[14057-91-1] · C8H12ClCuN4O4 · Tetrakis(acetonitrile)copper(I) Perchlorate · (MW 327.24)
Solubility: sol toluene, CH2Cl2, MeCN.
Form Supplied in: prepared as needed.
Preparative Methods: several available, e.g. modification of the known hexafluorophosphate procedure,11 reaction of Copper(I) Oxide and Acetonitrile in perchloric acid,12 the combination of CuClO4 and MeCN in 2-butanol,10 and refluxing Cu(ClO4)2 in MeCN with excess copper powder9 or turnings.2
Handling, Storage, and Precautions: irritant; moisture sensitive; handle under inert atmosphere. Occasional mild explosions have been reported with dry organic perchlorate salts.10 Use in a fume hood.
The title reagent eliminates the induction period in the Ullmann condensation reaction of 1-bromoanthraquinone with 2-aminoethanol. The CuI catalyst is first oxidized to a CuII species by electron transfer from CuI to the haloanthraquinone; this CuII species increases the catalytic activity of the CuI catalyst (eq 1).1
The reagent can react with the adducts formed from acyclic or cyclic cyclopropyl ketones and tris(methylthio)methyllithium (see Tris(methylthio)methane); the products have been rationalized via the intervention of epoxide intermediates.2,3 With acyclic cyclopropyl ketones, C-O epoxide bond cleavage occurs selectively, leading to a cyclopropylcarbinyl carbocation intermediate and subsequent thiomethyl group migration. With more sterically restricted substrates (eq 2), alternative C-O bond cleavage competes.2
Cu(MeCN)4ClO4 can catalyze the cyclopropanation of tetramethylethylene (TME) with Ethyl Diazoacetate (EDA).4 High TME/EDA and EDA/catalyst ratios, longer addition periods, and high reaction temperatures increase the product yield.
The reagent has been used to synthesize bis(oxazoline)copper(I) complexes that exhibit high enantioselectivity (up to 94% ee) in the catalytic cyclopropanations of trisubstituted and unsymmetrical cis-1,2-disubstituted alkenes.5 The use of diazoacetates with steric bulk (e.g. R = (-)-menthyl, dicyclohexylmethyl, di- and trimethylpentyl) (eq 3) gives trans:cis product ratios as high as 99:1.
Using PhI=NTs as a nitrene precursor, alkenes are converted to aziridines with Cu(MeCN)4ClO4 as catalyst (eq 4).7
This copper(I) complex can serve as the precursor of other synthetically useful catalysts. For example, the addition reaction of tetrachloromethane to 1,5-hexadiene is catalyzed by a copper(I)-butylamine complex6 prepared from the title reagent. Cu(MeCN)4ClO4 also catalyzes the intramolecular cycloadditions of ketones with nitrogen heterocycles bearing a-carbonitrile functionality, as illustrated with pyridine-2-carbonitrile (pyCN) (eq 5).8
Edward J. Parish & Haoyu Qin
Auburn University, AL, USA