Synthesis and Characterization of New (η5‑Cyclopentadienyl)dicarbonylruthenium(II) Amine Complexes: Their Application as Homogeneous Catalysts in Styrene Oxidation

The water-soluble ruthenium­(II) mononuclear complexes [CpRu­(CO)2NH2R]­BF4 (Cp = η5-C5H5; R = C6H11 (1), C6H5 (2), CH2C6H5 (3), CH­(CH3)­C6H5 (4), CH2(C6H4O)­CH3 (5), CH2(C6H4)­CN (6), C6H2(CH3)3 (7), CH2CHCH2 (8), CH­(CH3)2 (9)) were synthesized from the reaction of the organometallic Lewis acid [CpRu­(CO)2]­BF4 with amine ligands at room temperature. These complexes are reported for the first time and have been fully characterized by IR, high-resolution mass spectrometry, 1H and 13C NMR spectroscopy, and elemental analysis. Spectral data show that the amines are σ-bonded to the metal center via the nitrogen atom. The crystal structures of complexes 3 and 8 were determined by single-crystal X-ray crystallography. The 4-methoxybenzylamine, 4-aminomethylbenzonitrile and allylamine groups preferentially bind to the metal center via the amine nitrogen. The ruthenium complexes 1, 3–6, 9, and [CpRu­(CO)2NH2CH3]­BF4 (10) and the dinuclear complex [CpRu­(CO)2NH2(CH2)6NH2(CO)2‑RuCp]­[BF4]2 (11) demonstrated excellent catalytic activity in the oxidation of styrene using NaIO4 as the co-oxidant with over 95% conversion and benzaldehyde yields, respectively, in some cases.