Steric/π-Electronic Insulation of the carbo-Benzene Ring: Dramatic Effects of tert-Butyl versus Phenyl Crowns on Geometric, Chromophoric, Redox, and Magnetic Properties.

Hexa-tert-butyl-carbo-benzene (C18 tBu6 ) and three phenylated counterparts (C18 tBum Ph6-m ; m=4, 2) have been synthesized. The peralkylated version (m=6) provides experimental access to intrinsic features of the insulated C18 core independently from the influence of π-conjugated substituent. Over the series, structural, spectroscopic, and electrochemical properties are compared with those of the hexaphenylated reference (m=0). Anchoring tBu substituents at the C18 macrocycle is shown to enhance stability and solubility, and to dramatically modify UV/Vis absorption and redox properties. Whereas all carbo-benzenes reported previously were obtained as dark-reddish/greenish solids, crystals and solutions of C18 tBu6 happen to be yellow (λmax =379 vs. 472 nm for C18 Ph6 ). In comparison to C18 Ph6 , the reduction of C18 tBu6 remains reversible, but occurs at twice as high an absolute potential (E1/2 =-1.36 vs. -0.72 V). Systematic XRD analyses and DFT calculations show that the C18 ring symmetry is the nearest to D6h for m=6, which indicates a maximum geometric aromaticity. According to calculated nucleus-independent chemical shifts (NICS), the macrocyclic magnetic aromaticity is also maximum for C18 tBu6 : NICS(0)=-17.2 ppm versus (-18.0±0.1) ppm for the theoretical references C18 H6 and C18 F6 , and -13.5 ppm for C18 Ph6 . Accurate correlations of NICS(0) with experimentally recorded or calculated maximum UV/Vis absorption wavelengths, λmax , and chemical hardness, η=ELUMO -EHOMO , are evidenced.

[1]  A. Poater,et al.  Carbo-biphenyls and Carbo-terphenyls: Oligo(phenylene ethynylene) Ring Carbo-mers. , 2018, Angewandte Chemie.

[2]  R. Tykwinski,et al.  Reductive Aromatization/Dearomatization and Elimination Reactions to Access Conjugated Polycyclic Hydrocarbons, Heteroacenes, and Cumulenes. , 2017, ChemPlusChem.

[3]  C. Duhayon,et al.  3D and 2D supramolecular assemblies and thermotropic behaviour of a carbo-benzenic mesogen. , 2017, Chemical communications.

[4]  J. Maldonado,et al.  Hexaaryl-carbo-benzenes revisited: a novel synthetic route, crystallographic data, and prospects of electrochemical behavior , 2017 .

[5]  C. Duhayon,et al.  Lipidic Carbo-benzenes: Molecular Probes of Magnetic Anisotropy and Stacking Properties of α-Graphyne. , 2017, The Journal of organic chemistry.

[6]  L. Zakharov,et al.  Modulating Paratropicity Strength in Diareno-Fused Antiaromatics. , 2016, Journal of the American Chemical Society.

[7]  R. Chauvin,et al.  carbo-Naphthalene: A Polycyclic carbo-Benzenoid Fragment of α-Graphyne. , 2016, Angewandte Chemie.

[8]  A. Poater,et al.  Aromatic Rings and Aromatic Rods: Nonplanar Character of an Indeno-dehydro[14]annulene , 2016, Synlett.

[9]  G. Trinquier,et al.  Towards Magnetic Carbo-meric Molecular Materials. , 2016, Chemistry.

[10]  Lukas J. Goossen,et al.  Cover Picture: Sandmeyer‐Type Trifluoromethylthiolation and Trifluoromethylselenolation of (Hetero)Aromatic Amines Catalyzed by Copper (Chem. Eur. J. 1/2016) , 2016 .

[11]  J. Maldonado,et al.  Difluorenyl carbo-Benzenes: Synthesis, Electronic Structure, and Two-Photon Absorption Properties of Hydrocarbon Quadrupolar Chromophores. , 2015, Chemistry.

