Synthesis, Structural Characterization, and Hydroformylation Activity of Rhodium(I) Complexes with a Polar Phosphinoferrocene Sulfonate Ligand
Abstract
1'-(Diphenylphosphino)ferrocene-1-sulfonic acid (HL), isolated from the salt (Et3NH)L on an ion exchanger, reacts with Rh(I) complexes [Rh(acac)(CO)(PR3)] (acac = acetylacetonato-kappa O-2,O') to give complexes of the type [Rh(CO)(PR3)(Ph(2)PfcSO(3)-kappa O-2,P)] (1ad; R = Ph (a), Cy (b), 2-furyl (c), and OMe (d); fc = ferrocene-1,1'-diyl). In an analogous reaction with [Rh(acac)(nbd)] (nbd = eta(2):eta(2)-norbornadiene), HL produces [Rh(nbd)(Ph(2)PfcSO(3)-kappa O-2,P)] (2).
Adding (Et3NH)L (2 equiv per Rh) to [Rh(;-Cl)(CO)(2)](2) and [Rh(acac)(CO)(2)] gives rise to the cationic complexes trans-(Et3NH)(2)[RhCl(CO)(Ph(2)PfcSO(3)-kappa P)(2)] (3) and (Et3NH)[Rh(CO)(Ph(2)PfcSO(3)-kappa O-2,P)(Ph(2)PfcSO(3)-kappa P)] (4), respectively. In complex 4, resulting from the simultaneous substitution of a CO ligand and acidbase replacement of the acac ligand, the P-monodentate and O,P-chelating phosphinoferrocene sulfonate ligands rapidly interconvert (in a solution).
All compounds were characterized by spectroscopic methods and by elemental analysis, and the crystal structures of 1aMe(2)CO, solvated 1b, 2, and 4H(2)O were determined. Furthermore, the catalytic activity of all Rh(I) complexes was assessed in hydroformylation of vinyl acetate under solvent-free conditions at 80 degrees C and at 20 bar of synthesis gas (H-2/CO = 1:1).
High conversion with good selectivity to iso-aldehyde was observed for 1a(1)/2H2O and 4(1)/2H2O. When applied to on-water hydroformylation of 1-hexene (80 degrees C/10 bar), the complexes mainly promoted 1-hexene isomerization to 2-hexene.
However, two of them, 1a(1)/2H2O and 1c, exhibited reasonable selectivity to aldehydes and preferentially produced the linear product (n/iso ratios up to 3).