# Structure and Properties of 9,14,15,16,17,18,19,20-Octahydro-9,14[1′,4′]-benzenobenzo[b]triphenylene

Authors: Michelle E. Masnovi; John Masnovi; Steven M. Schildcrout
Journal: Journal of Crystallography
 (2016)

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## Abstract

The compound 9,14,15,16,17,18,19,20-octahydro-9,14[1′,4′]-benzenobenzo[b]triphenylene, C28H24, was prepared by hydrogenation of the 4
π
s
+
4
π
s photocycloadduct of dibenz[a,c]anthracene and 1,3-cyclohexadiene with Pt/C in ethyl acetate. The X-ray diffraction analysis shows that the compound crystallizes in the monoclinic space group P
2
1
/
c with the geometric parameters of a = 11.0090(17) Å, b = 13.733(2) Å, c = 13.091(2) Å, and β = 109.583(13)°. In addition to several close intramolecular contacts involving hydrogens derived from the dibenzanthracene moiety, long interannular C–C single bonds of about 1.593 Å are present. These bonds are shorter by about 0.18 Å than the corresponding bonds in the unsaturated precursor, which can be attributed to reduced strain in the more saturated polycyclic ring system. Anisotropic shielding of the fourendo-methylene hydrogens in the 1H NMR spectrum is larger for the two hydrogens lying above the phenanthrene unit, which resonate at 1.03 ppm, than those above the benzenoid ring, which resonate at 1.24 ppm. Theoretical calculations reproduce the geometry with good agreement.


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## Body

## 1. Introduction

The photochemical cycloadditions of conjugated dienes to benzenoid aromatic hydrocarbons provide a test of the validity of Woodward-Hoffmann orbital symmetry theory [1]. Employment of naphthalene, benzanthracenes, and dibenzanthracenes has revealed the preferential formation of 4
π
s
+
4
π
s adducts which follow the Alder rule for maximization of secondary orbital overlap, diagnostic of processes involving concerted bond formation (Scheme 1) [2]. Such adducts have been found to contain unusually long interannular carbon-carbon single bonds [3–5], and theendo-hydrogens which lie above aromatic moieties in these structures resonate at relatively high field in the 1H NMR spectra [6] due to anisotropic shielding by the subjacent aromatic rings [7–9]. We prepared compound2, 9,14,15,16,17,18,19,20-octahydro-9,14[1′,4′]-benzenobenzo[b]triphenylene (Scheme 2), which is free of the disorder associated with other analogues [3, 4], and performed theoretical calculations in order to establish the specific relationships involved.Scheme 1
4
π
s
+
4
π
s photocycloaddition of 1,3-cyclohexadiene to dibenz[a,c]anthracene.Scheme 2
Preparation of 9,14,15,16,17,18,19,20-octahydro-9,14[1′,4′]-benzenobenzo[b]triphenylene (2) by catalytic hydrogenation of1.


