Hydrogenolysis of Cationic Half‐Sandwich Zinc Complexes Containing a Chelating Amine: Facile Cleavage of Zinc‐Carbon Bond by Dihydrogen to Give Zinc Hydride Cations

Abstract

AbstractCationic half‐sandwich zinc complexes containing chelating amines [Cp*Zn(Ln)][BAr4F] (2 a, Cp*=η3‐C5Me5, Ln=N,N,N’,N’‐tetramethylethylenediamine, TMEDA; 2 b, Ln=N,N,N’,N’‐tetraethylethylenediamine, TEEDA; 2 c, Cp*=η1‐C5Me5, Ln=N,N,N’,N’’,N’’‐pentamethyldiethylenetriamine, PMDTA; Ar4F=(3,5‐(CF3)2C6H3)4) reacted with dihydrogen (ca. 2 bar) in THF at 80 °C to give molecular zinc hydride cations [(Ln)ZnH(thf)m][BAr4F] (3 a,b, m=1; 3 c, m=0) previously reported along with Cp*H. Pseudo first‐order kinetics with respect to the concentration of 2 b suggests heterolytic cleavage of dihydrogen by the Zn−Cp* bond, reminiscent of σ‐bond metathesis. Hydrogenolysis of the zinc cation 2 b in the presence of benzophenone gave the zinc alkoxide [(TEEDA)Zn(OCHPh2)(thf)][BAr4F] (5 b). Cation 2 b was shown to catalytically hydrogenate N‐benzylideneaniline. The PMDTA complex 2 c underwent C−H bond activation in acetonitrile to give a dinuclear μ‐κC,κN‐cyanomethyl zinc complex [(PMDTA)Zn(CH2CN)]2[BAr4F]2 (6 c).