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

In situ high-pressure IR spectroscopy studies of the rhodium catalyst systems [Rh 2 {μ-S(CH 2 ) 3 N(Me 2 )} 2 (COD) 2 ]/PR 3 (R = Ph, OPh), [Rh 2 {μ-S(CH 2 ) 2 S}(COD) 2 ]/PPh 3, [Rh 2 {μ-S(CH 2 ) 4 S}(COD) 2 ] 2 /PPh 3, [Rh 2 {μ-XANTOSS}(COD) 2 ] 2 /PPh 3, and [Rh(acac)(CO) 2 ]/PR 3 (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 [Rh 2 {μ-S(CH 2 ) 3 N(Me 2 )} 2 (COD) 2 ]/PR 3 systems lent no support to a dinuclear mechanism.