Synthesis of a Dicyclopenta[a, e]pentalene by [6 + 2]‐Cycloaddition of 1,3‐Di‐tert‐butyl‐5‐vinylidenecyclopentadiene and Consecutive 8π‐Electrocyclic Reaction

Abstract

references cited therein; active MgHl can also be obtained by hydrogenation. B. BogdanoviC, Angew. Chem. 97 (1985) 253; Angew. Chem. in1 Ed. Engl. 24 (1985) 262. Active LiH can be prepared from 1-butyllithium and hydrogen under pressure. on the occasion of his 60th birthday Nonbenzenoid linear annelated [4n + 21-and [4n]-x-electron systems can be formally regarded as annulenes perturbed by central o-bonds. According to quantum chemical investigations the bonding behavior of these polycycles should be determined by the n-perimeter as well as by its partial structures. ['] Only three examples of linear annelated hydrocarbons containing more than two exclusively nonbenzenoid rings have so far been reported, namely cyclohepta[a]cyclopenta[e]-and cyclohepta[a]cyclopenta-[glazulene as well as azulen0~2,1-a]azulene.[*~ The partial structures of these aromatic 18n-electron systems also contain [4n f 2]-x-electron~.~~~ Consequently, the bonding situation in a representative of the hitherto unknown systems with [4n + 21-perimeter having [4n]-x-partial structures is of special interest. These prerequisites are fulfilled by dicyclopenta[a,e]pentalene 1. of its tetra-tert-butyl derivative 11 by a surprising, novel dimerization of the "pentafulveneallene" 5.I4] The synthesis concomitantly opens up an entry to the hitherto largely unexplored linear annelated tetraquinanes. The 14n-electron system of 1 formally consists of a pentalene and a 1 A 1 B pentafulvene partial structure (1A) or two pentalene units (1B). According to x-SCF-MO calculations the perimeter of 1 should exhibit a pronounced double-bond fixation determined by a pseudo-Jahn-Teller effect and the x-bonding isomer 1A (C, symmetry) should be ca. 4 kcal.mol-' lower in energy than 1B (C2,, symmetry) with two overlapping pentalenoid partial structures. The delocalized 14nelectron system should have an enthalpy of formation ca. 14 kcal mol-' higher than that of 1A.[Ia1For the synthesis of the tetra-tert-butyl derivative 11 of the tetracycle 1 we used 1,3-di-tert-butyl-5-vinylidenecyclopentadiene 5 as educt. While "pentafulveneallenes" were hitherto only accessible from diradical generators by pyrolysis or phot~lysis,[~] we prepared 5 in 88% yield as pale yellow crystals of m.p. 43-44°C (after sublimation) by r 1 2 L 3 J 4 + = Me,Cmetalation of the 6-chloropentafulvene 2['l with phenyllithium (tetrahydrofuran (THF), -78°C) to the carbenoid 3, followed by methylation with methyl trifluoromethanesulfonate (-78 "C) to give 4 (yellow leaflets, m.p. 71 "C, yield 33%) and subsequent HCI elimination with lithium 2,2,6,6-tetramethylpiperidide (LiTMP) (-78 to 25 oC).'61 5 dimerizes in a solid-state reaction at ca. 10°C within approx. 14 days to give 1,3,5,7-tetra-tert-butyl-4,4a,8,8a-tetrahydrodicyclopenta[a,e]pentalene 7 (from n-hexane, pale-5 t j?j-q(: H \ 466 0 VCH Verlagsgesellschafi mbH, 0-6940 Weinheim. 1986 0270-0833/86/0502-0466 $ 02.50/0 Angew Chem I n / Ed. Engl. 25 (1986) No. 5

Reactions of Metallacyclopentadiene with Terminal Alkynes: Isolation and Characterization of Metallafulvenallene Complexes

“…Metal-mediated and/or metal-catalyzed reactions involving metallafulvene intermediates have been reported by O’Connor and Rheingold in 1987, in which the C sp atoms of fulvenes have been replaced by metal fragments, providing a series of attractive organometallic molecules (Figure ). Although fulvenallenes have been isolated successfully in 1986, their organometallic analogous, metallafulvenallene derivatives have never been observed …”

Can a linear metal–metal bonded array of tetravanadium be stabilized between two dicyclopenta[a,e]pentalene ligands? A theoretical investigation

“…The two central vanadium atoms of 1b only coordinate with the 1,3-butadiene moiety at the dcpp ligand, since one derivative of dcpp could be readily reduced to its dianion form (Scheme 1). 15 Although the local minimum of 1b-T seems to be obtained by experiencing a subtle geometrical change from the C i symmetry (where a 12.2i cm À1 frequency is present) to C 1 , unfortunately the structure was found to be unreliable due to the large spin contamination (see the spin expectation value in Table 1). 1b-S lies higher in energy than 1b-T by 2.8 kcal mol À1 , and interestingly, the two central vanadium atoms in 1b-S have a very short distance of 2.103 Å.…”

“…[12][13][14] Noting that the derivatives of dicyclopenta[a,e]pentalene (dcpp, see Fig. 1) were synthesized [15][16][17] and that multiple M-M bonds were effectively stabilized between two pentalene (Pn) ligands, 14 we are interested in four metal atoms sandwiched by two dcpp ligands. Dcpp is a 14-p cross-linked annulene, and according to the crystal structures of its two derivatives, 17,18 all 14 carbon atoms of the p core maintain very good planarity.…”

Synthese und Eigenschaften des ersten [4.4]Ferrocenophan-1,3,15,17-tetrains

“…Das 1,1′‐Diethinylferrocen 3 d lässt sich leicht durch Deprotonierung von 1,3‐Di‐ tert ‐butyl‐5‐vinylidencyclopentadien 4 8 mit Lithium‐2,2,6,6‐tetramethylpiperidid (LiTMP) und anschließende Umsetzung des Lithiumsalzes 5 mit Eisen( II )‐chlorid herstellen (Schema ) 7b . 3 d wird dabei als rote Kristalle in 26 % Ausbeute erhalten.…”