## 2. Materials and Methods

All reagents and solvents were obtained from commercial sources and used as received. The preparation of the title compound, C28H24, followed the literature procedure with the substitution of 5% Pt/C for Adam’s catalyst [6]. The 1H-NMR spectrum was recorded on a Bruker AC300 spectrometer in CDCl3 with tetramethylsilane as the internal reference. Crystals suitable for X-ray analysis were obtained by slow evaporation from the dichloromethane-methanol mixed solvent system.Data collection was performed with an Enraf-Nonius CAD4 single crystal X-ray diffractometer using graphite monochromated Mo radiation (λ = 0.71073 Å) at room temperature in the omega scan mode. Profile analysis was obtained for all collected reflections. Data were corrected for Lorentz and polarization effects and secondary extinction. Cell dimensions were obtained from 25 reflections with 2
θ between 30 and 50°. Atomic scattering factors were taken from the International Tables for X-ray Crystallography [10]. Cell parameters, data reduction, and solution and refinement of the structure were achieved with the NRCVAX software suite [11–14]. The structure was solved by direct methods in the space groupP21/c. Crystallographic and refinement parameters are given in Table 1. Molecular graphics were created using ORTEP [15] (Figure 1) and packing diagrams using PLUTO [12] (Figure 2). All carbon atoms were located from the Fourier map and refined anisotropically. The hydrogens could be located in subsequent least-squares refinement cycles but refined to chemically unreasonable positions. This is a common occurrence due to the low electron density about hydrogen nuclei and, in this case, the low ratio of the number of observed reflections to the number of parameters. Therefore, the hydrogens were generated in geometrically idealized positions with aromatic C–H distances fixed at 1.000 Å and aliphatic C–H distances at 1.05 Å and refined with their parent atoms using a riding model. The carbon atomic parameters are given in Table 2.Table 1
Crystal and refinement data for compound2.
Chemical formula
C28H24
Formula weight (g/mole)
360.49
Cell setting
Monoclinic
Space group
P
2
1
/
c
a (Å)
11.0090(17)
b (Å)
13.733(2)
c (Å)
13.091(2)
β (°)
109.583(13)
Volume (Å3)
1864.7(5)
Z
4
Crystal size (mm)
0.47 × 0.41 × 0.23
Density (g/mL)
1.284
F
(
000
)
768.22
Temperature (K)
293
Mu
0.07
Number of reflections
3496
R (eq)
0.104
Unique reflections
3315
Reflections (gt)
1972
Extinction coefficient
9800(2600)
Number of reflections used
3315
Number of parameters
254
R (gt)
0.052
w
R (gt)
0.071
Goodness of fit
1.05
Shift/su (max)
<0.0005
Residual density (max)
0.17
Residual density (min)
−0.18Table 2
Atomic parameters for the carbon atoms of compound2.
Atom
x
y
z
B
i
s
o
a
C1
0.2553(3)
0.4240(2)
0.8743(2)
2.69(12)
C1a
0.0801(3)
0.2666(3)
0.8227(3)
3.98(16)
C2
0.2495(3)
0.4743(2)
0.9688(2)
2.79(13)
C3
0.1478(3)
0.5362(2)
0.9680(2)
3.51(14)
C4
0.1449(3)
0.5845(3)
1.0579(3)
3.98(16)
C5
0.2468(3)
0.5744(3)
1.1552(3)
4.07(16)
C6
0.3470(3)
0.5136(2)
1.1594(2)
3.35(14)
C7
0.3521(2)
0.4626(2)
1.0687(2)
2.58(12)
C8
0.4564(2)
0.3958(2)
1.0740(2)
2.62(12)
C9
0.5576(3)
0.3779(2)
1.1725(2)
3.30(14)
C10
0.6547(3)
0.3148(2)
1.1775(3)
4.01(15)
C11
0.6561(3)
0.2666(3)
1.0850(3)
4.05(16)
C12
0.5598(3)
0.2818(2)
0.9882(2)
3.42(14)
C13
0.4585(3)
0.3474(2)
0.9801(2)
2.72(12)
C14
0.3554(3)
0.3645(2)
0.8787(2)
2.66(12)
C14a
0.1962(3)
0.2004(2)
0.8303(2)
3.84(16)
C15
0.3528(3)
0.3165(2)
0.7738(2)
2.96(13)
C15a
0.2618(3)
0.2232(2)
0.7473(2)
3.30(14)
C16
0.3157(3)
0.3918(2)
0.6852(2)
3.15(13)
C16a
0.1586(3)
0.2248(2)
0.6349(2)
3.57(14)
C17
0.3779(3)
0.4039(3)
0.6103(3)
4.21(17)
C18
0.3382(4)
0.4753(3)
0.5317(3)
5.10(19)
C19
0.2348(4)
0.5332(3)
0.5265(3)
5.29(19)
C20
0.1731(3)
0.5223(3)
0.6011(3)
4.13(16)
C21
0.2120(3)
0.4520(2)
0.6804(2)
3.19(14)
C21a
0.0437(3)
0.2923(3)
0.6272(2)
3.74(15)
C22
0.1493(3)
0.4343(2)
0.7640(2)
3.05(13)
C22a
0.0534(3)
0.3435(2)
0.7336(2)
3.35(13)
B
i
s
o
a is the mean of the principal axes of the thermal ellipsoid.Figure 1
ORTEP (30% probability ellipsoids) of2 showing the atom labeling scheme.Figure 2
Stereoview of2 showing the molecular packing in the unit cell.Ab initio optimizations were performed using Gaussian software [16] through the Ohio Supercomputing Center [17] with both the restricted Hartree-Fock (RHF) and second-order Møller-Plesset (MP2) methods for the isolated molecule. MP2 is a perturbation theory that goes beyond RHF by adding electron-correlation effects. Inclusion of diffuse functions in the 6-31+G(d) basis set is appropriate especially with the elongated bonds in this system.


