Tetrabutylammonium bis[4,4′-dimethyl-2,2′-(3,7-dimethyl-1H-4,2,1-benzothiazasiline-1,1-diyl)dibenzenethiolato]vanadium(III) acetonitrile tetrasolvate

In the title compound, [N(C4H9)4][V(C23H21NS3Si)2]·4CH3CN, the VIII atom (site symmetry ) is coordinated by two N,S,S′-tridentate 4,4′-dimethyl-2,2′-(3,7-dimethyl-1H-4,2,1-benzothiazasiline-1,1-diyl)dibenzenethiolate ligands in a distorted trans-VN2S4 octahedral geometry. The complete cation is generated by crystallographic twofold symmetry, with the V atom lying on the rotation axis. The unusual ligand arose from nucleophilic attack on the coordinated nitrile by the thiolate precursor and reduction of nitrile to the imidate.


Experimental
Crystal data (C 16

Comment
Vanadium thiolate chemistry has been drawing much attention due to its biological relevance as well as its medical application (Rehder, 2008;Crans et al., 2004). For example, alternative nitrogenase is proposed to contain a [Fe 7 VS 9 ] cofactor, where V site likely binds to three sulfides, His442 and homocitrate (Eady, 2003). To elucidate the role of vanadium in the enzyme, it is essential to understand fundamental chemistry of vanadium, particularly in a S-rich ligation environment (Janas & Sobota, 2005). Thus, we have been exploring the reactions of vanadium ion with thiolato containing ligands (Ye et al., 2010;Tsai et al., 2007). At this work, the reaction of [VCl 3 THF 3 ] with H 3 L1 [H 3 L1 = HSi(5-Me-C 6 H 4 -2-SH) 3 ] and three equivalents of nBu-Li in CH 3 CN generated a deep purple solution. The addition of the cation, [N(C 4 H 9 ) 4 ]Br, to the reaction mixture yielded a crystalline solid of the title compound (I).
The molecular structure of the anion in (I) is shown in Fig 1. It consists a V III ion coordinated to two L2 ligands [L2 = Si{CH 3 (5-Me-C 6 H 4 -2-S)CN} (5-Me-C 6 H 4 -2-S) 2 ]. L2 ligand has a S2N donor set that contains two benzenethiolates and one thioimidate group. The formation of a thioimidate group in L2 ligand upon the reaction is likely a consequence of nucleophilic attack on the coordinated nitrile by thiolate and reduction of nitrile to the imidate. Similar chemistry was demonstrated in a rhenium complex with thiolate ligands (Block et al ., 1989). The V III ion lies on the inversion centre and forms a normal octahedral geometry with a S4N2 ligation environment, four S atoms from thiolate groups and two N atoms from thioimidate groups. Two N donor atoms of thioimidate groups are in trans positions.
The bond lengths and bond angles in compound (I) are shown in Table 1. The V-S distances of 2.416 (1) Å and 2.462 (1) Å are close to those of reported six-coordinate V III thiolate complexes (Ye et al., 2010;Zhu et al., 2002;Zhu et al., 1997).
The packing diagrams of compound (I) are shown in Fig 2. There is no interaction observed between molecules. The methyl groups on the phenyl rings of the ligands probably prevent the occurrence of inter-molecular π-π stacking interactions.
The shortest distance between centers of two phenyl rings is 5.181 (2) Å.

Figures
Crystal data (C 16

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.