钼系催化丁二烯聚合的研究—Mo(Ⅳ)络合物的紫外可见光谱

Study of 1, 2—Polybutadiene with Molybdenu m Catalyst System UV—VIS Spectrum of Mo(Ⅳ) Complexes

MoCl_4乙酸乙酯溶液呈棕红色,在光谱的紫区和红区共有三个自旋允许d—d跃迁吸收带。主催化剂Mo(Ⅳ)络合物具有八面体构型。各种配体:Cl-C_8H_(17)O-,PhO-,Bd,C_8H_(17)OH,PhOH和CH_3COOC_2H_5的交换对络合物的吸收谱带的位置无影响。Mo(Ⅳ)在512nm处的特征吸收带随Al(i—Bu)_3/Mo或Al(i—Bu)_2OPh/Mo增加而渐趋消失,这是Mo(Ⅳ)被还原为低价态的标志。Bd和PhO-共存的MoCl_(4-n)(OC_8H_(17))_n—Bd—Al(i—Bu)_2OPh体系中Mo(Ⅳ)的还原得到明显改善。

MoCl_5 in ethyl acetate is of a brown-yellow colour and paramagnetism, which is very sensitive to oxygen and the solution becomes green. The two characteristic absorption bands of Mo(Ⅴ) complex are due to the spin-allowed d-d transition at the range of 400-900nm The new absorption band at 452nm appears after exchange reaction between MoCl_5 and octanol-(1), which is the general characteristic of a σ-bond form ed in MoCl_(5-a)(OC_8H_(17))_(?)。It is found that the reducibilities of the cocatalysts in Mo(Ⅴ) catalyst system are as follows: Al(i-Bu)_3>Al(i-Bu)_2OPh>Al(i-Bu)_2OC_8H_(17) The new absorption band at 375 nm is attributed to the result of an al kyl-group reaction between MoCl_5 and aluminum alkyl. The characteristic absorption band of Mo(Ⅴ) complex at 725 nm decreases with the increase of the mole ratio of Al/Mo. The reduction of Mo(Ⅴ) and catalytic activity will be improved if the pre-mixture of Bd-Mo(Ⅴ) is made.