Atom-Economical Synthesis of the Versatile Ruthenium Precursor [TpRuCl(COD)] (Tp = Hydrotris(pyrazol-1-yl)borate) Discloses a Diamine Ligand Dealkylation Process

An atom-economical, more environmentally friendly alternative method of synthesis of the versatile complex [TpRuCl(COD)] (1) (Tp = hydrotris(pyrazol-1-yl)borate; COD = 1,5-cyclooctadiene) has been developed. Instead of starting from [RuHCl(COD)(NH2NMe2)3]+, 1 can be conveniently prepared by reaction of the derivative trans-[RuCl2(COD)(Me2NCH2CH2NHMe)] (2) with KTp in acetone at 55 °C. Compound 2, which has been structurally characterized by X-ray crystallography, results from an unexpected diamine dealkylation process which takes place in the course of the reaction of [{RuCl2(COD)}n] with tmeda (tmeda = Me2NCH2CH2NMe2) in toluene at 80 °C. This process had been overlooked in the literature, as compound 2 had been misidentified as cis-[RuCl2(COD)(tmeda)], and suggests that amine dealkylation might occur more commonly than previously anticipated.