N-(2,4,6-Trimethylphenyl)formamide

The title compound, C10H13NO, was obtained as the unexpected, almost exclusive, product in the attempted synthesis of a manganese(I)–N-heterocyclic carbene (NHC) complex. The dihedral angle between the planes of the formamide moiety and the aryl ring is 68.06 (10)°. In the crystal, molecules are linked by N—H⋯O hydrogen bonds, forming infinite chains along the c axis.


Related literature
For background to formamide formation from NHCs, see: Denk et al. (2001). The rotation of the formamide entity out of the plane of the aryl ring and the hydrogen-bonding motif displayed by this structure are similar to those observed for the related compound N-(2,6-dimethyl)-formamide, see: Hanson et al. (2004); Omondi et al. (2005).  Table 1 Hydrogen-bond geometry (Å , ).  4,-formamide (N-mesityl-formamide) (1) was formed as an unexpected product in the attempted synthesis of a manganese(I)-N-heterocyclic carbene (NHC) complex. Instead of the target complex, the mesityl formamide was obtained almost exclusively. The ylidene molecule, formed by deprotonation of 1,3-bis(2,4,6-trimethyl-phenyl)-imidazolium chloride (IMesHCl) by a strong base, is prone to undergo side reactions. Thus the strong base, and the subsequent addition of Mn(CO) 5 Br, resulted in the formation of N,N'-bis-mesityl-N-vinyl-formamidine and after hydrolysis of this molecule the NC-N bond dissociated to form 1 and a mesityl-vinyl-amine fragment which was not isolated. Denk et al. (2001) have reported the hydrolysis of NHCs, with formamide formation via ring opening, resulting in an acyclic product.

Experimental
The molecular structure of the title compound (1) (Fig. 1) is similar to that of the related compound, N-(2,6-dimethylphenyl)-formamide, the structure of which has been reported at 173 K (Hanson, et al., 2004) and 293 K (Omondi, et al., 2005). Owing to the influence of the bulky methyl substituents in the 2 and 6 positions, the formamide moiety is rotated out of the plane of the aryl ring: in 1, the angle between the planes of the formamide moiety (C1, N1, C10, O1) and the aryl ring is 68.06 (10)°. This compares with 64.75 (12)° (173 K) and 66.45 (12)° (293 K) found for the 2,6-dimethyl analogue.
In the formamide moieties of both structures the O atom is trans to N-H thus allowing the molecules to be linked to form infinite chains by N-H···O hydrogen bonds. However the spatial arrangements within the chains differ. In the 2,6-dimethyl analogue (space group P2 1 2 1 2 1 ), the axis of each chain is parallel to the a unit cell axis and neighbouring molecules within a chain are related by the a-axial unit cell translation. Thus the aryl ring of each molecule is parallel to those of its neighbours within the chain and they are stacked one above the other but with a step-wise offset. In contrast, in 1, the axis of each chain is parallel to the c unit cell axis and neighbouring molecules within a chain are related by a c-glide plane. Thus neighbouring molecules in a chain are arranged on opposite sides of the chain axis and the aryl rings are not mutually parallel (Fig. 2).

Experimental
Mn(CO) 5 Br (3 mmol, 0.74 g) and Me 3 NO (2.8 mmol, 0.21 g) were stirred in thf resulting in a red solution. IMesHCl (3 mmol, 1.02 g) was deprotonated in thf by the addition of base (3 mmol) and the ylidene was added to the solution and stirred overnight. The thf solvent was removed and the products were separated on an aluminium oxide 90 (alox) column.

Refinement
The coordinates and individual U iso parameters for all H atoms were freely refined.   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 > 2σ(F 2 ) is used only for calculating Rfactors(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.