Phosphirenylium cations

It is also worthy to note that the pentacarbonyl-tungsten complex of the phosphirenylium cation (5) has been recently reported, but no X-ray structure has been obtained. B3LYP/6-311G(d) optimization of the presumed -Cr(CO)5 complex of 5 resulted in an 7 -form (Figure 1) when starting from the bound chromium complex. Such a structure is in complete accord with a delocalized electronic structure of the cation. 

Phosphitenylium cations have been postulated as intermediates in numerous reactions of 1-chlorophosphirenes including phosphirene complexes. Recently, the uncomplexed cation has been generated in the gas phase from 4 upon 70 eV electron ionization and its reactivity toward representative nucleophiles and dienes has been studied by pentaquadrupole mass spectrometry <20030BC395>. The first complex of a phosphirenylium cation 9 was prepared from 8 according to Scheme 5. The phosphirene complex 8 is rather unstable in neat or in solution and decomposes with the formation of the bisphosphirenyl ether 10 <19990M817>. 

The 31P chemical shift of (21) is at relatively low field (531P = —9.5 vs. —73.4 for (6) in [Dg] toluene no J (170—31P) is observed both 31P and 13C ring resonances are shifted to low fields when the polarity of the solvent increases i.e., (531P = — 9.5-> +10.5 when toluene is replaced by nitromethane. The highly electrophilic nature of the system (21)o(22) is shown by the easy formation of a salt with pyridine and by the ready para-substitution of the phenyl ring of N,N-dimethylaniline <94RHA6l>. Definitive evidence for the formation of a phosphirenylium cation has been produced (Equation (10)) <94JA9407>. 

The phosphirenylium cation has been generated in the gas phase (13.146b) and other three-membered ring species such as (13.146c,d) have been studied [16-19]. 

The interaction of transition metal complexes with cyclopropenium cations 2C has been widely studied [48-50]. Besides the expected if (an example of if ligation has also been observed by Nixon et al. with phosphirenylium H [24 c])... 

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