Chemistry of o-xylidene-metal complexes. Part 3. Tungste o-xylidene complexes derived from tetrachloro(oxo)tungsteh(VI); X-ray crystal structures of [W(CH2C6H4CH2-o) 3]·0.5C6H6 and [{W(CH2C6H4CH2-o)2O} 2Mg(C4H8O)4]

Michael F. Lappert, Colin L. Raston, Graham L. Rowbottom, Brian W. Skelton, Allan H. White

Research output: Contribution to journalArticlepeer-review

33 Citations (Scopus)

Abstract

Reaction of WCl4O with the di-Grignard reagent o-C6H4(CH2MgCl)2 or the chloride-free 'o-xylidene' complex Mg(CH2C6H4CH2-o)(thf) in tetrahydrofuran (thf) yields either the thermally stable tris(chelate), [[graphic omitted]H2-o)3] (7), or the WV complex [{[graphic omitted]H2-o)2[graphic omitted]g(thf)4] (8) (a non-electrolyte in thf), in a manner critically dependent on reaction conditions. In both reactions a reduction step precedes alkylation, as determined by e.s.r., with probable intermediates being [WCl4O]-, [WCl5O]2-, and [WCl3O(thf)3]. The complex (7) undergoes reversible one-electron reduction as shown by cyclic voltammetry, E†red = -1.68 V, and the WV radical anion, gav. = 2.005, is also accessible from (7) and sodium dihydronaphthylide. X-Ray analysis shows that the o-xylenediyl ligand (1) behaves as a chelating ligand in both (7) and (8), but in (8) the two ligands (1) are bonded differently. One is typically metallacyclic in nature, W-Cα 2.16(2) Å, W-Cα-C(aromatic) 109(1)° with a fold angle (Φ) of 42.4°, whereas the other has a larger Φ (66.1°) with <W-Cα> 2.16(4) Å, and W-Cα-C(aromatic) 98(2) and 93(1)°, possibly arising from an aromatic π interaction with the tungsten atom. For the tris(chelate) (7) all ligands are equivalent, the tungsten symmetry is quasi-3/m, with a more pronounced W-π-arene interaction, possibly of a stabilising influence [W-C 2.21, W-C(aromatic) 2.49 Å; W-C-C(aromatic) 82.7°, Φ = 83.3°]. In complex (8), the magnesium atom is octahedrally co-ordinated, with the four thf ligands disposed equatorially; the WO bond is short, 1.71(1) Å.

Original languageEnglish
Pages (from-to)883-891
Number of pages9
JournalJournal of the Chemical Society, Dalton Transactions
Issue number5
DOIs
Publication statusPublished - May 1984
Externally publishedYes

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