Synthesis and Properties of NHC-Supported Palladium(I) Dimers with Bridging Allyl, Cyclopentadienyl, and Indenyl Ligands

The synthesis of a family of new Pd(I) dimers, (mu-All)(mu-Cp){Pd(IPr)}(2) (All = C3H5, Cp = C5H5, IPr = 1,3-bis(2,6-diisopropylphenyl)-1,3-dihydro-2H-imidazol-2-yli-dene), (mu-All)(mu-Ind){Pd(IPr)}(2) (Ind = C7H9), (mu-Cp)(mu-Cp){Pd(IPr)}(2), (mu-Cp)(mu-Ind){Pd(IPr)}(2), and (mu-Ind)(mu-Ind){Pd(IPr)}(2), which contain a combination of bridging ally!, Cp, and indenyl ligands and are all supported by IPr as the ancillary ligand, is reported. All of these compounds are thermally stable at room temperature, and the solid-state geometries, electronic structures, reactivity, and redox chemistry of these new compounds have been compared with those of the dimer (mu-All)(2){Pd(IPr)}(2), which was previously reported. This work provides further evidence that bridging allyl, Cp, and indenyl ligands bind in a similar manner to Pd(I). However, it is demonstrated that there are notable differences between the IPr-supported species and related Pd(I) diners with triethylphosphine ancillary ligands, which have been previously described.