Synthesis of Strontium and Barium Bis{tris[(trimethylsilyl)methyl]zincates} via the Transmetalation of Bis[(trimethylsilyl)methyl]zinc

The transmetalation of bis[(trimethylsilyl)methyl]zinc in THF with distilled strontium and barium yielded bis(tetrahydrofuran)strontium and tetrakis(tetrahydrofuran)barium bis{tris[(trimethylsilyl)methyl]zincates} (1 and 2, respectively). The reaction of barium with Zn(CH2SiMe3)2 in toluene gave bis(η6-toluene)barium bis{tris[(trimethylsilyl)methyl]zincate} (3) with rather short Ba−C bond lengths of 3.028(5) and 3.055(5) Å. All of these trialkylzincate anions coordinate as bidentate ligands with M−C−Zn three-center two-electron bonds. When carried out in the nondonor solvent heptane, the transmetalation reaction yielded barium bis{tris[(trimethylsilyl)methyl]zincate} (4), which reacts with THF to give the complex 2 and a small amount of [(THF)3Ba]2(μ4-O)2[(Me3SiCH2ZnCH2)2SiMe2]2 (5). The central moiety is a centrosymmetric Ba2O2 cycle with Ba−O distances of 2.514(2) and 2.570(3) Å. The oxygen dianion is surrounded, distorted tetrahedrally by two barium and two zinc atoms.