Research on zero-valent p-block elements is a recent hot topic in synthetic and theoretical chemistry because of their novel electronic states having two lone pairs in both the s- and p-orbitals. It is considered that σ-donating ligands bearing large substituents are essential to stabilize these species. Herein, we propose a new approach using butadiene as a 4π-electron donor to stabilize zero-valent group 14 elements. During our study to explore the coordination chemistry of stannacyclopentadienyl ligands, unexpected products, in which the tin atom is coordinated by a butadiene in a η(4)-fashion, were obtained. Because butadiene is a neutral 4π-electron donating ligand, the formal oxidation number of the tin atoms of the products should be zero, which is supported by X-ray diffraction analysis and theoretical calculations. A mechanism for the formation of the products is also described.
A neutral heterobimetallic triple-decker stannole complex was prepared by the reaction of an anionic ruthenocene bearing a stannole dianionic ligand with [Rh(cod)Cl]2 (cod = 1,5-cyclooctadiene), and the resulting Ru-Rh complex exhibits an electronic property different from those of the corresponding Ru-Ru and Rh-Rh complexes. The Ru-Rh complex can be decomposed in ionic liquids to metal nanoparticles.
The design of strong donor ligands has been one of the crucial tasks in the development of ligands for transition-metal complexes. One effective strategy is suppression of back-donation from a metal to a ligand by electron donation from adjacent main-group atoms bearing lone-pair electrons. We now report another method for suppression of back-donation: capping an accepting orbital by coordination of a transition metal. A lone pair on the triple-decker ruthenocene-type stannole complex can coordinate an Mo(CO) 5 moiety. In the resulting complex, back-donation from a Mo to an Sn moiety is effectively suppressed because of the occupation of a potentially electron-accepting 5p orbital on the Sn atom by coordination of the Ru moieties. The triple-decker ruthenocene-type stannole complex can also coordinate an Ag(I) atom to form a 1:2 complex, where two bulky ligands are oriented in a perpendicular fashion.
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