Steric Enhancement of Group 12 Metal Hydride Stability and the Reaction of an Arylzinc Hydride with Tetramethylpiperidinyl Oxide (TEMPO)

The synthesis and characterization of arylzinc hydrides Ar*Zn(μ-H)2ZnAr* (Ar* = C6H3-2,6-(C6H2-2,4,6-Pri3)2, 5) and {(4-Me3Si-Ar*)Zn(μ-H)2Zn(Ar*-4-SiMe3)} (4-Me3Si-Ar* = C6H2-2,6-(C6H2-2,4,6-Pri3)2-4-SiMe3, 7) as well as the monomeric arylcadmium hydride Ar*CdH (9) are described. They were prepared by the transmetalation of the corresponding aryl metal iodides with NaH. The Ar*CdH monomer displayed significantly greater thermal stability than its recently reported dimeric congener Ar′Cd(μ-H)2CdAr′ (Ar′ = C6H3-2,6-(C6H3-2,6-Pri2)2), which decomposed at room temperature to afford Ar′CdCdAr′. This result supports the proposal that decomposition of the metal hydrides occurs by an associative mechanism. The reactions of these compounds with TEMPO (2,2,6,6-tetramethylpiperidinyl oxide) were also examined, but the only crystalline product obtained was 4-Me3Si-Ar*ZnTEMPO, in which the metal is bound to the TEMPO ligand in a quasi side-on fashion primarily through the oxygen but with a significant zinc−nitrogen interaction.