Structurally Characterized Hetero‐Oligopolyphenylenes: Synthetic Advances Toward Next‐Generation Heterosuperbenzenes

Abstract

The successful Diels-Alder [2+4] cycloaddition of dipyrimidyl acetylene and suitably substituted 2,3,4,5-tetraarylcyclopenta-2,4-dien-1-ones (3-7) generates a series of selectively functionalized hexaarylbenzenes. Each has two pairs of peripheral functional groups (R' and R=tert-butyl 8 and R=methyl 9, methoxy 10, bromo 11, triisopropylsilylethynyl 12) and four ortho-imine nitrogen atoms. The dibromo derivative 11 is a useful precursor for the formation of a mono ethynyl 13 and diethynyl 14 substituted polyphenylene. Changing the dienophile to di(2-thienyl)acetylene gives an S-heteroatom polyphenylene 15. The compounds were fully characterized by using (1)H, (13)C and a range of 2 D NMR spectroscopic techniques, elemental analysis, and mass spectrometry. Oxidative cyclodehydrogenation of dimethoxy hexaphenylbenzene 10 by using iron(III) chloride results in the formation of a spirocyclic dienone 16, which in a separate reaction undergoes dienone/phenol rearrangement to give the first 4-fused-ring, N-heterosuperbenzene (HSB) 17. Six single crystal molecular structures reveal the commonality of unidirectional twisting of the external aromatic rings in these heteroatom polyphenylenes. The twist angles and any H-bonding or interdigitation in these structures are discussed.

Oxidative Bond Formation in Dithienyl Polyphenylenes: Optical and Electrochemical Consequences

“…The upfield shift in the 1 H NMR spectrum of two of the thiophene signals (between δ = 6.45 and 6.25 ppm) indicates that in this case the thienyl sulfur atoms point away from their neighboring phenyl rings, that is, the ortho phenyl groups shield the thienyl protons that point towards them. [13] The data are therefore consistent with only two possible dimers 7A and 7B (both shown in Scheme 2). Of these, 7A is preferred, as in this case both the intermolecular and intramolecular oxidations have occurred at the more reactive 2-and 5-positions on the thiophene rings.…”

“…[4,6] In comparison, little attention has been paid to the design of molecular systems containing multiple thiophene units where both inter-and intramolecular oxidations are possible. [9] Building on our recent work on monothienyl polyphenylenes [10] and our established expertise in dehydrogenation and carbon-carbon bond-forming processes, [11][12][13] we now present synthetic strategies for the generation of a series of dithiophene-containing polyaromatic compounds. A full discussion of the photochemical and electrochemical properties of the new molecules is provided.…”

“…The resulting dimers 4, 7, and 8 were identified through a series of 1 H, 13 C, and 2D NMR experiments. The electrochemical and photophysical properties of the dimers were examined.…”

Substituted pyridazines as ligands in homoleptic (fac and mer) and heteroleptic Ru(ii) complexes

“…8. The high-energy region of the spectra in each case is dominated by a ligand-centred p→p* transition which, for comparison appears at l 298 nm in [Fe(bpy) 3 ] 2+ . 30 Again, the meridional isomer of each complex absorbs at slightly longer wavelength than its facial analogue.…”

“…The UV-Vis absorption spectra of both isomers of [Ru(3a-5a) 3 to the increased electron withdrawing character of the pyridazine ring. The most interesting feature of the spectra is the small but consistent bathochromic shift of the mer isomers relative to their fac counterparts.…”