N-tert-Butyl-N′-(5,7-di­methyl-1,8-naphthyridin-2-yl)­urea

The title compound, C₁₅H₂₀N₄O, has been synthesized as an AADD recognition unit for quadruple hydrogen bonds. All non-H atoms of the mol­ecule apart from two methyl groups of the tert-butyl group lie in a common plane. An intramolecular hydrogen bond is formed connecting two N atoms. In the solid state, the title compound crystallizes as a centrosymmetric dimer connected by N—H...O=C interactions with an N...O distance of 2.824 (2) Å.

S1. Comment

Multiple hydrogen bonds attend increasing attention for the formation of host–guest complexes and for supramolecular self-assembly (Zimmerman & Corbin, 2000). Therefore quadruple hydrogen-bonding patterns based on four parallel and anti-parallel hydrogen bonds have been investigated. While a non-self-complementary pattern like DAAD·ADDA (D: hydrogen-bond donor, A: hydrogen-bond acceptor) (Lüning & Kühl, 1998), can be used for molecular recognition, the two conceivable self-complementary patterns of a four hydrogen-bond system AADD or ADAD may form dimers. This has been exploited by Sijbesma et al. (1997) and Beijer et al. (1998) to construct new types of polymers. Here we present a naphthyridyl urea (I) designed for self-complexation. It was synthesized from the literature known 7-amino-2,4-dimethyl-1,8-naphthyridine (Gorecki & Hawes, 1977) by addition to tert-butylisocyanate in 87% yield. \sch

Meijer's AADD systems (Sijbesma et al., 1997; Beijer et al., 1998) possess a linear orientation of the hydrogen bonds leading to dimers held together by four parallel and anti-parallel hydrogen bonds. Such a linear dimer of (I) could only be formed if the urea exists in a Z,Z conformation. However, the naphthyridyl urea (I) first forms an intramolecular hydrogen bond between the hydrogen atom of the tert-butyl NH group and atom N1 of the naphthyridyl ring which leads to a Z,E conformer. This was proven by X-ray analysis (see Figure 1). Bond lengths and angles of (I) are in the usual ranges. The molecule is essentially planar (except for two methyl groups of the tert-butyl group) (r.m.s. deviation 0.05 Å).

The twist from a Z to an E amide bond presents a hydrogen-bond donor D and a hydrogen-bond acceptor A on the surface of (I). Thus, self recognition (AD^.DA) forms a dimer which also contains four hydrogen bonds. However, two of these are intramolecular and only two are intermolecular. The dimerization of ureas which are substituted by N-heterocycles in an AD^.DA fashion has already been observed for pyridyl ureas (Bolte et al., 2001; Corbin & Zimmerman, 2000). The driving force for a dimer formation by only two hydrogen bonds accompanied by two intramolecular hydrogen bonds is possibly on steric grounds: the 7-methyl group and the tert-butyl group are in closer contact in the strictly intermolecular dimer than in the E,Z form. The new N-substituted naphthyridine (I) is also an interesting ligand for the complexation of two metal atoms in close proximity. Mintert & Sheldrick (1996) have reported complexes of related 2-amino and 2-oxo substituted naphthyridines containing Mo—Mo moieties.

Related literature

For related literature, see: Beijer et al. (1998); Bolte et al. (2001); Corbin & Zimmerman (2000); Gorecki & Hawes (1977); Lüning & Kühl (1998); Mintert & Sheldrick (1996); Sijbesma et al. (1997); Zimmerman & Corbin (2000).

