:Master's Thesis
Date of Publication:04/15/2009