High-Yield Synthesis of PPh3-Ligated Decanuclear Tl鈥揚d Cluster, Pd9[Tl(acac)](CO)9(PPh3)6: Comparative Analysis of Tl(I)鈥揚d(0) Bonding Connectivi

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• 作者：Evgueni G. Mednikov ; Nicky Vo ; Charles G. Fry ; Lawrence F. Dahl
• 刊名：Organometallics
• 出版年：2012
• 出版时间：April 9, 2012
• 年：2012
• 卷：31
• 期：7
• 页码：2878-2886
• 全文大小：358K
• 年卷期：v.31,no.7(April 9, 2012)
• ISSN：1520-6041

文摘

The new Tl(I)鈥揚d(0) cluster Pd₉[渭_3/3-Tl(acac)](渭₂-CO)₆(渭₃-CO)₃(PPh₃)₆ (1) was prepared in high yields (over 90%), both by reaction of Pd₁₀(CO)₁₂(PPh₃)₆ (4), PPh₃, and TlPF₆ in THF in the presence of acetylacetone (Hacac) and base (NEt₃) and by direct reaction of Pd₁₀(CO)₁₂(PPh₃)₆ with PPh₃ 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路1.5Hacac路0.5THF (1A) and 1路0.3THF (1B), which showed essentially identical geometries for the entire Pd₉Tl(CO)₉P₆ 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 Pd₆ octahedron (oct) with the three Pd(oct) atoms of one of its eight triangular faces connected both by three edge-bridging wingtip (wt) Pd(渭₂-CO)₂PPh₃ 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 Pd₆ octahedron, and the three other PPh₃ ligands are each coordinated to Pd atoms in the geometrically opposite staggered Pd(oct)₃ face. The 6s²5d¹⁰ Tl(I) is also equivalently attached to both chelating O atoms of a bidentate acetylacetonate (acac) monoanion. Although the C₂ axis of the pseudo-C_2v planar Tl(acac) fragment is approximately parallel to the pseudo-C₃ axis of the TlPd₉ core, the orientation of the Tl(acac) plane relative to the octahedral-based Pd₉ 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 Pd₉ core presumably occurs via its so-called 鈥渋nert鈥?6s² electron pair with resulting three short Tl鈥揚d(oct) connectivities of mean distance 2.83 脜; these connectivities together with three longer Tl鈥揚d(wt) ones of mean distance 3.15 脜 give rise to a (crown-like)Pd₆ sextuple (渭_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, Pd₉[渭₃-TlCo(CO)₃L](渭₂-CO)₆(渭₃-CO)₃L₆ (2) (with L = PEt₃ instead of PPh₃). In 2 the Tl(I) is alternatively attached to a trigonal-bipyramidal Co(CO)₃L monoanion and primarily coordinated to the three inner Pd(oct) atoms of a similar PR₃/CO-ligated octahedron; corresponding Tl鈥揚d(oct) and Tl鈥揚d(wt) mean distances for two independent molecules in 2 are 2.77 and 3.31 脜, respectively. Variable-temperature ³¹P{¹H} NMR solution data of 1 indicate the occurrence of presumed fast wobbling-like motion of the [渭_3/3-Tl(acac)] entity about the pseudo-C₃ axis of the Pd₉(渭₂-CO)₆(渭₃-CO)₃P₆ fragment without Pd鈥揟l detachment (i.e., the entire cluster of 1 remains intact). In direct contrast, corresponding temperature-dependent ³¹P and ¹³C NMR data of 2 instead are consistent with rapid, reversible dissociation/association of the entire [渭₃-TlCo(CO)₃L] ligand from the analogous Pd₉(渭₂-CO)₆(渭₃-CO)₃P₆ fragment of 2. This highly dissimilar dynamic solution behavior that points to a stronger Tl(I) attachment to the Pd₉ core in 1 than that in 2 may be attributed from the above crystallographic evidence to greater involvement of the outer three wingtip Pd(wt) atoms in bonding connectivities to the Tl(I) in 1 compared to predominant bonding connectivities of only the three inner Pd(oct) atoms to the Tl(I) in 2. ¹H NMR solution spectra of 1 also suggest significant covalent character in the bidentate Tl鈥揙(acac) bonding in 1 based upon the observation of H(acac)鈥揟l coupling; this premise is consistent with its Tl鈥揙 distances of 2.35 脜 (av) being ca. 0.2 脜 shorter than those of 2.52 脜 (av) found in crystalline Tl(acac), which with no observed H鈥揟l NMR coupling in solution implies ionicity of its bidentate Tl鈥揙 bonding. Both 1 and 2 conform to an 86 CVE count expected for an octahedral metal polyhedron based upon the Tl(I) and each wingtip Pd(渭₂-CO)₂L fragment contributing 2 and 4 CVEs, respectively.