Synthesis, Characterization And Catalytic Behavior Of Bridged Bis(Phenolate) Lanthanide Guanidinates Complexes

Using several bridged bis(phenolate)s as ancillary ligands,20lanthanide guanidinatecomplexes were synthesized. Among these complexes,15complexes were characterizedby X-ray single crystal diffraction. All complexes were also characterized by elementalanalysis, IR, as well as1H and13C NMR for the yttrium complexes. The influence of theligands and lanthanide metals on the synthesis, stability and reactivity of the bis(phenolate)lanthanide guanidinates were elucidated. The catalytic behavior of these lanthanidecomplexes for the ring-opeing polymerization (ROP) of rac-lactide (rac-LA),rac-β-butyrolactone (rac-BBL) and1,4-dioxan-2-one(PDO) were studied. Furthermore,these complexes were found to be efficient catalysts for organic reactions, such ashydrophosphonylation of aldehydes and guanylation reaction of amines.The bridged bis(phenol)s LH2used in this thesis were listed below:[Me2NCH2CH2N(CH-2-OC6H2-3,5-But2)2]H2，abbreviated as L12H2；[C3H6N2-1,4-(CH2-2-OC6H2-3,5-But2)2]H2，abbreviated as L2H2；[CH2N(Me)CH2-2-OCt6H2-3,5-Bu2]2H2，abbreviated as L3H2；[C5H10N2-1,4-(CH2-2-OC6H2-3,5-But2)2]H2，abbreviated as L4H2；[MeOCH2CH2N(CH2-2-OCt6H2-3,5-Bu2)2]H2，abbreviated as L5H2；[(CH2)3OCHCH2N(CH2-2-OC6H2-3,5-But2)2]H2，abbreviated as L6H2；[CH2(2-OC6H2-4-Me-6-But)2]H2，abbreviated as L7H2；The main contents of this thesis were listed below.1. Metathesis reactions of amine-bridged bis(phenolate) lanthanide chloridesL1LnCl(THF)(Ln=Y, Yb) with different lithium guanidinates generated in situ in a1:1molar ratio in THF gave the neutral yttrium guanidinates L1Yb[iPr2NC(NiPr)2](1),L1Y[iPr2NC(NiPr)2](2), L1Yb[Ph2NC(NiPr)2](3), L1Y[Ph2NC(NiPr)2](4),L1Yb[iPrHNC(NiPr)(NC6H4p-Cl)](5), L1Y[iPrHNC(NiPr)(NC6H4p-Cl)](6),L1Yb[(CH2)5NC(NCy)12](7), LY[(CH2)5NC(NCy)12](8), LYb[(TMS)2NC(NCy)2](9),L1Y[(TMS)2NC(NCy)12](10), LYb[(TMS)2NC(NiPr)2](11), L1Yb[(CH2)5NC(NiPr)2] (12) and L1Y[iPr2NC(NCy)2](13). X-ray diffraction analyses displayed that complexes1-13have monomeric structures in solid state. The metal ions in these complexes aresix-coordinated to two oxygen and two nitrogen atoms from the dianionicamine-bridged bis(phenolate) ligand, and two nitrogen atoms from the guanidinategroup. The coordination geometry around the metal center can be best described as adistorted octahedron.2. Treatment of the homoleptic Y[N(SiHMe2)2]3(THF)2with1equiv of L1H2-L7H2afforded the corresponding bridged bis(phenolate) yttrium amide. Insertion reactions ofN,N′-diisopropylcarbodiimide (DIC) with the isolated bridged bis(phenolate) yttriumamide gave seven neutral yttrium guanidinates L1Y[(SiHMe2)2NC(NiPr)2](14),L2Y[(SiHMe2)2NC(NiPr)2](THF)(15), L3Y[(SiHMe2)2NC(NiPr)2](16),L4Y[(SiHMe2)2NC(NiPr)2](17), L5Y[(SiHMe2)2NC(NiPr)2](18),L6Y[(SiHMe2)2NC(NiPr)2](19) and L7Y[(SiHMe2)2NC(NiPr)2](THF)2(20). Amongthese complexes, complexes15and16were characterized by X-ray single crystaldiffraction. The other5complexes were characterized by elemental analysis, IR, aswell as1H and13C NMR because of poor diffraction of crystals. X-ray diffractionanalyses displayed that complexes15and16also have monomeric structures in solidstate, and the coordination geometry of15and16is the same with1-13. The metal ionsin complex15is also six-coordinated, but coordinated to two oxygen and only onenitrogen atoms from the imidazolidine-bridged bis(phenolate) ligand, one oxygen atomfrom one THF molecule, and two nitrogen atoms from the guanidinate group. Thisreflects the structure of the bridged bis(phenolate) ligand has an effect on thecoordination mode of correspongding complex.3. The catalytic behavior of bridged bis(phenolate) lanthanide guanidinate complexes forthe ROP of rac-LA was explored. Complexes1-13were found to be very activesingle-site initiators for the ROP of rac-LA and give highly heterotactic PLAs withhigh molecular weights, relatively narrow molecular weight distributions. The ionicradii of the lanthanide metals have an effect on the catalytic activity. And the activityincreasing order of Yb <Y is in agreement with the order of their ionic radii. Theproperty of the guanidinate groups has no obvious effect on the controllability andselectivity, but has a profound effect on the catalytic activity for rac-LApolymerization. Steric hindrance of the guanidinate groups have effects on the polymerization activity.Complexes14-20with different bridged bis(phenolate) ligands also can catalyze theROP of rac-LA. The structure of the bridge on the bis(phenolate) ligands can affect thecatalytic activity and has a certain influence on the controllability. However, thestructure of the bridge on the bis(phenolate) ligands has a significant influence on thestereoselectivity for rac-LA polymerization. The initiation mechanism was elucidatedby end-group analysis of the oligomer of rac-LA, which was prepared by the reactionof complex9with rac-LA. End group