Octahedral Hexapalladium Pseudo-Td Pd6(μ3-CO)4(PEt3)6 with 80 Electron-Deficient Cluster Valence Electrons (CVEs) and a Comparison with Octahedral Hexapalladium Pseudo-C2v Pd6(μ3-CO)4(PMe3)7 with 82 CVEs: Computational Analysis and Resulting Implications.

Abstract

The elusive octahedral hexapalladium Pd6(μ3-CO)4(PEt3)6 (1) was obtained by the reaction of Pd10(CO)12(PEt3)6 with TlCo(CO)4 in tetrahydrofuran under N2 at 55 °C. Its pseudo-Td octahedral structure, established from a CCD X-ray diffractometry study at 100 K, has the highest ideal symmetry of any of the characterized octahedral-based CO/PR3-ligated homopalladium Pdn clusters (n = 6, 7, 8, 10). Each Pd atom in 1 is coordinated to a PEt3 ligand, and each nonadjacent triangular Pd3 face is capped by a triply bridging μ3-CO ligand. The 31P{1H} NMR and IR spectra of 1 are in accordance with its solid-state molecular structure. Cluster 1 has a total of 80 cluster valence electrons (CVEs), the lowest reported for octahedral-based metal polyhedra that normally conform to the Wade-Mingos bonding rule with an 86 CVE count. Comparative density functional theory calculations involving natural population analysis are presented for trimethylphosphine analogues of the triethylphosphine (1-Me) and the previously reported octahedral hexapalladium trimethylphosphine Pd6(μ3-CO)4(PMe3)7 (2), which has pseudo-C2v symmetry with 82 total CVEs.