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Synthesis, Characterization, and Ligand Exchange Studies of W6S8L6 Cluster Compounds

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posted on 04.05.2001, 00:00 by Song Jin, Ran Zhou, Ellen M. Scheuer, Jennifer Adamchuk, Lori L. Rayburn, Francis J. DiSalvo
Eleven organic Lewis bases were investigated as potential ligands (L) on W6S8L‘6 clusters by exploring ligand exchange reactions to form W6S8L6 clusters. Six new homoleptic W6S8L6 cluster complexes were prepared and characterized with L = tri-n-butylphosphine (PnBu3), triphenylphosphine (PPh3), tert-butylisocyanide (tBuNC), morpholine, methylamine (MeNH2), and tert-butylamine (tBuNH2). While partial replacement of ligands occurred with diethylamine (Et2NH) and dibutylamine (Bu2NH), homoleptic clusters could not be prepared by these exchange reactions. When aniline, tribenzylamine, and tri-tert-butylphosphine were the potential ligands, no exchange was observed. From ligand exchange studies of these ligands and others previously studied, a thermodynamic series of binding free energies for ligands on W6S8L6 clusters was established as the following:  non-Lewis base solvents, aniline, PtBu3, etc. ≪ Et2NH, Bu2NH < tBuNH2 < morpholine, piperidine ≤ nBuNH2, MeNH2 ≤ 4-tert-butylpyridine, pyridine < tBuNC < tricyclohexylphosphine (PCy3) < PPh3, PnBu3 ≤ triethylphosphine (PEt3). Structures of the new cluster complexes were determined by X-ray crystallography. The new compounds were also characterized by NMR spectroscopy and thermogravimetric analyses (TGA). The W−L bond orders and TGA data qualitatively agree with the thermodynamic series above.