Crystal structure of (2,2′-bipyridine-κ2 N,N′)-trans-bis(tert-butyldimethylsilyloxy)-cis-dioxidomolybdenum(VI)

In the title compound, [(tBuSiMe2O)2MoO2(2,2′-bipyridine)], the MoVI atom has a distorted octahedral environment with the siloxy substituents occupying the trans positions.

In the title compound, [( t BuSiMe 2 O) 2 MoO 2 (2,2 0 -bipyridine)] or [Mo(C 6 H 15 O-Si) 2 O 2 (C 10 H 8 N 2 )], the Mo VI atom has a distorted octahedral environment with the siloxy substituents occupying the trans positions. The complex contains a rare (R 3 SiO) 2 MO 2 (M = Mo, W) structural motif and was formed in a reaction between sodium molybdate and tert-butyldimethylsilyl chloride in the presence of 2,2-bipyridine. In the crystal, neighbouring molecules are linked by C-HÁ Á ÁO Mo hydrogen bonds, forming chains propagating along the a-axis direction.

Chemical context
Bulky siloxy ligands are of interest as they can stabilize transition metal complexes with low coordination numbers, providing attractive structures and chemistry (Eppley et al., 1991;Neithamer et al., 1989;Huang & DeKock, 1993). The structural and reactivity studies of cis-M VI O 2 and cis-M VI OS complexes (M = Mo, W), including siloxy derivatives, are essential for understanding the activity of specific enzymes (Thapper et al., 1999;Miao et al., 2000). Both Mo VI O 2 and Mo siloxy derivatives have attracted attention as precursors, or as real catalytic species, in various catalytic applications (Heppekausen et al., 2012;Arzoumanian et al., 2008;Coelho et al., 2011;Bruno et al., 2006). Herein, we report on the crystal structure and synthesis of the title complex, ( t BuSiMe 2 O) 2-MoO 2 (bipy) (I).

Supramolecular features
In the crystal, neighbouring molecules are linked by C-HÁ Á ÁO Mo hydrogen bonds, forming chains along the a-axis direction ( Fig. 3 and Table 2). Similar Mo OÁ Á ÁH Ar interactions can be found in the (Ph 3 SiO) 2 MoO 2 (L) complexes mentioned above. Other non-valent intermolecular short contacts present in the structure of (I) are less significant. The molecular structure of the title complex (I). Displacement ellipsoids are drawn at the 50% probability level and, for clarity, H atoms have been omitted. Table 1 Selected geometric parameters (Å , ).

Figure 3
A view along the b axis of the crystal packing of the title complex (I).
Only the H atoms involved in hydrogen bonding (dashed lines; see Table 2) are included.

Synthesis and crystallization
The title Mo VI complex was synthesized by a modification of previously reported methods for an analogous complex (Huang & DeKock, 1993;Bruno et al., 2006). Details of the synthesis are illustrated in Fig. 1. Under an argon atmosphere, a stirred mixture of anhydrous sodium molybdate (0.41 g, 2.0 mmol) and 2,2-bipyridine (0.310 g, 2.0 mmol) in CH 3 CN (15 ml) was cooled to 273 K and a solution of tert-butyldimethylsilyl chloride (0.603 g, 4.00 mmol) in CH 3 CN (10 ml) was slowly added. The obtained suspension was allowed to warm slowly to room temperature and was stirred overnight. All volatiles were removed under reduced pressure. The residue was extracted with THF (50 ml) and filtered. The filtrates were concentrated and cooled to 248 K to afford colourless crystals of (I) (yield 0.850 g, 1.55 mmol, 78%

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 3. All H atoms were found from difference-Fourier maps but positioned geometrically and refined as riding: C-H = 0.95-0.98 Å with U iso (H) = 1.5U eq (Cmethyl) and 1.2U eq (C) for other H atoms. A rotating group model was applied for the methyl groups. Reflections 001, 010 and 011 were omitted from the refinement as they were affected by the beam stop.

Special details
Experimental. All synthetic manipulations were conducted under an argon atmosphere, using a dry box and standard Schlenk and vacuum line techniques. THF was predried over NaOH and distilled from potassium/benzophenoneketyl under argon. CH3CN was distilled from calcium hydride under argon. CD2Cl2 was carefully distilled from LiAlH4 and stored over 4?Å molecular sieves. The Mo complex was synthesized by a modification of previously reported methods for an analogous complex (Huang & DeKock, 1993;Bruno et al., 2006). Elemental (C, H, N) analysis was performed with a PerkinElmer 2400 Series II elemental CHNS/O analyzer. NMR spectra were recorded with a Bruker AVANCE 400 spectrometer at 298K. 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 > 2sigma(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.