Ionic Phosphines:Synthesis,Characterization And Applications To Hydroformylation And Tandem Hydroformylation

Homogeneous hydroformylation is a 100%atom efficient route for the addition of syngas to olefins to produce aldehydes which is one of most important processes.Phosphines modified rhodium complexes are the most efficient catalysts for this reaction.The steric and electronic effects of phosphines are critical to the catalytic activity and chemo-/regio-selectivity of hydroformylation.Therefore,a great deal of work has been devoted to the design and synthesis of various ligands with uniquesteric and electronic effects.In addition,owing to the versatile chemical reactivity of aldehyde group,the obtained aldehyde products from hydroformylation are required to convert to more valuable and stable products such as alcohols,ketones,acetals,amines products etc.Therefore,hydroformylation combined with acetalization,condensation,or hydrogenation etc.to form tandem reaction sequences has become a promising and green synthetic method for production of high value-added chemicals with advantages of simplified process operation.On the other hand,the isolation and recycling of Rh-catalysts in homogeneous?tandem?hydroformylation of high boiling-point olefins remain challengeable.In this thesis,based on the importance and existing problems in hydroformylation and tandem hydroformylation,the following research work has been carried out which are summarized in three aspects:?1?Effects of diphosphines on catalytic activity and regioselectivity of Rh-catalysts for hydroformylation of 1-octene.In order to tailor the regioselectivity of hydroformylation?the ratio of the linear aldehydes to branched aldehydes?,a series of diphosphines with different electronic and steric effects were synthesized?Scheme 1?.The ionic diphosphines?L3 and L6?could be regarded as diphosphine-functionalized ionic liquids.Compared with the neutral diphosphines?L1 and L7?,the ionic diphosphines exhibited strong ?-acceptor ability and good tolerance to oxidative degradation?good stability?due to the intensive electron-withdrawing effect from positive-charged imidazolium rings on the neighbored P-atoms.The investigation of influence of the diphosphines as the auxiliary ligands on the catalytic performance of Rh?acac??CO?₂ for homogeneous hydroformylation of 1-octene indicated that,as for L1,without electrostatic repulsive effect,the two-PPh₂ were able to be conveniently located in cis-position?X-ray diffraction?,which is favorable for chelation to Rh-center.As a result,the regioselectivity to linear aldehydes could be significantly improved.The ratio of linear nonanals to branched nonanals was 7.1?L/B=7.1?.In contrast,due to the electrostatic repulsive force of the two positive charges of L3,the involved two-PPh₂ were located in tans-position,which renders less bulky steric hindrance for the regioselectivity to linear aldehydes as a result of low L/B?L/B=1.9?.Compared with L1(TOF=750 h^-1),L3 with strong ?-acceptor ability exhibited higher catalytic activity(TOF=805 h^-1).On the other hand,when the ionic diphosphine of L3 was used in combination with a RTIL?[PEmim]BF₄?as solvent,the Rh-L3 catalytic system could be locked in this ionic liquid solvent with the advantages of the facile separation,which solved the problem of catalyst recovery and recycling in homogeneous process.In addition,[PEmim]BF₄ could facilitate formation and stability of the Rh-H active species(v 2045 cm^-1),which were also supported by the in situ high-pressure FT-IR spectral analysis.?2?Bi-functional co-catalysis for tandem "hydroformylation-acetalization" over bi-functional ligandThe ionic ligand of L2?¹H/31P NMR,X-ray diffraction and CHN-elemental analysis etc,?as a bi-functinal ligand in combination of phosphino-frangement?-PPh₂?and Lewis acidic phosphonium was synthesized via the selective methylation of one P-atom in diphosphine L1.Due to the separation by the rigid phenyl ring,the incorporated-PPh₂ and Lewis acidic phosphonium were well retained without quenching problem.The investigation of influence of the bi-functinal ligand on the catalytic performance of Rh?acac??CO?₂ for homogeneous tandem"hydroformylation-acetalization" of 1-octene indicated that,L2 based Rh-catalyst exhibited bi-functional co-catalysis in terms of Rh-P complex catalyzed hydroformylation and Lewis acidic phosphonium catalyzed acetalization.As a result,the tandem "hydroformylation-acetalization" over L2 based Rh-catalyst could proceed more efficiently.In L2,the phosphonium not only acted as a Lewis acid organocatalyst to drive the sequential acetalization of aldehydes,but also contributed to the synergetic catalysis for the preceding hydroformylation through stabilizing the Rh-acyl intermediate with the phosphine cooperatively.In addition,L2 based Rh-catalyst was also generally applied to "hydroformylation-acetalization" of a wide range of olefins in the different alcohols with 42%-96%selectivities of acetals.Advantageously,as an ionic phosphonium-based ligand,L2 could be used with the RTIL?[Bmim]BF₄?solvent to immobilize the Rh-L2 catalysts,which solved the problem of catalyst recovery and recycling in homogeneous"hydroformylation-acetalization" process.?3?Tri-functional co-catalysis for tandem "hydroformylation-aldol condensation-hydrogenation"Anyway,the sole use of L2 didn't enable Rh-comlex to exhibit activity towards the expected tandem "hydroformylation-aldol condensation-hydrogenation".The wide uses of enamine catalyst for efficient aldol condensation inspired us to introduce the third component of aniline into the L2-based Rh-catalyst,which was found to successfully exhibit a tri-functional co-catalysis for one-pot tandem"hydroformylation-aldol condensation-hydrogenation" in acetone.In the developed tri-functional catalytic system in combination of bi-functional ligand L2-based Rh-complex and aniline,L2-Rh?acac??CO?₂ catalyzed hydroformylation and hydrogenation respectively in the way of transition metal catalysis.In addition,the phosphonium in L2 served as a Lewis acid to catalyze the condensation of acetone with aniline to form enamine intermediate catalyst in the way of Lewis acid catalysis.The latter?enamine intermediate?with more nucleophilicity was able to attack the aldehydes?formed from the preceding hydroformylation?to accomplish the subsequent aldol condensation in the way of enamine catalysis,along with the release of aniline.The reaction rate of aldol condensation was the slowest in this three-step tandem reactions.Such tri-functional catalytic system exhibited good generality for the tandem "hydroformylation-aldol condensation-hydrogenation" of the different olefins with 59%-95%selectivities of the saturated products.