High-Pressure Infrared Studies of Rhodium Complexes Containing Thiolate Bridge Ligands under Hydroformylation Conditions

Abstract

In situ high-pressure IR spectroscopy studies of the rhodium catalyst systems [Rh2{μ-S(CH2)3N(Me2)}2(COD)2]/PR3 (R = Ph, OPh), [Rh2{μ-S(CH2)2S}(COD)2]/PPh3, [Rh2{μ-S(CH2)4S}(COD)2]2/PPh3, [Rh2{μ-XANTOSS}(COD)2]2/PPh3, and [Rh(acac)(CO)2]/PR3 (R = Ph, OPh) revealed the presence of mononuclear rhodium hydride species under hydroformylation conditions (80 °C, 5−30 bar). The activities and selectivities, obtained during the hydroformylation of 1-hexene using these systems as catalyst precursors, can be fully accounted for by the mononuclear species observed. Deuterioformylation experiments using dinuclear [Rh2{μ-S(CH2)3N(Me2)}2(COD)2]/PR3 systems lent no support to a dinuclear mechanism.

Amino‐phosphanes in RhI‐Catalyzed Hydroformylation: New Mechanistic Insights Using D2O as Deuterium‐Labeling Agent

“…In other words, the amino-phosphane ligand does not act as a "proton messenger", unlike the pyridinylphosphane ligand in the palladium catalyzed alkyne methoxy-carbonylation process. [2] Furthermore, this result also excludes the possibility of a binuclear aldehyde elimination process between a rhodium acyl and a rhodium hydride species, [39,40] for this system. These observations are summarized in Scheme 4.…”

Synthesis and characterisation of a new class of phosphine-phosphonite ferrocenediyl dinuclear rhodium complexes

“…Interestingly, the signals for the other carbon atoms from the phenyl were detected as only five doublets, suggesting a fast exchange-rotation not observed for the menthyl moieties: n, d Dinuclear rhodium complexes have been subject of interest for use in the important oxo-process [7,8]. Potential cooperating effects between two metal centres have been studied and debated [9][10][11]. Stanley and coworkers, [7,12] have shown that the dinuclear symmetric rhodium complex rac-[Rh 2 H 2 (l-CO) 2 (CO) 2 (eLTTP)] [BF 4 ] 2 (where eLTTP is the ethyl-substituted linear tetratertiary phosphine Et 2 P-(CH 2 ) 2 PPh-(CH 2 )-PPh-(CH 2 ) 2 -PEt 2 ) catalyses the hex-1-ene hydroformylation at substrate/catalyst ratio of 900: with 85% conversion and high selectivity in a few hours, while its monometallic analogue only affords poor activity (2% conversion) and selectivity [13].…”

Dormant States of Rhodium Hydroformylation Catalysts: Carboalkoxyrhodium Complex Formed from Enones in the Alkene Feed

“…We have used in situ high-pressure IR spectroscopy in conjunction with (high-pressure) NMR spectroscopy to detect and characterize the catalyst under actual catalytic conditions. [5] Employing NMR spectroscopy studies Brown and Kent have shown that 1 exists as a mixture of two rapidly equilibrating trigonal-bipyramidal isomers in a diequatorial (ee) to equatorial-apical (ea) isomer ratio of 85:15 (Scheme 1). [6] The HP-IR spectrum of 1 has four carbonyl bands (atñ n = 2043, 1997, 1986, and 1953 cm À1 ) that have been assigned to the two isomers.…”