Chromous siloxides of variable nuclearity and magnetism.

Treatment of Cr[N(SiMe)](thf) with HOSiR (R = Et, Pr) in THF afforded the bridged Cr siloxide complexes Cr(OSiEt)(μ-OSiEt)(thf) and Cr(OSiPr)(μ-OSiPr)(thf) 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 Cr(μ-OSiEt) and Cr(OSiiPr)(μ-OSiPr), respectively, in moderate to high yield. Use of TMEDA as a potentially bidentate donor molecule gave the monomeric -coordinated siloxide Cr(OSiiPr)(tmeda) (tmeda = ,,','-tetramethylethane-1,2-diamine). Oxidation of Cr(OSiPr)(μ-OSiPr)(thf) with CHI and CCl produced the trigonal bipyramidal chromic compound Cr(OSiPr)(thf) and asymmetrically coordinated CrCl(OSiPr)(thf), respectively. Magnetic measurements (Evans and SQUID) hinted at (a) antiferromagnetic interactions between the Cr centres, (b) revealed higher effective magnetic moments () for -coordinated monomeric heteroleptic complexes compared to -coordinated ones, and (c) pointed out the highest () for the tetranuclear complex Cr(μ-OSiEt) (6.26, SQUID, 300 K; Cr⋯Cr avg. 2.535 A).