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

Abstract

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.