(1E,3E,5E)-1,2,3,4,5,6-Hexa­fluoro-1,6-di­phenyl­hexatriene

The title triene, C₁₈H₁₀F₆, was prepared via the Pd⁰ coupling reaction of (E)-(1,2-di­fluoro-1,2-ethenediyl)­bis­(tri­butyl­stan­nane) with (Z)-β-iodo-α,β-di­fluoro­styrene in N,N′-dimethylformamide/tetrahydrofuran. The crystal structure shows the product to be the 1E,3E,5E isomer. Due to steric interactions between F atoms, the double bonds are not coplanar. The planes defined by the two terminal double bonds are almost perpendicular.

S1. Comment

The chemistry of polyfluorinated polyene systems (beyond dienes) is virtually unknown. The few compounds reported were generally mixtures of all possible E/Z isomers (Yagupol'skii et al., 1976, 1977, 1985). This work was initiated to develop methodology for the stereospecific preparation of fluorinated polyenes in order to compare the effects of the fluorine substituents on conjugation, reactivity, and stability of the polyene. The titled triene was stereospecifically prepared via the route shown below. \sch

Fig. 1 shows that the triene is the (1E,3E,5E)-isomer and that the conjugated system has a conformation that is significantly distorted from overall planarity by intramolecular steric interactions. Although the overall molecule is not planar, the phenyl rings 1 (C7—C12) and 2 (C13—C18) and individual double-bond moieties (Db1: C7, F1, C1, C2, F2, C3; Db2: C2, F3, C3, C4, F4, C5; Db3: C4, F5, C5, C6, F7, C13) are planar. The largest r.m.s. deviation from least-squares plane is 0.03 Å for Db3. Ring 1 and Db1 are nearly coplanar [dihedral angle = 5.6 (2)°] as are ring 2 and Db3 [dihedral angle = 2.1 (2)°]. However, the double-bond moieties are not coplanar. Rotations of about 42° about the C2—C3 and C4—C5 bonds reduce intramolecular steric repulsion between adjacent fluoro-substituents. [Note: The barrier to full rotation (perpendicular double bonds) about these bonds should be similar to that of the central bond in 1,3-butadiene, calculated value = 5.9 kcal mol⁻¹ (Head-Gordon & Pople, 1993).] The longest F···F intramolecular distance is 0.375 Å shorter than the shortest F···F intermolecular distance (see Table 2). An additional result of these two rotations is that the phenyl rings are nearly perpendicular [dihedral angle = 88.3 (1)°]. Even though the double-bond moieties are not coplanar, the shortening of the C2—C3 and C4—C5 bonds show that they are part of a delocalized π system.

Fig. 2 shows the that packing of the molecules is organized by π···π and CH···π interactions. The molecules form a network via π···π interactions between adjacent (phenyl ring-double bond) π systems across inversion centers. The ring 1-π system (ring 1 and Db1) overlap occurs across the (1/2,0,1/2) set of inversion centers such that C7 is approximately centered over the adjacent phenyl ring (π···π spacing = 3.537 Å, C7 – Xc1ⁱ = 3.570 Å; Xc1ⁱ is the centroid of symmetry-related Ring 1, i = 1 − x, 2 − y, 1 − z). The ring 2-π system (ring 2 and Db3) has a greater degree of overlap and a closer π···π spacing·This interaction occurs across the (01/20) set of inversion centers such that C6 is approximately centered over the adjacent phenyl ring (π···π spacing = 3.427 Å, C6···Xc2ⁱⁱ = 3.455 Å; Xc2ⁱⁱ is the centroid of symmetry-related ring 2, ii = −x, 1 − y, −z). The network also includes C15—H15···ring 1 interactions that form dimers across the (1/2,1/2,0) set of inversion centers (H15···Xc1ⁱⁱⁱ = 2.89 Å, C15—H15···Xc1ⁱⁱⁱ = 143°; iii = 1 − x, 1 − y, −z). The crystal morphology appears to correlate with these interactions. The direction of the longest molecular dimension is approximately parallel to the (a+b)-face diagonal direction. The binding faces for the largest crystal dimension are the (110) and (110) faces. The direction of the C15—H15···ring 1 interaction is approximately parallel to the (a-c)-face diagonal. The binding faces for the smallest crystal dimension are the (101) and (101) faces.

