3-( 4 , 4 , 5 , 5-Tetramethyl-1 , 3 , 2-dioxaborolan-2-yl ) aniline

In the course of our studies (Giles et al., 2003; Coghlan et al., 2005) into the potential catalytic utility of bifunctional compounds (Rowlands, 2001) containing both a nitrogenbased Lewis base and a boron-based Lewis acid, we turned to the title compound, (I), as a protected precursor for the synthesis of phenylguanidine-2-boronic acid derivatives, which we were interested in as bifunctional catalysts. Unfortunately, synthesis of such compounds proved unsuccessful, producing a complex mixture of products.

In the title compound, C 12 H 18 BNO 2 , the amino group is less pyramidal than in aniline, only one of its H atoms forming a strong hydrogen bond.

Comment
In the course of our studies (Giles et al., 2003;Coghlan et al., 2005) into the potential catalytic utility of bifunctional compounds (Rowlands, 2001) containing both a nitrogenbased Lewis base and a boron-based Lewis acid, we turned to the title compound, (I), as a protected precursor for the synthesis of phenylguanidine-2-boronic acid derivatives, which we were interested in as bifunctional catalysts. Unfortunately, synthesis of such compounds proved unsuccessful, producing a complex mixture of products.
Compound (I) was prepared by a modified version of the procedure reported by Vogels et al. (1999), who synthesized it en route to various platinum complexes and imines (Vogels et al., 2001;King et al., 2002).
The asymmetric unit contains one molecule. The B atom has planar-trigonal coordination; the coordination plane is inclined by 10.4 (2) to the benzene ring plane. The borolane ring adopts a twist conformation, the C7 and C8 atoms deviating from the BO 2 plane by 0.20 (2) and 0.27 (2) Å in opposite directions, with two equatorial (C9 and C11) and two axial (C10 and C12) methyl substituents. The amino group forms one strong intermolecular hydrogen bond ( Table 2). The remaining amino hydrogen atom, H2N, points towards the p orbital of the benzene C4 atom of another molecule. The H2NÁ Á ÁC4 ii distance [2.61 (2) Å , corrected for the idealized N-H bond length of 1.01 Å ; symmetry code: (ii) 1 À x, 1 2 + y, 1 2 À z], which is considerably shorter than the sum of van der Waals radii of 2.88 Å (Rowland & Taylor, 1996) and the N-HÁ Á ÁC angle of 167 (2) suggest that this contact is a weak hydrogen bond. The N atom in (I) has a less pyramidal geometry than in unsubstituted aniline. The dihedral angle between the benzene ring and the NH 2 group (so-called 'inversion angle'), which equals 37-38 in both solid (Fukuyo et al., 1982) and gaseous (Lister et al., 1974) aniline, is reduced to 16 (2) in (I). The C1-N bond in (I) [1.3790 (18) Å ] is shorter than in aniline [solid: 1.392 (6) Å ; gas: 1.402 (2) Å ]. Both differences indicate that the boryl substituent enhances the interaction of the electron lone pair of N with the aromatic ring and hence sp 2 hybridization of the N atom. It is noteworthy that, in the two complexes of Pd and Pt where molecule (I) acts as an N-ligand (Vogels et al., 1999), the C-N bond is lengthened to 1.438 (4) and 1.45 (1) Å , respectively, as the -conjugation is disrupted, the lone pair being donated to the metal atom instead.
In (I), the N atom deviates by 0.081 (2) Å from the benzene ring plane, but its H atoms are situated on the other side of this plane, 0.04 (2) Å from it. A similar, but stronger, distortion is shown by the aniline molecule in its crystal structure, where the amino group both donates and accepts a hydrogen bond.
Amino H atoms were refined in an isotropic approximation, giving N-H distances of 0.92 (2) and 0.85 (2) Å . Phenyl H atoms were treated as riding in idealized positions with C-H bond lengths of 0.95 Å and U iso (H) = 1.2U eq (C). Methyl groups were refined as rigid bodies rotating around the C-C bonds, with C-H bond lengths of 0.98 Å and a common refined U iso (H) for all three H atoms of each methyl group.

sup-2
Acta Cryst. (2006). E62, o466-o468 Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes. 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.