Schulich Faculty of Chemistry, Technion-Israel Institute of Technology, Technion City, Haifa 32000, Israel.
Nat Chem. 2011 Jun 19;3(7):525-31. doi: 10.1038/nchem.1068.
Unlike N-heterocyclic carbenes (NHCs), which are now used ubiquitously in metal-based chemistry, the nitrogen-derived analogue (in which a carbon is replaced with the isoelectronic nitrogen cation, a nitrenium ion) has remained elusive as a ligand for metals. This is especially intriguing, because several other main-group analogues of NHCs have been prepared, and have been shown to coordinate with transition-metal complexes. Here, we describe the preparation of several N-heterocyclic nitrenium ions that are isoelectronic and isostructural to NHCs, and study their ligand properties. The formation of relatively strong nitrenium-metal bonds is unambiguously confirmed, in solution by selective (15)N-labelling experiments, and in the solid state by X-ray crystallography. Experimental and computational studies of the electronic properties of this novel type of ligand suggest that they are poor σ-donors and good π-acceptors.
与现在在金属基化学中广泛应用的 N-杂环卡宾（NHCs）不同，作为氮源的类似物（其中一个碳原子被等电子的氮阳离子，即氮鎓离子取代）作为金属配体一直难以捉摸。这尤其令人好奇，因为已经制备了几种 NHCs 的其他主族类似物，并已证明它们可以与过渡金属配合物配位。在这里，我们描述了几种 N-杂环氮鎓离子的制备方法，这些离子与 NHCs 等电子且等结构，并研究了它们的配体性质。通过选择性（15）N 标记实验在溶液中以及通过 X 射线晶体学在固态中明确证实了相对较强的氮鎓-金属键的形成。对这种新型配体电子性质的实验和计算研究表明，它们是不良的 σ-给体，而良好的 π-受体。
