Model Compounds for Intermediates and Transition States in Sonogashira and Negishi Coupling: d8-d10 Bonds in Large Heterobimetallic Complexes Are Weaker than Computational Chemistry Predicts

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.

Automated summary

We report an experimental study on a series of heterobimetallic complexes with Pd(II) and Cu(I), Ag(I), or Au(I), accompanied by DFT calculations. The isolable pincer complexes are models for the intermediates and transition state in Sonogashira and Negishi coupling reactions. According to the DFT calculations, only the transition state has the metal centers within bonding distance. We also report a substituted version of a similar heterobimetallic complex, in which competing dissociation limits the strength of the metal-metal bond. Analysis of the structures in different states and the gas phase dissociation experiment suggest that the dispersion-corrected DFT method overestimates the strength of the metal-metal interaction, distorting the computed potential energy surface for transmetalation.