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(eta (6)-toluene)barium bis{tris[(trimethylsilyl)methyl]zincate} (3) with rather short Ba-C bond lengths of 3.028(5) and 3 055(5) Angstrom. 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)(3)Ba](2)O-(mu (4)-O)(2)[(Me3SiCH2ZnC2)(2)SiMe2](2) (5). The central moiety is a centrosymmetric Ba2O2 cycle with Ba-O distances of 2.514(2) and 2.570(3) Angstrom. The oxygen dianion is surrounded, distorted tetrahedrally by two barium and two zinc atoms.