Metal exchange in lithiocuprates: implications for our understanding of structure and reactivityElectronic supplementary information (ESI) available. CCDC 1540280-1540286. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c7sc01423f

• Main Authors: Peel, Andrew J, Ackroyd, Ryan, Wheatley, Andrew E. H
• Format: Journal Article
• Language: English
• Published: 27.06.2017
• ISSN: 2041-6520; 2041-6539
• DOI: 10.1039/c7sc01423f

New reagents have been sought for directed ortho 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) 2 Cu 0.1 Li 0.9 (OCN)Li 2 (THF) 8 , whereby both Lipshutz-type lithiocuprate (TMP) 2 Cu(OCN)Li 2 (THF) 8a and trinuclear (TMP) 2 (OCN)Li 3 (THF) 8b are expressed. Treatment of a hydrocarbon solution of TMP 2 CuLi 9a with LiOCN and THF gives pure 8a . Meanwhile, formation of 8b is systematized by reacting (TMPH 2 )OCN 10 with TMPH and n BuLi to give (TMP) 2 (OCN)Li 3 (THF) 2 11 . Important to the attribution of lower/higher order bonding in lithiocuprate chemistry is the observation that in crystalline 8 , 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) 2 Cu 1.35 Li 0.65 9 in the solid state. NMR spectroscopy identifies 9 as a mixture of (TMP) 2 CuLi 9a and other copper-rich species. Crystals from which the structure of 8 was obtained dissolve to yield evidence for 8b coexisting in solution with in situ -generated 9a , 11 and a kinetic variant on 9a ( i -9a ), that is best viewed as an agglomerate of TMPLi and TMPCu. Moving to the use of DALi (DA = diisopropylamide), (DA) 2 Cu 0.09 Li 0.91 (Br)Li 2 (TMEDA) 2 12 (TMEDA = N , N , N ′, N ′-tetremethylethylenediamine) is isolated, wherein (DA) 2 Cu(Br)Li 2 (TMEDA) 2 12a exhibits lower-order Cu coordination. The preparation of (DA) 2 Li(Br)Li 2 (TMEDA) 2 12b was systematized using (DAH 2 )Br, DAH and n BuLi. Lastly, metal disorder is avoided in the 2 : 1 lithium amide : Lipshutz-type monomer adduct (DA) 4 Cu(OCN)Li 4 (TMEDA) 2 13 . A new class of lithium cyanatocuprates are elucidated whose structures reveal a preference by copper for lower order structure formation.