r-1,c-2,t-3,t-4-1,3-Bis(4-methoxy­phenyl)-2,4-bis(5-phenyl-1,3,4-oxa­diazol-2-yl)­cyclo­butane 1,4-dioxane solvate

The asymmetric unit of the crystal structure of C₃₄H₂₈N₄O₄.C₄H₈O₂, which is a 1:1 inclusion complex, consists of half a mol­ecule of the title compound t-DPC and half a mol­ecule of 1,4-dioxane. The structure shows that t-DPC is centrosymmetric; its cyclo­butane ring has an exactly planar conformation, and is nearly square. The four C-C single bonds are of equal length [1.569 (4) Å] and the bond angles are 91.6 (2) and 88.4 (2)°. The major photodimerization process is a head-to-tail reaction rather than a head-to-head one.

Key indicators

• Single-crystal X-ray study
• T = 298 K
• Mean [sigma](C-C) = 0.006 Å
• R factor = 0.068
• wR factor = 0.167
• Data-to-parameter ratio = 12.6

checkCIF results

No syntax errors found

ADDSYM reports no extra symmetry


 Alert Level B:



PLAT_360  Alert B Short  C(sp3)-C(sp3) Bond  C(18)  -   C(19)  =       1.24 Ang.

Author response: C(18) and C(19) are carbon atom of the solvent 1,4-dioxane.

 Alert Level C:



REFLT_03
         From the CIF: _diffrn_reflns_theta_max           25.03
         From the CIF: _reflns_number_total               2746
         TEST2: Reflns within _diffrn_reflns_theta_max
         Count of symmetry unique reflns         3011
         Completeness (_total/calc)             91.20%
          Alert C: < 95% complete


 0 Alert Level A = Potentially serious problem

 1 Alert Level B = Potential problem

 1 Alert Level C = Please check

---

S1. Comment

The cyclobutane rings for most tetraarylcyclobutanes have a puckered conformation, such as in r-1,c-2,t-3,t-4–1,3-bis[2-(4-R-phenyl)]-2,4-di-(4-pyridyl)cyclobutane (R = Cl, CH₃, C₆H₅). The average dihedral angles of the cyclobutane ring are 19.2, 24.6 and 16.4°, respectively, in the three structures (Busetti et al., 1980; Zhang et al., 1998; Zhang, Zhang et al., 2000). However, it is very interesting that some tetraoxazolyl-substituted cyclobutanes have planar four-membered rings, as found in r-1,c-2,t-3,t-4-tetrakis[2-(5-phenyl-oxazolyl)]cyclobutane (Zhang et al., 1996), r-1,c-2,t-3,t-4-tetrakis[2-benzoxazolyl]cyclobutane (Zhang, Li et al., 2000) and r-1,c-2,t-3,t-4-tetrakis[2-(6,7-dimethylbenzoxazolyl)]cyclobutane (Kao et al., 1989). This interesting phenomenon prompted us to generate a new heteroaryl-substituted cyclobutane in order to study the effect of the substitutent on the conformation of the cyclobutane ring. We report here for the first time that a diphenyl-diphenyloxadiazolyl-substituted cyclobutane (t-DPC) has a planar conformation.

The X-ray diffraction results clearly show that there are one t-DPC molecule and one 1,4-dioxane molecule in the unit cell and the molecules are exactly centrosymmetric, demonstrating that head-to-tail photodimerization process has occurred. The cyclobutane ring of t-DPC is planar, just as in tetraoxazolylcyclobutanes. It appears that the substituents in these compounds, lacking an α-H atom, have a relatively small steric requirement, allowing a planar four-membered ring.

The two independent pairs of C—C bonds of the cyclobutane ring are equal in length [1.569 (4) Å] and are longer than a normal C—C single bond. However, this elongation is common for cyclobutanes. The bond angles C8—C9—C8ⁱ and C9—C8—C9ⁱ are 91.6 (2) and 88.4 (2)° respectively, so that the cyclobutane ring is almost a square. The dihedral angle between the phenyloxadiazolyl plane and the 4-methoxyphenyl plane situated on the same side of the cyclobutane ring is 50.4 (3)°, intermediate between parallel and perpendicular.

For the five bonds in the oxadiazolyl ring, the C—O single bonds are shorter than that (1.365 Å) of 2,5-di(4-pyridyl)-1,3,4-oxadiazole (DPO), but the N—N single bond is much longer than that (1.409 Å) of DPO (Stockhause et al., 2001).

