Synthesis, Characterization and Catalysis of Aluminum or Lithium Complexes Incorporating the EDBP Chelating Ligand

• Main Authors: Bao-Tsan Ko, 柯寶燦
• Other Authors: Chu-Chieh Lin
• Format: Others
• Language: en_US
• Published: 2002
• Online Access: http://ndltd.ncl.edu.tw/handle/05697573197293050086

博士 === 國立中興大學 === 化學系 === 90 === The reaction of [(-EDBP)AlMe]2 (1) (EDBP-H2 = 2, 2’-ethylidene bis(4, 6-di-tert-butylphenol)) with 2 molar equiv of 2-propanol (HOiPr) or benzyl alcohol (HOBn) yields the tetra-coordinated complex [(EDBP)Al(-OR)]2 (OR = OiPr (2) and OBn (3)). Complex 2 has shown excellent catalytic activities toward hydrogen transfer reactions (Meerwein-Ponndorf-Verley (MPV) reactions) between aldehydes and 2-propanol. The reaction of 4 molar equiv of benzaldehyde, 4-chlorobenzaldehyde or 4-methoxybenzaldehyde with [(EDBP)Al(-OiPr)]2 (2) gives the penta-coordinated dimeric complex [(EDBP)Al(-OCH2C6H4-p-X)(p-X-C6H4CHO)]2 (4, X = H; 5, X = Cl; 6, X = OMe). However, unlike other benzaldehydes, in the reaction of 2 with 4 equiv of 4-nitrobenzaldehyde, only the four-coordinated complex [(EDBP)Al(-OCH2C6H4-p-NO2)]2 (7) was obtained. Complex 2 further reacts with 2 equiv of OPPh3 or hexamethylphosphoramide (HMPA), yielding the four-coordinated monomeric complex [(EDBP)Al(OiPr)(L)] (8, L = OPPh3; 9, L = HMPA). X-ray crystal structure determinations of compounds 2, 4, 6, and 8-9 have led us to describe the intermediate of the MPV reactions. The novel aluminum alkoxide, complex 3 has demonstrated efficient catalytic activities in both “living” and “immortal” ROP of lactones. An unusual “n-butyllithium trap“ mixed-ligand lithium aggregate, [(3, 3-EDBP)Li2]2[(3-nBu)Li(0.5Et2O)]2 (13) is obtained from the reaction of EDBP-H2 with 3.6 molar equiv of nBuLi in high yield. The reaction of 13 with 2 molar equiv of benzyl alcohol (BnOH) or n-Butanol (nBuOH) gives [(3, 3-EDBP)Li2]2[(3-OR)Li]2 (14, OR = OBn; 15, OR = OnBu). Also, compound 13 reacts with 2 molar equiv of bidentate ligand, 2-ethoxyethanol to yield [(3, 3-EDBP)Li2]2[(3-OCH2CH2- OEt)Li]2 (16). Further treatment of 14 or 15 with excess THF gives penta-nuclear species [(2, 3-EDBP)2Li4(THF)3][(4-OR)Li] (OR = OBn (17) and OnBu (18)). In addition, 14 reacts with 6 molar equiv of HMPA in toluene to furnish a tri-lithium aggregate [(2, 2-EDBP)Li2(HMPA)2]- [(3-OBn)Li(HMPA)] (19). In contrast to monodentate alkoxide supporting complexes, the products of bidentate alkoxide containing complex 16 in the presence of THF or HMPA are much different. The reaction of 16 with excess THF (> 50 equiv) at room temperature gives a mixture of [(2, 3-EDBP)2Li4(THF)][(4-OCH2CH2OEt)Li]2 (20) and [(2, 3-EDBP)2Li4(THF)3][(4-OCH2CH2OEt)Li] (21). However, 21 reacts with 5 molar equiv of HMPA in toluene to afford the ionic complex [(2, 2-EDBP)2Li4(4-OCH2CH2OEt)(HMPA)]-[Li(HMPA)4]+ (22). 22 can also be synthesized by the reaction of 16 with 6 molar equiv of HMPA in toluene. In particular, experimental results show that 14 and 16 efficiently initiate the ring-opening polymerization (ROP) of L-lactide in a “controlled” fashion yielding polymers with very narrow polydispersity indexes (PDIs) in a wide range of monomer to initiator ratios. More importantly, a combination of free radical polymerization and ROP of lithium alkoxide macroinitiator enables us to synthesize PS-b-PLLA copolymers in which are useful templates to nanoscale materials.