S2. Experimental

A three-neck 250 ml round bottom flask equipped with a teflon-coated stir bar, a cold water condenser attached to a nitrogen source, a thermometer, and a rubber septum was charged with CuI (1.48 g, 7.7 mmol), N,N'-dimethylformamide (35 ml), tetrahydrofuran (THF) (35 ml), Pd(PPh₃)₄ (0.44 g, 0.4 mmol), (E)-n-Bu₃SnCF═CFn-Bu₃ (4.95 g), and (Z)-PhCF═CFI (4.12 g, 15.5 mmol). The reaction mixture was stirred at room temperature for 14 h, at 310 K for 14 h, and at 318 K for 10 h.

The majority of the THF was removed by rotary evaporation. The residue was diluted with 80 ml of H₂O, extracted with Et₂O (4 x 80 ml), and the combined ether layers dried over anhydrous MgSO₄. The majority of the solvent was removed by rotary evaporation; the residue was poured onto a silica-gel chromatgraphy column and eluted with pentane, R_f = 0.88. Removal of most of the pentane yielded a mixture of the title compound, n-Bu₃SnI and (Z)-PhCF═CFI. This mixture was recrystallized twice from hexane to give 1.0 g (40% yield) of (1E,3E,5E)-1,2,3,4,5,6-hexafluoro-1,6-diphenylhexatriene as white crystals, mp. 344 K.

₁₉F NMR (CDCl₃) δ-140.8 (dt, 2 F, J = 126 Hz, 24 Hz), −149.4 (m, 2 F), −162.8 (ddd, 2 F, J = 127 Hz, 15 Hz, 6 Hz). ₁H NMR (CDCl₃) δ 7.8 (m, 2H), 7.5 (m, 3H). ₁₃C NMR (CDCl₃) δ 151.2 (dd, J = 248 Hz, 42 Hz), 140.2 (m), 130.7 (s), 128.7 (s), 126.4 (t, J = 8 Hz), 117.4 (d, J = 337 Hz). HRMS calcd. for C₁₈H₁₀F₆ = 340.0687, obsd. = 340.0679.

Computing details

Data collection: CAD4 Operations Manual (Enraf-Nonius, 1977); cell refinement: CAD4 Operations Manual; data reduction: MolEN (Fair, 1990); program(s) used to solve structure: SHELXTL (Sheldrick, 1995); program(s) used to refine structure: SHELXTL; molecular graphics: SHELXTL; software used to prepare material for publication: SHELXTL.

Figures

	Fig. 1. View of title compound. Displacement ellipsoids are shown at the 35% level.
	Fig. 2. Packing diagram of the title compound.

(I)

Crystal data

C18H10F6	Z = 2
Mr = 340.26	F(000) = 344
Triclinic, P1	Dx = 1.528 Mg m^−3
a = 9.138 (1) Å	Mo Kα radiation, λ = 0.71073 Å
b = 10.793 (2) Å	Cell parameters from 45 reflections
c = 8.249 (1) Å	θ = 11.7–17.4°
α = 90.76 (1)°	µ = 0.14 mm^−1
β = 94.26 (1)°	T = 210 K
γ = 65.75 (1)°	Plate, colorless
V = 739.6 (2) Å^3	0.53 × 0.23 × 0.09 mm

Data collection

Enraf-Nonius CAD4 diffractometer	Rint = 0.042
Radiation source: fine-focus sealed tube	θmax = 25.0°, θmin = 2.0°
Graphite monochromator	h = −10→10
θ–2θ scans	k = −12→12
4307 measured reflections	l = −9→5
2587 independent reflections	4 standard reflections every 120 min
1706 reflections with I > 2σ(I)	intensity decay: <2

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)] = 0.039	H-atom parameters constrained
wR(F^2) = 0.122	Calculated w = 1/[σ^2(Fo^2) + (0.0533P)^2 + 0.1953P] where P = (Fo^2 + 2Fc^2)/3
S = 1.05	(Δ/σ)max = −0.001
2587 reflections	Δρmax = 0.20 e Å^−3
218 parameters	Δρmin = −0.19 e Å^−3
0 restraints	Extinction correction: SHELXTL (Sheldrick, 1995), Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
Primary atom site location: structure-invariant direct methods	Extinction coefficient: 0.0074 (40)

