[54747-02-3] · C14H14CuLi · Lithium Di-p-tolylcuprate · (MW 252.77)
Physical Data: a clear yellow solution results from the reaction of a 1:1 mixture of (p-MeC6H4)4Cu4 and p-MeC6H4Li in Et2O, from which dimeric and tetrameric species have been isolated. Cryoscopic molecular weight determinations in C6H6 support a (p-MeC6H4)4Cu2Li2.2OEt2 composition. This complex is stable up to 135 °C. 1H NMR (C6D6) d = 0.64 (t, OCMe), 2.08 (s, p-Me), 2.72 (q, OCH2), 7.0 (d, H-3), 8.20 (d, H-2, J2,3 = 7.5 Hz). If prepared in C6H6, an unsolvated complex is formed which decomposes at ~110 °C.1c,8
Solubility: sol Et2O, THF.
Preparative Methods: prepared in situ from CuI salts (Copper(I) Iodide,5,6 Copper(I) Bromide9) under an inert atmosphere of N2 or argon in Et2O, THF, or C6H6.1c,8 See Lithium Dimethylcuprate for purification of CuI salts.
Handling, Storage, and Precautions: extremely sensitive to moisture and oxygen; ignites spontaneously in air. Use in a fume hood.
Lithium di-p-tolylcuprate displays the typical reactivity patterns of lithium diorganocuprates (See Lithium Dimethylcuprate).
Lithium di-p-tolylcuprate transfers the p-tolyl ligand in a 1,4-addition to enantiomerically pure 3-methyl-2-(p-tolylsulfinyl)cyclopentenones to give 3,3-disubstituted cyclopentanones (eq 1) with a high degree of enantioselectivity.2 2,4,6-Trimethyl-3 and 2-siloxypyrylium salts (eq 2)4 also undergo 1,4-addition to give 4H-pyrans with good to high regioselectivity. There are some differences in yield and reactivity between organolithium and Grignard-derived cuprate reagents. 1-Acylpyridinium salts, prepared in situ from Pyridine and Methyl Chloroformate, react with lithium di-p-tolylcuprate to afford 4-substituted 1,4-dihydropyridine derivatives5 with high regioselectivity (eq 3).
Lithium di-p-tolylcuprate participates in substitution reactions with alkyl (eq 4)6 and aryl halides.7 Aryl coupling with 1,8-diiodonaphthalene occurs to give 1,8-di-p-tolylnaphthalene.7
A transmetalation reaction with diborane9 can be effected to give aryl boron compounds which can be manipulated to give phenols, aryl amines, and triaryl boron complexes in limited yields. The reagent (p-MeC6H4)4Cu2Li2 reacts with rhodium(I) complexes10 under a carbon monoxide, nitrogen, or ethylene atmosphere to give 4,4´-bitolyl and 4,4´-ditolyl ketone. The product ratios and yields vary with reactant stoichiometry, and minor byproducts are formed.
Christopher W. Alexander & R. Karl Dieter
Clemson University, SC, USA