s ▁described ▁in ▁ 1 8 6 1 ▁Earth c ree per , ▁Buff - bre asted ▁Earth c ree per , ▁Buff - bre asted ▁Category : T ax onomy ▁articles ▁created ▁by ▁Pol bot <0x0A> </s> ▁Pl um by len es ▁( or ▁pl um by l iden es ) ▁are ▁div al ent ▁org ano le ad ( II ) ▁analog ues ▁of ▁car ben es , ▁with ▁the ▁general ▁chemical ▁formula , ▁R 2 P b , ▁where ▁R ▁denotes ▁a ▁subst itu ent . ▁Pl um by len es ▁possess ▁ 6 ▁electrons ▁in ▁their ▁val ence ▁shell , ▁and ▁are ▁considered ▁open ▁shell ▁species . ▁ ▁The ▁first ▁pl um by l ene ▁reported ▁was ▁the ▁d ial k yl pl um by l ene , ▁[( Me 3 Si ) 2 CH ] 2 P b , ▁which ▁was ▁synth es ized ▁by ▁Michael ▁F . ▁L app ert ▁et ▁al ▁in ▁ 1 9 7 3 . ▁ ▁Pl um by len es ▁may ▁be ▁further ▁class ified ▁into ▁carbon - subst it uted ▁pl um by len es , ▁pl um by len es ▁stabil ized ▁by ▁a ▁group ▁ 1 5 ▁or ▁ 1 6 ▁element , ▁and ▁mon oh al ogen ated ▁pl um by len es ▁( R P b X ). ▁ ▁Syn thesis ▁ ▁Pl um by len es ▁can ▁generally ▁be ▁synth es ized ▁via ▁the ▁trans met all ation ▁of ▁P b X 2 ▁( where ▁X