A molybdenum tris(dithiolene) complex coordinates to three bound cobalt centers in three different ways

A molybdenum tris(dithiolene) complex acts as a ligand towards three Co(CO)2 units.


Chemical context
Sulfur removal from crude petroleum is performed on a large industrial scale through a process called hydrodesulfurization. This involves use of hydrogen gas (the sulfur is removed as H 2 S) and addition of a catalyst, typically cobalt-doped MoS 2 (Hinnemann et al., 2008). MoS 2 is not a molecular compound but rather possesses an extended structure, consisting of closepacked sulfur layers between which molybdenum is sandwiched (Dickinson & Pauling, 1923). The coordination geometry around molybdenum is trigonal prismatic. Several attempts to model MoS 2 using molecular compounds have been made, often using dithiolene (S 2 C 2 R 2 ) ligands, where some examples also contain the hydrodesulfurization-relevant addition of cobalt. Complexes containing molybdenum, cobalt, and one or two (but not three) dithiolenes are known. A molybdenum bis(dithiolene) that coordinates to two cobalt centers has been characterized crystallographically (Nihei et al., 1999;Murata et al., 2006). The study reports [Mo(bdt) 2 (-CO) 2 (CpCo) 2 ], where bdt = o-C 6 H 4 S 2 and Cp = cyclo-C 5 H 5 . The methylated analog [Mo(bdt) 2 (CO) 2 (Cp*Co) 2 ], where Cp* = cyclo-C 5 Me 5 was also structurally characterized (Muratsugu et al., 2011). An analogous [Mo(ddds) 2 (CO) 2 (CpCo) 2 ] was reported by a different group, where ddds is the unusual di-thiolene 1,2-dicarba-closo-dodecaborane-1,2-disulfide (Chen et al., 2007). The above contribution also reported a molybdenum mono(dithiolene) complex coordinated to a cobalt fragment, namely [Mo(ddds)(CO) 2 (py) 2 (Cp*Co)], where py = pyridine. Coordinating to cobalt a molybdenum tris(dithioene), that is a compound where three dithiolenes are bound to molybdenum, would be interesting, because molybdenum tris(dithiolene)s mimic MoS 2 particularly well. Similar to MoS 2 , they contain molybdenum coordinated to six sulfur atoms, and, also, depending on the oxidation state of the compound, the environment of molybdenum can sometimes be trigonal prismatic (Beswick et al., 2004). However, we could not find any structurally characterized example for how a molybdenum tris(dithiolene) complex can act as ligand for cobalt. Such an example is provided here. In 2007, the mixed dithiolene complex Mo(tfd) 2 (bdt) [tfd = S 2 C 2 (CF 3 ) 2 ], an unsymmetrical tris(dithiolene), was reported for the first time (Harrison et al., 2007). Later, this complex, which contains two different dithiolenes, was used to create structural models for the active sites of MoS 2 hydrodesulfurization catalysts, albeit cobalt-free ones (Nguyen et al., 2010). In this current work, we have successfully linked three cobalt centers to one Mo(tfd) 2 (bdt) molecule. Surprisingly, each of the three cobaltcontaining units [each one is a Co(CO) 2 fragment] is bound to the molybdenum tris(dithiolene) center in a different way.

Supramolecular features
Molecules of Mo(tfd) 2 (bdt)(Co(CO) 2 ) 3 pack, without any solvent in the crystal, via contacting van der Waals surfaces. The packing pattern is shown in Fig. 2. Hydrogen atom H17A forms close intermolecular contacts to an oxygen atom from a neighboring carbonyl and to a fluorine atom of the major disorder component (F11), as well as to a fluorine atom of the minor disorder component (F10A). Details can be found in Table 1.

Database survey
The Cambridge Crystallographic Database (version 5.40, including updates up to May 2019; Groom et al., 2016) was searched. The search was performed as a substructure search containing the most general dithiolene S-C-C-S substructure (with any kind of bond allowed in the chain), plus a molybdenum and a cobalt atom. Since no specific requirement was imposed with regard to whether or in which way cobalt or molybdenum are bonded to the S-C-C-S structure, hits that do not contain a molybdenum dithiolene complex coordinated to cobalt where manually removed as follows. Seven hits were retrieved: EYUHIQ, JOQWIV, JOQWIV01, SEVMIQ, SEVMOW, TASDAT, OQAMEZ. Out of these, TASDAT and OQAMEZ are not relevant here, since they do not contain a molybdenum dithiolene unit that is directly bonded to cobalt. They contain, respectively, a cobalt-based counter-cation for an anionic molybdenum complex and a nickel bis(dithiolene) anion as a counter-anion for a molybdenum/cobalt sulfido cluster. The structures EYUHIQ, JOQWIV, JOQWIV01, SEVMIQ and SEVMOW are relevant, since they contain at least one molybdenum dithiolene unit that is directly bonded to cobalt. These structures are all discussed above in the Chemical context (Nihei et al., 1999;Murata et al., 2006;Muratsugu et al., 2011;Chen et al., 2007).

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. H atoms were placed in calculated positions and included in a riding-motion approximation with U iso (H) = 1.2U eq (C). The F atoms of the -CF 3 groups containing C7 and C8 were refined as disordered over two sets of sites with ratios of refined occupancies of 0.703 (7):0.297 (7) and 0.72 (2)   software used to prepare material for publication: SHELXTL (Sheldrick, 2008).

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq Occ. (