Heteroleptic Ruthenium p-Cymene Amidinate Complexes─A Synthetic Endeavor to Unearth Precursors for Ru Thin Films

Interest in small ruthenium coordination complexes is at an all-time high. They can find use as catalysts, in optoelectronics, and as precursor compounds for chemical vapor deposition (CVD) techniques. In this study, we introduce ten new Ru complexes synthesized from the versatile (p-cymene)ruthenium(II) chloride dimer, featuring 1,3-N-coordinating amidinate-type ligands and either methyl or acetate coligands. All compounds were characterized by nuclear magnetic resonance spectroscopy (NMR), infrared spectroscopy (IR), liquid injection field desorption ionization mass spectrometry (LIFDI-MS), and single-crystal X-ray diffraction (SC-XRD), which confirmed the structures of the chloride and acetate derivatives, allowing for assessment of their intermolecular interactions. Thermogravimetry (TG) revealed that the methyl-substituted complexes exhibit favorable one-step evaporation, rendering them promising candidates for vapor-phase deposition. Finally, the ease of synthesis, combined with good volatility, prompted us to select Ru p-cymene diacetate for proof-of-principle metal-organic CVD of Ru metal in a single-source route, as well as using either oxygen or ammonia as a coreactant. This work highlights the synthetic versatility of the Ru(II) p-cymene motif and its potential for CVD applications.