Phosphasilene

Phosphasilenes or silylidenephosphanes are a class of compounds with <a href="/facts/Silicon/cgWx0hdr">silicon</a>-<a href="/facts/Phosphorus/27xCeIqs">phosphorus</a> <a href="/facts/Double_bonds/qDemMn0c">double bonds</a>. Since the <a href="/facts/Electronegativity/H7Vq7Uah">electronegativity</a> of phosphorus (2.1) is higher than that of silicon (1.9), the "Si=P" moiety of phosphasilene is polarized. The degree of polarization can be tuned by altering the coordination numbers of the Si and P centers, or by modifying the electronic properties of the substituents. The phosphasilene Si=P double bond is highly reactive, yet with the choice of proper substituents, it can be stabilized via donor-acceptor interaction or by steric congestion.
The landmark discovery of the first phosphasilene by <a href="/facts/Nuclear_magnetic_resonance_spectroscopy/SFKgdthI">NMR spectroscopy</a> was made in 1984 by Bickelhaupt et al. The first phosphasilene came with bulky aryl substituents at the phosphorus and silicon atoms. Almost a decade after this spectroscopic observation, the first structural characterization of phosphasilene was achieved in 1993 by Niecke et al. The successful isolation of phosphasilenes with silicon-phosphorus double bonds represents one of the discoveries that challenged and disproved the "<a href="/facts/Double_bond_rule/kxtnRvH8">double-bond rule</a>".

Phosphasilene open-in-new

Phosphasilene