Syntheses, Structures, and Dimerizations of Ferrocenyl- and Fluorenylideneallenes: Push−Pull Multiple Bonds?

Abstract

Protonation of 9-(ferrocenylethynyl)fluoren-9-ol (9) yields the conjugated enone derived from a Meyer-Schuster rearrangement. However, treatment of 9 with thionyl chloride at -30°C proceeds with elimination of SO 2 to furnish 3,3-biphenylene-1-chloro-1-ferrocenylallene (14), the 13 C NMR data of which indicate that the central carbon does not have markedly carbenic character. Upon warming, this allene readily forms the sterically highly encumbered head-to-head dimer 15, whereby the 1,2-bis(alkylidene)cyclobutane adopts a butterfly conformation with two exocyclic Cl(Fc)Cd moieties and a very long (∼1.65 Å) C(3)-C(4) bond linking the two spiro-bonded fluorenyl fragments. In contrast, attempts to generate the analogous ferrocenylbromoallene 16 instead yielded the hexa-1,2-dien-5-yne 17, the product of allenyl radical head-to-tail coupling. Protonation of ferroceno[2,3]inden-1-ol (25) confirmed a proposal, originally put forward by Caïs in 1965, concerning the possible diradical nature of the resulting cation; the unambiguous characterization of the ferroceno[2,3]inden-1-yl dimer (29) provides experimental verification of Caïs's hypothesis. The X-ray crystal structures of 9-(ferrocenylethynyl)fluoren-9-ol (9) and of its isomer 1-(phenylethynyl)ferroceno[2,3]inden-1-ol (26) are reported along with, among others, the structures of 15, 17, 25, and 29. The possible role of these allenes as precursors to ferrocenylcontaining electroluminescent tetracenes is discussed.

Syntheses and Crystal Structures of Ferrocenoindenes

“…Single crystals of the starting material 1 were obtained from CH 2 Cl 2 . The radical cation of indene 3 yielded an interesting dimer, the crystal structure of which has been determined [15].…”

A Synthetic and X‐ray Crystallographic Study of Zinc and Platinum Complexes of 4,5‐Diazafluoren‐9‐one (Dafone) and Dicobalt Hexacarbonyl Derivatives of 9‐Phenylethynyl‐4,5‐Diazafluoren‐9‐ol: Chelation versus Monocoordination

“…[8] Subsequent thermolysis of the allenes yields tetracenes 5. This general procedure has since been extended to include allene dimers containing halogens, and also silyl, [8,9] phosphane [10] and ferrocenyl [11] substituents.…”

Solvent‐Mediated Generation of Cobalt‐Cluster‐Stabilised Propargyl Cations and Radicals: Allyl Migration versus Peroxide Formation

“…www.chemeurj.org of the sole product (27) revealed resonances very similar to those of the starting material, except for the absence of the alcoholic proton signal. In the absence of a distinct molecular ion in the mass spectrum, the unequivocal identification of 27 as either an ether or a peroxide could not be made, since the first major bond cleavage would be that of the oxygen-oxygen linkage, and the fragmentation patterns would not be expected to differ significantly.…”

“…Two crystallographically independent molecules are found in the unit cell, for which the four hydroxy groups adopt a slightly distorted square planar arrangement (see Table 1), and deviate merely 0.2 from planarity. [26,27] The hydrogen bonding within this species undoubtedly contributes to its stability and permits its isolation, whereas the corresponding hydroxylsilane may not be favoured in the analogous diphenyl system, because of rotational interference engendered by the aryl rings. With respect to the other unexpected product (21), our initial thought was that it may have arisen through reaction of the fluorenyl-alkynyl anion, generated in situ, with traces of acetone left from cleaning the glassware prior to conducting the experiment.…”

“…CCDC-693776 (17), CCDC-693777 (20), CCDC-693778 (21), CCDC-693779 (26), CCDC-693780 (27) and CCDC-693781 (28) contain the supplementary crystallographic data for this paper. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.…”