Unsymmetrical cyano-cuprates as reagents in substitution and addition reactions

Organocopper Compounds: From Elusive to Isolable Species, from Early Supramolecular Chemistry with RCuI Building Blocks to Mononuclear R2–nCuII and R3–mCuIII Compounds. A Personal View

“…A long debate preceded the classification of these reagents, and in the beginning it primarily was based on the observed difference in reactivity of the in situ formed organocuprate and its relation with the actual molar ratio RLi:CuX that was used for its generation. 63 For the neutral homoleptic lithium cuprates a series of different compounds were already known for a long time, e.g., Ph 4 Cu 2 Li 2 ·2Et 2 O 64 and R N 4 Cu 2 Li 2 (4) 65 (see Scheme 3), but examples of cuprates having either a RCuLiX or R 2 CuLi·LiX stoichiometry in which X is the monoanionic dummy ligand, e.g., halide, alkynyl, cyano, arylthio, amido, or phosphido, were reported much more recently. 37,38 It spurred the debate around the origin of the somewhat higher reactivity of the Lipshutz cyano cuprates that concentrated on a discussion about the role and the binding characteristics of the CN anion in the cuprate species.…”

The Use of15N NMR Spectroscopy To Resolve the “Higher Order Cyanocuprate” Controversy:15N,6Li, and13C NMR Spectroscopic Investigations of CuCN-Derived Butyl Cuprates

“…[2] Two-bond 13 C- 13 C coupling constants 2 J across copper proved that the R group and the CN group are both bonded to the same Cu in these 1:1 reagents. [3] In 1981 Lipshutz et al added two equivalents of RLi to CuCN and claimed not only a new class of highly reactive reagents but a new kind of organocopper(i) species, the ªhigher order cyanocuprates.º [4] Spectroscopic evidence was not presented, but NMR and IR data were reported later.…”

Synthesis and Characterization of (THF)3Li(NC)CU(C6H3-2,6-Mes2)and Br(THF)2Mg(C6H3-2,6-Trip2) (Mes = C6H2-2,4,6-Me3; Trip = C6H2-2,4,6-i-Pr3): The Structures of a Monomeric Lower-Order Lithi

“…11,12 Consequently, it was suggested that there was no such higher-order cyanocuprate species formed. The claim for the non-existence of higher-order cyanocuprates was strengthened by the independent isolation of two polymeric lithium cyanocuprate compounds: [(tBu) 2 Cu{Li(THF)(pmteda) 2 3 ] in THF solvent. However, they were not able to present a detailed structure in the paper due to the high R value in the crystal refinement data.…”

“…3 This adaptation was based on earlier work 4 involving related mixed lithium cuprate of the type Li[Cu(C ≡ C-R')R], which showed that the R group was preferentially transferred, thereby conserving an equivalent of the potentially valuable R group in forming the alkylation agent. Subsequently, the addition of 2 equivs of an organolithium reagent LiR to CuCN was reported 5 to give a new type of highly reactive organocyanocuprate reagent of the proposed formula Li 2 -[Cu(CN)R 2 ] in which the two R groups and CN − ligand were assumed to be bound directly to copper to give a "higherorder" cyanocuprate.…”