Chemistry of o-xylidene-metal complexes. Part 4. Stereospecific synthesis of the early transition metal meso-metallacycles: [M{CH(SiMe3)C6H4CHSiMe 3-o}(η-C5H5)2] (M = Ti, Zr, Hf, or Nb), their reversible one-electron reduction (M = Ti, Zr, Hf, or Nb) and oxidation (M = Nb); and the X-ray crystal structure of the zirconium complex

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

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33 Citations (Scopus)

Abstract

The reaction of the organodilithium reagent [{o-C6H4(CHSiMe3)2}{Li(tmen)} 2] (tmen = Me2NCH2CH2NMe2) and the appropriate metallocene(IV) chloride [M(η-C5H5)2Cl2] in OEt2 at ca. 35 °C yields the corresponding crystalline, thermally stable, stereospecifically pure meso-metallaindane meso-[[graphic omitted]HSiMe3-o}(η-C5H5)2] [M = Ti (2), Zr (3), Hf (4), or Nb (5)]; by-products in two of these reactions are [{Ti(η-C5H5)2Cl}2] or the binuclear zirconium compound (6) formulated as meso-[[graphic omitted]HSiMe3-o}(μ-σ: η-C5H4)2Zr(η-C5H 5)2]. Compounds (2) - (5) are sublimable at ca. 140 °C (10-3 Torr), and on pyrolysis afford o-C6H4(CH2SiMe3)2; they are reasonably air-stable and inert to CO under ambient conditions. Compound (6) is also accessible from (3) in OEt2 and successively Li(tmen)Bun in n-C6H14 and [Zr(η-C5H5)2Cl2]. Assignment of the meso (rather than rac) diastereoisomeric configuration for complexes (2) - (4) rests on their n.m.r. spectra and for (3) on X-ray data. E.s.r. data on complex (5), or the Na(C10H8)-tetrahydrofuran reduction products of each of (2) - (4), are consistent with each being a d1 complex. The electrochemical reduction [-E†red = 1.46 (Ti), 2.02 (Zr), or 2.26 V (Hf)] of each of the complexes (2) - (4) is pseudo-reversible, but the anions [[graphic omitted]HSiMe3-o}(η-C5H5)2] - tend to lose C5H5-. The niobium complex (5) undergoes reversible one-electron oxidation (E†ox = -0.47 V) or reduction (-E†red = 1.63 V). The X-ray structure of the title metallaindane (3) shows pseudo-tetrahedral co-ordination of Zr with a centroid-Zr-centroid' angle of 125.1° and bite angle Cα-Zr-Cα′ of 80.2(2)°, with <Zr-Cα, Cα′> 2.305(4) and <Zr ⋯ Cβ,Cβ′> 2.71(1) Å; hence the o-C6H4{CH(SiMe3)}2-metal bonding is best described as intermediate between that appropriate for metalla(IV)cyclic and an η4-5,6-dimethylenecyclohexa-1,3-diene-metal(II) structure; consistent also is the fold angle, Φ, of 66.7° (Φ being the dihedral angle between the ZrCαCα′ plane and the C8 extension of the aromatic plane).

Original languageEnglish
Pages (from-to)893-902
Number of pages10
JournalJournal of the Chemical Society, Dalton Transactions
Issue number5
DOIs
Publication statusPublished - May 1984
Externally publishedYes

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