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The title compound, C22H24N4O4, was prepared from propyl chloro­formate and 3,6-di­phenyl-1,2-di­hydro-s-tetrazine. This reaction yields the title compound rather than di­propyl 3,6-di­phenyl-1,4-di­hydro-s-tetrazine-1,4-di­carboxyl­ate. The 2,3-di­aza­buta­diene group in the central six-membered ring is not planar; the C=N double-bond length is 1.285 (2) Å, and the average N-N single-bond length is 1.401 (3) Å, indicating a lack of conjugation. The ring has a twist conformation, in which adjacent N atoms lie \pm0.3268 (17) Å from the plane of the ring. The mol­ecule has twofold crystallographic symmetry.

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S0108270103007212/fr1397sup1.cif
Contains datablocks I, global

hkl

Structure factor file (CIF format) https://doi.org/10.1107/S0108270103007212/fr1397Isup2.hkl
Contains datablock I

CCDC reference: 186802

Comment top

S-Tetrazine derivatives have a high potential for biological activity, possessing a wide spectrum of antiviral and antitumor properties. These derivatives have been widely used in pesticides and herbicides (Sauer, 1996). Dihydro-s-tetrazine has four isomers, namely 1,2-, 1,4-, 1,6- and 3,6-dihydro-s-tetrazines. In almost all the cases that have been studied by X-ray diffraction, the dihydro derivatives were best described as 1,4-dihydro isomers, with the 1,2-dihydro isomer being very rare. There still seems to be much confusion over the structure of the 1,2- and 1,4-dihydro-s-tetrazines. Every compound should have a unique CAS number in Chemical Abstracts, but some 1,2- and 1,4-dihydro-s-tetrazines have the same CAS number. For example the CAS number of both 3,6-diphenyl-1,2-dihydro-s-tetrazine, (II), and 3,6-diphenyl-1,4- dihydro-s-tetrazine, (III), is [14478–73-0] (see Chemical Abstracts, Subject Index 8t h Coll, 30704 s). Some scientists believe that there is rearrangement between (II) and (III), so that there is a mixture of two isomers (Neunhoeffer, 1984).

In a continuation of our work on the structure–activity relationship of s-tetrazine derivatives (Hu et al., 2001, 2002), we have obtained a colourless crystalline compound that was the sole product of the reaction of propyl chloroformate and 3,6-diphenyl-dihydro-s- tetrazine. 3,6-Diphenyl-dihydro-s-tetrazine was prepared according to the procedure of Abdel-rahman et al. (1968). If 3,6-diphenyl-dihydro-s-tetrazine were a mixture of (II) and (III), two products, (I) and (IV), should be obtained when reacting with propyl chloroformate. If 3,6-diphenyl-dihydro-s-tetrazine were compound (II), the product (I) should be obtained when reacting with propyl chloroformate. If 3,6-diphenyl-dihydro-s-tetrazine were compound (III), the product, (IV), should be obtained when reacting with propyl chloroformate. However, IR, 1H NMR and MS studies failed to prove whether the N,N'-disubstituents are located at the 1,2 or 1,4 positions. The question of structural identity of our product was resolved using single-crystal X-ray diffraction.

The molecular structure of our product, (I), is illustrated in Fig. 1. Selected bond lengths, bond angles and torsion angles are listed in Table 1. In (I), the interatomic distance for the two C7N1 bonds is 1.285 (2) Å, which shows that they are normal CN double bonds. The C7—N2 [1.416 (2) Å], N1—N1i [1.406 (3) Å] and N2—N2i [1.395 (3) Å] bond lengths correspond to single bonds. The normal lengths of the CN double bond, the C—N single bond and the N—N single bond are 1.279–1.329, 1.336–1.416 and 1.366–1.454 Å, respectively (Allen et al., 1987). These show that the tetrazin ring is 1,2-dihydro-s-tetrazine and the N,N'-disubstituents are at the 1,2 positions, thus proving that (I) is dipropyl 3,6-diphenyl-1,2- dihydro-s-tetrazine-1,2-dicarbonate. It is therefore clear that the raw material prepared according to the Abdel-rahmann procedure is 3,6-diphenyl- 1,2-dihydro-s-tetrazine, (II), rather than the 1,4-isomer, (III), or a mixture of two isomers, and that there is no rearrangement between the two isomers.

The C7, N1, N1i and C7i atoms of the 2,3-diazabutadiene in the ring are not coplanar, which demonstrates the lack of conjugation in the CN—NC group. Theoretically, in (I), the N1—N1i bonds should be shorter than N2—N2i, since N1 and N1i with the atoms C7 and C7i form the CN double bond. However the reverse is true, because of the stereo effect of the 1,2-disubstituents.

