Hannah Tyler J, McCarvell W Michael, Kirsch Tamina, Bedard Joseph, Hynes Toren, Mayho Jacqueline, Bamford Karlee L, Vos Cyler W, Kozak Christopher M, George Tanner, Masuda Jason D, Chitnis S S
Chemistry Department, Dalhousie University 6274 Coburg Rd Halifax NS B3H 4R2 Canada
Department of Chemistry, Memorial University of Newfoundland St. John's NL A1B 3X7 Canada.
Chem Sci. 2023 Apr 6;14(17):4549-4563. doi: 10.1039/d3sc00917c. eCollection 2023 May 3.
Geometric deformation in main group compounds can be used to elicit unique properties including strong Lewis acidity. Here we report on a family of bismuth(iii) complexes ( typically pyramidal structure for such compounds), which show a geometric Lewis acidity that can be further tuned by varying the steric and electronic features of the triamide ligand employed. The structural dynamism of the planar bismuth complexes was probed in both the solid and solution phase, revealing at least three distinct modes of intermolecular association. A modified Gutmann-Beckett method was used to assess their electrophilicity by employing trimethylphosphine sulfide in addition to triethylphosphine oxide as probes, providing insights into the preference for binding hard or soft substrates. Experimental binding studies were complemented by a computational assessment of the affinities and dissection of the latter into their intrinsic bond strength and deformation energy components. The results show comparable Lewis acidity to triarylboranes, with the added ability to bind two bases simultaneously, and reduced discrimination against soft substrates. We also study the catalytic efficacy of these complexes in the ring opening polymerization of cyclic esters ε-caprolactone and -lactide. The polymers obtained show excellent dispersity values and high molecular weights with low catalyst loadings used. The complexes retain their performance under industrially relevant conditions, suggesting they may be useful as less toxic alternatives to tin catalysts in the production of medical grade materials. Collectively, these results establish planar bismuth complexes as not only a novel neutral platform for main group Lewis acidity, but also a potentially valuable one for catalysis.
主族化合物中的几何变形可用于引发包括强路易斯酸性在内的独特性质。在此，我们报道了一族铋（III）配合物（此类化合物通常具有金字塔形结构），它们展现出一种几何路易斯酸性，可通过改变所使用的三酰胺配体的空间和电子特性来进一步调节。在固相和溶液相中对平面铋配合物的结构动力学进行了探究，揭示了至少三种不同的分子间缔合模式。除了使用三乙膦氧化物作为探针外，还采用了三甲基膦硫化物，通过一种改进的古特曼 - 贝克特方法来评估它们的亲电性，从而深入了解与硬或软底物结合的偏好。实验性结合研究通过对亲和力的计算评估以及将后者分解为其固有键强度和变形能成分得到了补充。结果表明，这些配合物的路易斯酸性与三芳基硼烷相当，同时具有能够同时结合两个碱的能力，并且对软底物的区分能力降低。我们还研究了这些配合物在环状酯ε - 己内酯和丙交酯的开环聚合反应中的催化效果。所得到的聚合物具有优异的分散度值和高分子量，且使用的催化剂负载量低。这些配合物在工业相关条件下仍保持其性能，这表明它们在医用级材料生产中作为毒性较低的锡催化剂替代品可能是有用的。总体而言，这些结果确立了平面铋配合物不仅是主族路易斯酸性的新型中性平台，而且是潜在有价值的催化平台。
