New high-nuclearity homometallic/heterometallic palladium and gold-nickel carbonyl clusters

Giant-sized metal carbonyl clusters are of particular interest due to their great potential as catalysts and as models for carbonyl coordination modes on small metal particles. Systematic studies of physical properties of high-nuclearity close-packed metal clusters should provide insight concerning the evolution of metallic-like behavior as a function of increasing metal-core size. My research has been directed towards the preparation and structural/physical characterization of new high-nuclearity metal carbonyl clusters containing Pd, Pd-Ni, Pd-Ni-Au, and Ni-Au cores. Pd₁₆(CO)₁₃(PMe ₃)₉ (1), Pd₃₅(CO)₂₃(PMe ₃)₁₅ (2), Pd₃₉(CO)₂₃(PMe ₃)₁₆ (3), and Pd₅₉(CO)₃₂(PMe ₃)₂₁ (4), and the bimetallic Pd₂₉Ni ₃(CO)₂₂(PMe₃)₁₃ (5) were obtained from reactions of a Pd-Ni cluster precursor and PMe₃ (with or without acetic acid). 1 contains a centered icosahedron, both 2 and 3 display the face-fusion of two centered icosahedra, 4 has two outer centered icosahedra indirectly connected via trans double face-sharing with an inner face-shared bioctahedron, and 5 consists of four interpenetrating centered icosahedra with the four Pd-centered atoms tetrahedrally linked to one another. The latter four Pd cores point to new possible condensation growth patterns for transition-metal icosahedral oligomerization. 4 is the largest crystallographically determined discrete metal cluster with direct metal-metal bonding reported to date. Reactions of $Ni6CO122-$ with Pd(OAc)₂ in DMF or $PdCH3CN4BF42$ in DMSO produced $Pd13Ni13CO344-$ (6) in high yields; its Pd₁₃Ni₁₃ core possesses a closest-packed pseudo-C_3v arrangement of five stacked $aNi6bPd7Ni3aPd6cNi3bNi1$ layers. Efforts to obtain large trimetallic Au-Pd-Ni carbonyl clusters gave rise to the first high-nuclearity trimetallic carbonyl cluster $Au6Pd6P\; d6-xNixNi20CO446-$ (7). Its 38-atom metal core consists of a hcp 4-layer arrangement of 30 atoms containing a central Au₆ octahedral kernel together with 8 triangular capping Ni atoms. A substitutional Pd/Ni crystal disorder was found at only six specific pseudo-equivalent metal sites. A designed reaction produced the corresponding hypothetical isostructural $Au6Ni32CO446-$ (8), in which all Pd atoms were replaced with Ni ones, along with two other...