S2. Experimental

Under N₂, 7-amino-2,4-dimethyl-1,8-naphthyridine (Gorecki & Hawes, 1977) (866 mg, 5.01 mmol) was dissolved in dry toluene (50 ml), tert-butylisocyanate (500 mg, 5.05 mmol) was added, and the mixture was heated to reflux for 2 h. After cooling to room temperature, the solid was filtered off, washed with toluene and dried. Recrystallization from ethanol, toluene/ethanol (10:1) and then toluene gave 1.19 g (87%) of a colourless solid, m. p. 513 K. IR (KBr): cm^-1 ν^σim 3360, 3187, 3119, 3042 (N—H), 2968 (aliphat. C—H), 1682 (C═O), 1601, 1523 (arom.), 1566 (N—H), 1401 (tert-butyl, C—H). ¹H-NMR (200 MHz, CDCl₃) δ: 1.54 [s, 9H, C(CH₃)₃], 2.61 (s, 3H, CH₃), 2.69 (s, 3H, CH₃), 7.05 (s, 1H, ArH), 7.46 (d, J = 8.9 Hz, 1H, ArH), 8.18 (d, J = 8.9 Hz, 1H, ArH), 9.59 (br. s, 1H, NH), 10.08 (br. s, 1H, NH). MS (EI,70 eV): m/z (%) = 272 (3), 257 (16), 200 (57), 173 (100). MS (CI/isobutane): m/z (%) = 273 (100). C₁₇H₂₂N₄O (272.4): calculated C 66.15, H 7.40, N 20.57%; found C 66.04, H 7.42, N 20.48%.

S3. Refinement

All H atoms were located by difference Fourier synthesis and refined with fixed individual displacement parameters [U(H) = 1.5 U_eq(C_methyl), or U(H) = 1.2 U_eq(C)] using a riding model with C—H_aromatic 0.95 and C—H_methyl 0.98 Å. The methyl groups attached to the aromatic system were allowed to rotate about their local threefold axis. The H atoms bound to N were refined isotropically.

Computing details

Data collection: SMART (Siemens, 1995); cell refinement: SMART; data reduction: SAINT (Siemens, 1995); program(s) used to solve structure: SHELXS97 (Sheldrick, 1990); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: XP in SHELXTL-Plus (Sheldrick, 1991).

Figures

Fig. 1. A perspective view of the title compound with the atom-numbering scheme. Displacement ellipsoids are at the 50% probability level and H atoms are drawn as small spheres of arbitrary radii. Hydrogen bonds are drawn as dotted lines. The second molecule is generated applying the symmetry operator (2 - x, 1 - y, 1 - z).

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Crystal data

C15H20N4O	Dx = 1.154 Mg m^−3
Mr = 272.35	Melting point: 513 K
Monoclinic, P21/c	Mo Kα radiation, λ = 0.71073 Å
a = 12.7129 (2) Å	Cell parameters from 5891 reflections
b = 11.2067 (1) Å	θ = 1–25°
c = 11.6822 (2) Å	µ = 0.08 mm^−1
β = 109.578 (1)°	T = 140 K
V = 1568.14 (4) Å^3	Block, colourless
Z = 4	0.40 × 0.20 × 0.08 mm
F(000) = 584

Data collection

Siemens CCD three-circle diffractometer	3174 independent reflections
Radiation source: fine-focus sealed tube	2135 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.051
ω scans	θmax = 26.4°, θmin = 1.7°
Absorption correction: empirical (SADABS; Sheldrick, 1996)	h = −15→15
Tmin = 0.970, Tmax = 0.994	k = −13→13
10199 measured reflections	l = −13→14

Refinement

Refinement on F^2	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: inferred from neighbouring sites
R[F^2 > 2σ(F^2)] = 0.050	H atoms treated by a mixture of independent and constrained refinement
wR(F^2) = 0.136	w = 1/[σ^2(Fo^2) + (0.0636P)^2 + 0.4824P] where P = (Fo^2 + 2Fc^2)/3
S = 1.02	(Δ/σ)max < 0.02
3174 reflections	Δρmax = 0.29 e Å^−3
192 parameters	Δρmin = −0.23 e Å^−3
0 restraints	Extinction correction: SHELXL97, Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
Primary atom site location: structure-invariant direct methods	Extinction coefficient: 0.014 (2)

Special details

Experimental. ;