[12]  R. Chauvin,et al.  "Carbo-aromaticity" and novel carbo-aromatic compounds. , 2015, Chemical Society reviews.

[13]  Mark A Ratner,et al.  Towards graphyne molecular electronics , 2015, Nature Communications.

[14]  R. Chauvin,et al.  Carbo-benzene's aromaticity, before and beyond: a tribute to Nozoe. , 2015, Chemical record.

[15]  Alexandra B. Ormond,et al.  Effects of substituents on the photophysical properties of symmetrical porphyrins , 2013 .

[16]  R. Chauvin,et al.  Highly π electron-rich macro-aromatics: bis(p-aminophenyl)-carbo-benzenes and their DBA acyclic references. , 2012, Chemical communications.

[17]  R. Chauvin,et al.  From hexaoxy-[6]pericyclynes to carbo-cyclohexadienes, carbo-benzenes, and dihydro-carbo-benzenes: synthesis, structure, and chromophoric and redox properties. , 2012, Chemistry.

[18]  B. Singaram,et al.  Mild and expedient asymmetric reductions of α,β-unsaturated alkenyl and alkynyl ketones by TarB-NO2 and mechanistic investigations of ketone reduction. , 2010, The Journal of organic chemistry.

[19]  R. Chauvin,et al.  Variation of aromaticity by twisting or expanding the ring content , 2010 .

[20]  P. Chattaraj,et al.  Electrophilicity Equalization Principle , 2010, 1001.4944.

[21]  H. Hopf,et al.  The Ever-Elusive Tetra-tert-butylethene (TTBE, 3,4-Di-tert-butyl- 2,2,5,5-tetramethylhex-3-ene): Further Insight on Its Preparation† , 2009 .

[22]  R. Chauvin,et al.  Synthesis and stereochemical resolution of a [6]pericyclynedione: Versatile access to pericyclynediol precursors of carbo-benzenes , 2009 .

[23]  Miquel Solà,et al.  Modeling the structure‐property relationships of nanoneedles: A journey toward nanomedicine , 2009, J. Comput. Chem..

[24]  P. Fowler,et al.  Aromaticity of ring carbo-mers of [N]annulenes and [N]cycloalkanes. , 2008, Physical chemistry chemical physics : PCCP.

[25]  C. Duhayon,et al.  Hexasilylated total carbomer of benzene. , 2007, Angewandte Chemie.

[26]  L. Vendier,et al.  Functional [6]pericyclynes: synthesis through [14+4] and [8+10] cyclization strategies. , 2007, Chemistry.

[27]  M. Amini,et al.  An Ab Initio Study and NBO Analysis of the Stability and Conformational Properties of Hexakis(trimethylelementhyl)benzene (Element = C, Si, Ge, and Sn) , 2006 .

[28]  A. J. Sobral,et al.  Electrochemical and spectroelectrochemical characterization of meso-tetra-alkyl porphyrins , 2005 .

[29]  R. Cox,et al.  Room temperature palladium catalysed coupling of acyl chlorides with terminal alkynes. , 2005, Chemical communications.

[30]  Richard I. Cooper,et al.  CRYSTALS version 12: software for guided crystal structure analysis , 2003 .

[31]  A. Katritzky,et al.  To what extent can aromaticity be defined uniquely? , 2002, The Journal of organic chemistry.

[32]  R. Pascal,et al.  Synthesis of an extremely crowded naphthalene via a stable norbornadienone. , 2001, Journal of the American Chemical Society.

[33]  Kevin M. Smith,et al.  Synthesis, reactivity and structural chemistry of 5,10,15,20‐tetraalkylporphyrins , 1999 .

[34]  Brett M. Bode,et al.  MacMolPlt: a graphical user interface for GAMESS. , 1998, Journal of molecular graphics & modelling.

[35]  I. Ueda,et al.  Synthesis, structure and properties of 3,9,15-tri- and 3,6,9,12,15,18-hexasubstituted dodecadehydro[18]annulenes (C18H3R3 and C18R6) with D6h-symmetry , 1998 .

