From a Zwitterionic Phosphasilene to Base Stabilized Silyliumylidene-Phosphide and Bis(silylene) Complexes

The
reactivity of ylide-like phosphasilene 1 [LSi­(TMS)P­(TMS),
L = PhC­(NtBu)2] with group 10 d10 transition metals is reported. For the first time, a reaction of
a phosphasilene with a transition metal that actually involves the
silicon–phosphorus double bond was found. In the reaction of 1 with ethylene bis­(triphenylphosphine) platinum(0), a complete
silicon–phosphorus bond breakage occurs, yielding the unprecedented
dinuclear platinum complex 3 [LSi­{Pt­(PPh3)}2P­(TMS)2]. Spectroscopic, structural, and theoretical
analysis of complex 3 revealed the cationic silylene
(silyliumylidene) character of the silicon unit in complex 3. Similarly, formation of the analogous dinuclear palladium complex 4 [LSi­{Pd­(PPh3)}2P­(TMS)2]
from tetrakis­(triphenylphosphine) palladium(0) was observed. On the
other hand, in the case of bis­(cyclooctadiene) nickel(0) as starting
material, a distinctively different product, the bis­(silylene) nickel
complex 5 [{(LSi)2P­(TMS)}­Ni­(COD)], was obtained.
Complex 5 was fully characterized including X-ray diffraction
analysis. Density functional theory calculations of the reaction mechanisms
showed that the migration of the TMS group in the case of platinum
and palladium was induced by the oxidative addition of the transition
metal into the silicon–silicon bond. The respective platinum
intermediate 2 [LSi­{Pt­(TMS)­(PPh3)}­P­(TMS)]
was also experimentally observed. This is contrasted by the reaction
of nickel, in which the equilibrium of phosphasilene 1 and the phosphinosilylene 6 [LSiP­(TMS)2]
was utilized for a better coordination of the silicon­(II) moiety in
comparison with phosphorus to the transition metal center.