Stereoselective synthesis of chlorido–phosphine ruthenium complexes bearing a pyrazole-based protic tripodal amine ligand

Abstract

Octahedral ruthenium(II) complexes bearing a tripodal amine ligand featuring three ionizable pyrazole NH groups, tris((5-mesitylpyrazol-3-yl)methyl)amine (LH3), have been synthesized in a stereoselective manner. Treatment of the chlorido complex [{RuCl(LH3)}2(μ2-Cl)]Cl (1) with triphenylphosphine in methanol and subsequent anion exchange with potassium hexafluorophosphate resulted in the clean formation of the phosphine complex cis(P,Namine)-[RuCl(PPh3)(LH3)]PF6 (cis(P,Namine)-2), in which the phosphine ligand lies in the position cis to the amine nitrogen atom. Similarly, diphosphines Ph2P(CH2)nPPh2 reacted with 1 under the same conditions to give the diphosphine-bridged dinuclear ruthenium complexes cis(P,Namine)-[{RuCl(LH3)}2{μ2-Ph2P(CH2)nPPh2}](PF6)2 (3a: n=4; 3b: n=3; 3c: n=2). The cis-selectivity is in marked contrast with the reaction in toluene, which affords the trans isomer exclusively (Yamagishi et al., Inorg. Chem. 54 (2015) 11584.). On the other hand, a related chlorido–(dimethyl sulfoxide) complex trans(S,Namine)-[RuCl(Me2SO-S)(LH3)]Cl (4) was synthesized by the reaction of cis-[RuCl2(Me2SO)4] with LH3. Detailed structures of cis(P,Namine)-2, 3a, and 4 have been determined by X-ray crystallography.