Synthesis and Structural Elucidation of Alkyl, Amido, and Mixed Alkyl−Amido “Highly-Coordinated” Zincates

The solution and solid-state characterization of the tetraorganozincates [(TMEDA)<sub>2</sub>Li<sub>2</sub>ZnMe(NMe<sub>2</sub>)<sub>3</sub>] (<b>2</b>) and [(TMEDA)<sub>2</sub>Li<sub>2</sub>ZnMe<sub>4</sub>] (<b>4</b>) and the all-amido triorganozincate [{(TMEDA)LiZn(NMe<sub>2</sub>)<sub>3</sub>}<sub>2</sub>] (<b>3</b>) are reported. X-ray crystallographic studies reveal that <b>2</b> and <b>4</b> exhibit similar structural motifs, namely trinuclear Li···Zn···Li chain arrangements held together by a methyl and three amido ligands in the former and exclusively by methyl groups in the latter, whereas <b>3</b> adopts a longer tetranuclear Li···Zn···Zn···Li chain arrangement with all NMe<sub>2</sub> ligands. The zinc coordination in all these structures is distorted tetrahedral. DFT calculations revealed that the formation of tetraorganozincate <b>4</b> by cocomplexation of 2 equiv of MeLi and Me<sub>2</sub>Zn is thermodynamically preferred over the parent triorganozincate [(TMEDA)LiZnMe<sub>3</sub>]. Preliminary studies show that the tris(amido)alkyl zincate <b>2</b> is a poor Brønsted base for metalation (zincation) of functionalized aromatic substrates such as anisole, <i>N</i>,<i>N</i>-diisopropylbenzamide, and benzonitrile.