Eiji Ihara

Rare Earth Metal-Initiated Polymerizations of Polar and Nonpolar Monomers

This review article shows that by using the versatile functions of rare earth metal complexes we can polymerize both polar and nonpolar monomers in living fashion to obtain monodisperse high molecular weight polymers at high conversions. A typical example is the polymerization of methyl methacrylate with [SmH(C5Me5 2)]2 or LnMe(C5Me5)2 (THF) (Ln = Sm, Y, Lu), which leads quantitatively to high molecular weight syndiotactic polymers (M n > 500 000, syndiotacticity > 95%) at low temperature (- 95 °C). The initiation mechanism was discussed on the basis of X-ray analysis of the 1:2 adduct (molar ratio) of [SmH(C5Me5)2]2 with MMA. Living polymerizations of alkyl acrylates (methyl acrylate, ethyl acrylate, butyl acrylate) were also made possible by using LnMe(C5Me5)2(THF) (Ln = Sm, Y), with the results: poly(methyl acrylate) M n = 48 × 103, M w/M n = 1.04, poly(ethyl acrylate) M n = 55 × 103, M w/M n = 1.04, and poly(butyl acrylate) M n = 70 × 103, M w/M n = 1.05. By taking advantage of the ABA triblock copolymerization of MMA/butyl acrylate/MMA, it was possible to obtain rubberlike elastic polymers. Lanthanum alkoxide(III) has good catalytic activity for the polymerization of alkylisocyanates (M n > 106, M w/M n = 2.08). Monodisperse polymerization of lactones, lactide, and oxirane was also achieved by polymerization with rare earth metal complexes. C1 symmetric bulky organolanthanide(III) complexes such as SiMe2[2(3),4-(SiMe3)2C5H2]2LnCH(SiMe3)2 (Ln = La, Sm, Y) show high activity for linear polymerization of ethylene. Organolanthanide(II) complexes such as racemic SiMe2[2-SiMe3-4-tBu-C5H2]2Sm(THF)2 as well as C1 symmetric SiMe2[2(3),4-(SiMe3)2C5H2]2 Sm(THF)2 were also found to have a very high activity for polymerization of ethylene. Thus, polyethylene of M n > 106 (M w/M n = 1.60) was obtained by using SiMe2[2(3),4-(SiMe3)2C5H2]2 Sm(THF)2. 1,4-cis Conjugated diene polymers of butadiene and isoprene became available by the efficient catalytic activity of C5H5NdCl/AlR3 or Nd(octanoate)3/AlR3. The Ln(naphthenate)3/ AliBu3 system allows selective polymerization of acetylene in cis fashion to take place at high yield. Considering the fact that rare earth metal-initiated living polymerization can be achieved for both polar and nonpolar monomers, attempts have been made to block copolymerization of ethylene with MMA or lactones yielding polyethylene derivatives having high chemical reactivity.

Catalytic activity of allyl-, azaallyl- and diaza-pentadienyllanthanide complexes for polymerization of methyl methacrylate ☆

Abstract A variety of allylic, aza-allylic and 1,5-diazapentadienyllanthanide compounds were synthesized and their polymerization catalysis toward methyl methacrylate were examined. Divalent Sm[1,3-bis(trimethylsilyl)propenyl] 2 (THF) 2 1 and Sm(1,3-diphenylpropenyl) 2 (THF) 2 2 were synthesized by the reaction of potassium 1,3-bis(trimethylsilyl)propenide or potassium 1,3-diphenylpropenide with SmI 2 . The aza-allyllanthanide compound was synthesized by the reaction of 2-pyridylbenzyllithium with SmCl 3 followed by the reaction with LiCH(SiMe 3 ) 2 to give (2-pyridylbenzyl) 2 SmCH(SiMe 3 ) 2 3 . 1,5-Diazapentadienyllanthanide was prepared by the reaction of K[(C 5 H 4 N) 2 CPh] with YbBr 2 to give Yb[(C 5 H 4 N) 2 CPh] 2 (THF) 2 4 , which crystalizes monoclinic, space group C 2/ C (No. 15), with a =35.19(1), b =13.613(3), c =26.552(7) A, β =133.77(1)°, and Z =8. Preparations of divalent samarium and ytterbium complexes with bis(2-pyridylphenylmethyl)dimethylsilane ligand ( 6 and 7 ) were carried out by the reaction of dipotassium salt of bis(2-pyridylphenylmethyl)dimethylsilane with SmI 2 or YbBr 2 . By using the resulting compounds 1 , 2 , 3 , 4 , 6 and 7 as initiator, we have examined their catalytic activities for the polymerization of methyl methacrylate and found that compounds 6 and 7 are effective to give high molecular weight isotactic polymers.

