Photolysis of Phosphaketenyltetrylenes with a 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 Cbz substituent ( Cbz=1,8-bis(3,5-ditertbutylphenyl)-3,6-ditertbutylcarbazolyl) to prepare such phosphaketenyltetrylenes [( 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 [( Cbz)EP] (E=Ge, Sn) were obtained. In contrast, photolysis of the phosphaketenylplumbylene, via isomerisation of the [( Cbz)PbP] intermediate to [( Cbz)PPb], afforded an unsymmetric and incompletely decarbonylated product [( Cbz) Pb P CO] formally comprising a [( Cbz)PPb] and a [( Cbz)PbPCO] moiety.