Group ib organometallic chemistry : XXXIV. Thermal behaviour and chemical reactivity of tetranuclear Me 2N-substituted diarypropenylcopper-copper anion (Vi 2Cu 4X 2) and mixed diarylpropenyl/organocopper (Vi 2Cu 4R 2) compounds

Abstract

Thermal decomposition of configurationally pure 1,2-diarylpropenylcopper compounds Z-Vi 2CU 4Br 2 and Z-Vi 2Cu 4R 2 [Vi  (2-Me 2NC 6H 4)CC(Me)-(C 6H 4Me-4), R  2-Me 2NC 6H 4 or 4-MeC 6H 4CC] predominantly results in the formation of ViH. In contrast, only dimers (ViVi) were formed on thermolysis of ( Z-ViCu 2OTf) η which is a further illustration of the influence of the counter anion on the reactivity of organocopper cluster compounds. However, in both cases partial inversion of configuration, giving mixtures of isomers, was observed. The thermolysis of ( Z-ViCu 2OTf) η is discussed in terms of OTf-enhanced intraaggregate electron-transfer processes. The formation of incipient vinyl cations which are η 2-coordinated to the copper cluster can explain the observed isomerization. Also in the hydrolysis reaction of Z-Vi 2Cu 4Br 2 mixtures of isomeric ViH compounds were obtained, the E/Z ratio being dependent on the type of reagent used. Mixtures of isomeric ViX compounds (X  Br, Cl, I) were formed in the reaction of Z-Vi 2Cu 4Br 2 with I 2 and CuCl 2. An explanation for the occurrence of isomerization is presented. Dimers (ViVi) were almost absent in the product mixture resulting from the reaction of Z-Vi 2Cu 4Br 2 with CuCl 2. In contrast, ViVi is obtained in about 50% yield from the reaction of ViLi with CuCl 2 which is in accord with earlier observations for the reaction of aryllithium compounds with cupric halides. Highly selective E-ViBr formation was observed in the reaction of E-ViLi with AgBr. This reaction probably proceeds via a thermally unstable Z-ViAg 2Br intermediate.