The molecule has twofold crystallographic symmetry, with the twofold axis through the centers of the N1—N1i and N2—N2i bonds. The central ring has a twist conformation in which N2 lies 0.3268 (17) Å out of the central least-squares plane and the adjacent N2i lies an equal distance to the opposite side.

Experimental top

3,6-Diphenyl-1,2-dihydro-s-tetrazine, (II), (1.0 g, 4.2 mmol), prepared according to the Abdel-rahman procedure (Abdel-rahman et al., 1968), was dissolved in dichloromethane (40 ml) with stirring. Propyl chloroformate (0.96 ml, 8.5 mmol) and pyridine (0.68 ml, 8.5 mmol) were added to the mixture on an ice bath. The mixture was stirred at room temperature for 6 h and dried in vacuo to give a light-red solid, (I) (1.1 g, yield 64%), which was then recrystallized from ethanol to give colourless blocks (m.p. 384–385 K).

Refinement top

H atoms were added at calculated positions and refined using a riding model. H atoms were given isotropic displacement parameters equal to 1.2 (or 1.5 for methyl H atoms) times the equivalent isotropic displacement parameters of their parent atoms, and C—H distances were restrained to 0.93 Å for phenyl H atoms, 0.96 Å for methyl H atoms and 0.97 Å for the remainder.

Computing details top

Data collection: CAD-4 EXPRESS (Enraf-Nonius, 1994); cell refinement: CAD-4 EXPRESS; data reduction: XCAD4 (Harms & Wocadlo, 1995); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEP-3 for Windows (Farrugia, 1997); software used to prepare material for publication: SHELXL97.

Figures top
[Figure 1] Fig. 1. View of a molecule of (I), showing the atomic numbering scheme. Displacement ellipsoids are shown at the 30% probability level for non-H atoms. [Symmetry code: (i) 2 − x, 3/2 − y, z.]
dipropyl 3,6-diphenyl-1,2-dihydro-s-tetrazine-1,2-dicarbonate top
Crystal data top
C22H24N4O4Dx = 1.313 Mg m3
Mr = 408.45Melting point = 384–385 K
Tetragonal, I41/aMo Kα radiation, λ = 0.71073 Å
Hall symbol: -I 4adCell parameters from 25 reflections
a = 15.655 (13) Åθ = 11.5–13.5°
c = 16.869 (13) ŵ = 0.09 mm1
V = 4134 (5) Å3T = 293 K
Z = 8Prismatic, colorless
F(000) = 17280.60 × 0.40 × 0.38 mm
Data collection top
CAD4
diffractometer
Rint = 0.046
Radiation source: fine-focus sealed tubeθmax = 25.2°, θmin = 1.8°
Graphite monochromatorh = 1618
ω/2–θ scansk = 1816
8309 measured reflectionsl = 1620
1873 independent reflections3 standard reflections every 60 min
1404 reflections with I > 2σ(I) intensity decay: 0.3%
Refinement top
Refinement on F2Secondary atom site location: difference Fourier map
Least-squares matrix: fullHydrogen site location: inferred from neighbouring sites
R[F2 > 2σ(F2)] = 0.038H-atom parameters constrained
wR(F2) = 0.111 w = 1/[σ2(Fo2) + (0.0477P)2 + 2.1561P]
where P = (Fo2 + 2Fc2)/3
S = 1.05(Δ/σ)max < 0.001
1873 reflectionsΔρmax = 0.26 e Å3
139 parametersΔρmin = 0.16 e Å3
0 restraintsExtinction correction: SHELXL, Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4
Primary atom site location: structure-invariant direct methodsExtinction coefficient: 0.0062 (6)
Crystal data top
C22H24N4O4Z = 8
Mr = 408.45Mo Kα radiation
Tetragonal, I41/aµ = 0.09 mm1
a = 15.655 (13) ÅT = 293 K
c = 16.869 (13) Å0.60 × 0.40 × 0.38 mm
V = 4134 (5) Å3
Data collection top
CAD4
diffractometer
Rint = 0.046
8309 measured reflections3 standard reflections every 60 min
1873 independent reflections intensity decay: 0.3%
1404 reflections with I > 2σ(I)
Refinement top
R[F2 > 2σ(F2)] = 0.0380 restraints
wR(F2) = 0.111H-atom parameters constrained
S = 1.05Δρmax = 0.26 e Å3
1873 reflectionsΔρmin = 0.16 e Å3
139 parameters
Special details top

Experimental. IR(KBr) vmax: 2971, 2937, 2901, 2879, 1762, 1600, 1535, 1516, 1490, 1473, 1445, 1392 cm−1. 1H NMR(400 MHz, CDCl3): δ 0.64(6H,t), 1.45(4H,q), 3.98–4.04(2H,m), 4.11–4.17(2H,m), 7.46–7.55(6H,m), 8.06(4H,d). MS(m/z, relative intensity): 408(M+,1.04), 236(30.79), 235(20.56), 104 (100), 103(27.03), 77(17.98), 76(14.36), 43(99.9), 41(51.04). Anal. calc. for C22H24N4O4(%): C 64.69, H 5.92, N 13.72. Found: C 64.65, H 6.04, N 13.81.

