Tethered Tungsten-Alkylidenes for the Synthesis of Cyclic Polynorbornene via Ring Expansion Metathesis: Unprecedented Stereoselectivity and Trapping of Key Catalytic Intermediates
Tethered Tungsten-Alkylidenes for the Synthesis of Cyclic Polynorbornene via Ring Expansion Metathesis: Unprecedented Stereoselectivity and Trapping of Key Catalytic Intermediates
复制标题
DOI：
10.1021/jacs.0c12248
复制
发表时间：
2021-01-08
影响因子：
15
通讯作者：
Veige, Adam S.
中科院分区：
文献类型：
--
作者：
Jakhar, Vineet;Pal, Digvijayee;Veige, Adam S.
本文报道了一种以四阴离子钳形配体为特征的亚烷基钨-亚胺配合物的制备方法。用异氰酸酯（RNCO; R =Bu-（t）、Cy和Ph）处理钨次烷基[（BuOCO）-Bu-t]-W（CBu）-Bu-t（THF）（2）（1）导致仅在C=N键处发生环加成以产生栓系的钨-亚氨基次烷基（6-NR）。在6-NR的形成途径上，意外的中间体出现了，包括发现[（（O2 CBuC）-Bu-t=W（eta（2）-（N，C）-RNCO）（THF）]（11-R）和前所未有的脱羰基产物[（（BuOCO）-Bu-t）W（NR）（（BuCCO）-Bu-t）]（14-R）。配合物11-R对空间位阻较大的异氰酸酯R = Bu-t（11-Bu-t）是动力学稳定的，并通过单晶X-射线衍射分离和表征。最后，添加到能够进行扩环复分解聚合（REMP）的催化剂的短列表中，络合物6-NR和11-Bu-t对于环状聚异戊二烯的立体选择性合成是活性的。
This report describes an approach for preparing tethered tungsten-imido alkylidene complexes featuring a tetraanionic pincer ligand. Treating the tungsten alkylidyne [(BuOCO)-Bu-t]-W (CBu)-Bu-t(THF)(2) (1) with isocyanates (RNCO; R =Bu- (t), Cy, and Ph) leads to cycloaddition occurring exclusively at the C=N bond to generate the tethered tungsten-imido alkylidenes (6-NR). Unanticipated intermediates reveal themselves, including the discovery of [((O2CBuC)-Bu-t=W(eta(2)-(N,C)-RNCO)(THF)] (11-R) and an unprecedented decarbonylation product [((BuOCO)-Bu-t)W( NR)((BuCCO)-Bu-t)] (14-R), on the pathway to the formation of 6-NR. Complex 11-R is kinetically stable for sterically bulky isocyanate R = Bu-t (11-Bu-t) and is isolated and characterized by single-crystal X-ray diffraction. Finally, adding to the short list of catalysts capable of ring expansion metathesis polymerization (REMP), complexes 6-NR and 11-Bu-t are active for the stereoselective synthesis of cyclic polynorbornene.