First high-nuclearity palladium halide/carbonyl/phosphine cluster, [Pd12(μ3-I)2(μ4-I)3(μ2-CO)6(PEt3)6]+ monocation containing an octacapped octahedral Pd6(μ3-Pd)6(μ3-I)2 fragment: structure-to-synthesis generation from different synthetic routes

The original synthesis and stereochemical characterization of the [Pd12(μ3-I)2(μ4-I)3(μ2-CO)6L6]+ monocation (1) (L = PEt3; [PF6]− salt) was an outgrowth of our investigation of the chemical behavior of two unusual thallium–palladium clusters: (μ6-Tl)[Pd3(CO)3L3]2+ (2) which possesses a Pd3TlPd3 sandwich framework, and [Tl2Pd12(CO)9L9]2+ (3) which may be viewed as edge-fusions of three Pd5 trigonal bipyramids to a central Tl2Pd3 trigonal bipyramid. Room-temperature reactions of 2 and 3 with I2 in THF gave rise in each case to small yields (<10%) of 1 along with two square-planar palladium(II) co-products, trans -Pd2(μ2-I)2I2L2 (7) and trans -PdI2L2 (8) (L = PEt3). The geometries and compositions of 1, 7, and 8 were unequivocally established from low-temperature CCD X-ray crystallographic determinations. 1 was characterized by solid-state/solution IR and multinuclear (31P, 13C, 1H) NMR spectra. The 12-atom metal-core architecture of this geometrically unprecedented Pd6(μ3-Pd)6(μ3-I)2(μ4-I)3 kernel of 1 of crystallographic D 3 (32) site symmetry may be envisioned as a distorted hexacapped octahedral Pd(oc)6Pd(cap)6 core with its two metal-uncappedtrans octahedral Pd(oc)3 faces additionally capped by iodide μ3-I atoms. The three tetracapping μ4-I atoms are each coordinated to two Pd(oc) and two adjacent Pd(cap) atoms. A comparative geometrical/qualitative bonding analysis of the hexacapped octahedral Pd(oc)6Pd(cap)6 core in 1 with the structurally analogous cores in the recently reported Pd12 clusters, Pd12(μ2-CO)6(μ3-CO)6(PR3)6 (R = n -Bu (4), Ph (5)), revealed significantly different architectural features but yet emphasized the importance of the Pd(cap) atoms in stabilizing the Pd(oc) octahedra in 1, 4, and 5. In fact, strong bonding interactions of the μ3-I and μ4-I atoms to the Pd12 polyhedron in 1 are evidenced by its black-violet crystals being air-stable for at least one month and by 1 dissolved in THF, acetone, or acetonitrile not undergoing decomposition to AgI upon addition of Ag(OAc). An exploration via the structure-to-synthesis approach of possible preparative pathways involving 14 different chemical reactions was carried out in order to isolate 1 in much higher yields. This systematic investigation demonstrated the importance of conproportionation reactions (i.e., Pd(0) + Pd(II) → Pd(1/2) in 1) utilizing the co-products trans -Pd2(μ2-I)2I2L2 (7) and trans -PdI2L2 (8), in different chemical reactions as palladium(II) precursors; high yields of 1 (ca. 50% based upon 6) were obtained from conproportionation reactions in THF of palladium(0) Pd10(CO)12L6 (6) with 7 in the presence of Pd(OAc)2 and View the MathML source(NBu4n)(PF6). The square-planar palladium(II) geometries of the iodide-bridged dimeric 7 and monomeric 8 are compared with each other and with those of the previous crystallographically determined 8 (at room temperature) and several crystallographically known analogues (with different phosphine ligands); corresponding molecular parameters were found to be in remarkably close agreement with distinct bond-length variations in bridging Pd–I(b) and terminal Pd–P bonds being readily attributed to the well-documented trans influence.