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{mu-S(CH2)(3)N(Me-2)}(2)(COD)(2)]/PR3 (R = Ph, OPh), [Rh-2{mu-S(CH2)(2)S}(COD)(2)]/PPh3, [Rh-2{mu-S(CH2)(4)S}(COD)(2)](2)/PPh3, [Rh-2{mu-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 degrees C, 5-30 bar). The activities and selectivities, obtained during the hydroformylation of l-hexene using these systems as catalyst precursors, can be fully accounted for by the mononuclear species observed. Deuterioformylation experiments using dinuclear [Rh-2{mu-S(CH2)(3)N(Me-2)}(2)(COD)(2)]/PR3 systems lent no support to a dinuclear mechanism.