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 F² against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F², conventional R-factors R are based on F, with F set to zero for negative F². The threshold expression of F² > σ(F²) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F² 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 (Ų)

	x	y	z	Uiso*/Ueq
N1	0.85531 (12)	0.54915 (14)	0.48862 (14)	0.0231 (4)
H1	0.8923 (16)	0.4926 (19)	0.4634 (18)	0.026 (5)*
C2	0.92330 (14)	0.63554 (16)	0.56465 (15)	0.0205 (4)
O2	1.02662 (9)	0.62078 (11)	0.59955 (11)	0.0254 (3)
N3	0.87183 (13)	0.72830 (14)	0.59484 (14)	0.0249 (4)
H3	0.7957 (19)	0.7260 (19)	0.563 (2)	0.042 (6)*
C4	0.92836 (15)	0.82712 (16)	0.67685 (17)	0.0257 (4)
C41	1.00999 (19)	0.8910 (2)	0.6270 (2)	0.0410 (6)
H41A	0.9697	0.9211	0.5453	0.062*
H41B	1.0679	0.8349	0.6233	0.062*
H41C	1.0447	0.9578	0.6804	0.062*
C42	0.83422 (17)	0.91287 (19)	0.6775 (2)	0.0416 (6)
H42A	0.7820	0.8714	0.7093	0.062*
H42B	0.7945	0.9401	0.5945	0.062*
H42C	0.8661	0.9817	0.7292	0.062*
C43	0.98812 (17)	0.77897 (19)	0.80489 (18)	0.0356 (5)
H43A	0.9341	0.7383	0.8347	0.053*
H43B	1.0223	0.8453	0.8593	0.053*
H43C	1.0462	0.7224	0.8026	0.053*
C11	0.73957 (14)	0.54333 (16)	0.43817 (16)	0.0218 (4)
N12	0.67811 (12)	0.62899 (13)	0.46135 (14)	0.0239 (4)
C13	0.56386 (14)	0.61944 (17)	0.41554 (17)	0.0248 (4)
N14	0.50809 (12)	0.71130 (15)	0.44676 (15)	0.0301 (4)
C15	0.39668 (15)	0.70527 (19)	0.40751 (19)	0.0341 (5)
C15'	0.33656 (17)	0.8068 (2)	0.4442 (2)	0.0458 (6)
H15A	0.3651	0.8158	0.5327	0.069*
H15B	0.2564	0.7896	0.4175	0.069*
H15C	0.3492	0.8808	0.4061	0.069*
C16	0.33698 (16)	0.6101 (2)	0.3365 (2)	0.0382 (5)
H16	0.2577	0.6103	0.3111	0.046*
C17	0.39086 (16)	0.5164 (2)	0.30286 (18)	0.0352 (5)
C17'	0.32876 (18)	0.4114 (2)	0.2298 (2)	0.0522 (7)
H17A	0.3469	0.3391	0.2798	0.078*
