(E)-3-(1-Naphthyl­amino)­methyl­ene-(+)-camphor

Jesús Pastrán; Emilio Ineichen; Giuseppe Agrifoglio; Anthony Linden; Romano Dorta

doi:10.1107/S1600536810052487

. 2010 Dec 18;67(Pt 1):o188–o189. doi: 10.1107/S1600536810052487

(E)-3-(1-Naphthylamino)methylene-(+)-camphor

Jesús Pastrán ^a, Emilio Ineichen ^a, Giuseppe Agrifoglio ^a, Anthony Linden ^b,^*, Romano Dorta ^a,^*

PMCID: PMC3050145 PMID: 21522692

Abstract

In the crystal structure of the title ketoamine {systematic name: (E)-1,7,7-trimethyl-3-[(1-naphthylamino)methylidene]bicyclo[2.2.1]heptan-2-one}, C₂₁H₂₃NO, there are two independent molecules in the asymmetric unit. Both molecules have an E configuration about the alkene function. The main conformational difference between the molecules is in the orientation of the plane of the naphthyl rings with respect to the camphor fragment. The torsion angle about the enamine C—N bond is 21.3 (7)° for molecule A, but −24.4 (8)° for molecule B. Intermolecular N—H⋯O hydrogen bonds between the amino and ketone groups of adjacent independent molecules sustain the crystal, and the resulting extended chains, containing an alternating sequence of the two independent molecules, run parallel to the [001] direction and can be described by a graph-set motif of C ₂ ²(12).

Related literature

For the conformations of β-ketoamines, see: Zharkova et al. (2009 ▶). For chiral camphor-derived β-aminoketonate ligands, see: Everett & Powers (1970 ▶); Casella et al. (1979 ▶). For reactions involving aminoketonate complexes, see: Hsu, Chang et al. (2004 ▶); Hsu, Li et al. (2007 ▶); Lai et al. (2005 ▶); Pan et al. (2008 ▶); Wang et al. (2006 ▶). For the coordination chemistry of β-aminoketonate ligands, see: Lesikar et al. (2008 ▶); Sedai et al. (2008 ▶). For the synthesis of (+)-hydroxymethylenecamphor, see: Lintvedt & Fatta (1968 ▶). For related (1-naphthylamino)methylene structures, see: Li et al. (2009 ▶); Özek et al. (2005 ▶). For graph-set theory, see: Bernstein et al. (1995 ▶).

Experimental

Crystal data

C₂₁H₂₃NO
M _r = 305.42
Monoclinic,
a = 23.807 (2) Å
b = 11.9688 (12) Å
c = 12.0192 (8) Å
β = 95.672 (5)°
V = 3408.1 (5) Å³
Z = 8
Mo Kα radiation
μ = 0.07 mm⁻¹
T = 160 K
0.25 × 0.20 × 0.12 mm

Data collection

Nonius KappaCCD area-detector diffractometer
21618 measured reflections
3170 independent reflections
2227 reflections with I > 2σ(I)
R _int = 0.092

Refinement

R[F ² > 2σ(F ²)] = 0.059
wR(F ²) = 0.155
S = 1.05
3170 reflections
428 parameters
1 restraint
H atoms treated by a mixture of independent and constrained refinement
Δρ_max = 0.24 e Å⁻³
Δρ_min = −0.17 e Å⁻³

Data collection: COLLECT (Nonius, 2000 ▶); cell refinement: DENZO-SMN (Otwinowski & Minor, 1997 ▶); data reduction: DENZO-SMN and SCALEPACK (Otwinowski & Minor, 1997 ▶); program(s) used to solve structure: SIR92 (Altomare et al., 1994 ▶); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008 ▶); molecular graphics: ORTEPII (Johnson, 1976 ▶); software used to prepare material for publication: SHELXL97 and PLATON (Spek, 2009 ▶).

Supplementary Material

Crystal structure: contains datablocks I, global. DOI: 10.1107/S1600536810052487/su2235sup1.cif

e-67-0o188-sup1.cif^{(32.5KB, cif)}

Structure factors: contains datablocks I. DOI: 10.1107/S1600536810052487/su2235Isup2.hkl

e-67-0o188-Isup2.hkl^{(155.5KB, hkl)}

Additional supplementary materials: crystallographic information; 3D view; checkCIF report

Table 1. Hydrogen-bond geometry (Å, °).

