Bis(μ2-η2:η2-2,4,6-trimethylbenzonitrile)bis[(N-isopropyl-3,5-dimethylanilido)molybdenum(III)](Mo—Mo)

The title compound, [Mo2(C11H16N)4(C10H11N)2], is a dinuclear molybdenum complex with a formal metal–metal bond [Mo⋯Mo separation = 2.5946 (8) Å], four anilide-type ligands and two bridging mesityl nitrile groups. There are two inversion symmetric molecules in the unit cell (an inversion center is localized at the mid-point of the Mo—Mo bond), each with approximate non-crystallographic C 2h symmetry. The molecules contain disordered isopropyl and 3,5-C6H3Me2 groups on different anilido ligands; the major component having an occupancy of 0.683 (7). The complex was obtained in low yield as the product from the reaction between the bridging pyrazine adduct of molybdenum tris-anilide ([μ2-(C4H4N2){Mo(C11H16N)3}2]) and mesityl nitrile with a loss of one anilido ligand.

The title compound, [Mo 2 (C 11 H 16 N) 4 (C 10 H 11 N) 2 ], is a dinuclear molybdenum complex with a formal metal-metal bond [MoÁ Á ÁMo separation = 2.5946 (8) Å ], four anilide-type ligands and two bridging mesityl nitrile groups. There are two inversion symmetric molecules in the unit cell (an inversion center is localized at the mid-point of the Mo-Mo bond), each with approximate non-crystallographic C 2h symmetry. The molecules contain disordered isopropyl and 3,5-C 6 H 3 Me 2 groups on different anilido ligands; the major component having an occupancy of 0.683 (7). The complex was obtained in low yield as the product from the reaction between the bridging pyrazine adduct of molybdenum trisanilide ([ 2 -(C 4 H 4 N 2 ){Mo(C 11 H 16 N) 3 } 2 ]) and mesityl nitrile with a loss of one anilido ligand.

Related literature
For the synthesis of molybdenum(III) tris-anilide nitrides and structures of similar complexes, see: Johnson et al. (1997);Tsai et al. (1999). For reactions of three-coordinate Mo(III) complexes with dinitrogen, organic nitriles and isocyanides, including a base-catalysed dinitrogen cleavage, see: Tsai et al.

S1. Comment
For more than fifteen years, low-coordinate molybdenum(III) tris-anilide complexes, [Mo(N{R 1 }Ar) 3 ] and [HMo(η 2 -Me 2 CNAr)(N{R 2 }Ar) 2 ] (where R 1 = t-Bu; R 2 = i-Pr or CH(CD 3 ) 2 ; Ar = 3,5-C 6 H 3 Me 2 ), have attracted the attention of inorganic chemists and crystallographers due to their unusual coordination geometries and their remarkable ability to activate small molecules, including triply-bonded dinitrogen (Tsai et al., 1999;Curley et al., 2008;Germain et al., 2009 ). Furthermore, the rate of N 2 uptake increases in the presence of bases such as 1-methyl-imidazole, 2,6-dimethylpyrazine or pyridine (Tsai et al., 2003). Thus, the study of molybdenum tris-anilide adducts with additional ligands will help in understanding the N 2 uptake, a critical step in the overall N 2 cleavage mechanism. Additionally, molecules with element-element triple bonds, such as nitriles, can be viewed as dinitrogen surrogates, and provide structural information on molybdenum interacting with multiply bonded substrates in cases when N 2 binding affinity is too low, and N 2 complexes cannot be isolated and crystallized.

S2. Experimental
All synthetic operations were performed in an air-free MBraun drybox under an argon atmosphere. Me 2 CNAr)(N{i-Pr}Ar) 2 ] (0.03 g, 0.05 mmol) in dry diethyl ether (3 ml). The resulting dark blue mixture was stirred for 20 min, followed by solvent evaporation under reduced pressure. In the second step the crude product was redissolved in diethyl ether and 0.008 g (0.06 mmol) of mesityl nitrile was added. The mixture was stirred for 30 min, then the solvent was evaporated under reduced pressure. The product was redissolved twice in dry n-hexane to remove the traces of the THF, then the solvent was again evaporated and the solid was dissolved in dry n-pentane (2 ml) and left for crystallization at 238 K (-35 °C) inside the glove box. Dark blue crystals suitable for X-ray analysis formed after one week (Yield (crude): 20%). 1 H NMR (500 MHz, 298 K, C 6 D 6 ): δ -8.94, -1. 79, 0.62, 3.06, 8.84, 9.02, 15.96 ppm.

S3. Refinement
Methyl H atoms were placed in geometrically idealized positions allowing the initial torsion angle to be determined by a

Bis(µ 2 -η 2 :η 2 -2,4,6-trimethylbenzonitrile)bis[(N-isopropyl-3,5-dimethylanilido)molybdenum(III)](Mo-Mo)
Crystal data   (2) Special details Geometry. All s.u.'s (except the s.u. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell s.u.'s are taken into account individually in the estimation of s.u.'s in distances, angles and torsion angles; correlations between s.u.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell s.u.'s is used for estimating s.u.'s involving l.s. planes. Refinement. Methyl H atoms were placed in geometrically idealized positions allowing the initial torsion angle to be determined by a difference Fourier analysis [C-H = 0.96 Å and U iso (H) = 1.5U eq (C)]. Other H atoms were placed in geometrically idealized positions and included as riding atoms [C-H = 0.93-0.98 Å and U iso (H) = 1.2U eq (C)]. Disordered i-Pr and disordered aryl group reside next to each other in the unit cell which causes a correlation in the model of the disorder, the ratios between the two components were refined freely. The geometries of the two PARTs of the disordered groups were kept similar using the SAME (it was applied for all atoms in the disordered i-Pr and disordered aryl groups) and SADI (it was used to restrain N2-C19A, N2-C19B and N3-C22A, N3-C22B bond distances) restraints of the program Shelxtl (Sheldrick, 2008) which allowed the 1,2-and 1,3-distances of corresponding atoms to be equal within determined standard deviations (0.02 Å for 1,2-and 0.04 for 1,3-distances); rigid bond restraints for anisotropic displacement parameters of atoms of the disordered i-Pr and disordered aryl group were applied using the DELU command (standart deviation is 0.01 Å). In addition, anisotropic displacement parameters of the pairs of overlapping disordered atoms of the major and minor components of the disorder were made equal using the EADP constraint.

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