H17B	0.3509	0.4008	0.1578	0.078*
H17C	0.2482	0.4263	0.2046	0.078*
C18	0.51024 (15)	0.52085 (18)	0.34368 (17)	0.0276 (4)
C19	0.57963 (15)	0.43159 (18)	0.31861 (18)	0.0298 (5)
H19	0.5467	0.3649	0.2695	0.036*
C20	0.69254 (15)	0.44170 (17)	0.36482 (17)	0.0270 (4)
H20	0.7393	0.3825	0.3487	0.032*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
N1	0.0187 (8)	0.0226 (8)	0.0282 (9)	0.0039 (6)	0.0083 (7)	−0.0045 (7)
C2	0.0217 (9)	0.0218 (10)	0.0186 (9)	0.0014 (7)	0.0075 (7)	0.0008 (7)
O2	0.0182 (6)	0.0292 (7)	0.0269 (7)	0.0040 (5)	0.0052 (5)	−0.0043 (6)
N3	0.0188 (8)	0.0246 (9)	0.0302 (9)	0.0008 (6)	0.0068 (7)	−0.0063 (7)
C4	0.0253 (9)	0.0225 (10)	0.0279 (10)	0.0005 (7)	0.0071 (8)	−0.0061 (8)
C41	0.0456 (13)	0.0345 (12)	0.0447 (13)	−0.0109 (10)	0.0174 (10)	−0.0029 (10)
C42	0.0351 (12)	0.0343 (12)	0.0479 (14)	0.0079 (9)	0.0039 (10)	−0.0172 (10)
C43	0.0393 (11)	0.0377 (12)	0.0272 (11)	0.0033 (9)	0.0075 (9)	−0.0041 (9)
C11	0.0208 (9)	0.0223 (9)	0.0239 (10)	0.0009 (7)	0.0096 (7)	0.0016 (7)
N12	0.0204 (8)	0.0248 (9)	0.0275 (9)	0.0017 (6)	0.0093 (6)	−0.0004 (7)
C13	0.0206 (9)	0.0291 (10)	0.0255 (10)	0.0028 (8)	0.0089 (8)	0.0054 (8)
N14	0.0233 (8)	0.0320 (9)	0.0372 (10)	0.0070 (7)	0.0132 (7)	0.0059 (8)
C15	0.0255 (10)	0.0414 (12)	0.0379 (12)	0.0086 (9)	0.0138 (9)	0.0130 (10)
C15'	0.0332 (12)	0.0485 (14)	0.0602 (15)	0.0177 (10)	0.0215 (11)	0.0136 (12)
C16	0.0188 (9)	0.0560 (14)	0.0398 (12)	0.0034 (9)	0.0097 (9)	0.0110 (11)
C17	0.0250 (10)	0.0487 (13)	0.0305 (11)	−0.0038 (9)	0.0075 (9)	0.0042 (10)
C17'	0.0263 (11)	0.0716 (18)	0.0539 (15)	−0.0142 (11)	0.0070 (11)	−0.0143 (13)
C18	0.0233 (10)	0.0347 (11)	0.0255 (10)	−0.0037 (8)	0.0092 (8)	0.0027 (9)
C19	0.0286 (10)	0.0329 (11)	0.0291 (11)	−0.0072 (8)	0.0115 (9)	−0.0069 (9)
C20	0.0267 (10)	0.0276 (10)	0.0294 (11)	−0.0006 (8)	0.0127 (8)	−0.0029 (8)