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 (Å2) top
xyzUiso*/Ueq
O10.88593 (8)0.77760 (8)0.32244 (8)0.0586 (4)
O20.84517 (8)0.65989 (8)0.25519 (8)0.0597 (4)
N11.00106 (9)0.70510 (9)0.09547 (8)0.0491 (4)
N20.97304 (10)0.71453 (8)0.23092 (8)0.0463 (4)
C10.95192 (12)0.52633 (12)0.09801 (11)0.0550 (5)
H10.94110.55390.05020.066*
C20.94569 (14)0.43839 (12)0.10308 (13)0.0663 (6)
H20.93140.40670.05840.080*
C30.96053 (13)0.39753 (12)0.17378 (14)0.0641 (6)
H30.95560.33840.17690.077*
C40.98258 (13)0.44356 (12)0.23957 (13)0.0636 (5)
H40.99310.41560.28720.076*
C50.98925 (12)0.53112 (11)0.23555 (11)0.0562 (5)
H51.00380.56220.28050.067*
C60.97429 (10)0.57303 (10)0.16455 (10)0.0446 (4)
C70.98197 (10)0.66649 (10)0.16029 (9)0.0440 (4)
C80.89779 (11)0.72230 (10)0.27522 (9)0.0458 (4)
C90.77048 (13)0.64460 (13)0.30384 (13)0.0664 (6)
H9A0.72050.63950.27020.080*
H9B0.76180.69260.33920.080*
C100.78086 (14)0.56577 (16)0.35073 (14)0.0781 (7)
H10A0.82760.57340.38780.094*
H10B0.79580.51920.31540.094*
C110.70162 (17)0.54228 (18)0.39585 (17)0.0929 (8)
H11A0.68650.58810.43090.139*
H11B0.71200.49150.42620.139*
H11C0.65570.53220.35930.139*
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
O10.0699 (9)0.0549 (8)0.0511 (7)0.0113 (6)0.0006 (6)0.0129 (6)
O20.0648 (8)0.0540 (8)0.0602 (8)0.0065 (6)0.0148 (6)0.0105 (6)
N10.0616 (9)0.0459 (7)0.0398 (8)0.0010 (7)0.0014 (7)0.0021 (6)
N20.0632 (9)0.0380 (7)0.0375 (7)0.0048 (6)0.0044 (6)0.0016 (6)
C10.0616 (11)0.0549 (11)0.0485 (11)0.0033 (8)0.0034 (9)0.0089 (8)
C20.0750 (13)0.0541 (11)0.0697 (14)0.0087 (10)0.0051 (11)0.0220 (10)
C30.0671 (13)0.0404 (10)0.0848 (15)0.0016 (9)0.0085 (11)0.0061 (10)
C40.0759 (13)0.0458 (10)0.0691 (13)0.0033 (9)0.0030 (10)0.0059 (9)
C50.0699 (12)0.0464 (10)0.0523 (11)0.0014 (8)0.0048 (9)0.0018 (8)
C60.0451 (9)0.0427 (9)0.0460 (9)0.0008 (7)0.0046 (7)0.0057 (7)
C70.0493 (9)0.0432 (9)0.0395 (9)0.0014 (7)0.0006 (7)0.0039 (7)
C80.0619 (11)0.0404 (9)0.0351 (8)0.0077 (8)0.0024 (8)0.0026 (7)
C90.0601 (12)0.0672 (12)0.0718 (14)0.0017 (9)0.0141 (10)0.0001 (11)
C100.0667 (13)0.0892 (16)0.0783 (15)0.0075 (11)0.0026 (11)0.0179 (13)
C110.0890 (17)0.0928 (18)0.0971 (19)0.0228 (13)0.0169 (15)0.0085 (15)
Geometric parameters (Å, º) top
O1—C81.191 (2)C4—C51.376 (3)
O2—C81.322 (2)C4—H40.9300
O2—C91.448 (2)C5—C61.386 (3)
N1—C71.285 (2)C5—H50.9300
N1—N1i1.406 (3)C6—C71.470 (2)
N2—N2i1.395 (3)C9—C101.475 (3)
N2—C81.400 (2)C9—H9A0.9700
N2—C71.416 (2)C9—H9B0.9700
C1—C21.383 (3)C10—C111.501 (3)
C1—C61.385 (2)C10—H10A0.9700
C1—H10.9300C10—H10B0.9700
C2—C31.373 (3)C11—H11A0.9599
C2—H20.9300C11—H11B0.9599
C3—C41.368 (3)C11—H11C0.9599
C3—H30.9300
C8—O2—C9118.72 (15)N1—C7—C6121.94 (14)
C7—N1—N1i117.70 (10)N2—C7—C6118.65 (14)
N2i—N2—C8116.10 (14)O1—C8—O2127.66 (17)
N2i—N2—C7111.29 (11)O1—C8—N2123.45 (16)
C8—N2—C7125.33 (14)O2—C8—N2108.89 (14)
C2—C1—C6119.57 (18)O2—C9—C10110.69 (17)
C2—C1—H1120.2O2—C9—H9A109.5
C6—C1—H1120.2C10—C9—H9A109.5
C3—C2—C1120.37 (19)O2—C9—H9B109.5
C3—C2—H2119.8C10—C9—H9B109.5
C1—C2—H2119.8H9A—C9—H9B108.1
C4—C3—C2120.14 (18)C9—C10—C11112.7 (2)
C4—C3—H3119.9C9—C10—H10A109.1
C2—C3—H3119.9C11—C10—H10A109.1
C3—C4—C5120.3 (2)C9—C10—H10B109.1
C3—C4—H4119.9C11—C10—H10B109.1
C5—C4—H4119.9H10A—C10—H10B107.8
C4—C5—C6120.09 (18)C10—C11—H11A109.5
C4—C5—H5120.0C10—C11—H11B109.5
C6—C5—H5120.0H11A—C11—H11B109.5
C1—C6—C5119.57 (16)C10—C11—H11C109.5
C1—C6—C7120.44 (16)H11A—C11—H11C109.5
C5—C6—C7119.99 (15)H11B—C11—H11C109.5
N1—C7—N2119.29 (15)
C6—C1—C2—C30.8 (3)C1—C6—C7—N127.2 (2)
C1—C2—C3—C40.8 (3)C5—C6—C7—N1152.98 (18)
C2—C3—C4—C50.6 (3)C1—C6—C7—N2156.67 (16)
C3—C4—C5—C60.5 (3)C5—C6—C7—N223.2 (2)
C2—C1—C6—C50.7 (3)C9—O2—C8—O112.3 (3)
C2—C1—C6—C7179.48 (17)C9—O2—C8—N2167.97 (15)
C4—C5—C6—C10.6 (3)N2i—N2—C8—O114.1 (2)
C4—C5—C6—C7179.62 (17)C7—N2—C8—O1161.51 (16)
N1i—N1—C7—N29.8 (3)N2i—N2—C8—O2165.65 (12)
N1i—N1—C7—C6174.06 (16)C7—N2—C8—O218.2 (2)
N2i—N2—C7—N131.5 (2)C8—O2—C9—C10107.2 (2)
C8—N2—C7—N1117.28 (18)O2—C9—C10—C11174.14 (19)
N2i—N2—C7—C6144.77 (16)C7i—N1i—N1—C732.0 (3)
C8—N2—C7—C666.5 (2)C7i—N2i—N2—C750.9 (3)
Symmetry code: (i) x+2, y+3/2, z.

