Crystal Structure of 1,1,1-Triphenyl-4-(10-benz[a]azulenyl)-3,4-buten-2-one

aromatic hydrocarbons, are of interest not only from fundamental viewpoints, but also from applied ones, such as physiological activities and advanced materials. Benz[a]azulene and its derivatives, formed by condensation of a benzene ring with an azulene ring, are also interesting compounds. During the course of our work on the reaction of o-[2-furyl]cycloheptatrienylbenzene and triphenylmethyl tetrafluoroborate, we isolated neutral-black crystals together with a small amount of bright-blue crystals. The NMR spectra of these compounds are too complex to elucidate their structures. Their X-ray structures showed that they were 1,1,1triphenyl-4-(10-benz[a]azulenyl)-3,4-buten-2-one and 1,1,1triphenyl-4-(10-benz[a]azulenyl)-2-butanone, respectively.1 Despite the chemical and physical importance of annelated azulenes, such as benz[a]azulene, the X-ray structures have been reported only for azuleno[1,2-b]thiophene2 and 9phenylbenz[a]azulene.3 In this paper we report on the X-ray structure of the former crystal. A single crystal of the title compound was recrystallized from a benzene solution. Reflections were measured on a RIGAKU AFC5R diffractometer with Mo Kα radiation with a θ – 2θ scan (2θ < 55 ̊). The crystal data and experimental details are given in Table 1. The structure was solved by a direct method with SIR88. Non-hydrogen atoms were refined with anisotropic thermal parameters, and all of the hydrogen atoms were constrained with isotropic thermal parameters. Structure refinements against F2 data (4400 reflections) gave R = 0.141 and Rw = 0.081. Conventional R values based on F (>1.5σ (F)) data are given in Table 1. The fractional coordinates and selected bond lengths are listed in Tables 2 and 3, respectively. ORTEP drawings are given in Fig. 2. The benz[a]azulene moiety is planar, the largest deviation from its mean plane being 0.05 Å for C2. However, the atoms in the side chain (C15, C16, C17 and O1) deviate from the mean plane by 0.17, 0.62, 0.69, and 0.40 Å, respectively. The bond-length alternation in the seven-membered ring4 is ambiguous, probably owing to the effect of conjugation with the enone moiety. Overcrowding of the triphenylmethyl group seems to be responsible for the C17–C18 bond length of 1.577(5)Å, which is significantly longer than that of the normal C–C single bond. Similar to the case of 4-(4-azuleno[1,2-b]thienyl)but-3-en-2one,5 C–H···O hydrogen bonds appear to contribute to the formation of the dimer structure shown in Fig. 2(b); O1···C6 = 3.622 Å and O1···H6 = 2.57 Å. Two adjacent benz[a]azulene planes, related by an inversion center, overlap considerably with an inter-plane distance of ca. 3.53 Å. This overlapping would be responsible for the fact that the crystal is black, while its solution is yellow. 373 ANALYTICAL SCIENCES MARCH 2002, VOL. 18 2002 © The Japan Society for Analytical Chemistry