Chromous siloxides of variable nuclearity and magnetism†
b
Reiner
Anwander
*a
Abstract
Treatment of Cr[N(SiMe3)2]2(thf)2 with HOSiR3 (R = Et, iPr) in THF afforded the bridged CrII siloxide complexes Cr3(OSiEt3)2(μ-OSiEt3)4(thf)2 and Cr2(OSiiPr3)2(μ-OSiiPr3)2(thf)2 in high yield. Exposure of these compounds to vacuum in aliphatic solvents led to the loss of coordinated THF and to the formation of the homoleptic chromous siloxides Cr4(μ-OSiEt3)8 and Cr3(OSiiPr3)2(μ-OSiiPr3)4, respectively, in moderate to high yield. Use of TMEDA as a potentially bidentate donor molecule gave the monomeric cis-coordinated siloxide Cr(OSiiPr3)2(tmeda) (tmeda = N,N,N′,N′-tetramethylethane-1,2-diamine). Oxidation of Cr2(OSiiPr3)2(μ-OSiiPr3)2(thf)2 with CHI3 and C2Cl6 produced the trigonal bipyramidal chromic compound CrIII(OSiiPr)3(thf)2 and asymmetrically coordinated Cr2Cl3(OSiiPr3)3(thf)3, respectively. Magnetic measurements (Evans and SQUID) hinted at (a) antiferromagnetic interactions between the CrII centres, (b) revealed higher effective magnetic moments (μeff) for cis-coordinated monomeric heteroleptic complexes compared to trans-coordinated ones, and (c) pointed out the highest (μeff) for the tetranuclear complex Cr4(μ-OSiEt3)8 (6.26μB, SQUID, 300 K; Cr⋯Cradjacent avg. 2.535 A).
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