page_title: Plumbylene
section_title: Structure and bonding
hierarchical_section_title: Plumbylene / Structure and bonding
caption_attribution_description: English: Dimethyllead diphenyllead
context_page_description: Plumbylenes are divalent organolead(II) analogues of carbenes, with the general chemical formula, R₂Pb, where R denotes a substituent. Plumbylenes possess 6 electrons in their valence shell, and are considered open shell species.
  The first plumbylene reported was the dialkylplumbylene, [(Me₃Si)₂CH]₂Pb, which was synthesized by Michael F. Lappert et al in 1973.
  Plumbylenes may be further classified into carbon-substituted plumbylenes, plumbylenes stabilized by a group 15 or 16 element, and monohalogenated plumbylenes.
context_section_description: The key aspects of bonding and reactivity in plumbylenes are dictated by the inert pair effect, whereby the combination of a widening s–p orbital energy gap as a trend down the group 14 elements and a strong relativistic contraction of the 6s orbital lead to a limited degree of sp hybridization and the 6s orbital being deep in energy and inert. Consequently, plumbylenes exclusively have a singlet spin state due to the large singlet–triplet energy gap, and tend to exist in an equilibrium between monomeric and dimeric forms in solution. This is in contrast to carbenes, which often have a triplet ground state and readily dimerize to form alkenes.
  In dimethyllead, (CH₃)₂Pb, the Pb–C bond length is 2.267 Å and the C–Pb–C bond angle is 93.02°; the singlet–triplet gap is 36.99 kcal mol⁻¹.
  
  Diphenyllead, (C₆H₅)₂Pb was computed with GAMESS at the B3PW91 level of theory using the basis sets 6-311+G(2df,p) for C and H and def2-svp for Pb with the ECP60MDF pseudopotential, in an adapted procedure (which uses the cc-pVTZ basis set for Pb instead). The molecular orbitals (MOs) (visualized using Chimera) and natural bond orbitals (NBOs) (visualized using multiwfn) generated are produced below, and qualitatively identical to the literature. As expected, the HOMO is 6s-dominated, and the LUMO is 6p-dominated. The NBOs are of the 6s lone pair and vacant 6p orbital respectively.
  The Pb–C bond distance was found to be 2.303 Å and the C–Pb–C angle 105.7°. Notwithstanding the different levels of theory, the larger bond angle for (C₆H₅)₂Pb compared to (CH₃)₂Pb can be rationalized by the greater repulsion between the sterically bulkier phenyl groups relative to methyl groups.
  Atoms in molecules (AIM) topology analysis revealed critical points in (C₆H₅)₂Pb, and is consistent with the literature.
  Plumbylenes occur as reactive intermediates in the formation of tetravalent plumbanes (R₄Pb). Although the inert pair effect suggests the divalent state should be thermodynamically more stable than the tetravalent state, in the absence of stabilizing substituents, plumbylenes are sensitive to heat and light, and tend to undergo polymerization and disproportionation, forming elemental lead in the process.
  Plumbylenes can be stabilized as monomers by the use of sterically bulky ligands (kinetic stabilization) or heteroatom-containing substituents that can donate electron density into the vacant 6p orbital (thermodynamic stabilization).
caption: Dimethyllead, (CH3)2Pb, and diphenyllead, (C6H5)2Pb
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