Metal Alkoxides: Models for Metal Oxides. 7.1Trinuclear and Tetranuclear Alkylidyne Clusters of Tungsten Supported by Alkoxide Ligands

Malcolm H. Chisholm, Kirsten Folting, Joseph A. Heppert, David M. Hoffman, John C. Huffman

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Abstract

The ethylidyne capped triangulo compound Wi(μ3-CMe)(μ2-O-i-Pr)3(O-i-Pr)6is formed competitively with W2-(O-i-Pr)6(μ-C4Me4)(C2Me2) in the reaction between W2(O-i-Pr)6(py)2and 1 equiv of MeC=CMe and is the major and sole isolable product in the reaction between W2(O-i-Pr)6(py)2and (t-BuO)3W═CMe carried out in hexane/i-PrOH. Similarly, (t-BuO)3W=CMe and Mo2(O-i-Pr)6react in hexane/i-PrOH to give Mo2W(CMe)(0-/-Pr)9 which is isomorphous with the tritungsten compound. The W3(CMe)(O-i-Pr)9molecule has virtual C3V symmetry: each tungsten atom is in a square based pyramidal geometry with the W-C bond in the apical position. Pertinent averaged bond distances (A) are W-W = 2.74 (1), W-C = 2.06 (1), W-O = 1.91 (1) (terminal OR), and W-O = 2.04 (2) (bridging OR). Variable-temperature NMR 1H studies on the W3 and Mo2W compounds indicate that a similar structure is maintained in solution and that site exchange between the terminal O-i-Pr ligands involves a pseudorotation mechanism. No evidence is found for bridge ⇋ terminal exchange on the NMR time scale. The reaction between (Me3SiCH2)4W2(ju-CSiMe3)2and excess EtOH in hexane yields W4-(CSiMe3)2(OEt)14and Me4Si. In the solid state, there are discrete centrosymmetric W4(CSiMe3)2(OEt)l4molecules. The four tungsten atoms form a zigzag chain, W-W-W = 141.64 (2)°, with alternating short, 2.516 (1) A, and long, 3.513 (1) A, distances corresponding formally to W-W single and nonbonding distances, respectively. The molecule may be viewed as a dimer [W2(M-CSiMe3)(OEt)7]2with the two halves being joined by a pair of alkoxy bridges. Each tungsten is in a distorted octahedral geometry, and the W4C2014 core represents the fusing together of two confacial bioctahedra along a common edge. The M-CSiMe3ligand occupies one site of the face shared by two tungsten atoms. The W-C distances are notably asymmetric, 1, 922 (7) and 2.087 (7) A, representing formally W-W double and single bond distances. The tetranuclearity is maintained in benzene solution, and bridge ⇋ terminal OEt site exchange is rapid on the NMR time scale. These are the first trinuclear and tetranuclear alkylidyne clusters of tungsten supported exclusively by alkoxide ligands. Comparisons with related molecules are made.

Original languageEnglish
Pages (from-to)1234-1241
Number of pages8
JournalJournal of the American Chemical Society
Volume107
Issue number5
DOIs
StatePublished - Mar 1985

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