Induction and Stabilization of Columnar Mesophases in Fluorinated Polycyclic Aromatic Hydrocarbons by Arene-Perfluoroarene Interactions

The straightforward synthesis of several Fluorinated Polycyclic Aromatic Hydrocarbons by the efficient, transition-metal-free, arene fluorine nucleophilic substitution reaction is described, and the full investigation of their liquid crystalline and optical properties reported. The key precursors for this study, i. e. 2,2'-dilithio-4,4',5,5'-tetraalkoxy-1,1'-biphenyl derivatives, were obtained in two steps from the highly selective Scholl oxidative homo-coupling of 3,4-dialkoxy-1-bromobenzene, followed by quantitative double-lithiation. In situ room temperature nucleophilic annulation with either perfluorobenzene or perfluoronaphthalene leads to 1,2,3,4-tetrafluoro-6,7,10,11-tetraalkxoytriphenylenes and 9,10,11,12,13,14-hexafluoro-2,3,6,7-tetraalkoxybenzo[f]tetraphenes, respectively, in good yields. Exploiting the same strategy, subsequent double annulations resulted in the formation of 9,18-difluoro-2,3,6,7,11,12,15,16-octa(alkoxy)tribenzo[f,k,m]tetraphenes and 9,10,19,20-tetrafluoro-2,3,6,7,12,13,16,17-octakis(hexyloxy)tetrabenzo[a,c,j,l]tetracenes, respectively. Despite the presence of only four alkoxy chains, the polar "Janus" mesogens display a columnar hexagonal mesophase over broad temperature ranges, with higher mesophase stability than the archetypical 2,3,6,7,10,11-hexa(alkoxy)triphenylenes and their hydrogenated counterparts. The improvement or induction of mesomorphism is attributed to efficient antiparallel face-to-face π-stacking driven by the establishment of non-covalent perfluoroarene-arene intermolecular interactions. The larger lipophilic discotic π-extended compounds also exhibit columnar mesomorphism, over similar temperature ranges and stability than their hydrogenated homologs. Finally, these fluorinated molecules form stringy gels in various solvents, and show interesting solvatochromic emission properties in solution as well as strong emission in thin films and gels.

Transition Metal Catalyst-Free, Base-Promoted 1,2-Additions of Polyfluorophenylboronates to Aldehydes and Ketones

A novel protocol for the transition metal-free 1,2-addition of polyfluoroaryl boronate esters to aldehydes and ketones is reported, which provides secondary alcohols, tertiary alcohols, and ketones. Control experiments and DFT calculations indicate that both the ortho-F substituents on the polyfluorophenyl boronates and the counterion K+ in the carbonate base are critical. The distinguishing features of this procedure include the employment of commercially available starting materials and the broad scope of the reaction with a wide variety of carbonyl compounds giving moderate to excellent yields. Intriguing structural features involving O-H⋅⋅⋅O and O-H⋅⋅⋅N hydrogen bonding, as well as arene-perfluoroarene interactions, in this series of racemic polyfluoroaryl carbinols have also been addressed.

Base-Free Pd-Catalyzed C-Cl Borylation of Fluorinated Aryl Chlorides

Catalytic C-X borylation of aryl halides containing two ortho-fluorines has been found to be challenging, as most previous methods require stoichiometric amounts of base and the polyfluorinated aryl boronates suffer from protodeboronation, which is accelerated by ortho-fluorine substituents. Herein, we report that a combination of Pd(dba)2 (dba=dibenzylideneacetone) with SPhos (2-dicyclohexylphosphino-2',6'-dimethoxybiphenyl) as a ligand is efficient to catalyze the C-Cl borylation of aryl chlorides containing two ortho-fluorine substituents. This method, conducted under base-free conditions, is compatible with the resulting di-ortho-fluorinated aryl boronate products which are sensitive to base.

Synthesis of Highly Fluorinated Arene Complexes of [Rh(Chelating Phosphine)]+ Cations, and their use in Synthesis and Catalysis

The synthesis of rhodium complexes with weakly binding highly fluorinated benzene ligands is described: 1,2,3-F3 C6 H3 , 1,2,3,4-F4 C6 H2 and 1,2,3,4,5-F5 C6 H are shown to bind with cationic [Rh(Cy2 P(CH2 )x PCy2 )]+ fragments (x=1, 2). Their structures and reactivity with alkenes, and use in catalysis for promoting the Tishchenko reaction of a simple aldehyde, are demonstrated. Key to the synthesis of these complexes is the highly concentrated reaction conditions and use of the [Al{OC(CF3 )3 }4 ]- anion.

Synthesis of [18 F]Fluoroarenes by Nucleophilic Radiofluorination of N-Arylsydnones

A practical method for radiofluorination of anilines with [18 F]fluoride via N-arylsydnone intermediates is described. These precursors are stable, easy to handle and facilitate direct and regioselective 18 F-labeling to prepare [18 F]fluoroarenes. The value of this methodology is further highlighted by successful application to prepare an 18 F-labeled neuropeptide.