Extending motifs in lithiocuprate chemistry: unexpected structural diversity in thiocyanate complexes

Since the advent in 2007 of directed ortho cupration, effort has gone into understanding the structure-reactivity effects of amide ligand variation in and alkali metal salt abstraction from Lipshutz-type cuprates such as (TMP)2Cu(CN)Li2(THF) 1 (TMP = 2,2,6,6-tetramethylpiperidide). The replacement of CN– with SCN– is investigated presently as a means of improving the safety of lithium cuprates. The synthesis and solid state structural characterization of reference cuprate (TMP)2Cu(CN)Li2(THP) 8 (THP = tetrahydropyran) precedes that of the thiocyanate series (TMP)2Cu(SCN)Li2(L) (L = OEt2 9 , THF 10, THP 11). For each of 9-11, preformed TMPLi was combined with CuSCN (2:1) in the presence of sub-stoichiometric Lewis base (0.5 eq. wrt Li). The avoidance of Lewis basic solvents incurs formation of the unsolvated Gilman cuprate (TMP)2CuLi 12, whilst multidimensional NMR spectroscopy has evidenced the abstraction of LiSCN from 9-11 in hydrocarbon solution and the in situ formation of Gilman reagents. The synthetic utility of 10 is established in the selective deprotometalation of chloropyridine substrates, including effecting transition metal-free homocoupling in 51-69% yield.This work was supported by the U.K. EPSRC through grant EP/J500380/1 (A. P.) and the Ministère de l'Enseignement Supérieur et de la Recherche scientifique Algérien (M. H.). F. M.This is the final version of the article. It was first available from the Royal Society of Chemistry via http://dx.doi.org/10.1039/C5DT03882