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 on F² for ALL reflections except for 0 with very negative F² or flagged by the user for potential systematic errors. Weighted R-factors wR and all goodnesses of fit S are based on F², conventional R-factors R are based on F, with F set to zero for negative F². The observed criterion of F² > σ(F²) is used only for calculating R factor obs 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	0.4979 (3)	0.7999 (2)	0.2747 (3)	0.0480 (6)
F1	0.3703 (2)	0.8514 (2)	0.1642 (2)	0.0723 (5)
C2	0.5281 (3)	0.6768 (2)	0.3303 (3)	0.0507 (6)
F2	0.6617 (2)	0.6131 (2)	0.4307 (2)	0.0802 (5)
C3	0.4352 (3)	0.5968 (2)	0.3005 (3)	0.0530 (6)
F3	0.5264 (2)	0.46226 (14)	0.2918 (2)	0.0759 (5)
C4	0.2762 (3)	0.6379 (2)	0.2924 (3)	0.0511 (6)
F4	0.1864 (2)	0.76861 (14)	0.3238 (2)	0.0681 (5)
C5	0.1833 (3)	0.5574 (2)	0.2646 (3)	0.0479 (6)
F5	0.0607 (2)	0.59361 (15)	0.3616 (2)	0.0642 (4)
C6	0.2036 (3)	0.4577 (2)	0.1600 (3)	0.0447 (5)
F6	0.3244 (2)	0.43336 (14)	0.0607 (2)	0.0590 (4)
C7	0.5783 (3)	0.8909 (2)	0.3122 (3)	0.0457 (5)
C8	0.5230 (3)	1.0142 (2)	0.2271 (3)	0.0560 (6)
H8	0.4376	1.0366	0.1482	0.067*
C9	0.5947 (4)	1.1034 (3)	0.2598 (4)	0.0661 (7)
H9	0.5565	1.1861	0.2035	0.079*
C10	0.7213 (4)	1.0708 (3)	0.3745 (4)	0.0673 (8)
H10	0.7695	1.1309	0.3954	0.081*
C11	0.7771 (3)	0.9497 (3)	0.4588 (3)	0.0657 (7)
H11	0.8627	0.9282	0.5373	0.079*
C12	0.7075 (3)	0.8593 (3)	0.4281 (3)	0.0559 (6)
H12	0.7471	0.7769	0.4851	0.067*
C13	0.1195 (3)	0.3690 (2)	0.1339 (3)	0.0433 (5)
C14	0.1655 (3)	0.2723 (2)	0.0137 (3)	0.0521 (6)
H14	0.2491	0.2654	−0.0486	0.063*
C15	0.0898 (3)	0.1863 (3)	−0.0154 (3)	0.0608 (7)
H15	0.1229	0.1219	−0.0963	0.073*
C16	−0.0337 (3)	0.1951 (3)	0.0744 (4)	0.0637 (7)
H16	−0.0844	0.1367	0.0555	0.076*
C17	−0.0823 (3)	0.2913 (3)	0.1929 (4)	0.0690 (8)
H17	−0.1677	0.2987	0.2528	0.083*
C18	−0.0060 (3)	0.3772 (3)	0.2245 (3)	0.0600 (7)
