The Studies Of Olefin Hydroformylation Catalyzed By Rhodium-Phosphine Complexes

Oil-soluble diphosphine ligands: 2,2'-bis(diphenylphosphinomethyl) -1,1'-biphenyl (BISBI), l,2-bis(diphenylphosphinomethyl) benzene (BDPX), 1,8-bis (diphenylphosphinomethyl) naphthalene (BDNA), 2,2'-bis(diphenylphosphino) -l,l'-binaphthyl (BINAP), water-soluble diphosphine ligands: solphonated l,2-bis(diphenylphosphmomethyl) benzene (BDPXS), solphonated 2,2'-bis (diphenylphosphinomethyl)-l,r-biphenyl(BISBIS),and amphiphilic diphosphine ligand with N atom: (Ph2PCH2)2NCH2CH2OCH2CH2NHCH2CH2P03Na2 were studied hi olefin hydroformylation with rhodium-phosphuie complexes. The diphosphine ligands can form two chelated isomers of trigonal bipyramidal diphosphine-rhodium complexes by means of the exchange between monophospbine and diphosphine. hi the complexes the diphosphines might occupy two equatorial sites (ee configuration) or one equatorial and one apical sites (ae configuration).The lower conversions of olefins hi the presence of diphosphines than that of monophosphinescan be attributed to me stabilization of rhodium complexes by the chelation of diphosphine ligands. Owing to the chelation of diphosphine ligands with the metal center, the coordination environments of rhodium complexes become sterically more congested. Accordingly, less-crowed linear alkyl-rhodium intermediates are favorably formed, thereby the yields of linear aldehyde hi the products increase.The BISBI and BISBIS ligands which show the highest regioselectivity for linear aldehyde not only have relatively wide natural bite angles but also aremore flexible and can accommodate the bite angles with little additional strain energy. They preferentially occupy diequatorial sites and form the rhodium complexes of ee configuration, which have higher selectivity for linear aldehyde formation than apical-equatorial chelate rhodium complexes of ae configuration.Cationic surfactant cetyltrimethyl ammonium bromide (CTAB) is effective for accelerating 1-dodecene hydroformylation in the organic-aqueous biphasic system. The addition of butanol can decrease the CMC (critical micelle concentration) of CTAB, so the reaction rates increase obviously in low concentration of CTAB. The reaction rate of 1-dodecene hydroformylation in bicontinuous phase is faster than that in dominant-organic solvent phase or in dominant-aqueous phase. The results suggest that the microcircumstances in three catalytic systems are different.The hydroformylation of acrylic esters including methyl acrylate, butyl acrylate and methyl methacrylate was carried out in the biphasic systems in the presence of rhodium-phosphine complexes with the water-soluble ligands. The results suggest that the electronic effect exerted by functional groups of esters is an important factor for the rate and the regioselectivity of hydroformylation. Acrylic esters show in general a strong preference for the formation of the branched isomers. It was suggested that this might be due to the higher stability of rhodium- alpha -C bond hi acrylic ester formed upon alkene insertion Rh~H bond than rhodium-beta-C bond because of substantial stabilization of the formal negative charge developing at alpha -C.In aquous-organic biphasic systems, the TOF values are 3.3 min-1,2.3 min-1, 1.8 min-1 for methyl acrylate, butyl acrylate and methyl methacrylate, respectively. The decrease of TOF values is consistent with the change of their solubilities in water. It suggests that the reaction rates are governed by the transfer of substrates.