Experimental details

Crystal data
Chemical formulaC22H24N4O4
Mr408.45
Crystal system, space groupTetragonal, I41/a
Temperature (K)293
a, c (Å)15.655 (13), 16.869 (13)
V3)4134 (5)
Z8
Radiation typeMo Kα
µ (mm1)0.09
Crystal size (mm)0.60 × 0.40 × 0.38
Data collection
DiffractometerCAD4
diffractometer
Absorption correction
No. of measured, independent and
observed [I > 2σ(I)] reflections
8309, 1873, 1404
Rint0.046
(sin θ/λ)max1)0.599
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.038, 0.111, 1.05
No. of reflections1873
No. of parameters139
H-atom treatmentH-atom parameters constrained
Δρmax, Δρmin (e Å3)0.26, 0.16

Computer programs: CAD-4 EXPRESS (Enraf-Nonius, 1994), CAD-4 EXPRESS, XCAD4 (Harms & Wocadlo, 1995), SHELXS97 (Sheldrick, 1997), SHELXL97 (Sheldrick, 1997), ORTEP-3 for Windows (Farrugia, 1997), SHELXL97.

Selected geometric parameters (Å, º) top
N1—C71.285 (2)N2—N2i1.395 (3)
N1—N1i1.406 (3)N2—C71.416 (2)
C7—N1—N1i117.70 (10)N1—C7—N2119.29 (15)
N2i—N2—C7111.29 (11)
N1i—N1—C7—N29.8 (3)C7i—N1i—N1—C732.0 (3)
N2i—N2—C7—N131.5 (2)C7i—N2i—N2—C750.9 (3)
Symmetry code: (i) x+2, y+3/2, z.
 

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