H18	−0.0388	0.4406	0.3065	0.072*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
C1	0.0435 (12)	0.0494 (13)	0.0461 (13)	−0.0150 (10)	−0.0023 (10)	0.0001 (10)
F1	0.0760 (10)	0.0684 (9)	0.0759 (10)	−0.0382 (8)	−0.0302 (8)	0.0197 (8)
C2	0.0398 (12)	0.0515 (14)	0.0567 (14)	−0.0158 (11)	−0.0046 (11)	0.0014 (11)
F2	0.0547 (9)	0.0675 (10)	0.1184 (14)	−0.0301 (8)	−0.0296 (9)	0.0313 (9)
C3	0.0499 (14)	0.0444 (13)	0.063 (2)	−0.0184 (11)	0.0011 (12)	0.0000 (11)
F3	0.0498 (8)	0.0467 (8)	0.1265 (15)	−0.0165 (7)	−0.0023 (9)	0.0019 (8)
C4	0.0499 (14)	0.0477 (13)	0.0545 (14)	−0.0195 (11)	0.0011 (11)	−0.0047 (11)
F4	0.0523 (8)	0.0559 (9)	0.0925 (11)	−0.0196 (7)	0.0043 (8)	−0.0277 (8)
C5	0.0413 (12)	0.0527 (13)	0.0470 (13)	−0.0165 (11)	0.0045 (11)	−0.0038 (11)
F5	0.0552 (8)	0.0750 (10)	0.0687 (9)	−0.0309 (7)	0.0209 (7)	−0.0246 (8)
C6	0.0413 (12)	0.0455 (12)	0.0427 (12)	−0.0131 (10)	0.0038 (10)	0.0011 (10)
F6	0.0593 (8)	0.0617 (8)	0.0638 (9)	−0.0303 (7)	0.0226 (7)	−0.0138 (7)
C7	0.0452 (12)	0.0480 (13)	0.0438 (12)	−0.0180 (10)	0.0095 (10)	−0.0070 (10)
C8	0.0578 (15)	0.0515 (14)	0.0576 (15)	−0.0215 (12)	0.0030 (12)	−0.0002 (11)
C9	0.086 (2)	0.0514 (15)	0.068 (2)	−0.0337 (14)	0.017 (2)	−0.0036 (13)
C10	0.082 (2)	0.073 (2)	0.067 (2)	−0.049 (2)	0.023 (2)	−0.0190 (15)
C11	0.065 (2)	0.082 (2)	0.061 (2)	−0.043 (2)	−0.0002 (13)	−0.0093 (14)
C12	0.0577 (15)	0.0563 (14)	0.0561 (15)	−0.0258 (12)	0.0034 (12)	−0.0021 (12)
C13	0.0412 (12)	0.0396 (11)	0.0442 (12)	−0.0122 (10)	−0.0003 (10)	0.0035 (9)
C14	0.0432 (12)	0.0511 (13)	0.0592 (15)	−0.0166 (11)	0.0049 (11)	−0.0075 (11)
C15	0.060 (2)	0.0519 (14)	0.069 (2)	−0.0222 (13)	0.0024 (14)	−0.0128 (12)
C16	0.062 (2)	0.0497 (14)	0.083 (2)	−0.0274 (13)	0.0005 (15)	0.0015 (13)
C17	0.071 (2)	0.063 (2)	0.084 (2)	−0.0350 (14)	0.025 (2)	−0.0009 (15)
C18	0.072 (2)	0.0531 (14)	0.062 (2)	−0.0303 (13)	0.0195 (14)	−0.0073 (12)

