We report an improved synthesis of 1,1′-diaminoferrocene, employing the reduction of 1,1′diazidoferrocene with H 2 -Pd/C, along with extensive characterization data for both compounds. Diaminoferrocene undergoes a reversible 1eoxidation in CH 3 CN at a potential of -602 mV vs Fc 0/+ , one of the most negative redox potentials for a ferrocene derivative. The chemical reversibility of this process was confirmed by isolation of the stable, 17-electron [Fc(NH 2 ) 2 ] + cation as PF 6 -, OTf -, and TCNEsalts. In the solid state, diaminoferrocene exists in two conformations: one with the NH 2 groups eclipsed, and the other with the NH 2 groups offset by one-fifth turn around the Cp-Fe-Cp axis. Diazidoferrocene, on the other hand, exhibits only the fully eclipsed conformation in the solid state. The Fe-Cp(centroid) vectors in the diazidoferrocene molecules are roughly aligned with the crystallographic c-axis, and the molecules form layers perpendicular to this axis. The compound is thermally unstable at elevated temperatures, and rapid heating above its melting point results in explosion.

An application of alkyne metathesis to 1,2-di(prop-1-ynyl)arenes, producing dehydrobenzannulenes, is described. An efficient method for selective Sonogashira couplings of bromoiodoarenes under conditions of microwave irradiation is also reported. Keywords:alkyne metathesis, 1,2-di(prop-1-ynyl)arenes, dehydrobenzannulenes, microwave irradiation, Sonogashira coupling Alkyne metathesis (Scheme 1) has not been used widely in organic syntheses until recently, even though the first reports of its homogeneous, catalytic version date back to as early as 1974 with results of Mortreux et al. 1 A resurgence of the field occurred in the 1990s, based on the work by the groups of Bunz 2 and Fürstner, 3 which includes examples of ring closures, one notably leading to a meta-dehydrobenzannulene system. 2e We report here the investigation of the potential of alkyne metathesis in the construction of dehydrobenzannulenes (Scheme 2). 4 This class of molecules is interesting in several respects -it provides attractive ligands to transition metal complexes, 5 models for subunits of graphyne, a novel allotrope of carbon, 6 precursors to ordered carbon nanostructures, 7 scaffolds for molecules on which to study supramolecular phenomena, 8 and materials with interesting photophysical properties. 9 Our need for an efficient synthetic entry into substituted derivatives stems from our quest for the first members of the circular phenylenes, such as antikekulene. 10 As representative targets, we directed our initial efforts to examples of tribenzocyclyne 1, as in Scheme 3, and subsequently the more challenging tetrabenzocyclyne 2, as well as the fused systems 3 and 4. The parent 1a and its derivatives have received considerable attention as synthetic targets, 4 whereas a substituted version of 2 8f and parent 3 6c have been prepared for the first time only recently, the latter two through relatively long sequences.

Hexaferrocenylbenzene has been synthesized by six-fold Negishi type ferrocenylation of hexabromo- or hexaiodobenzene.

The cover picture shows the molecular structure of the helically extended angular [8]phenylene. An unprecedented cobalt-catalyzed triple cyclization of an appropriate nonayne was successful in assembling the largest crystallographically characterized helical phenylene (heliphene). Its properties are intriguing; the heliphene is unusually configurationally labile and has a strongly attenuated bathochromic increment in the UV spectrum, shielding of the terminal rings as a result of spatial overlap, and alternating ring-current intensities along the angular frame. The X-ray crystallographic data detail the helical and s ± p distortive features. Most surprisingly, the remarkable flexibility of the heliphene provided an unusually low barrier (DG = (À 4.5 8C) 13.4 AE 0.4 kcal mol À1 ) for enantiomerization. The 1 H NMR spectrum was consistent with the alternation of cyclohexatrienoid and aromatic character; the terminal rings are the most diatropic and the penultimate ones the least. Further details about this chiral polycyclic benzenoid hydrocarbon are described by K. P. C. Vollhardt, et al. on p 3227 ff.