Crystal structure of bis(1-mesityl-1H-imidazole-κN
 3)diphenylboron trifluoromethanesulfonate

In this manuscript, we report the the crystal structure of diphenylbis(mesitylimidazole)borane trifluoromethanesulfonate. Weak interactions, such as π–π stacking are present in the structure.

The solid-state structure of bis(1-mesityl-1H-imidazole-N 3 )diphenylboron trifluoromethanesulfonate, C 36 H 38 BN 4 + ÁCF 3 SO 3 À or (Ph 2 B(MesIm) 2 OTf), is reported. Bis(1-mesityl-1H-imidazole-N 3 )diphenylboron (Ph 2 B(MesIm) 2 + ) is a bulky ligand that crystallizes in the orthorhombic space group Pbcn. The asymmetric unit contains one Ph 2 B(MesIm) 2 + cationic ligand and one trifluoromethanesulfonate anion that balances the positive charge of the ligand. The tetrahedral geometry around the boron center is distorted as a result of the steric bulk of the phenyl groups. Weak interactions, such asstacking are present in the crystal structure.

Chemical context
Ph 2 B(MesIm) 2 + (Fig. 1) can undergo C-H activation on the imidazole functionalities, generating a bi(carbene)borate ligand, which can coordinate to a metal center with two carbenes. The ligand is bulky and has strong -donor character. For this reason, it can be used to stabilize a metal center. Similar bulky ligands, such as tris(mesitylimidazole)phenylborane, PhB(MesIm) 3 (Fig. 2) have been used to synthesize    iron nitride complexes (Smith & Subedi, 2012), which have shown promising applications in catalysis (Scepaniak et al., 2009) and in the production of ammonia both in biological and in industrial processes (Smith & Subedi, 2012). The threefold symmetry and the bulk of [PhB(MesIm) 3 ] 2+ ligand are key to stabilizing iron-nitrogen multiple bonds and isolate the terminal iron nitride complexes (Smith & Subedi, 2012).
In this paper, we discuss the synthesis and crystal structure of Ph 2 B(MesIm) 2 OTf, which can potentially be used to synthesize low-coordinate metal complexes for small-molecule activation and catalysis. The synthesis of Ph 2 B(MesIm) 2 OTf started from the reaction of 1 eq. of Ph 2 BCl with 2 eq. of 1-mesityl-1H-imidazole. The product was further reacted with 1 eq. of trimethylsilyl trifluoromethanesulfonate (TMSOTf) to yield the title compound.

Structural commentary
The title compound crystallizes in the orthorhombic space group Pbcn. The asymmetric unit consists of one Ph 2 B(MesIm) 2 + ligand and one triflate anion that balances the total positive charge of Ph 2 B(MesIm) 2 + (Fig. 3). The boron atom has tetrahedral geometry. As a result of the steric repulsion of the phenyl groups, the angle between the boron and the two phenyl groups (C1-B1-C7) is 116.7 (3) and larger than the typical tetrahedral angle (109 ), whereas the angle between the imidazole moieties and the boron center (N1-B1-N3) is smaller at 105.8 (3) . The remaining two angles are 107.4 (3) and 109.3 (3) . The bulky mesityl groups point away from each other, creating a pocket in which the triflate molecule is located (Fig. 4). The dihedral angles between the imidazole and mesityl mean planes are 63.1 (2) for N1/N2/C13-C15 and C16-C21, and 67.85 (17) for N3/N4/ C25-C27 and C28-C33. The dihedral angle between the mean planes defined by the phenyl rings on the boron atom (C1-C6 and C7-C12) is 58.28 (19) .

Supramolecular features
Although no classical hydrogen bonds were found in the structure, weak intermolecular interactions between the triflate anion and the protons on the imidazole groups are present (Table 1). The triflate anion also interacts weakly with one of the imidazole rings (N3/N4/C25-C27) through one Molecular structure of Ph 2 B(MesIm) 2 OTf with atom labels. Displacement ellipsoids are shown at the 50% probability level. Hydrogen atoms are omitted for clarity.

