A compound exhibiting multiple bonds between lead and carbon has been isolated and characterized. This heteronuclear ‘plumbyne’ addresses a gap among group 14 alkyne analogues and may serve as a foundation for synthesizing more unusual main group species.
The bonding in organo-lead compounds is generally confined to single lead–carbon bonds, due to the substantial atomic size of lead and its poor orbital energy compatibility with other atoms. Relativistic effects further hinder lead’s potential to establish higher-order π bonds. While compounds involving multiple bonds between lead and other lead, transition metal, or non-metal atoms do exist, they are infrequent.
By balancing electronic and steric considerations, scientists in China have successfully synthesized a compound that includes multiple bonds between lead and carbon.1 An aryl group with large substituents and an N-heterocyclic carbene containing phosphorus are linked to the terminal ends of a central lead–carbon bond. Previously, the team employed a similar framework to develop the lighter tin ‘stannyne’ counterpart.2
X-ray diffraction analysis indicated that the lead–based compound assumed a trans bonding configuration, with a central carbon–lead bond length measuring 2.172Å. The substituents were found to be almost orthogonal to one another, which is believed to enhance orbital overlap and bolster the stability of the P–C–Pb connection. Computational evaluations of a simplified structure unveiled that the dominant resonance form features a P=C=Pb bonding arrangement.
Reactions involving the compound were feasible, where the addition of ammonium hydrochloride easily saturated the multiple carbon–lead bond, which the researchers ascribe to the bond’s relatively weak characteristics. The use of a tin-based reagent facilitated bond–metathesis, resulting in a new tin compound and lead byproduct, although the precise reaction mechanism remains uncertain. The researchers aspire for this plumbyne compound to serve as a platform for the exploration of other rare main group species.