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
N1—H1⋯O2ⁱ	1.03 (4)	1.93 (4)	2.909 (5)	157 (4)
N2—H2⋯O1	0.83 (5)	2.08 (5)	2.913 (5)	174 (5)

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Symmetry code: (i) Inline graphic .

Acknowledgments

This work was financed by FONACIT (project S1-2001000851).

supplementary crystallographic information

Comment

β-Ketoamines are the neutral protic form of β-aminoketonate bidentate anionic ligands that have been used in the coordination chemistry of transition and main group metals (Lesikar et al., 2008; Sedai et al., 2008). The electronic and steric dissymmetry of these ligands is easily modified in order to tune the reactivity of the metal centre. β-Aminoketonate complexes have been used effectively in stoichiometric (Hsu, Chang et al., 2004; Hsu, Li et al., 2007) and catalytic processes, such as Suzuki cross-coupling (Lai et al., 2005), polymerization (Wang et al., 2006) and copolymerization (Pan et al., 2008) reactions. Interestingly, there are only a few reports on chiral camphor-derived β-aminoketonate ligands (Everett & Powers, 1970; Casella et al., 1979). Generally, β-ketoamines have Z conformations that are stabilized by intramolecular hydrogen bonding (Zharkova et al., 2009). The structure of the title compound was determined in order to confirm the anticipated E conformation about the alkene bond for the major product of the synthesis.

There are two molecules (A and B) of the title compound in the asymmetric unit (Fig. 1). The slightly twisted conformations of the (1-naphthylamino)methylene fragments are similar to that in the structure of 2,2-dimethyl-5-(1-naphthylaminomethylene)-1,3-dioxane-4,6-dione (Li et al., 2009): the absolute values of the torsion angle about the enamine C—N bond for the two structures lie in the narrow range of 21–25°. In contrast, the same group in 2-hydroxy-6-[(1-napthylamino)methylene]cyclohexa-2,4-dien-1-one is almost planar (Özek et al., 2005).

The preference for the E conformation during the synthesis of the title compound may be attributed to the large size of the naphthyl group, whose steric pressure overcomes the competing intramolecular N—H···O hydrogen bonding, which is facilitated in the Z conformer. The observed intermolecular N—H···O hydrogen bonds between the amino and keto groups of adjacent independent molecules, which link the molecules into extended chains running parallel to [001] (Fig. 2), are an additional stabilizing factor of the E conformation. They can be described by a graph-set motif of C²₂(12) [Bernstein et al., 1995].

While the chirality of the (+)-camphor fragment means that both symmetry-independent molecules are of the same enantiomer, it is interesting to note that there is significant pseudo-inversion symmetry in the structure, with 82% of the atoms in one molecule matching closely with those of the inverted structure of the other molecule; the r.m.s. fit of 21 atoms from each molecule is 1.14 Å. Slight in-plane disorder of the naphthyl groups leads to enlarged displacement ellipsoids for some of the atoms of these groups with the direction of elongation being in the naphthyl plane.

Experimental

The title compound was prepared by refluxing 1-naphthylamine (6.77 g, 37.6 mmol) with (+)-hydroxymethylenecamphor (Lintvedt & Fatta, 1968) (5.92 g, 41.3 mmol) in dry ethanol (200 ml) and formic acid (2.5 ml) for 48 h. After removing the solvent under reduced pressure, the resulting yellow solid was dried in vacuo for 4 h. The crude product contained both conformers, which after washing with hexane and HV drying afforded 6.53 g (57%) of the pure (E)-conformer [the (Z)-conformer being more soluble in alkanes]. Yellow single crystals suitable for an X-ray analysis were grown from a saturated and filtered ethanol solution that was cooled slowly to 263 K (m.p. 351–353 K). Elemental analysis calculated for C₂₁H₂₃NO: C 82.58, H 7.59, N 4.59%; found: C 85.26, H 7.99, N 4.61%. NMR and IR Spectroscopic data are available in the archived CIF.