Dihydrogen Cleavage by a Zinc–Zinc Bond of a Heteroleptic Dizinc(I) Cation

Abstract

Oxidative addition of dihydrogen across a metal−metal bond to form reactive metal hydrides in homogeneous catalysis is known for transition metals but not for zinc(I)−zinc(I) bond as found in Carmona's eponymous dizinconene [Zn 2 Cp* 2 ] (Cp* = η 5 -C 5 Me 5 ). Dihydrogen reacted with the heteroleptic zinc(I)−zinc(I) bonded cation [(L 2 )Zn−ZnCp*][BAr 4 F ] (L 2 = TMEDA, N,N,N′,N′-tetramethylethylenediamine, TEEDA, N,N,N′,N′-tetraethylethylenediamine; Ar F = 3,5-(CF 3 ) 2 C 6 H 3 ) under 2 bar at 80 °C to give the zinc(II) hydride cation [(L 2 )ZnH(thf)][BAr 4 F ] along with zinc metal and Cp*H derived from the intermediate [Cp*ZnH]. DFT calculations show that the cleavage of dihydrogen occurs through a highly unsymmetrical transition state. Mechanistic studies agree with a heterolytic cleavage of dihydrogen as a result of the cationic charge and unsymmetrical ligand coordination. To explore the existence of zinc(I) hydride, thermally unstable hydridotriphenylborate complexes of zinc(I) [(L 2 )Zn(HBPh 3 )−ZnCp*] (L 2 = TMEDA, TEEDA; TMPDA, N,N,N′,N′-tetramethyl-1,3-propylenediamine) have been prepared by salt metathesis and were shown to undergo fast exchange with both BPh 3 and [HBPh 3 ] − .