[36]  Ralph G. Pearson,et al.  Chemical Hardness: PEARSON:CHEM.HARDNESS O-BK , 1997 .

[37]  Paul von Ragué Schleyer,et al.  Nucleus-Independent Chemical Shifts:  A Simple and Efficient Aromaticity Probe. , 1996, Journal of the American Chemical Society.

[38]  R. Chauvin,et al.  “Carbomers”. II. En route to [C,C]6carbo-benzene , 1995 .

[39]  Y. Kuwatani,et al.  Synthesis of the first 3,6,9,15,18,18-hexa-substituted-1,2,4,5,7,8,10,11,13,14,16,17-dodecadehydro[18]annulenes with D6h-symmetry , 1995 .

[40]  Kevin M. Smith,et al.  5,10,15,20‐Tetra‐tert‐butylporphyrin and Its Remarkable Reactivity in the 5‐ and 15‐Positions , 1994 .

[41]  Mark S. Gordon,et al.  General atomic and molecular electronic structure system , 1993, J. Comput. Chem..

[42]  A. Becke.  Density-functional thermochemistry. III. The role of exact exchange , 1993 .

[43]  L. D. Sparks,et al.  Nonplanar distortion modes for highly substituted porphyrins , 1992 .

[44]  Wang,et al.  Accurate and simple analytic representation of the electron-gas correlation energy. , 1992, Physical review. B, Condensed matter.

[45]  Ralph G. Pearson,et al.  Absolute Electronegativity and Hardness: Application to Inorganic Chemistry , 1988 .

[46]  R. Pearson,et al.  Absolute electronegativity and hardness correlated with molecular orbital theory. , 1986, Proceedings of the National Academy of Sciences of the United States of America.

[47]  L. T. Scott,et al.  Cyclynes. Part 4. Pericyclynes of the order [5], [6], [7], and [8]. Simple convergent syntheses and chemical reactions of the first homoconjugated cyclic polyacetylenes , 1985 .

[48]  L. T. Scott,et al.  Decamethyl[5]pericyclyne. A novel homoconjugated cyclic polyacetylene , 1983 .

[49]  Timothy Clark,et al.  Efficient diffuse function‐augmented basis sets for anion calculations. III. The 3‐21+G basis set for first‐row elements, Li–F , 1983 .

[50]  M. Gouterman,et al.  Porphyrins. 40. Electronic spectra and four-orbital energies of free-base, zinc, copper, and palladium tetrakis(perfluorophenyl)porphyrins , 1980 .

[51]  L. Birkofer,et al.  Silyl‐Derivate von Pyrazol, Isoxazol und 1,2,3‐Triazol , 1979 .

[52]  J. Pople,et al.  Self‐Consistent Molecular‐Orbital Methods. IX. An Extended Gaussian‐Type Basis for Molecular‐Orbital Studies of Organic Molecules , 1971 .

[53]  Martin Gouterman,et al.  Study of the Effects of Substitution on the Absorption Spectra of Porphin , 1959 .

[54]  R. Chauvin,et al.  DFT exploration of structural and magnetic properties of [n]annulene ring carbomers , 2000 .

[55]  Kevin M. Smith,et al.  EVIDENCE FOR UNUSUALLY STRONG INTRAMOLECULAR HYDROGEN BONDING IN HIGHLY NONPLANAR PORPHYRINS , 1999 .

[56]  Mathias O. Senge,et al.  5, 10, 15, 20‐Tetra‐tert‐butylporphyrin und seine bemerkenswerte Reaktivität in 5, 15‐Stellung , 1994 .

[57]  A. Krebs,et al.  Isolierbare cyclobutadiene-VI. 1,2,3,4-tetra-tert.butylbenzol, 2,3,4,5-tetra-tert.butylbiphenyl, 2,3,4,5-tetra-tert.butylpyridin und 2,3,4,5-tetra-tert.butylfuran , 1981 .

[58]  Martin Gouterman,et al.  Spectra of porphyrins , 1961 .