“…Either the resulting monometallic complex can dimerize to form the double-ligand dirhodium complex 2 , or the et,ph-P4 ligand can wrap around a single rhodium, forming the η 4 -coordinated complex 3 . The closely related complexes [ rac,rac -Rh 2 (et,ph-P4) 2 ] 2+ and [ rac -RhCl 2 (η 4 -et,ph-P4)] + have been characterized …”
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.
“…Either the resulting monometallic complex can dimerize to form the double-ligand dirhodium complex 2 , or the et,ph-P4 ligand can wrap around a single rhodium, forming the η 4 -coordinated complex 3 . The closely related complexes [ rac,rac -Rh 2 (et,ph-P4) 2 ] 2+ and [ rac -RhCl 2 (η 4 -et,ph-P4)] + have been characterized …”
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.
“…The smaller spatial extent of the internal phosphorus lone pair can lead to somewhat shorter Rh−P distances. We have observed these effects in other transition metal et,ph-P4 structures. − ,, 1 ORTEP plots for 3a (top) and the overlapping disordered complexes 3c and 4 (bottom). Hydrogens, counteranions, and solvent molecules are not shown for clarity on both structures.…”
Section: Resultsmentioning
confidence: 69%
“…Given the mainly alkylated, strongly coordinating nature of the et,ph-P4 ligand, this is not especially surprising. Our studies into the nature of the complexes formed when 2 equiv of et,ph-P4 ligand are reacted with 2 equiv of [Rh(nbd) 2 ](BF 4 ) revealed the formation of the double-ligand dinuclear complexes meso,meso- ( 2 mm ), meso,rac- ( 2mr ), and [ rac,rac -Rh 2 (et,ph-P4) 2 ] 2+ ( 2rr ) in low yields …”
Section: Introductionmentioning
confidence: 89%
“…The best isolated yield, for example, was only 20% for the [ rac,rac -Rh 2 (et,ph-P4) 2 ] 2+ complex,12a while the mixed meso,rac ( 2mr) complex was only made in trace amounts. The 31 P{ 1 H} NMR spectra of these reaction solutions clearly indicated the presence of a simple set of 31 P resonances (dt) at 56 and 9 ppm that stood out from the complex second-order resonances for the dirhodium double-P4 ligand complexes.…”
The first Rh complex with an eta(4)-coordinated rac-et,ph-P4 ligand [et,ph-P4 = (Et2PCH2CH2)(Ph)PCH2P(Ph)(CH2CH2PEt2)] has been synthesized by reacting [Rh(nbd)2]BF4 with meso- or rac-et,ph-P4 in dichloromethane. The reaction occurs fairly rapidly at room temperature to form [rac-RhCl2(eta(4)-et,ph-P4)](+) in high yields, regardless of whether one starts with mixed or even pure meso-et,ph-P4 ligand. This unusual and highly selective metal assisted isomerization of the meso-et,ph-P4 ligand to its rac-et,ph-P4 disastereomer will be discussed.
“…Neither of the rhodium products shown in Figure 2 is active for hydroformylation. Their structures are based on similar rhodium complexes that have been crystallographically characterized 10,11 and on 1 H and 31 P{ 1 H} NMR experiments of [Rh 2 (nbd) 2 (racet,ph-P4)] 2+ under H 2 /CO pressure. Therefore, the synthesis of a new tetraphosphine ligand in which the rotationally flexible ethylene linkage between the internal and external phosphines is replaced by a rigid phenylene group will lead to a much stronger chelate effect, inhibiting phosphine arm dissociation.…”
A new binucleating tetraphosphine ligand, rac- and meso-(Et2P-1,2-C6H4)P(Ph)CH2(Ph)P(1,2-C6H4PEt2) (et,ph-P4-Ph), has been synthesized. Separation and purification of the ligand diastereomers have been accomplished via column chromatography. Ni2Cl4(et,ph-P4-Ph) complexes of both diastereomers have been prepared in high yield and crystallographically characterized.
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