If the Crown Fits:\nSterically Demanding <i>N</i>‑Heterocyclic Carbene\nPromotes the Formation of Au<sub>8</sub>Pt Nanoclusters

While <i>N</i>-heterocyclic carbenes (NHCs)\nhave recently\nbeen shown to be effective ligands for gold nanoclusters, very few\nexamples of heterometallic clusters incorporating nongroup 11 metals\nare known. We present herein an Au–Pt NHC cluster featuring\na crown-shaped [Au<sub>8</sub>Pt(NHC)<sub>8</sub>]<sup>2+</sup> core,\nproduced in high yield without the need for chromatographic purification.\nThe method was largely independent of the substitution pattern of\nthe NHC backbone; however, bulky wingtip groups were needed for clean\nconversion to the Au<sub>8</sub>Pt cluster. Clusters were characterized\nusing single crystal X-ray diffraction, multinuclear nuclear magnetic\nresonance, electrospray ionization mass spectroscopy, and ultraviolet–visible\nspectroscopy, and electrochemical features of the cluster are also\npresented. A detailed analysis of the in-progress reaction mixture\nby ESI-MS supports the direct involvement of Au–H species as\nintermediates in cluster formation. These studies further demonstrate\nthat NHC wingtip sterics play a key part in determining the nature\nof the initial cluster species, providing critical information for\nthe generation of new NHC-stabilized nanoclusters.