Nonapentafulvalen

Abstract

~ ~ _ _ _ _ _ _~Nonapentafulvalene Nonapentafulvalene (1) has been prepared by oxidative coupling of sodium cyclopentadienide (6) and sodium cyclononaietraenide (7) with CuCI, in THF, two-fold deprotonation of cyclopentadienyl-cyclononatetraene 8 to give dianion 16, and oxidative treatment of 16 with CuCI, (Schemm 2 and 3). Compound 1 is a highly reactive and thermally instable molecule, since valence isomerisation 1+ 17 proceeds easily even at low temperature (the half-life of 1 is ca. 30 min at -15" in CDCI,). NMR investigations show that nonapentafulvalene is an olefinic molecule with strongly alternating bond lengths, its nine-membered ring deviating strongly from planarity.Comparison of the NMR data of 1 with those of a series of sterically similar pentafulvenes 18 and nonafulvenes 19 (Tables 1 and 2) demonstrates that a ) with regard to the pentafulvene unit of 1, the cyclononatetraene ring acts as very weak electron-donating group, while b ) with regard to the nonafulvene unit of 1, the cyclopentadiene ring acts as weak electron-accepting group. So nonapentafulvalene may be regarded as a 'nonafulvene of inverse n-polarisation'. Einleitung

The Fulvalenes

“…Like 165, 11 is thermally unstable undergoing facile electrocyclic ring closure to 166 at room temperature (Scheme 36). [220] The NMR spectroscopic data confirm 11 as olefinic with strongly alternating bond lengths and a nine-membered ring that is bent markedly from planarity. Furthermore, comparison with data from various pentafulvenes and nonafulvenes demonstrates that the large ring of 11 acts as a weak electron donor to the five-membered ring, viz.…”

“…equivalents of CuCl 2 in THF at -50°C results in the dihydro derivatives 165 and 14 (Scheme 36) with only traces of the [9.9] coupled molecule. [27,220] Scheme 36.…”

Oxidative Coupling of 6,6‐Dimethylpentafulvenyl Anion

“…and we realized later a straightforward synthetic concept') for pentafulvalene 4 ( / I = 2) [19], nonapentafulvalene [20], and nonafulvalene 4 (n = 4) […”

Synthetic Attempts towards ‘Aromatic’ Nonafulvenes

“…First synthesis of 10: [15]; a nearly quantitative coupling takes place, if 6 is reacted with AgBF, [16] NMR Spectra of nonafulvenes and nonafulvalenes will be extcnsively discussed elsewhcrc.…”

“…of Na-( Z Z 2 E ) B (Scheme 7, upper part), then the reaction mixture obtained, after chromatographic workup, consists of a 9 : 1 mixture of bicyclic 16 together with nonafulvene In. It is well-known that ( Z Z Z E ) d has several nucleophilic centres [24]: nucleophilic attack with C(1) leads to cyclononatetraenes 8, while attack with C(4) to C(7) gives, after rearrangement, bicyclo[6.1 .O]nonatrienes of type 16.…”