We
report an experimental study, with accompanying DFT calculations,
on a series of heterobimetallic complexes with Pd(II) and Cu(I), Ag(I),
or Au(I). The isolable pincer complexes are models for the intermediates
and transition state for the transmetalation step in Sonogashira and
Negishi coupling reactions, among which, according to the DFT calculations,
only the transition state has the two metal centers within bonding
distance. Furthermore, we report a substituted version of an analogous
heterobimetallic complex in which a competing dissociation sets an
upper-bound on the strength of the d
8–d
10 metal–metal bond. Analysis of the
structures in the solid state and in solution, and the competitive
dissociation experiment in the gas phase, indicate that the dispersion-corrected
DFT method used in the study appears to overestimate the strength
of the metal–metal interaction, thus distorting the shape of
the computed potential energy surface systematically for transmetalation.
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