Synthesis and Crystal Structure of Overcrowded Non-photochromic Organometallic Fulgide

ةصلاخ : دياجلوفلا بكرم ىلع لوصحلا مت 7 هباشملا ةئيه ىلع ً ايغارف محدزملاو E بوتش فثاكت قيرط نع كلذو ،طقف . دنع بكرملا عيعشت 7  مادختساب ةيجسفنبلا قوف ةعشلأا ) 366 nm ( لا  شملا ىلإ قلحت ثدحي قت 8،1 أ نيلاثفنورديه يئانث 3 . متو بيكرت نم تبثتلا  دياجلوف 7 تارولبلل ةينيسلا ةعشلأا ليلحت ةطساوب .  ABSTRACT: Pure E-isomer overcrowded organometallic fulgide 1 was obtained by using successive Stobbe condensations between ketones and succinate diester. Upon irradiation with UV light at (366 nm) it did not cyclise photochemically to the 1,8a-dihydronaphthalene derivative (1,8aDHN) 8. The structure of 7 was confirmed by X-ray crystallographic analysis.


Introduction
F ulgides with aryl ring undergo ring-closure photochemically to give highly coloured tricyclic dihydronaphthalene derivatives (Heller 1978).It was found that the preferred isomer was the E-isomer in sterically-hindered fulgide systems (Hart and Heller 1972;McCabe et al. 1993;Liang et al. 2001).McCabe et al. (1993) synthesized the first organometallic fulgide 1, which was obtained as E-isomer 1. Irradiation of 1 underwent E/Z isomerization to Z-isomer 2 rather than ring-closure, despite the introduction of donating groups on the ferrocenyl moiety Scheme 1.In the present work diphenylidene was introduced to the system to investigate whether or not photocyclization would occur, according to electrocyclization reaction, in agreement with Woodward-Hofmann rules (Yokoyama 2000).

Experimental
General: Melting points were recorded on a Gallenkamp melting point apparatus and were uncorrected.NMR spectra were obtained in CDCl 3 on a Jeol 400 MHz with TMS as internal reference; chemical shifts were expressed in δ (ppm).Irradiation of the prepared fulgide in toluene at 366 nm for 48 hrs was carried out, using UV lamp (UV GL-58, 254/366 nml lamp, 50/60 Hz), while UV-Visible double beam spectrophotometer (Shimadzu UV-1601PC) was used to follow up the irradiation effect.

X-Ray analysis
A dark purple crystal with dimensions 0.483 x 0.260 x 0.188mm 3 was placed and optically centered on the Bruker SMART CCD system at -80°C.The initial unit cell was indexed using a least-squares analysis of a random set of reflections collected from three series of 0.3° wide ω scans (25 frames/series) that were well distributed in reciprocal space.Data frames were collected [MoKα] with 0.3° wide ω-scans, 30 seconds/frame, 606 frames per series.Five complete series were collected, including an additional partial, first 160 frames, run of the first series for decay purposes, with a crystal to detector distance of 4.94cm, thus providing a complete sphere of data to 2θ max =55°.A total of 30967 reflections was collected and corrected for Lorentz and polarization effects and absorption using Blessing's method as incorporated into the program SADABS (Blessing 1995 andSheldrick 1996) with 5041 unique [R(int)=0.0273].

Results and Discussion
Stobbe condensation of benzophenone and dimethyl succinate in the presence of potassium tbutoxide in toluene and subsequent methylation of the condensation product gave dimethyl (diphenylmethylene)succinate 4. A second Stobbe condensation using acetyl ferrocene yielded the half-ester, which was hydrolysed and cyclised using acetyl chloride, to afford solely fulgide 7 as dark purple crystals in 30% yield (Scheme 2).
Irradiation of fulgide 7 reveals no changes in wavelengths of absorption bands located at λ max 392 and 544 nm ε 11300, 3940 dm 3 .ml -1 .cm -1 respectively.This may indicate that there is neither E/Z isomerisation, nor electrocyclic ring closure taking place in this specific fulgide, as normally seen in simple fulgides (Yokoyama 2000) (Scheme 3): The structure and stereochemistry of fulgide 7 was confirmed by X-ray crystallographic analysis which is shown in Figure 1.Of particular interest in this fulgide are the following features: • The phenyl rings and the ferrocenyl moiety are rotated from the plane of the anhydride ring.

•
The single bond C11-C12 (1.509 Å) is longer than the single bond C10-C11 (1.457 Å), while the single bonds C17-C18 and C17-C24 have almost the same length 1.489 and 1.484 Å, respectively.Selected bond lengths and angles are given in Table 1.indicated the non-standard centrosymmetric space group P2 1 /n (no.14).The structure was determined by direct methods with the successful location of nearly all atoms using the program XS (Sheldrick 1990).The structure was refined with XL (Sheldrick 1993).After the initial refinement difference-Fourier cycle, additional atoms were located and input.After several of these refinement difference-Fourier cycles, all of the atoms were refined isotropically, then anisotropically.Hydrogen atoms were located directly from difference-Fourier maps and input; these atoms were freely refined.Centroids of the Cp rings were calculated.

Acknowledgements
The author would like to thank Dr. J. Fitteger, X-Ray Crystallographic Facility, Chemistry and Biochemistry College Park, University of Maryland, USA, for carrying out the x-ray performance.

Figure 1 .
Figure1.The molecular structure of 7 with the atom-numbering scheme.Hydrogen atoms are drawn as circles of arbitrary small radii for clarity.