Revisiting the Schlenk dimerisation reaction of 1,1-diphenylethene

Abstract

The reaction between 1,1-diphenylethene and two equivalents of lithium in THF gave the complex [(Ph2CCH2CH2CPh2)Li2(THF)4] (3), which crystallised from Et2O/THF as the dialkyllithate salt [Li(THF)4][(Ph2CCH2CH2CPh2)Li(THF)] (3a). A similar reaction between 1,1-diphenylethene and sodium metal in THF gave [(Ph2CCH2CH2CPh2)Na2(THF)1.5] (4), which crystallised from THF as the polymer [(Ph2CCH2CH2CPh2)Na2(THF)3]∞ (4a). In contrast, reactions between 1,1-diphenylethene and potassium under the same conditions gave intractable mixtures of products. However, treatment of 3 with two equivalents of KOtBu in THF yielded the complex [(Ph2CCH2CH2CPh2)K2(THF)0.5] (5) as a deep red powder; treatment of 5 with two equivalents of 12-crown-4, followed by crystallisation from methylcyclohexane/THF, gave the adduct [(Ph2CCH2CH2CPh2)K2(THF)2(12-crown-4)2] (5a). A similar reaction between 3 and 12-crown-4 gave the separated ion pair [Li(THF)(12-crown-4)][Li(THF)0.5(OEt2)0.5(12-crown-4)](Ph2CCH2CH2CPh2) (3b), which contains the free 1,1,4,4-tetraphenyl-1,4-butanediide dicarbanion. X-ray crystallography revealed that the C3C centres of the ligands adopt a near planar geometry, irrespective of whether a metal cation is in close contact.