Fang Yang-Yang, Gong Wei-Jie, Shang Xiu-Juan, Li Hong-Xi, Gao Jun, Lang Jian-Ping
College of Chemistry, Chemical Engineering and Materials Science, Soochow University, Suzhou 215123, People's Republic of China.
Dalton Trans. 2014 Jun 14;43(22):8282-9. doi: 10.1039/c4dt00475b.
The reaction of FeCl3 with a pincer ligand, 2,6-di(1H-pyrazol-3-yl)pyridine (bppyH2), produced a mononuclear Fe(III) complex [Fe(bppyH2)Cl3] (1), which could be reduced to the corresponding Fe(II) dichloride complex [Fe(bppyH2)Cl2] (2) by suitable reducing agents such as Cp2Co or Fe powder. 1 and 2 exhibited a reversible transformation from each other with appropriate redox reagents. 1 could be utilized as a pre-catalyst to initiate the ring-opening polymerization of ε-caprolactone in the presence of alcohol but did not work. The 1/alcohol system displayed characteristics of a well-controlled polymerization with the resulting poly(ε-caprolactone) having low molecular weight distributions, a linear tendency of molecular weight evolution with conversion, and polymer growth observed for the sequential additions of ε-caprolactone monomer to the polymerization reaction. The polymerization was completely turned off by the in situ reduction of the catalytic Fe center via Cp2Co and then turned back upon the addition of [Cp2Fe]PF6. The rate of polymerization was modified by switching in situ between the Fe(III) and Fe(II) species.
三氯化铁与钳形配体2,6-二(1H-吡唑-3-基)吡啶(bppyH₂)反应生成单核铁(III)配合物[Fe(bppyH₂)Cl₃] (1)，通过合适的还原剂如二茂钴或铁粉可将其还原为相应的二氯化铁(II)配合物[Fe(bppyH₂)Cl₂] (2)。1和2在合适的氧化还原试剂作用下表现出相互之间的可逆转化。1可作为预催化剂在醇存在下引发ε-己内酯的开环聚合，但未起作用。1/醇体系显示出可控聚合的特征，所得聚(ε-己内酯)具有低分子量分布、分子量随转化率呈线性增长趋势，并且在向聚合反应中依次加入ε-己内酯单体时观察到聚合物增长。通过二茂钴对催化铁中心进行原位还原，聚合反应完全停止，然后加入[Cp₂Fe]PF₆后又恢复。通过在铁(III)和铁(II)物种之间原位切换来改变聚合速率。
