The Early Transition Metals

BY F. L. BOWDEN, P. F. HEVELDT, AND D. J. WATSON

PART I: Titanium, Zirconium, Hafnium, Vanadium, Niobium, and Tantalum

by F. L. Bowden

1 Titanium

Introduction. — Reviews have appeared on the structural, organometallic, and general chemistry of titanium. The organometallic chemistry of titanium is included in a text published this year." A new measurement of the natural abundances of the titanium isotopes gives 47.875285 as the atomic weight of titanium (C = 12).

Titanium compounds containing sulphide and amino-groups have been extracted from plant cells by acetone extraction. The reducing activity of the titanium compounds isolated from cells kept in the dark is higher than that after photosynthesis.

Vapour deposition experiments on titanium have shown that on increasing the rate of titanium deposition at constant argon deposition rate, three new absorptions were observed in the spectrum of the matrix in addition to those due to matrix-isolated atoms. These absorptions have been attributed to the dititanium species for which MO calculations indicate a strong 4s–4s σ-interaction.

Reduction of Cp2TiCl2 with A1 in THF under 1 atm CO is the most efficient, giving the red crystalline Cp2Ti(CO)2 in quantitative yields (cf. 80 % with Na-Hg as reducing agent). The carbonyl can also be obtained from Cp2TiBH4 and CO in the presence of Et3N. Reduction of CpTiCl3 with Mg in the presence of C7H7 gives CpTiC7H7. Derivatives of this compound, ([FORMULA NOT REPRODUCIBLE IN ASCII], or indenyl) and (η7-C7H6C6H5)(η5- C5H5)Ti, have been prepared. Their mass spectra indicate the occurrence of CH or CR migrations affording π-C6H6Ti species. Similar fragmentation patterns in the mass spectrum of the green product from CpTiCl3 or CoTiCl2 and C9H9Li are cited in support of a [FORMULA NOT REPRODUCIBLE IN ASCII] structure.

Hydrolysis of titanocene produces the complex [Cp(C5H4)TiOH]2; X-ray crystallography has established that this has the fulvalene structure (1) characteristic of the titanocene molecule (Vol. 4, FORMULA p. 2) and that the titanium atoms are bridged by the two hydroxy-groups.

Oxidative coupling of the PhC [equivalent to] C fragment occurs in the reaction between PhC [equivalent to] CNa and [FORMULA NOT REPRODUCIBLE IN ASCII] to afford [FORMULA NOT REPRODUCIBLE IN ASCII] (2). The η5-C5H5 analogue of (2) has been obtained directly from (η5-C5H5)2Ti and 1,4-diphenylbuta-1,3-diyne. A purple intermediate found in the oxidative coupling reaction has v(C [equivalent to] C) at ca. 2045 cm-1 and was assigned the σ, π-bridged structure (3).

The electronic configuration of dicyclo-octatetranyltitanium has been derived on the basis of C8v local symmetry for the metal. The overall molecular symmetry is much lower than this with one C8H8 ring symmetrically bound (C8v) and the other one unsymmetrically bound (Cs). Vibrational spectroscopic data indicated the former to be the most firmly bound.

Binary Compounds and Related Systems —Halides and Oxyhalides. The heat capacity of TiF4 has been determined. The peculiar temperature dependence of the magnetic susceptibility of β-TiCl3 is attributed to the presence of two kinds of chain-end site. The kinetics of disproportionation of TiCl3 have been measured over the temperature range 873 — 1373 K.

Molecular force constants for TiCl4 have been calculated from i.r. data on the isotopic species 48TiCl4 and Ti35Cl4 in argon matrices, and 48Ti35Cl4 in the gas phase. MO calculations of the ground state of TiCl4 show that as expected, the higher filled MOs are mainly chlorine 3p in character. A formal metal charge of only 1.0 + indicates a considerable deviation from the simple d° description of the molecule. The energy levels of TiCl4 have been calculated by the CNDO method. The existence of long-lived negatively charged molecular ions in the mass spectra of several titanium compounds including TiCl4, is an indication that these compounds have positive electron affinities.

Oxides. Ti2O3 has been investigated by X-ray spectroscopy and by e.p.r. spectroscopy and magnetic susceptibility measurements; there has been an improved MO calculation of its band structure. A band model has been proposed to account for the origin of the magnetic moment and metallic transition of vanadium-doped Ti2O3. According to e.p.r. measurements the Ti3+ ions in mixed valence phases of the system TinO2n-1 have D2h symmetry; the rhombic field splitting parameters were determined.

Chalcogenides. Vapour pressure measurements on sulphur in equilibrium with TixS2 (1.11 >x > 1.00) at 773 — 973 K have provided thermodynamic data on which to base a preparation of TixS2 crystals with well-defined Ti: S ratios, and in addition have confirmed the existence of stoicheiometric TiS2. This has been confirmed independently by intercalation ratios, electron microscopy, and by measurements of electron transport and magnetic susceptibilities. TiS2 has nearly ideal octahedral co-ordination of the metal in a hexagonal laminar structure with an interlayer S — S distance of 3.462(5) Å. Titanium oxides and oxide-carbon mixtures undergo a two-stage sulphidization with H2S at 773 — 1773 K, affording non-stoicheiometric Ti1.25S2.

The structure of 12R-Ti8S1 2 has been refined to an R index of 2.8%, and the structures of a new poly-type 24R of TiS1.80±0.02 and TiS3 have been determined. n-Butyl-lithium in hexane has been found to be a mild but highly efficient reagent for the intercalation of lithium into layered chalcogenides; reaction with chalco-genides of Group IVB is sufficiently exothermic to cause the hexane to boil. This method avoids the problems of decomposition and partial intercalation experienced with high-temperature methods and also avoids the intercalation of ammonia when solutions of lithium in liquid ammonia are used. Moreover, the limiting stoicheiometry LiMX2 (M = Ti or Zr) can be achieved which represents more lithium than can be intercalated by either of the other methods. The view that intercalation involves electron transfer from the (Bun)- anion and intercalation of the Li+ cation to balance the charge is in keeping with the results of an n.m.r. study of LixTiS2 which indicate the donation of an appreciable fraction of the Li 2s electron to the TiS2 layers, the fraction decreasing as x increases. The reaction between TiS2 an alkali-metal halide and H2S at 1073 — 1273 K affords A0.5TiS2 (A = Li, Na, K, Rb, or Cs), whereas TiS2 and sodium naphthalenide afford a product Na0.8TiS2, with a higher alkali-metal concentration.

Two families of copper titanium sulphides have been prepared; they are: [FORMULA...