Metal exchange in lithiocuprates: implications for our understanding of structure and reactivity

• Published in: Chemical science (Cambridge) Vol. 8; no. 7; pp. 4904 - 4916
• Main Authors: Peel, Andrew J, Ackroyd, Ryan, Wheatley, Andrew E H
• Format: Journal Article
• Language: English
• Published: England 01.07.2017
• Subjects: Agglomeration; Copper; Crystal structure; Disorders; Exchange; Lithium; Monomers; Reagents
• ISSN: 2041-6520; 2041-6539
• DOI: 10.1039/c7sc01423f

New reagents have been sought for directed cupration in which the use of cyanide reagents is eliminated. CuOCN reacts with excess TMPLi (TMP = 2,2,6,6-tetramethylpiperidide) in the presence of limited donor solvent to give crystals that are best represented as (TMP) Cu Li (OCN)Li (THF) , whereby both Lipshutz-type lithiocuprate (TMP) Cu(OCN)Li (THF) and trinuclear (TMP) (OCN)Li (THF) are expressed. Treatment of a hydrocarbon solution of TMP CuLi with LiOCN and THF gives pure . Meanwhile, formation of is systematized by reacting (TMPH )OCN with TMPH and BuLi to give (TMP) (OCN)Li (THF) . Important to the attribution of lower/higher order bonding in lithiocuprate chemistry is the observation that in crystalline , amide-bridging Cu and Li demonstrate clear preferences for di- and tricoordination, respectively. A large excess of Lewis base gives an 8-membered metallacycle that retains metal disorder and analyses as (TMP) Cu Li in the solid state. NMR spectroscopy identifies as a mixture of (TMP) CuLi and other copper-rich species. Crystals from which the structure of was obtained dissolve to yield evidence for coexisting in solution with -generated , and a kinetic variant on ( ), that is best viewed as an agglomerate of TMPLi and TMPCu. Moving to the use of DALi (DA = diisopropylamide), (DA) Cu Li (Br)Li (TMEDA) (TMEDA = , , ', '-tetremethylethylenediamine) is isolated, wherein (DA) Cu(Br)Li (TMEDA) exhibits lower-order Cu coordination. The preparation of (DA) Li(Br)Li (TMEDA) was systematized using (DAH )Br, DAH and BuLi. Lastly, metal disorder is avoided in the 2 : 1 lithium amide : Lipshutz-type monomer adduct (DA) Cu(OCN)Li (TMEDA) .