## 3. Results and Discussion

Crystallographic and theoretical bond lengths and angles for2 are in good agreement (Table 3), although experimental results show distortion, discussed below, from the theoretical C
s point-group symmetry of the isolated molecule. A vibrational frequency analysis by RHF showed the optimized geometry to correspond to a potential-energy minimum.Table 3
Carbon-carbon bond distances (Å) and angles (°) in compound2.
Distance
Observed
RHFa
MP2b
C1–C2
1.437(4)
1.452
1.437
C1–C14
1.358(4)
1.349
1.382
C1–C22
1.529(4)
1.528
1.511
C1a–C14a
1.544(5)
1.551
1.550
C1a–C22a
1.527(5)
1.540
1.538
C2–C3
1.403(4)
1.414
1.421
C2–C7
1.422(4)
1.407
1.432
C3–C4
1.361(5)
1.368
1.386
C4–C5
1.393(5)
1.400
1.407
C5–C6
1.370(5)
1.368
1.387
C6–C7
1.395(4)
1.412
1.417
C7–C8
1.454(4)
1.460
1.452
C8–C9
1.414(4)
1.412
1.417
C8–C13
1.405(4)
1.407
1.432
C9–C10
1.360(5)
1.368
1.387
C10–C11
1.386(5)
1.400
1.407
C11–C12
1.368(4)
1.368
1.386
C12–C13
1.410(4)
1.414
1.421
C13–C14
1.447(4)
1.452
1.437
C14–C15
1.516(4)
1.528
1.511
C14a–C15a
1.525(5)
1.540
1.538
C15–C15a
1.591(4)
1.592
1.589
C15–C16
1.504(4)
1.515
1.503
C15a–C16a
1.528(4)
1.540
1.538
C16–C17
1.381(4)
1.384
1.399
C16–C21
1.395(4)
1.389
1.401
C16a–C21a
1.545(5)
1.551
1.550
C17–C18
1.382(6)
1.391
1.400
C18–C19
1.372(7)
1.385
1.401
C20–C21
1.377(4)
1.384
1.399
C21–C22
1.495(4)
1.515
1.503
C21a–C22a
1.532(4)
1.540
1.538
C22–C22a
1.595(4)
1.592
1.589
Angle
Observed
RHFa
MP2b
C2–C1–C14
121.5(2)
121.0
121.0
C2–C1–C22
121.9(2)
122.2
122.2
C14–C1–C22
116.6(2)
116.8
116.8
C14a–C1a–C22a
113.6(3)
113.8
113.9
C1–C2–C3
123.4(3)
122.0
121.8
C1–C2–C7
119.1(2)
119.5
119.5
C3–C2–C7
117.5(3)
118.5
118.6
C2–C3–C4
122.6(3)
121.7
121.5
C3–C4–C5
119.8(3)
119.7
119.8
C4–C5–C6
119.2(3)
119.7
119.9
C5–C6–C7
122.2(3)
121.8
121.6
C2–C7–C6
118.7(3)
118.5
118.4
C2–C7–C8
119.1(2)
119.5
119.5
C6–C7–C8
122.2(2)
122.0
122.1
C7–C8–C9
121.4(3)
122.0
122.1
C7–C8–C13
120.1(2)
119.5
119.5
C9–C8–C13
118.5(3)
118.5
118.4
C8–C9–C10
121.4(3)
121.8
121.6
C9–C10–C11
120.1(3)
119.7
119.9
C10–C11–C12
120.3(3)
119.7
119.8
C11–C12–C13
121.0(3)
121.7
121.5
C8–C13–C12
118.8(2)
118.5
118.6
C12–C13–C14
122.0(3
)
122.0
121.8
C8–C13–C14
119.2(2)
119.5
119.5
C1–C14–C13
120.8(3)
121.0
121.0
C1–C14–C15
117.0(2)
116.8
116.8
C13–C14–C15
122.1(2)
122.0
122.2
C1a–C22a–C21a
108.2(3)
107.7
108.8
C14–C15–C15a
111.5(2)
113.0
111.9
C14–C15–C16
108.6(2)
107.5
108.3
C15a–C15–C16
113.4(2)
113.7
113.3
C14a–C15a–C15
115.1(2)
115.0
114.3
C14a–C15a–C16a
108.2(3)
107.7
108.8
C15–C15a–C16a
114.2(3)
115.0
114.3
C15–C16–C17
124.0(3)
123.8
123.5
C15–C16–C21
116.6(3)
116.2
116.5
C17–C16–C21
119.4(3)
119.9
120.0
C15a–C16a–C21a
113.5(2)
113.7
113.9
C16–C17–C18
120.4(3)
120.2
120.1
C17–C18–C19
119.9(3)
119.9
120.0
C18–C19–C20
120.1(3)
119.9
120.0
C19–C20–C21
120.8(3)
120.2
120.1
C16–C21–C20
119.5(3)
119.9
120.0
C16–C21–C22
116.3(3)
116.2
116.5
C20–C21–C22
124.2(3)
123.8
123.5
C16a–C21a–C22a
114.2(2)
113.7
113.9
C1–C22–C21
108.2(2)
107.5
108.3
C1–C22–C22a
113.3(2)
113.0
111.9
C21–C22–C22a
111.9(2)
113.7
113.3
C1a–C14a–C15a
114.3(3)
113.8