High polymerization of methyl methacrylate with organonickel/MMAO systems

A series of nickel complexes, including Ni(acac)2, (C5H5)Ni(η3-allyl), and [NiMe4Li2(THF)2]2, that were activated with modified methylaluminoxane (MMAO) exhibited high catalytic activity for the polymerization of methyl methacrylate (MMA) but showed no catalytic activity for the polymerization of ethylene and 1-olefins. The resulting polymers exhibited rather broad molecular weight distributions and low syndiotacticities. In contrast to these initiators, the metallocene complexes (C5H5)2Ni, (C5Me5)2Ni, (Ind)2Ni, and (Me3SiC5H4)2Ni provided narrower molecular weight distributions at 60 °C when these initiator were activated with MMAO. Half-metallocene complexes such as (C5H5)NiCl(PPh3), (C5Me5)NiCl(PPh3), and (Ind)NiCl(PPh3) produced poly(methyl methacrylate) (PMMA) with much narrower molecular weight distributions when the polymerization was carried out at 0 °C. Ni[1,3-(CF3)2-acac]2 generated PMMA with high syndiotacticity. The NiR(acac)(PPh3) complexes (R = Me or Et) revealed high selectivity in the polymerization of isoprene that produced 1,2-/3,4-polymer at 0 °C exclusively, whereas the polymerization at 60 °C resulted in the formation of cis-1,4-rich polymers. The polymerization of ethylene with Ni(1,3-tBu2-acac)2 and Ni[1,3-(CF3)2-acac]2 generated oligo-ethylene with moderate catalytic activity, whereas the reaction of ethylene with Ni(acac)2/MMAO produced high molecular weight polyethylene.

Polymerization of olefins by rare earth metal complex with bulky substituents

Sterically bulky substituents, t-BuMe2Si groups, and Me3Si groups were introduced into Me2Si bridged Cp rings and the compound, Me2Si(Me3Si-t-BuC5H3)2, was used as a ligand for rare earth metal complex. As a result of the complexation, new yttrium complexes, Me2Si(2-Me3Si-4-t-BuMe2SiC5H2)2YCl2Li(THF)2 and Me2Si(2-Me3Si-4-t-BuMe2SiC5H2)2YCH(SiMe3)2, were synthesized. Hydride derivative of these complexes, [Me2Si(2-Me3Si-4-t-BuMe2SiC5H2)2YH]2, showed high activity for olefin polymerization. α-Olefins such as 1-hexene and 1-pentene were transformed into their polymers in high yield (>75%). The polymerization proceeded in a stereoselective manner, giving highly isotactic poly(α-olefin)s (selectivity>95%). The hydride complex can polymerize 1,5-hexadiene, affording high molecular weight poly(methylene-1,3-cyclopentane) (Mn>10×104).

Synthesis of 2,6-dialkoxylphenyllanthanoid complexes and their polymerization catalysis

Abstract The 1:1–2:1 reaction of [2,6-( i PrO) 2 C 6 H 3 ]Li with anhydrous SmCl 3 in THF gave [2,6-( i PrO) 2 C 6 H 3 ] 3 Sm 1 exclusively, while the 3:1 reaction gave [2,6-( i PrO) 2 C 6 H 3 ] 4 SmLi 2 as major product, which crystallizes in the monoclinic space group C 2/ c (No. 15) with a =47.52(1) A, b =11.680(9) A, c =18.862(9) A, β =112.19(3)°, V =9694(8) A 3 , Z =8, R =0.077 and R w =0.074. In a similar manner, [2,6-( i PrO) 2 C 6 H 3 ] 3 La was obtained by reacting with LaCl 3 (THF) 2 . The 2:1 reaction of [2,6-( i PrO) 2 C 6 H 3 ]Li with YbCl 3 gave [2,6-( i PrO) 2 C 6 H 3 ] 2 YbCl, which produces [2,6-( i PrO) 2 C 6 H 3 ] 2 Yb[CH(SiMe 3 ) 2 ] 2 Li 4 by reaction with (SiMe 3 ) 2 CHLi. Polymerizations of ϵ -caprolactone and alkyl isocyanates were examined using the resulting complexes.

