Trichlorido{2-[2-(η5-cyclopentadienyl)-2-methylpropyl]-1-trimethylsilyl-1H-imidazole-κN 3}titanium(IV) tetrahydrofuran hemisolvate

The title compound, [Ti(C15H23N2Si)Cl3]·0.5C4H8O, has been prepared from {2-[2-(η5-cyclopentadienyl)-2-methylpropyl]-1H-imidazolyl-κN 1}bis(N,N-diethylamido-κN)titanium(IV), (C12H14N2)Ti(NEt2)2, by reaction with excess of Me3SiCl in tetrahydrofuran (THF) at 353 K. The crystal structure contains THF as adduct solvent, disordered around a center of inversion. The presence of THF and the adduct ratio has been independently supported by 1H NMR spectroscopy. The coordination polyhedron of the Ti atom is distorted square-pyramidal, assuming the cyclopentadienyl (Cp) ring occupies one coordination site. The Ti, Si and CH2 group C atoms only deviate slightly from the imidazole ring plane [by 0.021 (4), 0.133 (4) and 0.094 (4) Å, respectively]. Comparison of the principal geometric parameters with those of the few known structurally characterized analogues reveal small differences in bond lengths and angles at the Ti atom. The title complex is only stable in THF-d 8 in the presence of excess Me3SiCl, otherwise it exists in an equilibrium with equimolar amounts of dichlorido{2-[2-(η5-cyclopentadienyl)-2-methylpropyl]-1H-imidazolyl-κN 3}titanium(IV) and chlorotrimethylsilane.

The title compound, [Ti(C 15 H 23 N 2 Si)Cl 3 ]Á0.5C 4 H 8 O, has been prepared from {2-[2-( 5 -cyclopentadienyl)-2-methylpropyl]-1H-imidazolyl-N 1 }bis(N,N-diethylamido-N)titanium(IV), (C 12 H 14 N 2 )Ti(NEt 2 ) 2 , by reaction with excess of Me 3 SiCl in tetrahydrofuran (THF) at 353 K. The crystal structure contains THF as adduct solvent, disordered around a center of inversion. The presence of THF and the adduct ratio has been independently supported by 1 H NMR spectroscopy. The coordination polyhedron of the Ti atom is distorted squarepyramidal, assuming the cyclopentadienyl (Cp) ring occupies one coordination site. The Ti, Si and CH 2 group C atoms only deviate slightly from the imidazole ring plane [by 0.021 (4), 0.133 (4) and 0.094 (4) Å , respectively]. Comparison of the principal geometric parameters with those of the few known structurally characterized analogues reveal small differences in bond lengths and angles at the Ti atom. The title complex is only stable in THF-d 8 in the presence of excess Me 3 SiCl, otherwise it exists in an equilibrium with equimolar amounts of dichlorido{2-[2-( 5 -cyclopentadienyl)-2-methylpropyl]-1Himidazolyl-N 3 }titanium(IV) and chlorotrimethylsilane.
All complexes of question exhibit one and the same structural motif. They are mononuclear complexes, with the coordination environment of the Ti-atoms being a distorted square pyramid (assuming Cp-rings occupy one coordination site; "four-leg piano stool"). Contents of the unit cells are presented by pairs of enantiomorphic conformers connected by inver-supplementary materials sup-2 sion symmetry operations. In all complexes under discussion, ligating N-atoms are linked to Cp-groups with a C 2 [(IV)-(VI)] or C 3 [(I) and (III)] bridges. Noteworthy, that no structurally characterized complexes of type η 5 -CpTiCl 3 -NR n with a non-linked to Cp NR n functionality are known at the moment.
Compounds (I) and (III) represent a pair of the "closest relatives", and, despite of the evident differences in their chemical structure (CPh 2 against CMe 2 and NMe against NSiMe 3 ), the geometrical parameters of the coordination environment of the Ti-atoms and imidazole rings nearly match (see Table 1). This is the same for the torsion angles in the bridge and Cp cent denote r.m.s. plane and centroid of the Cp-ring, respectively) distances, as well as on the angle Cl2-Ti1-Cp cent and "cis-angles" Cl2-Ti1-Cl1, Cl2-Ti1-Cl3, Cl1-Ti1-N2, and Cl3-Ti1-N2. However, the angles N2-Ti1-Cp cent in (I) and (III) are expanded by approximately 10° compared to those in (IV)-(VI) while the "trans-angle" Cl2-Ti1-N2 is tightened by the same value. The angles Cl1-Ti1-Cp cent and Cl3-Ti1-Cp cent in (I) and (III) are decreased by approximately 5°c omparatively to those in (IV)-(VI) while the "trans-angle" Cl1-Ti1-Cl3 is increased by approximately 10°.

Experimental
All operations were performed in all-sealed evacuated glass vessels with application of the high-vacuum line (the residual pressure of non-condensible gases within 1.5-1.0×10 -3 Torr range, 1 Torr = 133.322 Pa). Complex (II) was prepared as described in our earlier work (Wang et al., 2009). THF and THF-d 8 were kept with disodium benzophenone ketyl and transferred into reaction vessels and/or NMR tubes on the high-vacuum line by trapping the vapour with liq. N 2 . Chlorotrimethylsilane was refluxed with and kept over CaH 2 and transferred into reaction vessels in a similar way. -NMR spectra were recorded on Varian INOVA-400 instrument. For 13 C{ 1 H}and 1 H NMR spectra, the 13 C and residual proton resonance of the d-solvent [δ H = 1.73 and δ C = 25.3 (THF-d 8 )] were used as internal reference standards.
Complex (I): To a solution of (II) (0.282 g, 0.75 mmol) in THF (20 ml), an excess of Me 3 SiCl (0.6 ml, 4.71 mmol) was added at approx. 253 K. An immediate precipitation of a yellow fine-crystalline solid occurred. The reaction mixture was then heated at 353 K until all the solid dissolved, the volume was reduced two times and the mother liquor was allowed to cool gradually along with the water bath down to ambient temperature. On the walls of the reaction vessel well formed bright-orange crystals grew. The orange mother liquor was removed from the crystals by decantation, the solid was rinsed once with cold (253 K) THF and the crystals were quickly dried by trapping all volatiles with liquid N 2 . Yield 0.275 g (82%).  Low concentration of (VII) made its signals in 13 C{ 1 H} NMR spectrum of the equilibrium mixture invisible.
Single crystal of I suitable for X-ray diffraction analysis were picked up directly from the isolated materials (N 2 -filled glove-box) and mounted inside a Lindemann glass capillary (diameter 0.5 mm).

Special details
Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.
Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating Rfactors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.