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

Cationic half-sandwich zinc complexes containing chelating amines [Cp*Zn(L n )][BAr 4 F ] (2 a, Cp*=η 3 -C 5 Me 5 , L n =N,N,N',N'-tetramethylethylenediamine, TMEDA; 2 b, L n =N,N,N',N'-tetraethylethylenediamine, TEEDA; 2 c, Cp*=η 1 -C 5 Me 5 , L n =N,N,N',N'',N''-pentamethyldiethylenetriamine, PMDTA; Ar 4 F =(3,5-(CF 3 ) 2 C 6 H 3 ) 4 ) reacted with dihydrogen (ca. 2 bar) in THF at 80 °C to give molecular zinc hydride cations [(L n )ZnH(thf) m ][BAr 4 F ] (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(OCHPh 2 )(thf)][BAr 4 F ] (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(CH 2 CN)] 2 [BAr 4 F ] 2 (6 c).