analysis by1H NMR spectroscopy clearlyshowed that the polymerization proceeds via coordination insertion mechanism.4. The catalytic behavior of bridged bis(phenolate) lanthanide guanidinate complexes forthe ROP of rac-BBL was also explored. Complexes1-13were found to be activeinitiators for ROP of rac-BBL and give syndiotactic-enriched polymers (Pr=82%)with high molecular weights, relatively narrow molecular weight distributions. Theionic radii of the lanthanide metals have an significant effect on the catalytic activity.The activity increasing order of Yb> Y is opposite to the order of their ionic radii. Theproperty of the guanidinate groups has no effect on the controllability and selectivity,but has a profound effect on the catalytic activity for rac-BBL polymerization. Thenature of the guanidinate groups has effect on the polymerization activity. Complexes14-20with different bridged bis(phenolate) ligands also can catalyze the ROP ofrac-BBL. Structure of the bridge on the bis(phenolate) ligands can significantly affectthe activity and stereoselectivity, and has slight influence on the controllability. Most ofthe catalysts showed low activity toward rac-BBL polymerization compared with LApolymerization because of the low activity of BBL monomer. The initiation mechanismwas elucidated by analysis of the oligomer of rac-BBL, which was prepared by thereaction of complex9with rac-BBL. The results clearly showed the polymerizationproceeds via coordination-insertion mechanism.5. The catalytic behavior of bridged bis(phenolate) lanthanide guanidinate complexes forthe ROP of PDO was explored. This is the first time that single-site initiators wereintroduced in the ROP of PDO, and the thermodynamic, kinetic aspects were alsoinvestigated. Complexes1-13were found to be very active initiators for ROP of PDOto give PPDO with high molecular weights, relatively broad molecular weight distributions. The ionic radii of the lanthanide metals have no effect on the catalyticactivity. The property of the guanidinate groups has somewhat effect on the catalyticactivity for PDO polymerization. The electronic effect of the guanidinate groups haseffect on the polymerization activity. The thermodynamic study showed that thepolymerization of PDO may be an equilibrium reaction and the activity can be affectedobviously by the temperature. The kinetic study showed that the bulk polymerizationinitiated by lanthanide complexes is of first order in both monomer and initiator.Complexes14-20with different bridged bis(phenolate) ligands also can catalyze theROP of PDO. Structure of the bridge between two phenolate ligands can affect thecatalytic activity and has a certain influence on the controllability. The initiationmechanism was elucidated by end-group analysis of the oligomer of PDO, and it wasfound that the ROP proceeds through a coordination-insertion mechanism with O-acylrupture of the endocyclic ester bond of the monomer. MALDI-TOF mass spectrumanalysis of the oligomer revealed that there are two kinds of polymer chains in thiscatalytic system, e.g. the linear chains H [OCH2CH2OCH2CO]n OH and the PPDOmacrocycles.6. It was found that these new lanthanide guanidinate complexes can be used as efficientcatalysts for the hydrophosphonylation of aldehydes with diethyl phosphite, affordingthe α-hydroxyphosphonates in high yields by employing a low catalyst loading (0.05mol%) at room temperature in a short time (5min). Under the optimized reactionconditions, the generality and scope of the hydrophosphonylation reaction catalyzed bycomplex9were investigated. All reactions proceeded smoothly for both aromatic andaliphatic aldehydes to produce the corresponding α-hydroxyphosphonates in goodyields. The catalytic behaviour of complex9for the hydrophosphonylation of ketonewith diethyl phosphite was also tested. It was found that complex9showed lowactivity for the transformation of ketone, which may be attributed to the stericcongestion around the metal center. The mechanism of hydrophosphonylation reactionshas also been elucidated via1H NMR monitoring of reaction.7. These amine-bridged bis(phenolate) lanthanide guanidinates complexes were alsofound to be efficient catalyst for the addition of amines to carbodiimides yieldingguanidines under mild conditions. Complex10showed the highest activity affording the guanidines in high yields by employing a low catalyst loading (0.5mol%) at25oCunder solvent-free condition. A possible mechanism of the catalytic cycle for theaddition of amines into carbodiimides was proposed. Complex10underwent anacid base reaction with amine to give an orgnic guanidine and active intermediateamide complex. Insertion of carbodiimides into the Ln–N bond of appropriate amidesled to the formation of the guanidinate species. The guanidinate species then captures aproton from amine to generate the product guanidine, which produces the activeintermediate that participates in a new cycle.