Bis(μ-2-hydroxymethyl-2-methylpropane-1,3-diolato)bis[dichloridotitanium(IV)] diethyl ether disolvate

The title complex, [Ti2Cl4{CH3C(CH2O)2(CH2OH)}2], lies across a centre of symmetry with a diethyl ether solvent molecule hydrogen bonded to the –CH2OH groups on either side of it. The TiIV atom is coordinated in a distorted octahedral geometry by a tripodal ligand and two terminal chloride atoms. There are three coordination modes for the tripodal ligand distinguishable on the basis of their very different Ti—O bond lengths. For the terminal alkoxo ligand, the Ti—O distance is 1.760 (1) Å, the asymmetric bridge system has Ti—O bond lengths of 1.911 (1) and 2.048 (1) Å. The Ti—O bond length for the alcohol O atom is the longest at 2.148 (1) Å.

The title complex, [Ti 2 Cl 4 {CH 3 C(CH 2 O) 2 (CH 2 OH)} 2 ], lies across a centre of symmetry with a diethyl ether solvent molecule hydrogen bonded to the -CH 2 OH groups on either side of it. The Ti IV atom is coordinated in a distorted octahedral geometry by a tripodal ligand and two terminal chloride atoms. There are three coordination modes for the tripodal ligand distinguishable on the basis of their very different Ti-O bond lengths. For the terminal alkoxo ligand, the Ti-O distance is 1.760 (1) Å , the asymmetric bridge system has Ti-O bond lengths of 1.911 (1) and 2.048 (1) Å . The Ti-O bond length for the alcohol O atom is the longest at 2.148 (1) Å .

Experimental
Crystal data
We are grateful to Massey University for the award of a Post-Doctoral Fellowship to CS, and to Ms T. Groutso of the University of Auckland for the data collection.

Comment
Transition metal complexes that arise from the tris-hydroxymethyl ethane ligand CH 3 C(CH 2 OH) 3 are not widely reported in the literature. Structures identified by X-ray crystallography include the triply deprotonated form in cluster compounds of molybdenum and tungsten (Liu et al. 1990;Delmont et al. 2000) and dimeric and cluster compounds of chromium (Talbot-Eeckelaers et al. 2006), the doubly deprotonated form in dimeric vanadium-oxo complexes (Chang et al. 1993;Salta & Zubieta 1997) and the fully protonated form in monomeric yttrium complexes (Chen et al. 1997). For titanium only µ3-O and µ2-O coordination modes have been identified (Boyle et al. 1995).
When TiCl 4 in diethyl ether was reacted with a mixture of CH 3 C(CH 2 OSiMe 3 ) 3 and CH 3 C(CH 2 OSiMe 3 ) 2 (CH 2 OH) we obtained a small amount of colourless crystals analysing as TiCl 2 [(OCH 2 ) 2 (HOCH 2 )CCH 3 ]. 0.5 diethyl ether. One crystal was characterized by X-ray crystallography. The structure consists of a centrosymmetric dimer made up of two [(OCH 2 ) 2 (HOCH 2 )CCH 3 ] ligands forming a tripodal bridging system across two titanium atoms each of which also contain two terminal chloro ligands. One tripodal ligand is positioned above the two Ti atoms and out towards the rear of the molecule and the other is below and out the front with the two related by an inversion centre. The distorted octahedral geometry about Ti is made from one arm of a terminal alkoxo ligand (O2), another from an alcohol ligand (O3) and a third arm from the bridging alkoxo atoms (O1 and O1 i ). These latter each lie in trans-positions to the two cis-related chloro ligands.
For the terminal alkoxo ligand the Ti-O2 distance is 1.760 (1) Å which is indicative of strong π-bonding (see later). The asymmetric bridge system has Ti-O bond lengths of 1.991 (1) and 2.048 (7) Å and the Ti-Cl bonds trans to these bridging O atoms also show differences in length, 2.3184 (4) Å for Ti-Cl1 which is trans to the longer Ti-O1 and 2.3292 The overall coordination geometry and deprotonation features of the two ligands are identical with that found in the vanadium (v) complex {V 2 O 2 Cl 2 ([(OCH 2 ) 2 (HOCH 2 )CCH 3 ] 2 } (Chang et al. 1993;Salta & Zubieta 1997). In than observed for isopropyl alcohol ligated to titanium [bond lengths 2.087 (4) and 2.093 (4) Å] (Wu et al. 1996). The Ti-Cl1 and Ti-Cl2 bond lengths [2.3184 (4) and 2.3292 (4) Å] do not differ significantly from each other and are typical of Ti-Cl bonds observed elsewhere. Wu et al. 1996).

Experimental
Using normal bench-top techniques for air-sensitive compounds, TiCl 4 (1.25 g, 6.59 mmol) was cooled to dry-ice temperature and diethyl ether (50 ml) chilled to -20 °C was added. The mixture was warmed to room temperature, heated until all the yellow solid had dissolved and 1,1,1-tris(hydroxymethyl)ethane (2.2 g, 6.6 mmol) in diethyl ether (50 ml) was added to the rapidly stirred solution whereupon a dense colourless precipitate was formed. The mixture was refluxed for 3 h, cooled to room temperature and the remaining solid allowed to settle and the solution was filtered. The volume was reduced to ca 30 ml and the solution stood at -20 ° C whereupon a mass of crystalline colourless material was deposited. Found: C, 31.06; H, 6.15%. C 14 H 30 Cl 4 O 6 Ti 2 (i.e. C 10 H 20 Cl 4 O 6 Ti 2 .diethyl ether) requires C, 31.61; H, 5.69%. A crystal was chosen from the mass and the X-ray crystal structure obtained. This molecule corresponded to C 10 H 20 Cl 4 O 6 Ti 2 .bis-diethyl ether.

Refinement
All H atoms (except H3) were included in calculated positions and refined using a riding model with U iso = 1.2U eq (C) for H on secondary C atoms and 1.5U eq (C) for those on tertiary C atoms. C-H distances of 0.99Å and 0.96Å were assumed for tertiary C and secondary C atoms respectively. H3 was located on a difference map and its x, y, z co-ordinates and isotropic thermal parameter refined.

Computing details
Data collection: SMART (Siemens, 1995); cell refinement: SAINT (Siemens, 1995); data reduction: SAINT (Siemens, 1995); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEP-3 for Windows (Farrugia, 2012); software used to prepare material for publication: SHELXL97 (Sheldrick, 2008  ORTEP diagram of molecule, at the 50% probability level, showing the numbering system. Symmetry code: (i) -x + 1, -y + 1, -z + 1. 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 R-factors(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.