113.9
C1a–C22a–C22
114.1(2)
115.0
114.3
C21a–C22a–C22
115.1(3)
115.0
114.3
aRestricted Hartree-Fock theory with 6-31+G(d) basis set.
bSecond-order restricted Møller-Plesset theory with the same basis set.Compound2 contains a phenanthrene moiety (including carbons C1–C14) and a benzenoid ring (including carbons C16–C21). The aliphatic carbons C15 and C22 derive from the original dibenzanthracene and the remaining six methylene and methine carbons (C1a, C14a, C15a, C16a, C21a, and C22a) derive from the cyclohexadiene addend. Two interannular bonds (C15–C15a and C22–C22a) were formed by the photocycloaddition (Scheme 1). The six carbons of the benzenoid ring are essentially coplanar, and the aromatic bond distances are rather uniform; the shortest at about 1.372 Å involve the distal bonds (C18–C19 and C19–C20) and the longest at 1.395(4) the proximal bond (C16–C21). However, the fourteen carbons of the phenanthrene are less so in both respects (Table 3). Dissecting these atoms into three six-carbon ring systems (two exterior rings including C2–C7 and C8–C13 and an internal ring including C1–C2, C7–C8, and C13–C14), the least-squares planes of the two exterior rings are rotated by 3.41° relative to one another and both rotate about equally towards the cyclohexyl group by about 1.8° from that of the internal ring. This rotation is seen also in the theoretical results and likely is due to unfavorable nonbonded intramolecular interactions involving aromatic and bridgehead hydrogens with distances H3⋯H22 and H12⋯H15 being about 1.93 Å. Similarly the distance between two aromatic hydrogens, H6⋯H9, is 1.97 Å and may account for a chiral twist in the phenanthrene group with a torsion angle of 2.3° for H6–C6–C9–H9. The absence of such a twist in the theoretical geometry, however, suggests that it may be due to a packing effect instead.Furthermore, significant bond alternation is present. The shortest bond at 1.358(4) Å occurs between the proximal carbons C1–C14, with C3–C4, C5–C6, C9–C10, and C11–C12 also being within 1.37 Å. This is consistent with the structures found for other substituted phenanthrenes [18–20] and indicates electronic localization imparting greater double bond character to the C1–C14 bond. The bond alternation is an intramolecular effect as supported by its agreement with the theoretical results, which pertain to an isolated molecule.Another unusual feature of the structure concerns the relatively long interannular C–C bonds between C15–C15a and C22–C22a, which average 1.593 Å. An even greater elongation is observed in the adduct1, for which the corresponding bond distances average 1.611 Å [5]. This is most likely due to strain [21, 22] rather than to hyperconjugation as proposed for compounds like1 [23, 24] which contain additional unsaturation, nor can it be ascribed to steric effects involving the methylene carbons, as theendo-hydrogens (H1aA and H14aA) lie closer to the subjacent carbons (C1 and C14) in2 than do the olefinic hydrogens in1. Noteworthy is the same distance, 1.593(2) Å, found