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

Abstract

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)(NH 2 NMe 2 ) 3 ] + , 1 can be conveniently prepared by reaction of the derivative trans-[RuCl 2 (COD)(Me 2 NCH 2 -CH 2 NHMe)] (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 [{RuCl 2 (COD)} n ] with tmeda (tmeda = Me 2 NCH 2 CH 2 NMe 2 ) in toluene at 80°C. This process had been overlooked in the literature, as compound 2 had been misidentified as cis-[RuCl 2 (COD)(tmeda)], and suggests that amine dealkylation might occur more commonly than previously anticipated.

Activation of Propargyl Alcohols by TpRu Complexes Bearing a Bidentate NHC Ligand

“…All solvents were deoxygenated immediately before use. [TpRuCl­(COD)] was prepared according to a recently reported procedure . The imidazolium salt bis­(3-methylimidazolium)­methane dichloride ([ L H 2 ]­Cl 2 ) was prepared following suitable adaptations of published procedures .…”

“…[TpRuCl(COD)] was prepared according to a recently reported procedure. 46 The imidazolium salt bis(3methylimidazolium)methane dichloride ([LH 2 ]Cl 2 ) was prepared following suitable adaptations of published procedures. 30 IR spectra were taken in Nujol mulls on a FTIR spectrophotometer.…”

Direct Chlorination of Trispyrazolyl Borate Ligands in Tp-Ruthenium Complexes

“…TpRu(cod)Cl (1a) was synthesized as a strategic intermediate 14 to access a variety of halogenated complexes since the diene ligand could be later removed by hydrogenation or heating, 15 or the diene could be exchanged for a variety of phosphine ligands (Scheme 1). The unfunctionalized Tp ligand also offered potential diversification via electrophilic reactions, and so we initially targeted chlorination as a representative transformation.…”

“…Jimeńez-Tenorio and Puerta's procedure 14 was used to obtain intermediate 1a. We initially looked at the removal of the cod ligand from 1a, but found that neither hydrogenation nor elevated temperatures allowed for a discrete product to be obtained.…”

“…KTp was prepared by a known method. 12 TpRu(COD)Cl was prepared by the same procedure as previously reported, 14 but was purified differently. The rest of the reagents are commercially available, and were degassed before usage as necessary.…”