Chromium Metal Nanoparticles, Their Reactivity and Reactions

Abstract

AbstractZerovalent chromium nanoparticles (2.2±0.2 nm in size) are prepared in the liquid phase (THF) by reduction of CrCl2 with lithium naphthalenide ([LiNaph]). The deep black Cr(0) nanoparticle suspensions in THF are colloidally and chemically highly stable. On the other hand, the Cr(0) nanoparticles are highly reactive, e. g., when in contact to O2, H2O, or other oxidizing agents. To probe the reactivity of the Cr(0) nanoparticles in the liquid phase near room temperature (50–80 °C), they are reacted with different coordinatively demanding, N−H, S−H or O−H acidic reactants. This includes the amines 2,2′‐dipyridylamine (HDPA), 2‐(1H‐imidazol‐2‐yl)pyridine (HImPy) and carbazole (HCbz), the thiol 2‐mercaptopyridine (HMPy), and benzoic acid (HBz) as a carboxylate. As a result, the five novel compounds [Cr(DPA)3], [Cr(ImPy)3] ⋅ HImPy, [Cr(MPy)3] ⋅ 0.5 Tol (Tol: toluene), [Na2Cr(Cbz)4(THF)3], and [Cr2(Bz)4(THF)2] are obtained. [Cr(DPA)3] and [Cr(ImPy)3] ⋅ HImPy show Cr(III) coordinated by nitrogen only; [Cr(MPy)3] ⋅ 0.5 Tol shows a coordination of Cr(III) by both N and S atoms. [Na2Cr(Cbz)4(THF)3] and [Cr2(Bz)4(THF)2] contain Cr(II) and exhibit an infinite chain‐like structure and pairs of chromium atoms with fourfold binding.