Coordination of allenyl/propargyl group to samarium(III): the first crystal structures of η3-allenyl and η1-propargyl lanthanide complexes

Abstract The synthesis and crystal structures of samarium complexes incorporating bridged Cp′ue5f8SiMe 2 ue5f8allenyl/propargyl ligands [Cp′=(Me 3 Si) 2 (C 5 H 2 )] are described. The reaction of a dilithium salt of [(Me 3 Si) 2 (C 5 H 3 )]SiMe 2 CH 2 Cue606CSiMe 3 ( 1a ) with SmCl 3 yielded an η 3 -allenyl complex {[(Me 3 Si) 2 (C 5 H 2 )]SiMe 2 (η 3 -Cue605Cue605C[ H ]SiMe 3 )}SmCl 3 Li 2 (TMEDA) 2 ( 2a ) (TMEDA= N , N , N ′, N ′-tetramethylethylenediamine). On the other hand, the reaction of a dilithium salt of a Ph 3 Si substituted ligand [(Me 3 Si) 2 (C 5 H 3 )]SiMe 2 CH 2 Cue606CSiPh 3 ( 1b ) with SmCl 3 yielded an η 1 -propargyl complex {[(Me 3 Si) 2 (C 5 H 2 )]SiMe 2 (η 1 -CHCue606CSiPh 3 )}Sm(TMEDA)[Cl 2 Li(TMEDA)] ( 2b ). A conversion of bonding mode from η 1 -propargyl to η 3 -allenyl was observed when 2b was treated with (Me 3 Si) 3 CLi/LiI to give an η 3 -allenyl complex {[(Me 3 Si) 2 (C 5 H 2 )]SiMe 2 (η 3 -CHue605Cue605CSiPh 3 )}SmI 2 Li(TMEDA) ( 3b ). The same structural conversion was also observed when 2b was treated with (Me 3 Si) 2 CHLi to give an anionic ate complex ({[(Me 3 Si) 2 (C 5 H 2 )]SiMe 2 (η 3 -CHue605Cue605CSiPh 3 )}SmCl[CH(SiMe 3 ) 2 ])[Li(TMEDA) 2 ] ( 4b ), which had the η 3 -allenyl bonding structure. The structures of these four complexes ( 2a , 2b , 3b , and 4b ) were revealed by X-ray crystallography. These are the first examples of the structural characterization of η 3 -allenyl and η 1 -propargyl lanthanide complexes.

Characterization of lactone oligomers isolated by preparative SFC

Oligomerization of e-caprolactone and δ-valerolactone was performed by use of SmMe-(C 5 Me 5 ) 2 (THF) 2 initiator, and the 26-mer, 28-mer and 30-mer of e-caprolactone were isolated in pure form by preparative SFC. The MALDI-TOF mass spectrum of the 28-mer indicates that the parent peak (3256.1) emerges as 28-mer + 2Na - H (3256.9). The ESI mass spectrum of the 28-mer indicates that the molecular weight (3211.7) is consistent with the calculated value (3211.9). In a similar manner, the 19-, 25- and 32-mers of δ-valerolactone were isolated. The MALDI-TOF mass spectrum of the 19-mer indicates that the parent peaks (1896.6 and 1879.9) emerge as 19-mer + Na + K + MeOH - I-hexanol-5-one (1896.3) and 19-mer + 2Na + MeOH - I-hexanol-5-one (1880.2). Glass transition and melting temperatures (T g and T m ) of oligo-e-caprolactones and oligo-δ-valerolactones increase wh increasing degree of polymerization.

22. High Molecular Weight Monodisperse Polymers Synthesized by Rare Earth Metal Complexes

Abstract High molecular weight polyethylene ( M n > 300,000, M w / M n = 1.6) was obtained by using bulky Sm(II) or Sm(III) species such as Me 2 Si(2-SiMe 3 -4-tBu-C 5 H 2 ) 2 Sm(THF) and Me 2 Si[2(3),4-(SiMe 3 ) 2 -C 5 H 2 ] 2 SmCH(SiMe 3 ) 2 as initiator. These complexes also conduct the polymerization of 1-pentene and 1-hexene to give isotactic polymers of M n > 20,000 with M w / M n = 1.6. By contrast the polar monomers such as methyl methacrylate and alkyl acrylates also proceeded the living polymerization by using Ln(C 5 Me 5 ) 2 R (R = H, Me) to give high molecular weight polymers ( M n > 450,000) with extremely low polydispersity ( M w / M n