Designing Stability into Thermally Reactive Plumbylenes

We complete the picture of thermally stable and volatile <i>N-</i>heterocyclic metallylenes with the synthesis, structural analysis, and thermal characterization of <i>rac</i>-<i>N</i><sup>2</sup>,<i>N</i><sup>3</sup>-di-<i>tert</i>-butylbutane-2,3-diamido lead(II) (<b>1Pb</b>). Transamination of bis[bis(trimethylsilyl)amido] lead(II) with the free diamino ligand yields <b>1Pb</b> in high yield, whereas salt-metathesis leads to oxidative cleavage of the butane backbone and production of acetaldehyde-<i>tert-</i>butylimine. <b>1Pb</b> itself undergoes [2+2+1] cycloreversion at 150 °C to the same imine, but with a vapour pressure of 1 Torr at 94 °C a wide thermal window is available for use as a vapour deposition precursor.<div><br></div><div>We contrast this with the the extreme instability of its sisters <i>N</i><sup>2</sup>,<i>N</i><sup>3</sup>-di-<i>tert</i>-butylethane-2,3-diamido lead(II) (<b>2Pb</b>) and <i>N</i><sup>2</sup>,<i>N</i><sup>3</sup>-di-<i>tert</i>-butylethylene-2,3-diamido lead(II) (<b>3Pb</b>), which both reductively eliminate Pb(0) at or below room temperature. This is also in start contrast to the stability of the lighter Si, Ge and Sn congeners.</div>