High-Yield Synthesis of PPh₃-Ligated Decanuclear Tl–Pd Cluster, Pd₉[Tl(acac)](CO)₉(PPh₃)₆: Comparative Analysis of Tl(I)–Pd(0) Bonding Connectivities with Known Tl–Pd Clusters and Resulting Insight Concerning Their Dissimilar Dynamic Solution Behavior

Abstract

The new Tl(I)−Pd(0) cluster Pd 9 [μ 3/3 -Tl-(acac)](μ 2 -CO) 6 (μ 3 -CO) 3 (PPh 3 ) 6 (1) was prepared in high yields (over 90%), both by reaction of Pd 10 (CO) 12 (PPh 3 ) 6 (4), PPh 3 , and TlPF 6 in THF in the presence of acetylacetone (Hacac) and base (NEt 3 ) and by direct reaction of Pd 10 (CO) 12 (PPh 3 ) 6 with PPh 3 and Tl(acac). The composition and molecular structure of 1 were unambiguously established from 100 K CCD X-ray diffractometry studies of two solvated crystals, 1·1.5Hacac·0.5THF (1A) and 1·0.3THF (1B), which showed essentially identical geometries for the entire Pd 9 Tl-(CO) 9 P 6 fragment of pseudo-C 3v symmetry; its composition is in agreement with X-ray Tl/Pd field-emission microanalysis with a scanning electron microscope for crystals of 1B. This cluster can be viewed as a markedly deformed Pd 6 octahedron (oct) with the three Pd(oct) atoms of one of its eight triangular faces connected both by three edge-bridging wingtip (wt) Pd(μ 2 -CO) 2 PPh 3 fragments and by a symmetrical capping Tl(I). Three triply bridging carbonyl ligands asymmetrically cap the lower alternate 3-fold-related triangular faces of the Pd 6 octahedron, and the three other PPh 3 ligands are each coordinated to Pd atoms in the geometrically opposite staggered Pd(oct) 3 face. The 6s 2 5d 10 Tl(I) is also equivalently attached to both chelating O atoms of a bidentate acetylacetonate (acac) monoanion. Although the C 2 axis of the pseudo-C 2v planar Tl(acac) fragment is approximately parallel to the pseudo-C 3 axis of the TlPd 9 core, the orientation of the Tl(acac) plane relative to the octahedral-based Pd 9 geometry is considerably different for each of the three independent nondisordered molecules of 1 in 1A and 1B; these different planar Tl(acac) orientations may be mainly attributed to anisotropic crystal-packing effects. Coordination of the Tl(I) atom to the three Pd(oct) atoms of the Pd 9 core presumably occurs via its so-called "inert" 6s 2 electron pair with resulting three short Tl−Pd(oct) connectivities of mean distance 2.83 Å; these connectivities together with three longer Tl−Pd(wt) ones of mean distance 3.15 Å give rise to a (crown-like)Pd 6 sextuple (μ 3/3 -Tl) coordination mode. Of particular stereochemical interest is a comparison of solution behavior of 1 with that for the known structurally related analogue, Pd 9 [μ 3 -TlCo(CO) 3 L](μ 2 -CO) 6 (μ 3 -CO) 3 L 6 (2) (with L = PEt 3 instead of PPh 3 ). In 2 the Tl(I) is alternatively attached to a trigonal-bipyramidal Co(CO) 3 L monoanion and primarily coordinated to the three inner Pd(oct) atoms of a similar PR 3 /CO-ligated octahedron; corresponding Tl−Pd(oct) and Tl−Pd(wt) mean distances for two independent molecules in 2 are 2.77 and 3.31 Å, respectively. Variable-temperature 31 P{ 1 H} NMR solution data of 1 indicate the occurrence of presumed fast wobbling-like motion of the [μ 3/3 -Tl(acac)] entity about the pseudo-C 3 axis of the Pd 9 (μ 2 -CO) 6 (μ 3 -CO) 3 P 6 fragment without Pd−Tl detachment (i.e., the entire cluster of 1 remains intact). In direc...

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

“…To the best of our knowledge, this is the most electron-deficient hexanuclear transition-metal carbonyl-containing octahedral cluster ever reported. If one considers the planar wingtip Pd­(CO) 2 (PR 3 ) unit, which is often present in various palladium clusters, as a ligand contributing two CVEs, then only one more octahedral-based palladium cluster with 80 CVEs had been previously reported by us, TlPd 9 (CO) 9 (PPh 3 ) 6 + , but it was mistakenly identified as an 86 CVE system …”

Boron, aluminium, gallium, indium and thallium

“…This cluster was shown to have dissimilar dynamic solution behaviour to related Tl-Pd clusters. 355 Hawthorne et al, have utilised thallium dicarbollides in combination with alkyldichloroboranes in a new synthetic route to 3-alkyl-1,2-dicarba-dodecarboranes. 356 Thallium cations partnered with [B(C 6 H 3 (CF 3 ) 2 ) 4 ] À counterions and ligated by 2,6-dimesitylpyridine have been isolated as arene solvated complexes which possess Tl-N distances significantly elongated compared to the neutral terphenyl analogues.…”