Reaction of the Diferrocenylphosphenium Ion with Diphenylacetylene and 2,3‐Dimethyl‐1,3‐Butadiene

The reaction of the diferrocenylphosphenium ion, [Fc 2 P][B(C 6 F 5 ) 4 ] with diphenylacetylene and 2,3‐dimethyl‐1,3‐butadiene, gives rise to the quantitative formation of the phosphirenium ion [Fc 2 P(CPh) 2 ][B(C 6 F 5 ) 4 ] ( 1 ) and the 3‐phospholenium ion [Fc 2 P(CH 2 CMe) 2 ][B(C 6 F 5 ) 4 ] ( 2 ), respectively. Compounds 1 and 2 are characterized by nuclear magnetic resonance (NMR) spectroscopy ( 1 H, 13 C, 31 P), high‐resolution mass spectrometry, and, in case of 2 , also X‐ray crystallography. According to density functional theory (DFT) calculations, the formation of 2 is more exothermic and exergonic compared to 1 . Orbital analysis of the cations reveals differences in the lowest unoccupied molecular orbital (LUMO) localization and predicts a decrease in the electron affinity in the row [Fc 2 P] +  > [Fc 2 P(CPh) 2 ] +  > [Fc 2 P(CH 2 CMe) 2 ] + . The addition of C 2 Ph 2 and 2,3‐Me 2 C 4 H 4 to [Fc 2 P] + is accompanied by a transfer of electron density from the P atom to the Fc and organic fragments.