Polar Phase Hydroformylation:  The Dramatic Effect of Water on Mono- and Dirhodium Catalysts

Abstract

The addition of 30% water (by volume) to acetone creates a remarkably effective polar phase solvent system for a dicationic dirhodium tetraphosphine hydroformylation catalyst. The initial turnover frequency (TOF) increases by 265% (to 73 min-1) for the hydroformylation of 1-hexene relative to the initial TOF in pure acetone (20 min-1). The aldehyde linear to branched (L:B) ratio increases to 33:1, and alkene isomerization and hydrogenation side reactions are essentially eliminated. Comparisons with monometallic rhodium catalysts based on PPh3, Bisbi, Naphos, and Xantphos ligands demonstrate that this polar-phase bimetallic catalyst is one of the fastest and most selective hydroformylation systems known under these mild conditions (90 degrees C, 6.2 bar H2/CO). The monometallic catalysts also show rate enhancements (although considerably smaller) in water-acetone, but Rh-Xantphos does show a large increase of 115%, with considerably reduced alkene isomerization side reactions. The dramatic effect of water on the dirhodium catalyst system is believed to be due to simple inhibition of the fragmentation of the catalytically active species into inactive mono- and bimetallic complexes.

21 Organometallic chemistry of bi- and poly-nuclear complexes

“…60,61 The hydroformylation activity of [rac-Rh 2 (nbd) 2 (Et,Ph-P 4 )][BF 4 ] 2 [nbd ñorbornadiene; Et,Ph-P 4 ~(Et 2 PCH 2 CH 2 )P(Ph)CH 2 P(Ph)(CH 2 CH 2 PEt 2 )] is significantly enhanced in 30% water-acetone solvent mixtures, thought to be due to the inhibition of phosphine dissociation and catalyst fragmentation in this medium. 62 IR spectra of Rh n (CO) (n ~6-20) have been recorded in the gas-phase using IR multiphoton depletion (IRMPD) spectroscopy. The n(CO) absorption is surprisingly invariate with cluster size, tending towards 1964 cm 21 in the larger clusters.…”

Promoting effect of water on 1-hexene hydroformylation catalyzed by aminophosphine–rhodium complexes

“…From all these data, we believe that the nitrogen atom of the P-N ligand is weakly coordinated to the Rh center in the complex trans-[Rh(CO)Cl (4) 2 ] and trans-[Rh(CO)Cl (5) 2 ]. Recently, it has been reported that added water causes a relatively dramatic 115% rate increase for Rh-Xantphos system [30] where the central oxygen atom of the Xantphos ligand is coordinated to the metal and have shown that is a very poor hydroformylation catalyst [31]. The addition of water was believed to engage in hydrogen bonding to the oxygen atom of the coordination and generating more of the active unsaturated HRh(CO)(g 2 -Xantphos) catalyst that could react with alkene to start hydroformylation.…”

Highly Efficient Hydroformylation of 1‐Hexene over an ortho‐Metallated Rhodium(I) Complex Anchored on a 2D‐Hexagonal Mesoporous Material

“…Different media are also frequently used for such conversions, for example, supercritical carbon dioxide, [34,35] ionic liquids [36,37] and organic solvents. [38][39][40] Rh I complexes have also been used for reductive carbonylation [41] and oxidation reactions. [42] He et al have reported a mesoporous silicaanchored Rh-P complex as a catalyst in olefin hydroformylation.…”