Article

Persistent Radicals of Trivalent Tin and Lead

Institut für Anorganische and Analytische Chemie, Johannes Gutenberg-Universität Mainz, Duesbergweg 10−14, 55128 Mainz, Germany, and Max-Planck-Institut für Polymerforschung, Ackermannweg 10, 55128 Mainz, Germany
Inorg. Chem., 2008, 47 (21), pp 9965–9978
DOI: 10.1021/ic801198p
Publication Date (Web): September 30, 2008
Copyright © 2008 American Chemical Society
* To whom correspondence should be addressed. E-mail: hinderberger@mpip-mainz.mpg.de (D.H.), klink@uni-mainz.de (K.W.K.)., †

Johannes Gutenberg-Universität Mainz.

, ‡

Max-Planck-Institut für Polymerforschung.

Synopsis

Homoleptic as well as heteroleptic silylsubstituted alkali metal stannanides and plumbanides were synthesized and subsequently oxidized, giving access to several novel persistent or stable mononuclear stannyl and plumbyl radicals, respectively. EPR and X-ray diffraction experiments on selected radicals gave deeper insight into their structure in solution and in the solid-state.

Abstract

Abstract Image

In this report we present synthetic, crystallographic, and new electron paramagnetic resonance (EPR) spectroscopic work that shows that the synthetic route leading to the recently reported, first persistent plumbyl radical •PbEbt3 (Ebt = ethylbis(trimethylsilyl)silyl), that is, the oxidation of the related PbEbt3-anion, was easily extended to the synthesis of other persistent molecular mononuclear radicals of lead and tin. At first, various novel solvates of homoleptic potassium metallates KSnHyp3 (4a), KPbHyp3 (3a), KSnEbt3 (4b), KPbIbt3 (3c), and KSnIbt3 (4c) (Hyp = tris(trimethylsilyl)silyl, Ibt = isopropylbis(trimethylsilyl)silyl), as well as some heteroleptic metallates, such as [Li(OEt2)2][SnnBuHyp2] (3d), [Li(OEt2)2][PbnBuHyp2] (4d), [Li(thf)4][PbPhHyp2] (3e), and [K(thf)7][PbHyp2{N(SiMe3)2}] (3f), were synthesized and crystallographically characterized. Through oxidation by tin(II) and lead(II) bis(trimethylsilyl)amides or the related 2,6-di-tert-butylphenoxides, they had been oxidized to yield in most cases the corresponding radicals. Five novel persistent homoleptically substituted radicals, that is, •SnHyp3 (2a), •PbHyp3 (1a), •SnEbt3 (2b), •SnIbt3 (2c), and •PbIbt3 (1c), had been characterized by EPR spectroscopy. The stannyl radicals 2a and 2c as well as the plumbyl radical 1c were isolated as intensely colored crystalline compounds and had been characterized by X-ray diffraction. Persistent heteroleptically substituted radicals such as •PbHyp2Ph (1e) or •PbHyp2Et (1g) had also been generated, and some selected EPR data are given for comparison. The plumbyl radicals •PbR3 exhibit a clean monomolecular decay leading to the release of a temperature-dependent stationary concentration of branched silyl radicals. They may thus serve as tunable sources of these reactive species that may be utilized as reagents for mild radical silylations and/or as initiators for radical polymerizations. We present EPR-spectroscopic investigations for the new tin- and lead-containing compounds giving detailed insights into their electronic and geometric structure in solution, as well as structural studies on the crystalline state of the radicals, some of their anionic precursors, and some side-products.

Tables with crystal and structure refinement parameters. This material is available free of charge via the Internet at http://pubs.acs.org.

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Received 28 June 2008
Published online 30 September 2008
Published in print 3 November 2008
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