Molecular Structure of 1,2-Dibenzoyl-1′,2′,3′,4′,5′-pentamethylruthenocene Dioxime Hydrochloride

The dioxime of 1,2-dibenzoylpentamethylruthenocene is synthesized from its parent diketone and hydroxylamine under standard basic conditions. The slightly air-sensitive product is crystallized in the form of its monohydrochloride. The solid-state structure is the first example of a dioxime monohydrochloride showing a typical metallocene core with peripheral intramolecular N–H–N and O–H–Cl hydrogen bonding. 1. Introduction Simple vicinal dioximes represent the well-known chelating ligands with numerous applications in coordination chemistry [1, 2], catalysis [3, 4], and supramolecular chemistry [5–7]. Based on our earlier work [8, 9] with metallocene metalloligands, we address in this work a new organometallic hybrid dioxime composed of a redox-responsive ruthenocene core and conjugated dioxime functional groups. Synthetic and structural properties in solution and in the solid state are reported. 2. Materials and Methods 2.1. 1,2-Dibenzoyl-1′,2′,3′,4′,5′-pentamethylruthenocene Dioxime In the first Schlenk vessel, a solution of 1,2-dibenzoyl-1′,2′,3′,4′,5′-pentamethylruthenocene [8, 9] (0.200？g, 0.40？mmol) in dry ethanol (5？mL) was prepared at room temperature. In the second Schlenk vessel, a solution of hydroxylamine hydrochloride (0.400？g, 5.76？mmol) in dry ethanol (5？mL) and freshly distilled, dry pyridine (4.96？mmol, 0.40？mL) was similarly prepared. Under protection from air, the two solutions were combined and heated to reflux for 45 minutes. Workup is as follows: pyridine and most volatile materials were removed on a vacuum line. Under protection from air, the residue was repeatedly extracted with small portions (2？mL) of warm, dry ethanol. The ethanolic solutions were filtered through a syringe filter, and the combined extracts were cooled in an ice/water-bath for crystallization. Without protection from air, the crystallized product was filtered off, washed with two portions of cold water, and dried under vacuum, affording 0.125？g of orange-yellow 1,2-dibenzoyl-1′,2′,3′,4′,5′-pentamethylruthenocene dioxime in 57.9% yield. Note that this compound is air-stable in the solid state but slightly air-sensitive in solution. M.p.: 163°C (dec.). 1H NMR (300？MHz, CD2Cl2): d 1.78 (s, 15H, Cp*), 4.43 (d, 2H, Cp), 4.56 (t, 1H, Cp), 7.57 (br s, 10H, phenyl), 12.16 (s, 2H, N–OH). 13C NMR (75？MHz, CD2Cl2): d 11.2 (Cp*), 78.1 (Cp), 79.8 (Cp), 81.2 (Cp*), 88.7 (Cp); 128.5, 129.2, 130.2, 131.0 (phenyl); 158.0 (C=N–OH). LSIMS: m/z 541.14 (M+？？+？？H). Single crystals of the hydrochloride of 1,2-dibenzoyl-1′,2′,3′,4′,5′-pentamethylruthenocene dioxime were obtained at