Department of Chemistry, National University of Singapore, 3 Science Drive 3, 117543 Singapore, Singapore.
Dalton Trans. 2012 Jul 28;41(28):8600-8. doi: 10.1039/c2dt30526g. Epub 2012 May 31.
The relative ligand donor strengths of 10 pyrazole-derived ligands has been determined with great accuracy, making use of the interdependence between the donor strength of the co-ligand and the (13)C NMR chemical shift of the (i)Pr(2)-bimy carbene signal in trans-[PdBr(2)((i)Pr(2)-bimy)L] complexes ((i)Pr(2)-bimy = 1,3-diisopropylbenzimidazolin-2-ylidene; L = pyrazole-derived ligand). Even subtle variations in the substitution pattern of the pyrazole backbone up to three bonds away from the coordinating nitrogen could be detected reliably using this methodology. Alkylation experiments conducted on the pyrazoles using electrophiles of varied reactivity (ethyl bromide, ethyl iodide, and trimethyloxonium tetrafluoroborate) served as a benchmark to rank the pyrazoles in three groups of gradually increasing nucleophilicity, which correlated well with their determined donor strength.
已经非常准确地确定了 10 种吡唑衍生配体的相对配体给体强度，利用共配体的给体强度与顺式-[PdBr2((i)Pr2-bimy)L]配合物中（i）Pr2-bimy 碳氮双键的（13）C NMR 化学位移之间的相互依存关系来实现，其中（i）Pr2-bimy = 1,3-二异丙基苯并咪唑啉-2-亚基；L = 吡唑衍生配体）。即使在与配位氮相隔三个键的吡唑骨架的取代模式发生细微变化的情况下，也可以使用这种方法可靠地检测到。使用不同反应性的亲电试剂（溴乙烷、碘乙烷和三甲基氧鎓四氟硼酸盐）对吡唑进行的烷基化实验作为基准，将吡唑分为三组，其亲核性逐渐增强，这与它们确定的给体强度很好地相关。