The bond angle C1—O1—C2 is 118.0 (4)°, which is quite large compared with that of common aliphatic ethers, and atoms C1 and O1 are almost coplanar with the benzene ring plane [the torsion angles C1—O2—C2—C3 and C1—O2—C2—C3 are -3(4) and 179 (8)°, respectively], which means that O1 is an sp² hybridized atom and there exists a n-π conjugation between O1 and the benzene ring. Because of the non-bonding repulsion between the methyl group and H3a (on C3), the bond angle C3—C2—O1 is increased to 125.0 (4)°, whereas the C7—C2—O1 angle is reduced to 114.7 (4)°.

S2. Experimental

trans-1-(4-Methoxyphenyl)-2-[2-(5-phenyl-1,3,4-oxadiazolyl)]ethene (PDE) was synthesized by condensing 4-methoxybenzaledhyde and 2-methyl-5-phenyl-1,3,4-oxadiazole in DMF with KOH catalysis at 348 K; m.p. 403–404 K. UV (1,4-dioxane): λ_max 338 (logε 4.58) nm; IR (KBr): 3056 (w), 1640 (m), 1606 (versus), 1528 (versus), 1246 (versus), 1176 (versus), 1012 (m), 960 (m) cm^-1; ¹H NMR (CDCl₃): δ 8.14–8.08 (4H, m), 7.60–7.47 (12H, m), 6.96–6.89 (6H, m), 4.10 (4H, t), 2.00 (4H, m) p.p.m. 1.0 g PDE was dissolved in 200 ml acetonitrile and irradiated with a 300 W medium-pressure mercury lamp for 70 h. Then 200 ml of water was added, the precipitate was filtered and recrystallized from ethanol to give 123 mg t-DPC; m.p. 504–505 K. λ_max 255 (logε 4.58) nm; IR (KBr): 3037 (w), 2958 (w), 1612 (s), 1563 (s), 1515 (versus), 1251 (versus), 1181 (s), 1037 (s), 829 (s), 775 (s) cm^-1; ¹H NMR (CDCl₃): δ 7.81 (4H, d), 7.47 (6H, m), 7.26 (4H, d), 6.77 (4H, d), 4.89 (2H, t), 4.80 (2H, d), 3.66 (6H, s) p.p.m. ¹³C NMR (CDCl₃): δ 165.65, 165.40, 159.19, 131.77, 129.37, 129.11, 128.60, 126.96, 123.97, 114.36, 55.39, 43.70, 39.93 p.p.m. A single-crystal of t-DPOE was grown in 1,4-dioxane by slow evaporation of the solvent.

Computing details

Data collection: SMART (Bruker, 1998); cell refinement: SMART; data reduction: SAINT and SHELXTL (Bruker, 1998); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: SHELXTL; software used to prepare material for publication: SHELXTL.

Figures

Fig. 1. View of t-DPC with 30% probability ellipsoids.

r-1,c-2,t-3,t-4–1,3-bis(4-methoxyphenyl)-2,4-bis[2-(5-phenyl-1,3,4- oxadiazolyl)]cyclobutane

Crystal data

C34H28N4O4·C4H8O2	Z = 1
Mr = 644.71	F(000) = 340
Triclinic, P1	Dx = 1.257 Mg m^−3
a = 5.995 (2) Å	Mo Kα radiation, λ = 0.71073 Å
b = 10.242 (4) Å	Cell parameters from 2713 reflections
c = 14.292 (5) Å	θ = 2.6–21.3°
α = 93.370 (6)°	µ = 0.09 mm^−1
β = 90.595 (6)°	T = 298 K
γ = 103.557 (6)°	Plate, colorless
V = 851.4 (5) Å^3	0.30 × 0.25 × 0.20 mm

Data collection

CCD area-detector diffractometer	1195 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	Rint = 0.043
Graphite monochromator	θmax = 25.0°, θmin = 1.4°
ϕ and ω scans	h = −7→6
3275 measured reflections	k = −12→7
2746 independent reflections	l = −16→16

Refinement

Refinement on F^2	H-atom parameters constrained
Least-squares matrix: full	w = 1/[σ^2(Fo^2) + (0.065P)^2] where P = (Fo^2 + 2Fc^2)/3
R[F^2 > 2σ(F^2)] = 0.068	(Δ/σ)max = 0.003
wR(F^2) = 0.167	Δρmax = 0.16 e Å^−3
S = 0.97	Δρmin = −0.19 e Å^−3
2746 reflections	Extinction correction: SHELXL97
218 parameters	Extinction coefficient: 0.023 (4)
0 restraints

