Insights into the reactivity and structure of silylene phosphonium ionsDedicated to Professor Edgar Niecke on the occasion of his 65th birthday.

Abstract

Experimental evidence for the intermediate occurrence of a so far unknown silylene phosphonium ion is presented and its reactivity and bond situation is discussed on the basis of ab initio calculations.

[3]Ferrocenophanes with the bisphosphanotetryl bridge: inorganic rings on the way to tetrylenes

“…10,11 Owing to our own interest in the low-coordinate chemistry of group 14 elements we wondered whether it might be feasible to embed heavier tetrylenes into a bridging unit of a [3]ferrocenophane with flanking phosphanyl groups. [12][13][14][15][16][17] Few years ago, Power et al have shown that a low-valent silylene center can be stabilized using two adjacent third row elements. 18 Therefore, we set out to investigate the possibility to access bisphosphano substituted tetrylenes embedded into a [3]ferrocenophane unit.…”

An Isolable Bis(Silanone–Borane) Adduct

“…[3] Althoughd ivalent carbon species such as N-heterocyclic carbenes (NHCs) have also been successfully probedi nF LP chemistry for the activation of CO 2 ,H 2 and N 2 O, the use of analogousL ewis pairs-containings ilylenes is less known. [4,5] The silicon(II) atom in silylenes exhibits an ambiphilic character due to its vacant 3p orbital (LUMO) and the 3s-centered lone pair (HOMO). Owing to their interesting property and reactivity, stable N-heterocyclic silylenes (NHSis), the heaviera nalogues of NHCs, have been utilized successfully for the metal-free activation of small molecules [6] and as powerful steering ligandsi n homogeneous catalysis.…”

Recent developments in the chemistry of stable silylenes

“…The reaction of 1 with the highly electrophilic diamino phosphenium species [P(NCy 2 ) 2 ] + [AlCl 4 ] À (Cy = cyclohexyl) at À80°C was recently reported [65]. The target species, the silylene phosphonium ion 61, was not directly observed but instead postulated as an intermediate to which a chloride ion is transferred (from the [AlCl 4 ] À anion), with formation of the observed phosphino(chloro)silane 62 (Scheme 30).…”

“…These products would not be expected on consideration of the relative electronegativity of the Si and P atoms (1.7 and 2.1, respectively, on the Allred-Rochow scale) hence interaction with the phosphenium cation must alter the nature of the silicon atom in the intermediate 61 from nucleophilic to primarily electrophilic. DFT calculations upon the model compound indicate that the lone pair of the silylene is donated into the vacant, phosphorus-based orbital of the phosphenium ion, suggesting that it is more appropriate to describe 61 as a phosphanylsilyl cation [65].…”