High-pressure NMR studies of the water soluble rhodium hydroformylation system

High‐Pressure 31P{1H} NMR Studies of RhH(CO)(TPPTS)3 in the Presence of Methylated Cyclodextrins: New Light on Rhodium‐Catalyzed Hydroformylation Reaction Assisted by Cyclodextrins

“…Without RAME-b-CD, a quartet at d À 9.7 ppm ( 2 J H-P 13.5 Hz) was clearly observed in the hydride region. This quartet is consistent with trigonal bipyramidal geometry of complex 1 as previously noted [14] and confirms the presence of three TPPTS phosphines on the rhodium. When increasing amounts of RAME-b-CD were added to the medium (3 and 9 equivalents), the hydride signal disappeared.…”

“…These results are in good agreement with those reported in the literature. [14] Indeed, as already shown by Horva ¬ th and co-workers, an aqueous solution containing 1 and a three molar excess of TPPTS did not lead to the formation of new species up to 200 atm of CO/H 2 . Actually, the fact that the fivecoordinate complex 2 could not be detected demonstrates that an excess of TPPTS displaced the equilibrium between 1 and 2 towards 1 even under CO pressure.…”

“…[12,14] The two small broad doublets with a 2 : 1 ratio at 24.5 ppm ( [12a,13] The percentage of each complex was estimated relative to the total amount of rhodium initially introduced in the medium by integration of the three signals. More precisely, the percentages calculation takes the number of phosphorus and rhodium atoms of each species into account.…”

“…This behavior was attributed to the high stability of complex 1 due to the presence of highly ordered hydration sphere around the complex 1. [14,17] In the presence of RAME-b-CD, the above equilibria lie undoubtedly in favor of phosphine low-coordinated rhodium species such as 2, 3, 4, 5 and likely 7 due to the formation of inclusion complexes between TPPTS and RAME-b-CD as evidenced by this HP NMR study. This shift of equilibria is very likely the …”

“…From the point of view of the linear to branched aldehydes ratio, detailed mechanistic studies on the [RhH(CO)(TPPTS) 3 ] hydroformylation catalyst systems have established that the two key catalytic species leading to linear and branched aldehydes are the coordinatively unsaturated complexes [RhH(CO)(TPPTS) 2 ] (6) and [RhH(CO) 2 (TPPTS)] (7), respectively (Scheme 5). [2,14] Without cyclodextrin, the reaction equilibria depicted in Scheme 5 lie in favor of 1 and 6 resulting in a high normal to branched aldehydes ratio. This behavior was attributed to the high stability of complex 1 due to the presence of highly ordered hydration sphere around the complex 1.…”