Special details

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
C1	−0.3133 (12)	−0.1523 (6)	−0.0055 (3)	0.160 (3)
H1A	−0.4122	−0.1540	−0.0590	0.240*
H1B	−0.3095	−0.2427	0.0074	0.240*
H1C	−0.1611	−0.1025	−0.0182	0.240*
O2	0.3104 (3)	0.3051 (2)	0.57005 (15)	0.0545 (7)
O1	−0.3966 (6)	−0.0904 (3)	0.0726 (2)	0.1250 (12)
C2	−0.2768 (8)	−0.0801 (4)	0.1579 (3)	0.0773 (12)
C3	−0.0896 (8)	−0.1309 (4)	0.1727 (3)	0.0834 (13)
H3A	−0.0353	−0.1785	0.1241	0.100*
C4	0.0216 (6)	−0.1115 (3)	0.2611 (3)	0.0646 (10)
H4A	0.1524	−0.1437	0.2703	0.078*
C5	−0.0618 (5)	−0.0454 (3)	0.3341 (2)	0.0485 (9)
C6	−0.2565 (6)	0.0027 (3)	0.3178 (2)	0.0591 (10)
H6A	−0.3149	0.0479	0.3665	0.071*
C7	−0.3649 (6)	−0.0159 (4)	0.2303 (3)	0.0699 (11)
H7A	−0.4968	0.0151	0.2207	0.084*
C8	0.0598 (5)	−0.0253 (3)	0.4283 (2)	0.0487 (9)
H8A	0.2160	−0.0380	0.4219	0.058*
C9	0.0628 (5)	0.1072 (3)	0.4897 (2)	0.0494 (9)
H9A	−0.0388	0.1573	0.4617	0.059*
C10	0.2916 (6)	0.1959 (3)	0.5100 (2)	0.0490 (9)
N1	0.4888 (5)	0.1817 (3)	0.4801 (2)	0.0648 (9)
N2	0.6531 (5)	0.2931 (3)	0.5227 (2)	0.0658 (9)
C11	0.5393 (5)	0.3593 (3)	0.5743 (2)	0.0519 (9)
C12	0.6285 (6)	0.4813 (3)	0.6347 (2)	0.0509 (9)
C13	0.8570 (6)	0.5469 (3)	0.6323 (2)	0.0627 (10)
H13A	0.9538	0.5126	0.5923	0.075*
C14	0.9436 (7)	0.6617 (4)	0.6876 (3)	0.0728 (12)
H14A	1.0983	0.7045	0.6852	0.087*
C15	0.8032 (7)	0.7132 (4)	0.7462 (3)	0.0820 (13)
H15A	0.8627	0.7910	0.7839	0.098*
C16	0.5771 (7)	0.6517 (4)	0.7498 (3)	0.0885 (13)
H16A	0.4817	0.6883	0.7891	0.106*
C17	0.4878 (6)	0.5334 (3)	0.6945 (3)	0.0736 (12)
H17A	0.3337	0.4900	0.6980	0.088*
C18	−0.2010 (15)	−0.4902 (10)	0.0342 (10)	0.213 (4)
H18A	−0.1529	−0.3928	0.0360	0.256*
H18B	−0.3574	−0.5175	0.0552	0.256*
O3	−0.169 (2)	−0.5559 (10)	−0.0619 (9)	0.310 (4)
C19	−0.067 (2)	−0.5407 (16)	0.0782 (9)	0.345 (11)
H19A	−0.0709	−0.6315	0.0534	0.414*
H19B	−0.1013	−0.5423	0.1444	0.414*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
C1	0.253 (8)	0.162 (5)	0.064 (3)	0.059 (5)	−0.014 (4)	−0.034 (3)
O2	0.0482 (14)	0.0503 (13)	0.0627 (15)	0.0118 (11)	−0.0036 (12)	−0.0158 (11)
O1	0.177 (3)	0.138 (3)	0.065 (2)	0.057 (2)	−0.040 (2)	−0.0237 (18)
C2	0.097 (3)	0.076 (3)	0.055 (3)	0.016 (3)	−0.005 (3)	−0.005 (2)
C3	0.109 (3)	0.081 (3)	0.060 (3)	0.031 (3)	0.014 (3)	−0.029 (2)
C4	0.065 (2)	0.065 (2)	0.064 (2)	0.0220 (19)	0.009 (2)	−0.0160 (19)
C5	0.0404 (18)	0.0499 (19)	0.052 (2)	0.0073 (16)	0.0089 (17)	−0.0145 (16)
C6	0.055 (2)	0.058 (2)	0.056 (2)	0.0000 (18)	−0.0041 (18)	−0.0105 (18)
C7	0.063 (2)	0.071 (2)	0.073 (3)	0.013 (2)	−0.008 (2)	−0.006 (2)
C8	0.0391 (17)	0.0459 (18)	0.059 (2)	0.0093 (15)	−0.0001 (17)	−0.0128 (16)
C9	0.0440 (18)	0.0449 (19)	0.060 (2)	0.0152 (16)	−0.0033 (17)	−0.0127 (17)
C10	0.058 (2)	0.0398 (18)	0.049 (2)	0.0145 (18)	−0.0043 (18)	−0.0124 (15)
N1	0.0535 (18)	0.0584 (18)	0.078 (2)	0.0099 (15)	−0.0012 (17)	−0.0216 (15)
N2	0.0526 (18)	0.0586 (18)	0.079 (2)	0.0053 (16)	−0.0009 (17)	−0.0197 (17)
C11	0.044 (2)	0.046 (2)	0.060 (2)	0.0011 (17)	−0.0057 (18)	−0.0050 (18)
C12	0.057 (2)	0.0431 (19)	0.051 (2)	0.0087 (17)	−0.0093 (18)	−0.0032 (16)
C13	0.055 (2)	0.055 (2)	0.069 (2)	−0.0010 (18)	−0.0097 (18)	−0.0109 (18)
C14	0.069 (3)	0.064 (3)	0.075 (3)	−0.003 (2)	−0.009 (2)	−0.008 (2)
C15	0.085 (3)	0.063 (3)	0.083 (3)	−0.009 (2)	−0.032 (3)	−0.012 (2)
C16	0.083 (3)	0.080 (3)	0.095 (3)	0.018 (2)	−0.008 (3)	−0.043 (2)
C17	0.057 (2)	0.068 (2)	0.088 (3)	0.007 (2)	−0.005 (2)	−0.032 (2)
C18	0.153 (7)	0.241 (9)	0.294 (12)	0.125 (7)	0.101 (9)	0.081 (10)
O3	0.316 (12)	0.348 (10)	0.268 (9)	0.103 (9)	−0.044 (9)	−0.057 (8)
C19	0.194 (9)	0.56 (2)	0.375 (17)	0.195 (12)	0.155 (10)	0.386 (18)

