Ion exchange in bimetallic cage copper organosiloxanes and the synthesis of polynuclear metal complexes containing Li and CuII atoms

Abstract

The replacement of sodium (potassium) atoms by lithium in a series of bimetallic (“alkaline”) cage copper organosiloxanes was investigated. The reactions of cage CuII(Na) or CuII(K) derivatives of organometallosiloxanes (OMS) with LiCl afford the corresponding CuII(Li) derivatives. The rate and degree of replacement are mainly determined by the structure of the molecular cage of the starting OMS. In the case of globular-like bimetallic OMS of the general formula [RSiO2]12[Cu4M4] (R = Me, H2C=CH-(Vin), or Ph; M = Na or K), the ion exchange occurs under mild conditions at a high rate to give the corresponding CuII(Li) derivatives [RSiO2]12Cu4Li4 with the same structure (∼80% yield). Sandwich-like bimetallic OMS of the general formula [RSiO2]6[Cu4M4][RSiO2]6 (R = Ph or Vin; M = Na or K) react more slowly, the reaction proceeding stepwise. In the latter case, partial substitution products, viz., heterometallic sandwich complexes, for example, {[VinSiO2]6}2Cu4K2Li2, were isolated. The structures and compositions of the reaction products were studied by X-ray diffraction, gel permeation chromatography, and elemental analysis. The selectivity of the replacement of alkali metal atoms allows the synthesis of the desired globular or sandwich cage Cu(Li) metallosiloxanes, which are difficult to prepare.