Synthesis and crystallographic characterization of a mononuclear cobalt(III) complex possessing both thiolate and thioether donors: reactivity of an thiolate-bridged pentanuclear Co2Ag3 complex with iodomethane

A new mononuclear cobalt(III) complex that has two thiolate and one thioether donor atoms is reported.

In the course of our continuing study of the alkylation reaction of metal complexes with aminothiolate ligands (Okamoto et al., 1999;Chikamoto et al., 2005Chikamoto et al., , 2007Yoshinari & Konno, 2008, 2009), we herein report that an S-bridged Ag I 3 Co III 2 pentanuclear complex, {Ag 3 [Co(L)] 2 } 3+ [L 3-= N(CH 2 NHCH 2 CH 2 S À ) 3 ] (Tokuda et al., 2000), in which two tris(thiolate)-type octahedrally shaped Co III moieties with an aet derivative ligand, [Co(L)], are linearly linked by three Ag I ions, reacts with iodomethane to give a mono(thiolate)bis(thioether)-type complex, [Co(LMe 2 )] 2+ [LMe 2 À = N(CH 2 NHCH 2 CH 2 S À )(CH 2 NHCH 2 CH 2 SCH 3 ) 2 ]. It is noteworthy that the complex was crystallized as a hexafluoridophosphate salt, [Co(LMe 2 )](PF 6 ) 2 , and its molecular structure was fully determined by single-crystal X-ray diffraction analysis. As far as we know, this is the first crystallographic characterization of a cobalt(III) complex that has two thioether and one thiolate donor groups. In addition, this is a unique example of a direct conversion of a thiolate-bridged multinuclear complex to a mononuclear thioether complex by alkylation reaction. Treatment of the thiolate-bridged pentanuclear complex {Ag 3 [Co(L)] 2 } 3+ with excess iodomethane in water gave a greenish-brown suspension. After removing the insoluble solid by filtration, the purple-brown filtrate was purified by a cation-exchange column (SP-Sephadex C-25). The product was isolated as purple-brown crystals by adding a hexafluoridophosphate anion. The geometrical parameters and stereoisomerism of the title compound based on the X-ray analysis, together with the spectroscopic data, are described in this paper.

Structural commentary
X-ray structural analysis revealed that there are two crystallographically independent yet essentially the same complex cations, [Co(LMe 2 )] 2+ , and four PF 6 À anions in the asymmetric unit (Fig. 1). The number of PF 6 À anions indicates that each complex cation is divalent. Each complex cation consists of a hexadentate-N,N 0 ,N 00 ,S,S 0 ,S 00 -binding LMe 2 À ligand that coordinates to a Co III atom in a slightly distorted octahedral geometry. This result clearly indicates that two of three thiolate groups in the [Co(L)] moiety were methylated to form [Co(LMe 2 )] 2+  Each Co III ion is surrounded by three S and three N atoms in a fac-(S) geometry, like the parent [Co(L)] units. Considering the absolute configurations of the cobalt(III) atom (Á and Ã) and the two asymmetric sulfur atoms (R and S), four pairs of diastereomers, Á SS /Ã RR , Á SR /Ã RS , Á RS /Ã SR and Á RR / Ã SS , are possible for [Co(LMe 2 )] 2+ . However, the asymmetric unit of this crystal contains two Ã RR isomers. As indicated by the space group C2/c, the title crystal is a racemic compound consisting of a pair of enantiomers, Ã RR and Á SS . This result is consistent with the observation that the 13 C{ 1 H} NMR spectrum of the title compound in DMSO-d 6 exhibits a total of 10 sharp singlet signals, assignable to the C 1 symmetrical Ã RR and Á SS isomers of [Co(LMe 2 )] 2+ (Fig. 2). For both complex cations [Co(LMe 2 )] 2+ in the crystal, two of three N,S-chelate rings have a gauche form with the lel ( for Á and for Ã) conformation, while one has a gauche form with the ob ( for Ã and for Á) conformation.
In summary, we report here the first example of a crystallographically characterized mono(thiolate)bis(thioether)-type mononuclear cobalt(III) complex, [Co(LMe 2 )] 2+ . This complex was obtained by the unprecedented direct conversion of a thiolate-bridged Ag I 3 Co III 2 pentanuclear complex by alkylation reaction using iodomethane. The selective formation of the Ã RR and Á SS isomers of [Co(LMe 2 )] 2+ observed in the crystal structure is consistent with the result of 13 C{ 1 H} NMR. The findings reported herein will provide insight into the synthesis and structures of coordination compounds containing both thiolate and thioether donor groups.

Supramolecular features
In the crystal, the complex cations and the PF 6 À anions are connected through many weak N-HÁ Á ÁF, C-HÁ Á ÁF and C-HÁ Á ÁS hydrogen bonds (Table 1), forming a three-dimensional structure.

Figure 2
13 C{H} NMR spectrum of the title compound in DMSO-d 6 .

Refinement details
Crystal data, data collection and structure refinement details are summarized in Table 2. H atoms bound to C atoms were placed at calculated positions [C-H = 0.99 Å (CH 2 ) or 0.98 Å (CH 3 )] and refined as riding with U iso (H) = 1.2U eq (C) for CH 2 and U iso (H) = 1.5U eq (C) for CH 3 . All H atoms bound to N atoms were refined with bond-length restraints [N-H = 0.90 (2) Å ] and with U iso (H) = 1.2U eq (N). Two F atoms in one PF 6 anion are disordered over two positions (F25A/F25B and F26A/F26B) with refined occupancies of 0.61 (4) and 0.39 (4). Two F atoms in another PF 6 anion are also disordered over two positions (F20A, F21A, F22A, F23A) with site occupancies of 0.5. Reflections (11 7 24) and (24 2 3) were omitted omitted owing to poor agreement between measured and calculated intensities.

{2-[(Bis{[2-(methylsulfanyl)ethyl]aminomethyl}aminomethyl)amino]ethanethiolato}cobalt(III) bis(hexafluoridophosphate)
Crystal data 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.
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )