[15418-29-8] · C8H12BCuF4N4 · Tetrakis(acetonitrile)copper(I) Tetrafluoroborate · (MW 314.60)
Physical Data: white crystals that decompose slowly in moist air9 to a greenish solid;10 mp 159-161 °C, dec 270 °C9 (161-171 °C, sealed tube;10 167-169 °C with decomposition11); d 1.466 g cm-3;10 IR n 2270, 2290 (CN) cm-1.9
Solubility: sol toluene, CH2Cl2, MeCN.
Form Supplied in: prepared as needed.
Analysis of Reagent Purity: gravimetric determination of Cu.9
Preparative Methods: several available, e.g. modification of the known hexafluorophosphate procedure,12 addition of Acetonitrile to the CuBF4-toluene complex,10 and treatment of Copper(I) Oxide with Boron Trifluoride Etherate in MeCN.11
Purification: can be recryst from hot MeCN and dried in vacuo at 80 °C for 12 h.13
Handling, Storage, and Precautions: irritant; moisture sensitive; handle under inert atmosphere. Use in a fume hood.
Autoxidation of Cu(MeCN)4BF4 in DMSO, followed by treatment with dioxane, gave [Cu2(O)(DMSO)4(dioxane)]2+ 2BF4-, a versatile redox catalyst which promotes the oxidation of 2,6-xylenol, benzoin, and 3,5-di-t-butylcatechol to poly(2,6-dimethyl-1,4-phenylene ether), benzil, and 3,5-di-t-butyl-o-benzoquinone, respectively (eq 1).1,2,4
The reagent Cu(MeCN)4BF4 catalyzes the Diels-Alder reactions of acrylic monomers with furan (eq 2).3 Lewis acids such as FeCl3, SnCl4, and ZnCl2 led to polymeric products. Many strongly activated dienophiles which are unreactive toward furan in the presence of Cu(BF4)2-hydroquinone, successfully reacted using the acetonitrile complex. Reactions can be performed at comparatively low temperature (34 °C) without the need for high-pressure apparatus.
The title reagent is also responsible for the catalysis of the Ullmann amination of halogenoarenes, the replacement of halogen attached to aromatic nuclei by amines (or ammonia) in the presence of copper salts.5 Electron-transfer processes and radical formation are mechanisms suggested in discussion of amination and other copper-assisted nucleophilic aromatic substitutions (also see Tetrakis(acetonitrile)copper(I) Perchlorate).
As a Lewis acid, Cu(MeCN)4BF4 promotes cyclization of o-aryl-1,1,1-tris(phenylthio)alkanes, e.g. 4-(m-methoxyphenyl)-1,1,1-tris(phenylthio)butane, to the corresponding tetralone in high yield (eq 3).6 The analogous tris(phenylthio)propane gave uncyclized phenylthio ketone, albeit in 90% yield. Silver(I) Trifluoromethanesulfonate (and other Lewis acids) gave somewhat lower yields.
Cu(MeCN)4BF4 (in stoichiometric amounts) allows propargyl derivatives of phenylenediamine to undergo cyclization and aromatization to the quinoxaline (eq 4).7 Attempted intramolecular amination using I2-THF, CuI-toluene, and bis(collidine)bromonium perchlorate-toluene was unsuccessful.
When used in the acid-catalyzed ring expansion reaction of a-hydroxy dithioacetal derivatives of 3-hydroxy-3-acetyl-14a-methyl-4-nor-5a- and -5b-cholest-8-ene (eq 5),8 exclusive migration of a secondary carbon atom results in the formation of 3,14a-dimethyl-4-oxo steroids. Cu(MeCN)4BF4 gave the best results compared with TiCl4 and HgCl2-BF3 etherate.
Edward J. Parish & Haoyu Qin
Auburn University, AL, USA