Asplund researchers are particularly interested in reactions where organometallic species are involved with the formation of new carbon-carbon bonds and the formation of rings.
An interesting class of such reactions is labeled the Pauson-Khand reaction. In its most general form, the Pauson-Khand reaction is the creation of a 5-membered cyclopenteneone ring by alkene, alkyne, and carbonyl.
The creation of the rings is a thermal reaction. A variant of the reactant that combined the alkene and alkyne is used to trace the reaction with time-resolved spectroscopic methods.
The reaction mechanism demonstrates first the removal of CO from the Mo(CO)6, then the formation of a complex between the complex and Mo(CO)5, then the formation of the ring.
The Asplund Lab currently seeks to establish which part of the ligand attaches to the metal first.
Catalystic systems currently require a rare, expensive metal atom. The Asplund Lab is extremely interested in replacing this rare metal with a bimetallic system, where two atoms cooperate to create a reaction similar to the rare metal.
While many catalytic reaction studies have established that this approach is viable, little is known about the details of bimetallic catalyst reactions. Asplund researchers are applying transient infrared spectroscopy to these bimetallic system in an effort to understand how these cooperative systems drive chemistry.
Using short-pulsed lasers, Asplund Lab researchers directly probe chemical reactions in real time. Typically, one laser pulse initiates a reaction, and a second pulse probes the intermediates or products some time later.
The Asplund Lab places particular importance on infrared spectroscopy in probing chemical species, since infrared spectroscopy affords easier, more efficient correlation with molecular structure than electronic spectroscopy does.
Because chemical reactions in condensed phases proceed from one step to the next very quickly—usually in less than a nanosecond—such reactions are well-suited to our laser techniques. Dr. Asplund and his researchers focus on the use of time-resolved techniques, both on the femtosecond/picosecond time scale as well as the nanosecond/microsecond time scale.
Dr. Asplund and his students also study reactions involving organometallic species involved in catalytic bond-breaking.
Asplund researchers discovered that molecules that break C-H alkane bonds work by dissociating a ligand from the metal center using a first photon. This metal center then reacts with the surrounding alkane solvent molecules to form an alkyl hydride product.
Currently, the Lab studies a related molecule that can break C-F bonds in perfluoro-benzene. This tungsten-containing organometallic reacts with the W atom and a tethered perfluorobenzene ring. The Lab recently published a work showing that the rate of the reaction is limited by the formation of a weak complex with the solvent. The Asplund Lab intends to measure the spectrum of this solvent complex on a nanosecond time scale before comparing the spectrum with prior calculations.
Asplund researchers study novel methods for using lasers to functionalize surfaces. Working with Dr. Matt Linford, the Lab uses high-intensity laser pulses to ablate (remove) atoms from the surface of silicon wafers.
The now-exposed Si atoms react rapidly with molecules in a liquid placed on the surface of the wafers. Using an array of micro-lenses, Dr. Asplund and his students found rapid functionalization and patterning in the surface with alkyl halides, epoxides, amines, and other chemically important groups.
The Asplund Lab's current setup allows for the creation of 2500 spots each with a diameter of 2-3 microns. These spots can be functionalized with DNA, proteins, or other chemical or biochemical sensors.