Alexis A. Oswald

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

Rh(CO)2(acac) reacts with P(m-C6H4SO3Na.H2O)3 (P/Rh > 3.5) in water under CO to give HRh(CO)[P(m-C6H4SO3Na)3]3 (1a), the structure of which is similar to HRh(CO) (PPh3)3 (1b). High pressure NMR spectra of an aqueous solution containing1a and three molar excess of P(m-C6H4SO3Na)3 does not show the formation of new species up to 200 atm of CO∶H2(1∶1). In contrast,1b, in the presence of three molar excess of PPh3, is completely converted to HRh(CO)2(PPh3)2 (2b) under 30 atm CO/H2(1∶1) in toluene. The activation energy of the dissociation of P(m-C6H4SO3Na)3 from1a in water was found to be 30±1 kcal/mol, which is 11±1 kcal/mol higher than the dissociation of PPh3 from1b in toluene.

Steric Effects on the Synthesis, Structure, Reactivity and Selectivity of t-Phosphine Rhodium Complex Hydroformylation Catalysts

Abstract Bulky trivalent phosphorus ligands of transition metal complexes were often observed to affect catalyst activity and selectivity. In the area of the low pressure hydroformylation of α-olefins in the presence of rhodium complexes, Pruett and Smith observed early (1) that the use of bulky ortho-substituted phosphite ester ligands leads to a decrease of the ratio of straight chain versus branched aldehyde products (n/i ratio). More recently van Leeuwen and Roobek have shown (2) that rhodium complexes of such bulky ligands are much more active catalysts than the much studied triphenylphosphine-rhodium catalyst system, in the hydroformylation of linear internal and branched terminal olefins. They suggested that for steric reasons only two bulky ligands could be coordinated to the same rhodium in such complexes and that such ligands could increase the coordinative unsaturation of rhodium, thus leading to a higher reactivity. Indeed a number of coordinatively unsaturated rhodium carbonyl complexes of bu...