OperandoHigh-Pressure NMR and IR Study of the Hydroformylation of 1-Hexene by 1,1‘-Bis(Diarylphosphino)metallocene-Modified Rhodium(I) Catalysts

Abstract

Some rhodium(I) complexes of the general formula [Rh(P−P)(COD)]X were synthesized and characterized by multinuclear NMR spectroscopy (COD = cyclocta-1,5-diene; P−P = 1,1‘-bis(diphenylphosphino)ferrocene, dppf, X = BPh4, PF6; P−P = 1,1‘-bis(diphenylphosphino)ruthenocene, dppr, X = BPh4; P−P = 1,1‘-bis(diphenylphosphino)osmocene, dppo, X = BPh4, PF6; P−P = 1,1‘-bis(diphenylphosphino)octamethylferrocene, dppomf, X = BAr‘4; P−P = (1,1‘-bis(di(o-isopropylphenyl)phosphino)ferrocene, o-iPr-dppf, X = BAr‘4). These complexes were employed as catalyst precursors for the hydroformylation of 1-hexene in THF either in standard autoclaves or in high-pressure (HP) NMR tubes and IR cells. All catalysts exhibited good activity (TOFs ranging from 700 to 1000 mol aldehyde (mol cat)-1 h-1) and moderate regioselectivity in n-heptanal (67−74%). Irrespective of the rhodium precursor, the HP-NMR experiments under catalytic conditions showed the formation of kinetic dicarbonyl products at room temperature, which were independentl...