Synthetic pathways to furan-containing cycloparaphenylenes (CPPs) as molecular nanohoops bearing 10, 12, and 15 aromatic units including furan-2,5-diyl or 2,2'-bifuran-5,5'-diyl units have been developed. The X-ray structures of a partially hydrogenated bifuran-containing CPP precursor and the corresponding fully aromatized bifuran-containing CPP were obtained to allow the determination of their conformational arrangements in the crystal lattice. The optical and electrochemical properties of the furan-containing CPPs were investigated.

Synthetic pathways to conjugated macrocycles containing one, two, or three 2,7-bis(2-thienyl)-9H-fluoren-9-one (TFOT) units in the macrocyclic frameworks bearing 10, 16, or 24 aromatic units were developed. The Diels-Alder reaction between (E,E)-1-(5-bromo-2-thienyl)-4-(5-iodo-2-thienyl)-1,3-butadiene and dimethyl acetylenedicarboxylate produced the key Diels-Alder adduct for the subsequent macrocyclic ring formation. UV-vis and fluorescence spectra of the TFOT-containing molecules were recorded, and their electrochemical properties were investigated by cyclic and differential pulse voltammetry. Solvatofluorochromic properties were observed for the TFOT-containing molecules.

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An experimental and computational mechanistic investigation of the key carboxylation step in copper­(I)-catalyzed boracarboxylation of vinyl arenes is presented here. Catalytically relevant intermediates, including a series of CuI-spiroboralactonate complexes with electronically differentiated vinyl arenes and stabilized by the N-heterocyclic carbene (NHC) ligand IPr (IPr = 1,3-bis­(2,6-diisopropylphenyl)­imidazol-2-ylidine), were isolated and characterized. In situ 1H NMR time course studies and subsequent Hammett analysis (σ p ) of carbon dioxide addition to (β-borylbenzyl)­copper­(I) complexes (benzyl = CH2Arp‑X) revealed a linear correlation with a negative rho (ρ) value. Density functional theory (DFT) calculations support a direct CO2 insertion as the primary mechanism for electron-rich benzyl–copper carboxylation. Kinetically sluggish carboxylation of the electron-poor trifluoromethyl-substituted benzyl–copper complex (benzyl = CH2Arp‑CF3) was accelerated upon the addition of exogenous triphenylphosphine (PPh3). Conversely, the additive inhibited the reactions of the electron-rich tert-butyl-substituted benzyl–copper complex (benzyl = CH2Arp‑tBu). These kinetic observations implied that a second carboxylation pathway was likely operative. DFT analysis demonstrated that prior binding of the electron-rich phosphine additive at (β-borylbenzyl)­copper­(I) yields a metastable intermediate that precedes an SE-carboxylation mechanism, which is kinetically favorable for electron-deficient benzyl–copper species and circumvents the kinetically challenging direct insertion mechanism. The mechanistic picture that emerges from this complementary experimental/computational study highlights the kinetic complexities and multiple pathways involved in copper-based carboxylation chemistry.

An experimental and computational mechanistic investigation of the key carboxylation step in copper(I)-catalyzed boracarboxylation of vinyl arenes is presented here. Catalytically relevant intermediates, including a series of Cu^I-spiroboralactonate complexes, with electronically differentiated vinyl arenes and stabilized by the NHC ligand IPr (IPr = 1,3-Bis(2,6-di-isopropylphenyl)-4,5-dihydroimidazol-2-ylidine), were isolated and characterized. In situ ¹H NMR timecourse studies and subsequent Hammett analysis (<i>_p</i>) of carbon dioxide addition to (β-borylbenzyl)copper(I) complexes (benzyl = CH₂Ar^p-X) revealed a linear correlation with a negative rho (<i>ρ</i>) value. Density functional theory (DFT) calculations support a direct CO₂ insertion as the primary mechanism for electron-rich benzyl-copper carboxylation. Kinetically sluggish carboxylation of electron-poor trifluoromethyl-substituted benzyl-copper complex (benzyl = CH₂Ar^p-CF³) was accelerated upon addition of exogenous PPh₃. Conversely, the additive inhibited reactions of electron-rich tert-butyl-substituted benzyl-copper complex (benzyl = CH₂Ar^p-tBu). These kinetic observations implied that a second carboxylation pathway was likely operative. DFT analysis demonstrated that prior binding of the electron-rich phosphine additive at (β-borylbenzyl)copper(I) yields a meta-stable intermediate that precedes an S<i>_E</i>-carboxylation mechanism, which is kinetically favorable for electron-deficient benzyl-copper species and circumvents the kinetically challenging direct insertion mechanism. The mechanistic picture that emerges from this complementary experimental/computational study highlights the kinetic complexities and multiple pathways involved in copper-based carboxylation chemistry.