Geometric parameters (Å, º)

N1—C11	1.391 (2)	N12—C13	1.374 (2)
N1—C2	1.400 (2)	C13—N14	1.367 (2)
N1—H1	0.90 (2)	C13—C18	1.417 (3)
C2—O2	1.249 (2)	N14—C15	1.336 (2)
C2—N3	1.337 (2)	C15—C16	1.407 (3)
N3—C4	1.483 (2)	C15—C15'	1.510 (3)
N3—H3	0.91 (2)	C15'—H15A	0.9800
C4—C41	1.527 (3)	C15'—H15B	0.9800
C4—C43	1.531 (3)	C15'—H15C	0.9800
C4—C42	1.537 (3)	C16—C17	1.381 (3)
C41—H41A	0.9800	C16—H16	0.9500
C41—H41B	0.9800	C17—C18	1.431 (3)
C41—H41C	0.9800	C17—C17'	1.512 (3)
C42—H42A	0.9800	C17'—H17A	0.9800
C42—H42B	0.9800	C17'—H17B	0.9800
C42—H42C	0.9800	C17'—H17C	0.9800
C43—H43A	0.9800	C18—C19	1.427 (3)
C43—H43B	0.9800	C19—C20	1.358 (3)
C43—H43C	0.9800	C19—H19	0.9500
C11—N12	1.322 (2)	C20—H20	0.9500
C11—C20	1.430 (3)
C11—N1—C2	129.94 (16)	C11—N12—C13	118.95 (16)
C11—N1—H1	115.2 (12)	N14—C13—N12	114.37 (16)
C2—N1—H1	114.6 (12)	N14—C13—C18	123.78 (16)
O2—C2—N3	124.82 (16)	N12—C13—C18	121.85 (17)
O2—C2—N1	118.28 (15)	C15—N14—C13	117.08 (18)
N3—C2—N1	116.90 (15)	N14—C15—C16	122.74 (19)
C2—N3—C4	125.23 (15)	N14—C15—C15'	116.3 (2)
C2—N3—H3	114.6 (14)	C16—C15—C15'	120.93 (18)
C4—N3—H3	120.1 (14)	C15—C15'—H15A	109.5
N3—C4—C41	110.34 (15)	C15—C15'—H15B	109.5
N3—C4—C43	110.01 (16)	H15A—C15'—H15B	109.5
C41—C4—C43	111.07 (16)	C15—C15'—H15C	109.5
N3—C4—C42	105.11 (14)	H15A—C15'—H15C	109.5
C41—C4—C42	109.80 (17)	H15B—C15'—H15C	109.5
C43—C4—C42	110.34 (17)	C17—C16—C15	121.55 (18)
C4—C41—H41A	109.5	C17—C16—H16	119.2
C4—C41—H41B	109.5	C15—C16—H16	119.2
H41A—C41—H41B	109.5	C16—C17—C18	116.79 (19)
C4—C41—H41C	109.5	C16—C17—C17'	122.51 (18)
H41A—C41—H41C	109.5	C18—C17—C17'	120.7 (2)
H41B—C41—H41C	109.5	C17—C17'—H17A	109.5
C4—C42—H42A	109.5	C17—C17'—H17B	109.5
C4—C42—H42B	109.5	H17A—C17'—H17B	109.5
H42A—C42—H42B	109.5	C17—C17'—H17C	109.5
C4—C42—H42C	109.5	H17A—C17'—H17C	109.5
H42A—C42—H42C	109.5	H17B—C17'—H17C	109.5
H42B—C42—H42C	109.5	C13—C18—C19	117.41 (16)
C4—C43—H43A	109.5	C13—C18—C17	118.06 (18)
C4—C43—H43B	109.5	C19—C18—C17	124.52 (18)
H43A—C43—H43B	109.5	C20—C19—C18	120.22 (18)
C4—C43—H43C	109.5	C20—C19—H19	119.9
H43A—C43—H43C	109.5	C18—C19—H19	119.9
H43B—C43—H43C	109.5	C19—C20—C11	118.59 (17)
N12—C11—N1	119.54 (16)	C19—C20—H20	120.7
N12—C11—C20	122.95 (16)	C11—C20—H20	120.7
N1—C11—C20	117.50 (16)
C11—N1—C2—O2	179.46 (17)	N14—C15—C16—C17	0.0 (3)
C11—N1—C2—N3	−0.3 (3)	C15'—C15—C16—C17	−179.7 (2)
O2—C2—N3—C4	−1.6 (3)	C15—C16—C17—C18	0.0 (3)
N1—C2—N3—C4	178.18 (16)	C15—C16—C17—C17'	178.1 (2)
C2—N3—C4—C41	59.2 (2)	N14—C13—C18—C19	−179.94 (17)
C2—N3—C4—C43	−63.7 (2)	N12—C13—C18—C19	−0.9 (3)
C2—N3—C4—C42	177.53 (18)	N14—C13—C18—C17	−0.9 (3)
C2—N1—C11—N12	−0.2 (3)	N12—C13—C18—C17	178.11 (17)
C2—N1—C11—C20	−178.79 (17)	C16—C17—C18—C13	0.5 (3)
N1—C11—N12—C13	−177.06 (16)	C17'—C17—C18—C13	−177.71 (19)
C20—C11—N12—C13	1.5 (3)	C16—C17—C18—C19	179.42 (19)
C11—N12—C13—N14	178.71 (16)	C17'—C17—C18—C19	1.2 (3)
C11—N12—C13—C18	−0.4 (3)	C13—C18—C19—C20	1.2 (3)
N12—C13—N14—C15	−178.25 (16)	C17—C18—C19—C20	−177.78 (19)
C18—C13—N14—C15	0.8 (3)	C18—C19—C20—C11	−0.2 (3)
C13—N14—C15—C16	−0.3 (3)	N12—C11—C20—C19	−1.2 (3)
C13—N14—C15—C15'	179.29 (18)	N1—C11—C20—C19	177.37 (17)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N1—H1···O2^i	0.90 (2)	1.93 (2)	2.824 (2)	175.7 (19)
N3—H3···N12	0.91 (2)	1.91 (2)	2.676 (2)	141 (2)

Symmetry code: (i) −x+2, −y+1, −z+1.