Geometric parameters (Å, º)

C1—C2	1.322 (3)	C9—H9	0.93
C1—F1	1.350 (3)	C10—C11	1.370 (4)
C1—C7	1.467 (3)	C10—H10	0.93
C2—F2	1.350 (3)	C11—C12	1.378 (4)
C2—C3	1.447 (3)	C11—H11	0.93
C3—C4	1.330 (3)	C12—H12	0.93
C3—F3	1.349 (3)	C13—C18	1.386 (3)
C4—F4	1.342 (3)	C13—C14	1.387 (3)
C4—C5	1.448 (3)	C14—C15	1.376 (3)
C5—C6	1.332 (3)	C14—H14	0.93
C5—F5	1.347 (2)	C15—C16	1.365 (4)
C6—F6	1.360 (2)	C15—H15	0.93
C6—C13	1.459 (3)	C16—C17	1.375 (4)
C7—C12	1.391 (3)	C16—H16	0.93
C7—C8	1.392 (3)	C17—C18	1.382 (4)
C8—C9	1.384 (4)	C17—H17	0.93
C8—H8	0.93	C18—H18	0.93
C9—C10	1.367 (4)
F1···F4	2.636 (2)	F4···F5	2.614 (2)
F2···F3	2.624 (2)	F2···F5^i	3.025 (2)
F3···F6	2.659 (2)
C2—C1—F1	114.5 (2)	C9—C10—C11	120.0 (3)
C2—C1—C7	131.4 (2)	C9—C10—H10	120.0
F1—C1—C7	114.1 (2)	C11—C10—H10	120.0
C1—C2—F2	118.4 (2)	C10—C11—C12	120.5 (3)
C1—C2—C3	128.9 (2)	C10—C11—H11	119.7
F2—C2—C3	112.8 (2)	C12—C11—H11	119.7
C4—C3—F3	117.8 (2)	C11—C12—C7	120.3 (2)
C4—C3—C2	128.5 (2)	C11—C12—H12	119.9
F3—C3—C2	113.6 (2)	C7—C12—H12	119.9
C3—C4—F4	117.8 (2)	C18—C13—C14	118.1 (2)
C3—C4—C5	128.4 (2)	C18—C13—C6	122.7 (2)
F4—C4—C5	113.6 (2)	C14—C13—C6	119.2 (2)
C6—C5—F5	118.7 (2)	C15—C14—C13	121.3 (2)
C6—C5—C4	129.3 (2)	C15—C14—H14	119.3
F5—C5—C4	112.1 (2)	C13—C14—H14	119.3
C5—C6—F6	114.6 (2)	C16—C15—C14	120.2 (2)
C5—C6—C13	131.3 (2)	C16—C15—H15	119.9
F6—C6—C13	114.2 (2)	C14—C15—H15	119.9
C12—C7—C8	118.6 (2)	C15—C16—C17	119.4 (3)
C12—C7—C1	123.0 (2)	C15—C16—H16	120.3
C8—C7—C1	118.4 (2)	C17—C16—H16	120.3
C9—C8—C7	120.2 (2)	C16—C17—C18	121.0 (3)
C9—C8—H8	119.9	C16—C17—H17	119.5
C7—C8—H8	119.9	C18—C17—H17	119.5
C10—C9—C8	120.4 (3)	C17—C18—C13	120.0 (2)
C10—C9—H9	119.8	C17—C18—H18	120.0
C8—C9—H9	119.8	C13—C18—H18	120.0
F1—C1—C2—F2	174.4 (2)	C2—C1—C7—C8	176.9 (2)
C7—C1—C2—F2	−5.8 (4)	F1—C1—C7—C8	−3.3 (3)
F1—C1—C2—C3	−6.4 (4)	C12—C7—C8—C9	−0.9 (3)
C7—C1—C2—C3	173.4 (2)	C1—C7—C8—C9	179.4 (2)
C1—C2—C3—C4	−40.2 (4)	C7—C8—C9—C10	0.7 (4)
F2—C2—C3—C4	139.0 (3)	C8—C9—C10—C11	−0.5 (4)
C1—C2—C3—F3	144.8 (3)	C9—C10—C11—C12	0.5 (4)
F2—C2—C3—F3	−36.0 (3)	C10—C11—C12—C7	−0.7 (4)
F3—C3—C4—F4	170.9 (2)	C8—C7—C12—C11	0.9 (3)
C2—C3—C4—F4	−3.9 (4)	C1—C7—C12—C11	−179.4 (2)
F3—C3—C4—C5	−4.4 (4)	C5—C6—C13—C18	−0.2 (4)
C2—C3—C4—C5	−179.2 (3)	F6—C6—C13—C18	179.3 (2)
C3—C4—C5—C6	−42.0 (4)	C5—C6—C13—C14	179.6 (2)
F4—C4—C5—C6	142.6 (2)	F6—C6—C13—C14	−0.9 (3)
C3—C4—C5—F5	138.1 (3)	C18—C13—C14—C15	−0.3 (3)
F4—C4—C5—F5	−37.3 (3)	C6—C13—C14—C15	180.0 (2)
F5—C5—C6—F6	176.4 (2)	C13—C14—C15—C16	0.3 (4)
C4—C5—C6—F6	−3.5 (4)	C14—C15—C16—C17	0.5 (4)
F5—C5—C6—C13	−4.1 (4)	C15—C16—C17—C18	−1.2 (4)
C4—C5—C6—C13	176.0 (2)	C16—C17—C18—C13	1.3 (4)
C2—C1—C7—C12	−2.8 (4)	C14—C13—C18—C17	−0.5 (4)
F1—C1—C7—C12	177.0 (2)	C6—C13—C18—C17	179.3 (2)

Symmetry code: (i) −x+1, −y+1, −z+1.