ホウ素アニオン含有<i>N</i>-ヘテロ環状カルベン配位子を有するイミド配位バナジウム（V）錯体によるエチレン重合およびノルボルネンとの共重合におけるAl助触媒の効果 Effect of Al Cocatalyst in Ethylene and Ethylene/Norbornene (Co)polymerization by (Imido)vanadium Dichloride Complexes Containing Anionic <i>N</i>-Heterocyclic Carbenes Having Weakly Coordinating Borate Moiety

<p>ホウ素アニオン含有<i>N</i>-ヘテロ環状カルベン（WCA-NHC）配位子を有するイミド配位バナジウム錯体，V（N-2,6-Me₂C₆H₃）Cl₂（WCA-NHC）（<b>1</b>），触媒によるエチレン重合およびノルボルネンとの共重合における触媒活性は，使用するAl助触媒の影響を強く受け，特にAl<i>ⁱ</i>Bu₃助触媒存在下でメチルアルミノキサン（MAO）より高活性を示した。触媒溶液の⁵¹V NMRスペクトル測定およびESR測定，V K-Edge XANES測定より，MAOの存在下での触媒溶液では価数変化が見られないのに対し，Al<i>ⁱ</i>Bu₃の存在下の触媒溶液ではNMRおよびESRスペクトルが観察されず，XANESスペクトルよりAlによる還元反応が進行している可能性が示唆された。したがって，この触媒反応で見られるAl助触媒の効果は，価数の異なる触媒活性種の生成に起因することが示唆された。</p>

<p>Effect of Al cocatalyst in ethylene polymerization using (imido)vanadium(V) complexes containing anionic <i>N</i>-heterocyclic carbenes with a weakly coordinating borate moiety in 4-position (WCA-NHC), [V(N-2,6-Me₂C₆H₃)Cl₂(WCA-NHC)] [<b>1</b>; NHC=1,3-bis(2,6-dimethylphenyl)-imidazolin-2-ylidene], have been explored. The activities by <b>1</b> upon presence of Al<i>ⁱ</i>Bu₃ in ethylene polymerization and in the copolymerization with norbornene (NBE) were higher than those in the presence of MAO, and the resultant poly(ethylene-<i>co</i>-NBE)s prepared by <b>1</b>-Al<i>ⁱ</i>Bu₃ catalyst possessed uniform molecular weight distributions and compositions. Formation of vanadium(III) species could be assumed upon presence of Al<i>ⁱ</i>Bu₃, especially on the basis of both NMR and ESR spectra (silent) and certain significant changes in the V K-edge XANES (pre-edge and edge region) spectrum, whereas no significant changes in the XANES spectrum were observed from the toluene solution containing <b>1</b> upon addition of MAO. It is thus suggested that a difference in the catalyst performances between in the presence of MAO and Al<i>ⁱ</i>Bu₃ should be due to a formation of different catalytically active species with different oxidation states.</p>