Geometric parameters (Å, º)

C1—O1	1.405 (5)	C10—N1	1.298 (4)
O2—C10	1.352 (3)	N1—N2	1.422 (3)
O2—C11	1.354 (3)	N2—C11	1.281 (4)
O1—C2	1.394 (5)	C11—C12	1.463 (4)
C2—C3	1.363 (5)	C12—C17	1.379 (4)
C2—C7	1.369 (5)	C12—C13	1.379 (4)
C3—C4	1.404 (5)	C13—C14	1.368 (5)
C4—C5	1.373 (4)	C14—C15	1.364 (5)
C5—C6	1.391 (4)	C15—C16	1.357 (5)
C5—C8	1.504 (4)	C16—C17	1.398 (5)
C6—C7	1.387 (4)	C18—C19	1.240 (9)
C8—C9	1.569 (4)	C18—O3	1.527 (10)
C8—C9^i	1.569 (4)	O3—C19^ii	1.552 (12)
C9—C10	1.472 (4)	C19—O3^ii	1.552 (12)
C9—C8^i	1.569 (4)
C10—O2—C11	102.9 (3)	N1—C10—C9	128.5 (3)
C2—O1—C1	118.0 (4)	O2—C10—C9	118.8 (3)
C3—C2—C7	120.3 (4)	C10—N1—N2	105.3 (3)
C3—C2—O1	125.0 (4)	C11—N2—N1	105.9 (3)
C7—C2—O1	114.7 (4)	N2—C11—O2	113.1 (3)
C2—C3—C4	120.1 (4)	N2—C11—C12	127.7 (3)
C5—C4—C3	120.4 (4)	O2—C11—C12	119.1 (3)
C4—C5—C6	118.4 (3)	C17—C12—C13	118.6 (3)
C4—C5—C8	119.6 (3)	C17—C12—C11	121.2 (3)
C6—C5—C8	122.0 (3)	C13—C12—C11	120.1 (4)
C7—C6—C5	121.1 (3)	C14—C13—C12	121.1 (4)
C2—C7—C6	119.7 (4)	C15—C14—C13	120.0 (4)
C5—C8—C9	118.3 (3)	C16—C15—C14	120.4 (4)
C5—C8—C9^i	117.8 (2)	C15—C16—C17	120.0 (4)
C9—C8—C9^i	88.4 (2)	C12—C17—C16	119.9 (3)
C10—C9—C8	115.4 (3)	C19—C18—O3	96.6 (10)
C10—C9—C8^i	117.5 (3)	C18—O3—C19^ii	94.7 (9)
C8—C9—C8^i	91.6 (2)	C18—C19—O3^ii	102.4 (8)
N1—C10—O2	112.7 (3)

Symmetry codes: (i) −x, −y, −z+1; (ii) −x, −y−1, −z.