Synthesis, structural authentication, and structurally defined metalation reactions of lithium and sodium da-zincate bases (da = diisopropylamide) with phenylacetylene

In a study aimed at developing the diisopropylamido (DA) chemistry of zincates, the new lithium DA-zincate [(TMEDA)·Li(tBu)(DA)Zn(tBu)] (4) has been synthesized by an interlocking cocomplexation approach comprising mixing of its three component chemicals, LDA, tBu2Zn, and TMEDA, in a 1:1:1 ratio in hexane solution. Previously made by transamination from the corresponding TMP-zincate, the known sodium congener [(TMEDA)·Na(tBu)(DA)Zn(tBu)] (2) was also synthesized by this approach, substituting NaDA for LDA. Closely resembling each other, their molecular structures determined by X-ray crystallography can be categorized as contact ion-pair ates of TMEDA-chelated alkali metal cations linked to trigonal-planar dialkyl-Zn anions via bridging DA ligands. Reaction of 4 and 2 with phenylacetylene affords the bimetallic acetylides [{(TMEDA)·Li(CCPh)2Zn(tBu)}2·(TMEDA)] (5) and [{(TMEDA)·Na(CCPh)2Zn(tBu)}2 ] (6), respectively. X-ray crystallographic studies reveal 5 is a pseudodimer (tetranuclear) with two (LiCZnC) rings linked at the Zn atoms by a bridging, nonchelating TMEDA ligand; in contrast 6 adopts a distorted cubane of alternating PhCC and metal (2 Na, 2 Zn) corners. For comparison, the synthesis and crystal structures of the neutral zinc complexes [(TMEDA)·Zn(CCPh)2] (7) and [(TMEDA)·Zn(tBu)(CCPh)] (8), formally components of the ate complexes 5 and 6, are also reported. In addition, the 1H and 13C NMR spectra of 2, 4, 5, 6, 7, and 8 recorded from solutions in C6D6 are disclosed. (Abstract from: http://pubs.acs.org/doi/abs/10.1021/om8001813)