The Substituent‐Effect in NHCP‐Plumbylenes with a Phosphaplumbene Character

This work explores the use of plumbylene‐phosphinidenes to address the challenge of isolating P=Pb bonds. Herein, we report the synthesis of three N‐heterocyclic carbene phosphinidene (NHCP) substituted chlorotetrylene dimers [(IDipp)PECl]2 (E = Ge, Sn, Pb; IDipp = C([N‐(2,6‐iPr2C6H3)CH]2)). Substituent attachment via salt metathesis (E = Sn, Pb) enables the isolation of NHCP‐silyl‐substituted stannylene (IDipp)PSn(SiTms2SiTol3) as well as NHCP‐silyl‐ and NHCP‐aryl‐substituted plumbylenes (IDipp)PPb(SiTms2SiTol3) and (IDipp)PPb(mTer) (mTer = 2,6‐Mes2C6H3, Tms = Trimethylsilyl). Access to these structures not only expands this chemistry to the heaviest of group 14 elements but also provides a deeper understanding of the substituent effect on NHCP‐tetrylene bonding. Computational studies demonstrate that both silyl‐ and aryl‐substituted species exhibit partial multiple bond character, with the silyl‐substituted species showing higher bond orders and reduced polarization. This is further supported by the short P‐E bond lengths observed in their solid‐state structures. Finally, the formal [2+2] cycloaddition of diphenylketene to (IDipp)PPb(mTer) provides experimental evidence for the ability of NHCP‐plumbylenes to serve as synthetic equivalents of P=Pb double bonds.