Preparation of New Ru(II) Complexes Supported by Tetra(pyrazolyl)methane: Efforts toward C-H Activation by Cationic Ru(II) Complexes

Cheap and abundant natural gas provides a Viable alternative to oil and coal with the opportunity to reduce CO2 emissions. Natural gas (primarily methane) is disadvantaged due to its low energy density and gaseous phase. Its broader use has been limited by safety and expense concerns associated with the transportation and storage of natural gas. As a result, the conversion of natural gas to liquid fuels (e. g., methanol) is of interest. The conversion of hydrocarbons to functionalized products catalyzed by transition metal complexes has been studied. Our group previously reported that TpRu(PMe3)2X (Tp = hydridotris(pyrazolyl)borate; X = NHPh, OH or Me) can activate benzene C - H bonds. However, studies of these reactions are complicated by the strongly coordinating PMe3 ligands, which must dissociate to coordinate benzene. Presented here are the efforts to prepare d6 charge neutral Ru(II) complexes [163- C(pz)4]Ru(L)(X)(Cl) [C(pz)4 = tetra(pyrazolyl)methane; X = NHPh, OH, OMe] and to exchange chloride with a non - coordinating anion to give the coordinatively unsaturated species {[1c3 - C(pz)4]Ru(L)(X)}+. [1c3 - C(pz)4]Ru(L)(X)(Cl) should provide more facile access to unsaturated reactive species than TpRu(PMe3)2X. In addition, the cationic charge in {[1c3 - C(pz)4]Ru(L)(X)}+ might facilitate C - H activation. Currently, {[1c3 - C(pz)4]Ru(L)(XH)(Cl)}+ (C(pz)4 = tetra(pyrazolyl)methane; X = NHPh, OH or OMe; L = P(OCH2)3CEt) have been synthesized. The preparation and isolation of corresponding Ru - X complexes was not successful due to fast decomposition after deprotonation. Further studies will focus on variation of ligands to stabilize Ru - X complexes.

Note: Abstract extracted from PDF file via OCR