Biomedical subjects

Benjamin T King

Publications and source records attributed to Benjamin T King.

5 recordsLinked to original sources

PubMed2006

Uncatalyzed zirconium-mediated biphenylation of o-dihalobenzenes to form triphenylenes.

The reaction of [Zr(biphe)3][(Li.(THF)4)2], where biphe is 2,2'-biphenyldiyl, with an o-dihaloarene produces a triphenylene. Two new bonds are created in this rare example of an uncatalyzed, Zr-mediated aryl-aryl bond formation. Multiple biphe fragments can be incorporated to give larger triphenylene-containing polycyclic aromatic hydrocarbons. This reaction can introduce significant strain and was demonstrated to tolerate alkyl and methoxy substituents.

Journal Article↗

PubMed2006

Investigation of the mechanism of the intramolecular Scholl reaction of contiguous phenylbenzenes.

Two mechanisms of the Scholl reaction were investigated in the series 1, 2, ..., n-oligophenylbenzenes (n = 2, 3, 4, 6) at the B3LYP/6-31G(d) level of theory. A mechanism involving generation of a radical cation followed by C-C bond formation and dehydrogenation is unlikely on the basis of unfavorable energies of activation. A mechanism involving generation of an arenium cation followed by C-C bond formation and dehydrogenation is energetically feasible. An explanation for the facile polycondensation of hexaphenylbenzene to hexa-peri-hexabenzocoronene, where six new aryl-aryl bonds are formed, is provided. Kinetic simulations based on the calculated activation energies of the arenium cation mechanism predict that intermediates will not accumulate; this is supported by mass balance experiments. Reaction optimization studies suggest that PhI(O2CCF3)2/BF3.OEt2 or MoCl5 are superior to FeCl3 or AlCl3/CuCl2. This is a full account of our work reported partially as a communication previously (Rempala, P.; Kroulík, J.; King, B. T. J. Am. Chem. Soc. 2004, 126, 15002-15003).

Benzene Derivatives↗

PubMed2005

Polycyclic aromatic hydrocarbons by ring-closing metathesis.

A strategy for the synthesis of polycyclic aromatic hydrocarbons (PAHs) by the ring-closing olefin metathesis (RCM) of pendant olefins on a phenylene backbone has been developed. RCM of 2,4',6',2' '-tetravinyl-[1,1';3',1' ']terphenyl and 2,2',5',2' '-tetravinyl-[1,1';4',1']terphenyl affords in high yield the isomeric [a,j] and [a,h] dibenzanthracenes, respectively. In contrast with other intramolecular annulation methods, such as Friedel-Crafts acylations, this reaction is completely regioselective. Since RCM is reversible and PAHs are often thermodynamic sinks, this strategy is an effective and general method for the preparation of PAHs. Density functional theory calculations support these results. Carbon disulfide is a suitable solvent for these reactions.

Carbon Disulfide↗

PubMed2004

A slippery slope: mechanistic analysis of the intramolecular Scholl reaction of hexaphenylbenzene.

DFT calculations support an arenium cation-based mechanism for the Scholl reaction converting hexaphenylbenzene to hexa-peri-benzocoronene. The curve connecting fully benzenoid intermediates on the potential energy diagram is convex. This "slippery slope" provides an explanation for the ease of this cascade Scholl reaction. The calculated reaction coordinate predicts that intermediates will not accumulate; this prediction is verified by experiment.

Journal Article↗

PubMed2004

Clar valence bond representation of pi-bonding in carbon nanotubes.

The application of the Clar aromatic sextet valence bond (VB) model to extended, defect-free single-walled carbon nanotubes (CNTs) with roll-up vectors (m, n) provides a real space model of their electronic structure. If m - n = 3k, where k is an integer, then all pi-electrons can be represented by aromatic sextets, and the CNT is fully benzenoid; the converse is also true. Since m - n = 3k is known to be a necessary criterion for conductivity in CNTs, only fully benzenoid CNTs are metallic, and only potentially metallic CNTs are fully benzenoid. This behavior contrasts with that of planar polycyclic aromatic hydrocarbons, in which the fully benzenoid structures are known to have large HOMO-LUMO gaps. For CNTs that are not fully benzenoid, e.g., m - n = 3k + l, where l = 1 or 2 and k is an integer, a seam of double bonds wraps about an otherwise benzenoid CNT at the chiral angle - 60 degrees or the chiral angle, respectively. Nucleus-independent chemical shift calculations on hydrogen-terminated CNT segments support this, and show that the magnetic manifestation of aromatic sextets is not due to electron correlation. The resonance hybrid of the Clar VB structures corresponds to patterns occasionally observed in scanning tunneling microscopy images of CNTs.

Journal Article↗