Redox Reactions with Calcium‐Metal Nanoparticles

Abstract Calcium is generally a highly reactive alkaline‐earth metal, but as bulk metal, it exhibits only low reactivity at ambient conditions due to small surface area, low solubility, and/or passivation. The reactivity can be significantly enhanced when using small‐sized calcium nanoparticles. In this regard, we describe the first synthesis of Ca(0) nanoparticles, 5.4 ± 1.2 nm in size, by TMEDA‐supported reduction of CaI 2 with lithium naphthalenide in toluene (TMEDA: N,N,N′,N′‐tetramethylethylenediamine). We also show Ca(0) nanoparticles to be substantially different from so‐called “ Rieke calcium ”. The high reactivity can be used for redox reactions, for instance, with [Cp 2 MoCl 2 ] and the sterically demanding β‐diketiminate ligand H Dipp NacNac (Dipp: 2,6‐ i Pr 2 C 6 H 3 ) or with [(Ph 3 P)AuCl] as a derivative of a ligand‐stabilized noble metal. The Ca(0)‐nanoparticle‐driven reactions result in the novel compounds [{( Dipp NacNac)(thf)Ca} 2 (naph)] ( 1 ) with a rare naphthalenide dianion, [{( Dipp NacNac)(thf)CaMo(Cp)H} 2 (fulvalene)] ( 2 ) with unusual MoH → Ca dative bonding, and [Au 9 (PPh 3 ) 8 ](naph)(tmeda) 0.5 ( 3 ) with a non‐charged body‐centered cubic Au 9 cluster core of zerovalent gold. Ca(0) nanoparticles and the compounds 1–3 are characterized by electron microscopy, X‐ray diffraction (single crystals, powders), spectroscopy (IR, UV‐Vis, NMR, EPR), and computation. Exemplarily, the formation of 1–3 points to the potential of nanosized alkaline‐earth metals for chemical syntheses and the different reactivity of nanosized and bulk metals.