for the interannular bonds in the corresponding anthracene-derived species containing two benzenoid rings [4]. The nonbonded intramolecular distances in2 are found to be 2.50 Å for H1aA⋯C1 and 2.45 Å for H14aA⋯C14. Similar distances (2.51 Å for H16aA⋯C16 and 2.45 Å for H21aA⋯C21) are observed for theendo-methylene hydrogens lying above the benzenoid ring. The slight differences (~0.05 Å) found in each pair are consistent with the relative skewing of the carbon framework to avoid the unfavorable interactions between neighboring hydrogens. The close contacts between theendo-hydrogens and the subjacent aromatic carbons result in diamagnetic shielding of these hydrogens, which are observed to resonate at 1.03 ppm for H1aA and H14aA and at 1.24 ppm for H16aA and H21aA. The greater shielding for the hydrogens lying above the phenanthrene structure is consistent with the presence of a greater aromatic “ring current” in the larger aromatic moiety [7–9]. Knowing the location of the atoms provides assistance in determining the shielding tensors which can be applied to provide information about the aromaticity of molecules with alternating bond lengths [25].Although large planar aromatic hydrocarbons often pack with parallel-planar stacking [26],2 is not planar and the phenanthrene moieties do not associate with this fashion. Instead, the benzenoid ring of one molecule orients in a “T”-type interaction [26] with C2, C3, C6, and C7 of the phenanthrene ring of an adjacent molecule, and the saturated ring orients towards the other side near C8, C9, C10, and C13 (Figure 3).Figure 3
Perspective perpendicular to the phenanthrene least-squares plane of one molecule (atoms shaded) showing the orientation of the neighboring subjacent molecule (atoms unshaded) in the unit cell of2.


## 4. Summary

The solid state structure of 9,14,15,16,17,18,19,20-octahydro-9,14[1′,4′]-benzenobenzo[b]triphenylene2 was determined by single crystal X-ray diffraction to have no disorder and revealed several close intramolecular nonbonded contacts involving hydrogens derived from the dibenzanthracene moiety. These steric effects produce a symmetric folding in the phenanthrene unit of about 3.4° between the two exterior rings as well as a smaller chiral twisting. Long interannular C–C single bonds of about 1.593 Å also are present due to strain, which is greater in1 with even longer interannular bonds, rather than steric effects, which would be smaller in1 than in2. The experimental results are in good agreement with calculations using RHF and MP2 theories, confirming that these effects originate mostly from intramolecular interactions, although the twisting may arise from intermolecular packing. Anisotropic shielding of the fourendo-methylene hydrogens in the 1H NMR spectrum is larger for the two hydrogens lying above the phenanthrene unit than those above the benzenoid ring, as expected for the greater diamagnetic ring current for the larger aromatic moiety.



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*Source: 8129210-2016-06-20.xml*