Photolysis of phosphaketenyltetrylenes with a bulky carbazolyl substituent

Phosphaketenes of divalent group 14 compounds can potentially serve as precursors for the synthesis of heavy multiple-bond systems. We have employed the $^{dtbp}$Cbz substituent ($^{dtbp}$Cbz=1,8-bis(3,5-ditertbutylphenyl)-3,6-ditertbutylcarbazolyl) to prepare such phosphaketenyltetrylenes [($^{dtbp}$Cbz)EPCO] (E=Ge, Sn, Pb). While the phosphaketenyltetrylenes are stable at ambient conditions, they can be readily decarbonylated photolytically. For the germylene and stannylene derivatives, dimeric diphosphene-type products [($^{dtbp}$Cbz)EP]$_2$ (E=Ge, Sn) were obtained. In contrast, photolysis of the phosphaketenylplumbylene, via isomerisation of the [($^{dtbp}$Cbz)PbP] intermediate to [($^{dtbp}$Cbz)PPb], afforded an unsymmetric and incompletely decarbonylated product [($^{dtbp}$Cbz)$_2$Pb$_2$P$_2$CO] formally comprising a [($^{dtbp}$Cbz)PPb] and a [($^{dtbp}$Cbz)PbPCO] moiety.