Crystal structure of bromidopentakis(tetrahydrofuran-κO)magnesium bis[1,2-bis(diphenylphosphanyl)benzene-κ2 P,P′]cobaltate(−1) tetrahydrofuran disolvate

The reduction of CoBr2 by the Grignard reagent p-tolylmagnesium bromide in the presence of 1,2-bis(diphenylphosphanyl)benzene (dbpz) resulted in the d 10, formally Co−1 anion, [Co(dpbz)2]−. The crystal structure of the [MgBr(THF)5]+ (THF is tetrahydrofuran) salt showed the anion to be pseudotetrahedral and packed in alternating layers of anions and cations.


Chemical context
Phosphane ligands, especially aryl ones, have been used for many years to support transition metals in low oxidation states (Chatt & Watson, 1961;Chatt & Rowe, 1961). Bidentate phosphanes, or bisphosphanes, such as 1,2-bis(diphenylphosphanyl)benzene (dbpz), have the added benefit of the chelate effect (Cotton et al., 1999). In an attempt to synthesize a cobalt(I) analog of the known iron(I) complex FeX(dpbz) 2 , X = Cl, Br, a species proposed to be an active catalyst in Negishi cross-coupling reactions (Adams et al., 2012), CoBr 2 was reacted with four equivalents of p-tolylMgBr in tetrahydrofuran (THF) at 298 K. The unexpected result was a cobalt complex in the formal À1 oxidation state, formulated as [MgBr(THF) 5 ][Co(dpbz) 2 ]Á2THF 1 (Fig. 1). Herein we examine the crystal structure of 1 and compare it with the free bisphosphane and related cobalt species.

Figure 1
Anisotropic displacement ellipsoid plot of 1 drawn at the 50% probability level with hydrogen atoms and solvent molecules omitted. Only the major component of the THF ligand disorder is shown. The reciprocal position of the two ions has been modified for clarity.
THF molecules of solvation are found in sheets normal to [100] that alternate with sheets of the anions (Fig. 2). Within each layer of anions there appear to be numerous potentialsystem interactions (Martinez & Iverson, 2012;McGaughey et al., 1998). Along [001] is an alternation between short intramolecular offset parallel stacking and longer intermolecular interactions with centroid-centroid distances of 3.533 (2) and 5.252 (2) Å , respectively (Fig. 3). On the opposite side of each molecule and also along the [001] direction is a second analogous set of potential -system interactions, but with longer centroid-centroid distances of 4.080 (2) and 5.786 (2) Å ; however, these rings are nearly coplanar (i.e. the open faces are not directed toward one another) and therefore they are unlikely to have any significant attractive intermolecular interactions. Upon further inspection, the onedimensional chains along [001] are linked to other parallel chains by phenyl rings that are oriented correctly for edge-toface C-HÁ Á Á attractive interactions (Fig. 4), thus providing a possible explanation for the two-dimensional packing motif of anions in the bc planes.

Database survey
The only other structure containing a four-coordinate cobalt(À1) anion with two aryl bisphosphanes is the potassium 18-crown-6 salt of [Co (

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 3. Three THF ligands and one co- Anisotropic displacement ellipsoid plot of 1 drawn at the 50% probability level of the edge-to-face -system contacts that link the chains aligned along [001] in the [010] direction as well, thus offering an explanation for the observed two-dimensional sheets of anions. Hydrogen atoms except for those on carbon atoms C51 and C52 (and their symmetry equivalents) were omitted. The symmetry-equivalent molecule was generated by a crystallographic inversion center with symmetry operator 1 À x, 2 À y, 1 À z.

Figure 3
Anisotropic displacement ellipsoid plot of 1 drawn at the 50% probability level showing the extended intra-and intermolecular -system interactions with hydrogen atoms omitted. The [001] direction (c axis) is to the right. (See Fig. 2 for view down [001].) Symmetry-equivalent molecules were generated by crystallographic twofold screw axes with symmetry operators x, 3 2 À y, À 1 2 + z and x, 3 2 À y, 1 2 + z.
crystallized THF solvent molecule were modeled as disordered over two sets of site each: O2/C65-C68, 0.650 (8) Analogous bond lengths and angles between the two positions of each disordered THF molecule were restrained to be similar. Anisotropic displacement parameters for proximal atoms were constrained to be equivalent. H atoms were refined using riding models: aromatic, C-H = 0.93 Å , and methylene, C-H = 0.97 Å , with U iso (H) = 1.2U eq (C).
The maximum residual peak of 0.64 e Å À3 and the deepest hole of À1.69 e Å À3 are found 0.84 and 0.83 Å from atoms H74A and Br1, respectively.