Thomas B. Higgins

Terthienyl-Based Redox-Switchable Hemilabile Ligands: Transition Metal Polymeric Complexes with Electrochemically Tunable or Switchable Coordination Environments?

By controlling the extent of oxidation of the polymeric forms of the new class of isolable, polymerizable terthienyl Ru(II) complexes 1, one can modulate both the binding strength of the polymer backbone for Ru(II) and the electronic nature of the bound metal centers.

Model compounds for polymeric redox-switchable hemilabile ligands

Abstract The syntheses and characterization of two new tetradentate hemilabile ligands 1,2-bis(2-diphenylphosphinoethoxy)benzene (5) and 2,2′-bis(2-diphenylphosphinoethoxy)-1,1′-binaphthalene (10) are reported. Ligands 5 and 10 were synthesized as models to test the suitability of specific phosphinoether coordination environments for complexing Rh(I) in high surface area thiophene-based, redox-active polymeric systems. Ligands 5 and 10 react with the product formed from the reaction between (bicyclo[2.2.1]hepta-2,5-diene)rhodium(I) chloride dimer and AgBF4 to form [η2-(1,2-bis(2-diphenylphosphinoethoxy)benzene) η4-norbornadiene rhodium(I)] tetrafluoroborate (6) and [η2-(2,2′-bis(2-diphenylphosphinoethoxy)-1,1′-binaphthalene) η4-norbornadiene rhodium(I)] tetrafluoroborate (11), respectively. Complexes 6 and 11 react with H2 in CD2Cl2 to form the two new square-planar cis-phosphine, cis-ether Rh(I) complexes 7 and 12, respectively. Compound 7, which could be characterized on the basis of its 31P NMR spectrum, is extremely reactive and decomposes in CD2Cl2. In THF compounds 6 and 11 react with H2 to form the dihydride, bis-THF adducts 8 and 16, respectively, which upon removal of solvent form 7 and 12, respectively. Compound 12 is a stable, isolable complex that reacts with acetonitrile to form a cis-phosphine, cis-acetonitrile adduct 15. Removal of solvent from 15 leads to the quantitative reformation of 12. Compound 12 does not react to a detectable extent with gross excesses of benzene or even thiophene, demonstrating the suitability of this ligand environment for implementation into a thiophene-based polymeric system. Compound 12 does catalyze the hydrogenation of cyclohexene to form cyclohexane, and mechanistic implications of such a transformation are discussed.

The effects of organic vapor on alkanethiol deposition via dip-pen nanolithography

Dip-pen nanolithography (DPN) is a scanning probe-based technique that allows for direct delivery of molecules to a range of substrates with sub-50 nm resolution. This study describes the effect of organic solvent vapor on the deposition rate and feature size of nanostructures deposited via DPN. The transport rate of model molecular inks, 1-octadecanethiol, and 16-mercaptohexadecanoic acid were examined under atmospheres of ethanol, methanol, hexane, and dichloromethane. In all cases, presence of an organic vapor increased deposition rate and feature size, in some cases by an order of magnitude. This underscores how the environment can be used to regulate molecular transport rates in a DPN experiment.