Octahedral Hexapalladium Pseudo-T_d Pd₆(μ₃-CO)₄(PEt₃)₆ with 80 Electron-Deficient Cluster Valence Electrons (CVEs) and a Comparison with Octahedral Hexapalladium Pseudo-C_2v Pd₆(μ₃-CO)₄(PMe₃)₇ with 82 CVEs: Computational Analysis and Resulting Implications

Abstract

The elusive octahedral hexapalladium Pd 6 (μ 3 -CO) 4 (PEt 3 ) 6 (1) was obtained by the reaction of Pd 10 (CO) 12 (PEt 3 ) 6 with TlCo(CO) 4 in tetrahydrofuran under N 2 at 55 °C. Its pseudo-T d 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/PR 3 -ligated homopalladium Pd n clusters (n = 6, 7, 8, 10). Each Pd atom in 1 is coordinated to a PEt 3 ligand, and each nonadjacent triangular Pd 3 face is capped by a triply bridging μ 3 -CO ligand. The 31 P{ 1 H} 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 Pd 6 (μ 3 -CO) 4 (PMe 3 ) 7 (2), which has pseudo-C 2v symmetry with 82 total CVEs. 3 10 4(5)