Database survey
A survey of the Cambridge Structural Database (CSD Version 5.41, 2020.0 CSD Release; Groom et al., 2016) was undertaken for structures related to Ph 2 B(MesIm) 2 OTf. One example is the structure of (3-butylimidazole)triphenylboron [Ph 3 B(3-ButIm); refcode OFAFIK; Stenzel et al., 2002), a neutral molecule with an additional phenyl ring instead of an imidazole group (three phenyl rings) and with an alkyl chain instead of the mesityl moiety. Ph 3 B(3-ButIm) crystallizes in the space group P1, and has a very different crystal packing from Ph 2 B(MesIm) 2 OTf. However, the two molecules have a similar geometry around the boron atom, with the tetrahedral angles around the boron atom impacted by the bulky phenyl groups. The C-B-C angles involving phenyl moieties range between 108 and 114 , while the angles between imidazole and phenyl moieties are accordingly smaller (C-B-N angles of about 104-109 ). Ph 3 B(3-ButIm) shows C-HÁ Á Á interactions from the imidazole hydrogen to the phenyl ring. These interactions are not present in Ph 2 B(MesIm) 2 OTf, where the imidazole interacts only weakly with the triflate oxygen atoms. Another similar example is phenylimidazole triphenylborane [Ph 3 B(PhIm); ACIPEH; Kiviniemi et al., 2001]. Ph 3 B(PhIm) is a neutral molecule with three phenyl rings on the boron atom and one phenyl ring on the imidazole functionality. Ph 3 B(PhIm) crystallizes in the monoclinic space group C2/c and again has a different crystal packing from Ph 2 B(MesIm) 2 OTf, characterized by chains that are stabilized by weakstacking interactions between the phenyl groups on the imidazole.
The CSD search also revealed one diphenylbis(adamantylimidazole)borane chloride salt, Ph 2 B(AdIm) 2 Cl (CAX-MAS; Xiong et al., 2017). In this compound, the imidazole functionalities are bound to adamantyl groups and the tetrahedral boron atom is bound to two toluene and two imidazole groups. The protons on the imidazole groups interact via hydrogen bonds with the chloride anion, which is located in a pocket between the two bulky adamantyl groups, similar to that observed for the triflate anion in Ph 2 B(MesIm) 2 OTf. The crystal packing shows weak intermolecular C-HÁ Á Á interactions between the methyl group on the toluene functionality and the aromatic ring on the neighboring toluene. Despite some similarities with the title compound, Ph 2 B(AdIm) 2 Cl crystallizes in the space group C2/c and has a different crystal packing structure.
Few boron dimers with bridging imidazole groups were found in the CSD. One example is [Ph 2 B(3-BuIm)] 2 (FULPAE; Arrowsmith et al., 2009), which crystallizes in the space group C2/c. In this boron dimer, the two tetrahedral boron centers are bridged by two 3-butylimidazole groups and each boron atom is bound to two phenyl groups. A second example of a boron dimer is [Ph 2 B(3-BuIm)] 2 (PONLOW; Su et al., 2019), space group P2 1 /n. In this compound one boron atom is bound to two phenyl groups and the second boron atom is bound to one chloride and one hydrogen atom. The boron atoms are bridged by two diphenylmesitylimidazole groups.

Synthesis and crystallization
The synthesis of Ph 2 B(MesIm) 2 OTf is shown in Fig. 6. A 25 mL flask was charged with Ph 2 BCl (914 mg, 4.5 mmol), 1-mesityl-1H-imidazole (1.7 g, 9 mmol) and toluene (10 mL). The mixture was stirred at room temperature for 2 h. During the course of the reaction, a white precipitate formed. Then TMS OTf (1.0 g, 4.5 mmol) was added as a brown liquid. The mixture was further stirred at 383 K overnight. The toluene was evaporated under vacuum, affording a white residue that was washed with Et 2 O (3 Â 10 mL) to obtain Ph 2 B(MesIm) 2 OTf as a white powder (2.6 g, 79% yield). Single crystals suitable for X-ray diffraction were grown by vapor diffusion using diethyl ether and DCM. 1  Reaction for the synthesis of Ph 2 B(MesIm) 2 OTf. Ph 2 BCl (1 equiv.), 1mesityl-1H-imidazole (2 equiv.) were stirred in toluene at room temperature for 2 h. TMS OTf (1 equiv.) was then added and the mixture was further stirred at 383 K overnight.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. The hydrogen atoms were placed in ideal positions and refined as riding atoms with relative isotropic displacement parameters [U iso (H) = 1.2 or 1.5 Â U eq (parent atom)].   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. A colorless crystal (plate, approximate dimensions 0.20 × 0.10 × 0.05 mm 3 ) was placed onto the tip of a MiTeGen pin and mounted on a Bruker Venture D8 diffractometer equipped with a Photon II detector at 100.0 K. The data collection was carried out using Mo Kα radiation (λ = 0.71073 Å, graphite monochromator) with a frame time of 0.5 seconds and a detector distance of 50 mm. Complete data to a resolution of 0.77 Å with a redundancy of 4 were collected. The frames were integrated with the Bruker software package SAINT using a narrow-frame algorithm (Bruker, 2016) to a resolution of 0.77 Å. The space group Pbcn was determined based on intensity statistics and systematic absences. The structure was solved using SHELXT (Sheldrick, 2015) and refined using full-matrix least-squares on F 2 with the OLEX 2 suite (Dolomanov et al., 2009). An intrinsic phasing solution was calculated, which provided most non-hydrogen atoms from the E-map. Fullmatrix least squares / difference Fourier cycles were performed, which located the remaining non-hydrogen atoms. All non-hydrogen atoms were refined with anisotropic displacement parameters.