Bis(pyrazolyl)acetate and bis(3,5-dimethylpyrazolyl)acetate tris-acetonitrile ruthenium(II) complexes: Synthesis, properties, and structure

Abstract

[(η6-p-cymene)RuI2]2 (1) was reacted with the heteroscorpionate ligands, bis(pyrazolyl)acetic acid (BPAH) or bis(3,5-dimethylpyrazoly)acetic acid (BMPAH), in the presence of potassium carbonate under various conditions to yield cationic Ru(II) complexes: [(BPA)Ru(cymene)]I (2), [(BMPA)Ru(cymene)]I (3), [(BPA)Ru(NCMe)3]I (4), and [(BMPA)Ru(NCMe)3)]I (5). The piano-stool, η6-cymene ruthenium complexes (2 and 3) are isolated when the reaction was conducted at room temperature, whereas the tris-acetonitrile ruthenium(II) complexes were isolated at elevated reaction temperatures. The iodide anion of 4 or 5 was easily replaced with tetrakis(3,5-bis(trifluoromethyl)phenyl)borate (BArF′) by reaction with silver tetrakis(3,5-bis(trifluoromethyl)phenyl)borate (Ag[BArF′]) to yield [(BPA)Ru(NCMe)3][BArF′] (6) and [(BMPA)Ru(NCMe)3)][BArF′] (7), which demonstrate improved solubility in organic solvents as compared to 4 and 5. The acetonitrile ligands cis to the carboxylate group in 4 and 5 were significantly more labile than the trans acetonitrile ligand. The rate of acetonitrile dissociation for 4 and 5 was found to be statistically equivalent. These complexes were characterized by 1H, 13C, 19F nuclear magnetic resonance spectroscopy, infrared spectroscopy, and elemental analyses. Compounds 2, 4, 5, and 7 were also characterized by single crystal X-ray crystallography.