4,4,5,5-Tetramethyl-2-[1,3,6,8-tetrabromo-7-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)pyren-2-yl]-1,3,2-dioxaborolane

The complete molecule of the title compound, C28H28B2Br4O4, is generated by the application of a centre of inversion. In the molecule, the BO2 plane is perpendicular to that through the pyrene ring [dihedral angle = 86.27 (13)°]. In the crystal, molecules stack into columns along the b axis, the closest contact between these being of the type C—Br⋯π.

The complete molecule of the title compound, C 28 H 28 B 2 -Br 4 O 4 , is generated by the application of a centre of inversion. In the molecule, the BO 2 plane is perpendicular to that through the pyrene ring [dihedral angle = 86.27 (13) ]. In the crystal, molecules stack into columns along the b axis, the closest contact between these being of the type C-BrÁ Á Á.

Experimental
Cg1 is the centroid of the C3-C5/C8/C9/C14 benzene ring.  The chemistry of pyrene is strongly position-dependent. For example, in the bromination reaction of 2,7-di-t-butylpyrene, the bromide atoms were connected at the 4,5,9,10-positions of pyrene (Miura & Yamano, 1995). However, to our surprise, when the t-butyl group is changed to pinacol boronate, the bromination reaction resulted in bromination at the 1,3,6,8-positions as confirmed by the crystal structure described herein.
The molecules pack into columns along the b axis, Fig. 2. The most prominent contacts in the structure appear to be of the type C-Br···π, Table 1.

Experimental
The title compound was synthesized via a one-step bromination reaction. The precursor compound, 2,7-di-Bpinpyrene (pin = O 2 C 2 Me 4 ) was prepared using the method of Ir-catalyzed borylation (Coventry et al., 2005). To a stirred mixture of 1.36 g (3.0 mmol) of 2,7-di-Bpinpyrene and a small amount of Fe powder (ca 0.10 g) in 80 ml of CCl 4 was added dropwise a solution of 2.88 g (0.78 mL, 18 mmol) of bromine in 20 ml of CCl 4 at room temperature. After stirring for 5 h, the mixture was slowly poured into ice water. Then the organic layer was collected and washed with aqueous Na 2 S 2 O 3 and dried over MgSO 4 . After evaporation, the residue was crystallized from hexane, giving 1.80 g (78% yield) of gray powdered product. Crystals were grown by slow evaporation from its hexane/dichloromethane solution.

Refinement
Carbon-bound H-atoms were placed in calculated positions [C-H 0.93-0.96 Å, U iso (H) 1.2-1.5U eq (C)] and were included in the refinement in the riding model approximation.   Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.

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