Chemistry of o-xylidene–metal complexes. Part 2. Preparation and properties of the o-xylidene–metal(IV) complexes [M(CH₂C₆H₄CH₂-o)(η-C₅H₄R)₂](M = Ti, Zr, Hf, or Nb; R = H or SiMe₃) and [{M′(CH₂C₆H₄CH₂-o)₂(OC₄H₈)}_n](M′= Ti, Zr, or Hf); X-ray crystal structures of the metallaindanes [M(CH₂C₆H₄CH₂-o)(η-C₅H₄R)₂](R = H, M = Ti, Zr, or Hf; R = SiMe₃, M = Nb)

Reaction of the di-Grignard reagent o-C6H4(CH2MgCl)2(1) in tetrahydrofuran (thf) with the appropriate metallocene(IV) chloride, [M(η-C5H4R)2Cl2], yields the corresponding crystalline, thermally robust metallaindane complexes [[graphic omitted]H2-o)(η-C5H4R)2][R = H or SiMe3, M = Ti, Zr, or Hf; R = SiMe3, M = Nb]. The Zr complex with R = H affords o-xylene either upon photolysis or pyrolysis. N.m.r. spectra of the d0 complexes show magnetically equivalent pairs of C5H4R and CH2 groups. The e.s.r. solution spectrum of the d1 Nb complex was second order, with gav= 1.9986 and a(93Nb)= 77.2 G, calculated using a modified Breit–Rabi equation. Reduction of each of the d0 Ti, Zr, or Hf compounds with Na[C10H8] in thf results in scission of an M–CH2 bond, as deduced by the appearance of a central triplet e.s.r. signal, with appropriate (except Hf) satellites, assigned to the d1 complex [M(η-C5H4R)n(o-CH2C6H4CH2Na)(thf)x](2–n)+(n= 1 or 2); cyclic voltammetry on one of the TiIV complexes shows a pseudo-reversible one-electron reduction, and hence the metallate(III) ion [Ti(η-C5H5)2{o-(CH2)2C6H4}]– may be a transient intermediate. Reactions of the Group 4A metallaindanes with CO under ambient conditions are sensitive to the nature of M: the Ti and Zr complexes yield [M(η-C5H4R)2(CO)2] and indan-2-one; whereas the Hf complex affords two conformers of the seven-membered, bis-σ-acyl, the metallabenzocycloheptene-dione complex [[graphic omitted]O-o}(η-C5H4SiMe3)2], in which the two CO groups are believed to have an anti relationship. The two conformers coexist in equilibrium in solution in CH2Cl2 or CHCl3 with one form (the less soluble) favoured at low temperature. Reaction of two equivalents of the di-Grignard reagent (1) with the appropriate Group 4A metal(IV) chloride in thf furnishes insoluble, pyrophoric powders of empirical formula M(CH2C6H4CH2-o)2(thf), which may well be oligomers having bridging o-xylidenes. The X-ray structures of the four title metallaindanes [M(η-C5H5)2{o-(CH2)2C6H4}](M = Ti, Zr, or Hf) and [Nb{η-C5H4(SiMe3)}2{o-(CH2)2C6H4}] confirm their formulae. Features of interest include (i) the bis-σ-co-ordinating mode of the chelating o-xylidene ligand; (ii) the bite angle (°) CαMCα′: 76.7(2) Ti, 77.3(2) Zr, 77.2(4) Hf, 72.4(7) Nb; (iii) the fold angle (°)[i.e. the angle subtended by the normals to (a) the MCαCα′ plane and (b) the C4 plane of the MC4 ring]: 41 Ti, 53 Zr, 53 Hf, 44 Nb; (iv) the 〈M–Cα〉 distances (A): 2.203(6) Ti, 2.300(8) Zr, 2.28(1) Hf, 2.286(9) Nb; (v) the 〈M-Cβ〉 distances (A): 2.913(6) Ti, 2.857(8) Zr, 2.91 (1) Hf, 3.079(21) Nb; and (vi) the fact that the C6 rings are planar while the α-CH2's lie 0.10 (Ti), 0.12 (Zr), 0.12 (Hf), or 0.07 A(Nb) out of this plane on the same side of the C6 plane as the metal atoms.