THE DECOMPOSITION REACTION OF THE DIALANE RADICAL ANION [R(2)AL(.)-ALR(2)](-) IN DME(II) - CRYSTAL STRUCTURES OF THE ALUMINIUM GLYCOLATES [R(2)AL(OCH2)(2)]K(DME) AND R(2)AL(OCH2)(2)AL(R)(OCH2)(2)ALR(2) (R=CH(SIME(3))(2))

摘要

Tetrakis[bis(trimethylsilyl)methyl]dialane(4) (1) reacts with potassium in 1,2-dimethoxyethane (DME) to yield the dark blue, surprisingly stable radical anion [R(2)Al-AlR(2)](-)[K(DME)(3)](+) (2) (R = CH(SiMe(3))(2)). An excess of potassium, however, and a longer reaction time leads to decomposition with the formation of three new compounds, which are identified now as: [R(2)Al(Me)(OC(2)H(4)OMe)][K(DME)] (3), [R(2)AlMe(2)][K(DME)(6)] (4), and the glycolato alanate [R(2)Al(OCH2)(2)][K(DME)] (7). These compounds verify that a dialkyl alanate(I) R(2)Al(-) with aluminium in a formal oxidation state of + I is an intermediate in the course of the decomposition reaction. 7 was synthesized by the reaction of the chloro compound Cl-AlR(2) with KOCH2CH2OK. Its crystal structure exhibits a dialkyl aluminium fragment bound to both oxygen atoms of a chelating glycolate unit; a one-dimensional coordination polymer is formed by bridging potassium cations. As a byproduct the compound RAl(OCH2CH2O)(2)(AlR(2))(2) (8) is isolated and characterized by a crystal structure determination showing a diglycolatomonoalkyl aluminium centre coordinated by two AlR(2) fragments. The central Al atom in 8 has a coordination number of five in a slightly distorted square pyramidal environment. [References: 59]