High-Yield Synthesis of PPh3-Ligated Decanuclear Tl-Pd Cluster, Pd-9 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 Behavio

The new Tl(I)-Pd(0) cluster Pd-9[mu(3/3)-Tl-(acac)](mu(2)-CO)(6)(mu(3)-CO)(3)(PPh3)(6) (1) was prepared in high yields (over 90%), both by reaction of Pd-10(CO)(12)(PPh3)(6) (4), PPh3, and TlPF6 in THF in the presence of acetylacetone (Hacac) and base (NEt3) and by direct reaction of Pd-10(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 center dot 1.5Hacac center dot 0.5THF (1A) and 1 center dot 0.3THF (1B), which showed essentially identical geometries for the entire Pd9Tl-(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(mu(2)-CO)(2)PPh3 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 PPh3 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 0 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 TlPd9 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 angstrom; these connectivities together with three longer Tl-Pd(wt) ones of mean distance 3.15 angstrom give rise to a (crown-like)Pd-6 sextuple (mu(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[mu(3)-TlCo(CO)(3)L](mu(2)-CO)(6)(mu(3)-CO)(3)L-6 (2) (with L = PEt3 instead of PPh3). 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 PR3/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 angstrom, respectively. Variable-temperature P-31{H-1} NMR solution data of 1 indicate the occurrence of presumed fast wobbling-like motion of the [mu(3/3)-Tl(acac)] entity about the pseudo-C-3 axis of the Pd-9(mu(2)-CO)(6)(mu(3)-CO)(3)P-6 fragment without Pd-Tl detachment (i.e., the entire cluster of 1 remains intact). In direct contrast, corresponding temperature-dependent P-31 and C-13 NMR data of 2 instead are consistent with rapid, reversible dissociation/association of the entire [mu(3)-TlCo(CO)(3)L] ligand from the analogous Pd-9(mu(2)-CO)(6)(mu(3)-CO)(3)P-6 fragment of 2. This highly dissimilar dynamic solution behavior that points to a stronger Tl(I) attachment to the Pd-9 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. H-1 NMR solution spectra of 1 also suggest significant covalent character in the bidentate Tl-O(acac) bonding in 1 based upon the observation of H(acac)-Tl coupling; this premise is consistent with its Tl-O distances of 2.35 angstrom (av) being ca. 0.2 angstrom shorter than those of 2.52 angstrom (av) found in crystalline Tl(acac), which with no observed H-Tl NMR coupling in solution implies ionicity of its bidentate Tl-O 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(mu(2)-CO)(2)L fragment contributing 2 and 4 CVEs, respectively.