Dispersion Energy Enforced Dimerization of a Cyclic Disilylated Plumbylene

By reaction of 1,4-dipotassio-1,1,4,4-tetrakis­(trimethylsilyl)­tetramethyltetrasilane
with PbBr2 in the presence of triethylphosphine a base
adduct of a cyclic disilylated plumbylene could be obtained. Phosphine
abstraction with B­(C6F5)3 led to
formation of a base-free plumbylene dimer, which features an unexpected
single donor–acceptor PbPb bond. The results of density functional
computations at the M06-2X and B3LYP level of theory indicate that
the dominating interactions which hold the plumbylene subunits together
and which define its actual molecular structure are attracting van
der Waals forces between the two large and polarizable plumbylene
subunits.