Xing Tian, Prior Timothy J, Redshaw Carl
Plastics Collaboratory, Department of Chemistry, University of Hull, Cottingham Road, Hull, HU6 7RX, UK.
Dalton Trans. 2021 Nov 2;50(42):15140-15152. doi: 10.1039/d1dt02790e.
Reaction of [LiPb(OPr)] (generated ) with either -butylcalix[4]areneH (LH) or -butylcalix[6]areneH (LH) resulted in the heterometallic lithium/lead complexes [PbLi(L)H(MeCN)]·4.5MeCN (1·4.5MeCN) and [PbLiCl(LH)(L)(OH)(O)(HO)(MeCN)]·14MeCN (2·14MeCN), respectively. Use of the dimethyleneoxa-bridged -butyltetrahomodioxacalix[6]areneH (LH) with five equivalents of [Pb(OPr)] afforded [Pb(L)O(PrOH)]·11MeCN (3·11MeCN). Use of the larger -butylcalix[8]areneH (LH) with [Pb(OBu)] or {Pb[N(TMS)]} (TMS = SiMe) afforded the products [Pb(L)O]·8.7CH (4·8.7CH) or [Pb(SiMe)(L)OCl] (5), respectively. Reaction of {Pb[N(TMS)]} (generated from (MeSi)NH, BuLi and PbCl) with LH afforded, after work-up (MeCN), the mixed-metal complex [PbLi(L)(OH)Cl(O)]·9.5MeCN (6·9.5MeCN). Reaction of distilled {Pb[N(TMS)]} (six equivalents) with LH resulted in the complex [Pb(L)O]·12MeCN (7·12MeCN). Complexes 1-7, Pb(OPr) and [Pb(N(TMS))] have been screened for their potential to act as pre-catalysts in the ring opening polymerization (ROP) of ε-caprolactone (ε-CL) and δ-valerolactone (δ-VL) and the copolymerization thereof. Generally, the lithiated complexes 1 and 2 exhibited better activities than the other pre-catalysts screened herein. For ε-CL and δ-VL, moderate activity at 130 °C over 24 h was observed for 1-7. In the case of the co-polymerization of ε-CL with δ-VL, 1-7, Pb(OPr) and [Pb(N(TMS))] afforded reasonable conversions and high molecular weight polymers. The systems 1-7, Pb(OPr) and [Pb(N(TMS))] also proved to be active in the ROP of the -lactide (-LA); the activity trend was found to be 1 > 2 ≈ Pb(OPr) ≈ [Pb(N(TMS))] > 4 > 5 ≈ 6 ≈ 7 > 3.
[LiPb(OPr)]（原位生成）与对叔丁基杯[4]芳烃H₄（LH₄）或对叔丁基杯[6]芳烃H₆（LH₆）反应，分别生成异金属锂/铅配合物[PbLi(L₄)H(MeCN)]·4.5MeCN（1·4.5MeCN）和[PbLiCl(LH₆)(L₄)(OH)(O)(HO)(MeCN)]·14MeCN（2·14MeCN）。使用二亚甲基氧桥连的对叔丁基四同二氧杂杯[6]芳烃H₆（LH₆）与五当量的[Pb(OPr)₂]反应，得到[Pb(L₆)O(PrOH)]·11MeCN（3·11MeCN）。使用更大的对叔丁基杯[8]芳烃H₈（LH₈）与[Pb(OBu)₂]或{Pb[N(TMS)₂]}（TMS = SiMe₃）反应，分别得到产物[Pb(L₈)O]·8.7CH₂Cl₂（4·8.7CH₂Cl₂）或[Pb(SiMe₃)(L₈)OCl]（5）。{Pb[N(TMS)₂]}（由(Me₃Si)₂NH、BuLi和PbCl₂原位生成）与LH₈反应，后处理（使用MeCN）后得到混合金属配合物[PbLi(L₈)(OH)Cl(O)]·9.5MeCN（6·9.5MeCN）。蒸馏后的{Pb[N(TMS)₂]}（六当量）与LH₈反应，得到配合物[Pb(L₈)O]·12MeCN（7·12MeCN）。已对配合物1 - 7、Pb(OPr)₂和[Pb(N(TMS)₂)]在ε-己内酯（ε-CL）和δ-戊内酯（δ-VL）的开环聚合（ROP）及其共聚反应中作为预催化剂的潜力进行了筛选。一般来说，锂化配合物1和2表现出比本文筛选的其他预催化剂更好的活性。对于ε-CL和δ-VL，在130℃下24小时观察到1 - 7具有中等活性。在ε-CL与δ-VL的共聚反应中，1 - 7、Pb(OPr)₂和[Pb(N(TMS)₂)]得到了合理的转化率和高分子量聚合物。体系1 - 7、Pb(OPr)₂和[Pb(N(TMS)₂)]在丙交酯（L-LA）的ROP中也被证明具有活性；活性趋势为1 > 2 ≈ Pb(OPr)₂ ≈ [Pb(N(TMS)₂)] > 4 > 5 ≈ 6 ≈ 7 > 3。
