Our research group is involved in modern organic and organometallic chemistry. Currently we are interested in the synthesis and dynamic behavior of organic macromolecules at the nanoscopic level and the use of organometallic chemistry for specific catalysis.
Mass Transfer and Catalysis with Dendrimers
The goal of this research effort is to design and create novel catalytic dendrimer assemblies capable of bringing about specific mass transfer of substrates from the macromolecule periphery to its catalytic core. Such dendrimers will benefit from the capacity of substituents located on the surface to backfold and move adjacent to the core where the catalysis occurs. The terminal substituents will be judiciously chosen to
trap (bond) substrates and naturally bring them close to the catalytic center, causing both increased rates and selectivity for specific reactions. The selectivity will be determined by the type of end-group chosen for the dendrimer, while the reactivity will be determined by the type of catalytic core used. The catalytic core and end-groups may be modularly altered to match the reaction requirements; however, it is the precise dendritic architecture and its conformational behavior that will ultimately control the overall efficiency of the system.
Our specific aims for this project are:
- To synthesize novel dendritic molecules bearing catalytic centers and substrate bonding terminal groups.
- To study the dynamic behavior of these dendrimers by observing the reaction rate acceleration effects of different catalytic dendrimer structures and generations.
- To develop a unique type of mass-transfer selective catalysis carried out by mimicking a
tentacle-likebehavior, where complementarily substituted dendrimer termini transport active specific substrates to the catalytic center.
Acetal Dynamic Combinatorial Libraries
Acetal chemistry is especially attractive for the creation of dynamic combinatorial libraries due to the relative ease of control over the reversibility of the reactions by simply adjusting the acidity of the media. The design of acetal based macromolecules is appealing due to the possibility of fine tuning hydrolytic degradation processes by electronic and steric effects.
Using Olefin Metathesis for Obtaining New Cross-Linked Organic Nanoparticles
Synthesis of polymers in a controlled fashion with regard to the microstructure as well as morphology is of fundamental interest and practical importance. Recent developments in polymerization, especially in olefin metathesis (ROMP) and atom-transfer radical polymerization (ATRP), allow polymers with more precise control of microstructure, molecular weight, and polydispersity to be made. Single strands of dendronized polymers will be intramolecularly cross-linked and rigidified to create organic nanoparticles.
Molecular simulation of dendronized polymer before and after cross-linking.Specific aims of this project are:
- to develop the preparation of several types of dendronized polymers, with allyl terminal groups on the dendrimers.
- to demonstrate the production of cross-linked polymers and rigid organic nanoparticles. To study the variation obtained by dendrimer generation and loading.
SEC analysis: Polymer only (blue), Dendronized Polymer (Violet), Cross-linked Dendronized Polymer (Red)
The resultant rigid organic nanoparticles obtained from intramolecular cross-link of the dendronized polymers posses reactive olefins that may be further functionalized to provide specific functions or to attach to nanodevices.
Switchable Olefin Metathesis Catalysts
Switchable ruthenium based olefin metathesis catalysts are an attractive target with many potential practical applications. Some success has been obtained for the ROMP reaction, but not for RCM. Going against the grain, we decided to prepare less active catalysts by using chelating atoms and checking their activity.
Thermoswitchable RCM of diethyldiallylmalonate at alternating temperaturesVarious catalysts are being prepared. Interestingly, both cis and trans configurations are being obtained and the consequence of this is being studied.
Dimer Ring Closing Reactions by Homo Bimetallic Catalysts
Our proposal is based on the assumption that the ability of N-heterocyclic carbenes to enhance transition metal catalytic reactions, together with efficient effective molarity effects to direct reactions towards a specific product, may be combined to produce new types of materials. To this avail, we envision the synthesis of two-centered catalysts linked by bis-N-heterocyclic carbene ligands. The main goal of our research proposal is the development of catalysts that preferentially form cyclic products from two substrates (a cyclic dimer) instead of the commonly obtained oligomers and/or cyclic monomers. We intend to use bimetallic catalysts spaced at the appropriate distance to carry out the desired dimer ring closing reaction (DRC).
DRC metathesis as opposed to ADMETWe prepared a series of flexible and rigid bis NHCs and started preparing bimetallic catalysts. Ruthenium (for olefin metathesis) and palladium (for C-C coupling) were chosen for the first trials.
X-Ray structure of a bis-Hoveyda type ruthenium catalyst
Additional projects that are going on in the group include:
- Exploring Multivalence by Dendrimers in Quorum Sensing.
- Dendritic Fiber Optic Bio-Sensors.