Gram-Scale Synthesis of the 1,1,n,n-Tetramethyl[n](2,11)teropyrenophanes.

A gram-scale synthesis of a series of 1,1,n,n-tetramethyl[n](2,11)teropyrenophanes (n=7-9) has been accomplished as well as the first synthesis of the next higher homologue 1,1,10,10-tetramethyl[10](2,11)teropyrenophane. The scale-up of the original small-scale synthesis required the development of several heavily modified synthetic methods, including a chlorination/Friedel-Crafts alkylation protocol and an iodination/Wurtz coupling protocol, which were performed on 25-30 g and 30-60 g scales, respectively. Two separate sets of conditions for the key teropyrene-forming cyclodehydrogenation reaction at the end of the synthetic pathway were developed, an acid-promoted one for the two less strained congeners and an acid-free method for the two more strained homologues.

"Shadow" Synthesis, Structure, and Electronic Properties of [2.2](1,6)(1,8)Pyrenophane-1-monoene.

An unexpected side product of a McMurry reaction was found to be a new [2.2]pyrenophane consisting of two pyrene units with different substitution patterns as well as different types and degrees of distortion from planarity. The new pyrenophane exhibits both monomer and intramolecular excimer fluorescence. Natural bond orbital (NBO) analysis revealed that there is an intramolecular charge-transfer interaction from the more distorted pyrene system to the less distorted one. The origin of the new pyrenophane was traced back to an impurity that was present a full five steps prior to the McMurry reaction from which it was isolated. The pathway to the pyrenophane shadowed that of the main synthetic route.

Endo or Exo? Structures of Gas-Phase Alkali Metal Cation/Aromatic Half-Belt Complexes.

1,1,9,9-Tetramethyl[9](2,11)teropyrenophane (TM9TP), a belt-shaped molecule, has a sizable cavity that molecules or ions could occupy. In this study, the question of whether TM9TP forms gas-phase ion-molecule complexes with metal cations (K+ , Rb+ , Cs+ ) situated inside or outside the TM9TP cavity was addressed using both experimental and computational methods. Complexes were trapped in a Fourier transform ion cyclotron resonance mass spectrometer and their structures were explored by some novel physical chemistry/mass spectrometry methods. Blackbody infrared radiative dissociation kinetics reveal two populations of ions, a fast dissociating fraction and a persistent fraction. Infrared multiphoton dissociation spectra (vibrational spectra) provide very strong evidence that the most abundant population is a complex where the metal cation is inside the TM9TP cavity, endo-TM9TP. Red-shifted C-H stretching bands present in the gas-phase vibrational spectra of these ionic complexes show that there is an interaction between the metal cation and bridge C-H bonds due to the cation sitting inside the cavity of TM9TP. B3LYP/6-31+G(d,p) calculations showed the endo complexes to be the lowest in energy; about 60 kJ mol-1 more thermodynamically stable and more than 120 kJ mol-1 kinetically more stable than the exo complex.

Gram-Scale Synthesis and Highly Regioselective Bromination of 1,1,9,9-Tetramethyl[9](2,11)teropyrenophane.

An improved synthetic pathway to the nanobelt-like 1,1,9,9-tetramethyl[9](2,11)teropyrenophane has been developed, and enables the synthesis of gram quantities of material. Key innovations are the development of a sequential chlorination/Friedel-Crafts alkylation reaction, a sequential iodination/Wurtz coupling reaction, and a room-temperature teropyrene-forming reaction. The teropyrenophane was found to form a very stable radical cation and undergo a completely regioselective fourfold bromination reaction.

Solid-state 13C NMR investigations of cyclophanes: [2.2]paracyclophane and 1,8-dioxa[8](2,7)pyrenophane.

Solid-state NMR (ssNMR) and ab initio quantum mechanical calculations are used in order to understand and to better characterize the molecular conformation and properties of [2.2]paracyclophane and 1,8-dioxa[8](2,7)pyrenophane. Both molecules are cyclophanes, consisting of an aromatic ring assembly and a cyclic aliphatic chain connected to both ends of the aromatic portion. The aliphatic chain causes curvature in the six-membered aromatic ring structures. This led us to examine how the ring strain due to curvature affects the chemical shifts. Using X-ray structures of both [2.2]paracyclophane and 1,8-dioxa[8](2,7)pyrenophane as our starting model, we calculate the chemical shielding tensors and compare these data with those collected from the (13)C ssNMR FIREMAT experiment. We define curvature of [2.2]paracyclophane and 1,8-dioxa[8](2,7)pyrenophane using the π-orbital axis vector (POAV) pyramidalization angle (θ(p)).

1,1,n,n-Tetramethyl[n](2,11)teropyrenophanes (n = 7-9): a series of armchair SWCNT segments.

A new iterative bridge formation strategy has been employed in the synthesis of a series of [n](2,11)teropyrenophanes (n = 7-9). The generation of the nonplanar teropyrene system, which is calculated to be bent through 178.7° for the smallest homologue (n = 7), is accomplished using a VID reaction of a cyclophanemonoene precursor for the first time.