RESUMEN
New types of metal-free white phosphorus (P4 ) activation are reported. While the phosphine-silylene-substituted dicarborane 1, CB-SiP (CB=ortho-C,C'-C2 B10 H10 , Si=PhC(tBuN)2 Si, P=P[N(tBu)CH2 ]2 ), activates white phosphorus in a 2 : 1 molar ratio to yield the P5 -chain containing species 2, the analogous bis(silylene)-substituted compound 3, CB-Si2 , reacts with P4 in the molar ratio of 2 : 1 to furnish the first isolable 1,3-diphospha-2,4-disilabutadiene (Si=P-Si=P-containing) compound 4. For the latter reaction, two intermediates having a CB-Si2 P4 and CB-Si2 P2 core could be observed by multinuclear NMR spectroscopy. The compounds 2 and 4 were characterized including single-crystal X-ray diffraction analyses. Their electronic structures and mechanisms were investigated by density functional theory calculations.
RESUMEN
Understanding the characteristics of radicals formed from silicon-containing heavy analogues of alkenes is of great importance for their application in radical polymerization. Steric and electronic substituent effects in compounds such as phosphasilenes not only stabilize the Si=P double bond, but also influence the structure and species of the formed radicals. Herein we report our first investigations of radicals derived from phosphasilenes with Mes, Tip, Dur, and NMe2 substituents on the P atom, using muon spin spectroscopy and DFT calculations. Adding muonium (a light isotope of hydrogen) to phosphasilenes reveals that: a)â the electron-donor NMe2 and the bulkiest Tip-substituted phosphasilenes form several muoniated radicals with different rotamer conformations; b)â bulky Dur-substituted phosphasilene forms two radicals (Si- and P-centred); and c)â Mes-substituted phosphasilene mainly forms one species of radical, at the P centre. These significant differences result from intramolecular substituent effects.
RESUMEN
We examine by the means of computational chemistry the ability of two phosphasilenes to transfer the phosphinidene moiety to four double bonded organic functional groups (>C=C<, -N=N-, >C=O, and >C=S) in the presence of different bulky ligands. We show that large bulky groups in the reactants can sterically prohibit the otherwise favored association of reactants and phosphasilenes and instead a new phosphinidene transfer reaction can occur. We find that the transfer reaction mechanism is generally present independent from the functional group and by introducing large enough trimethylsilyl or tert-butyl-dimethylsilyl ligands it can be used to transfer phosphinidene to organic functional groups such as thioformaldehydes or diazenes, respectively. We propose that by exploiting the complex bonding nature of low-valent main group complexes they can act as synthetic equivalents of hitherto unknown very reactive synthons. We encourage experimentalists to explore the reactivity of their main-group complexes by varying the size of the bulky substituents on the reactants that can result in new unexpected chemistry.
RESUMEN
Heavier alkene analogues possess unique electronic properties and reactivity, encouraging multidisciplinary research groups to utilize them in the rational design of novel classes of compounds and materials. Phosphasilenes are heavier imine analogues, containing highly reactive Si=P double bonds. Recent achievements in this field are closely related to the progress in the chemistry of stable low-coordinate silicon compounds. In this Review, we have attempted to summarize in a comprehensive way the available data on the structures, syntheses, electronic and chemical properties of these compounds, with an emphasis on recent achievements.
RESUMEN
The reaction of MesLi (Mes=2,4,6-trimethylphenyl) with the electrophilic phosphasilene R2 (NMe2 )Si-RSi=PNMe2 (2, R=Tip=2,4,6-triisopropylphenyl) cleanly affords R2 (NMe2 )Si-RSi=PMes and thus provides the first example of a substitution reaction at an unperturbed Si=P bond. In toluene, the reaction of 2 with lithium disilenide, R2 Si=Si(R)Li (1), apparently proceeds via an initial nucleophilic substitution step as well (as suggested by DFT calculations), but affords a saturated bicyclo[1.1.0]butane analogue as the final product, which was further characterized as its Fe(CO)4 complex. In contrast, in 1,2-dimethoxyethane the reaction of 1 with 2 results in an unprecedented metal-amino exchange reaction.