Richard Larock
Organic Chemistry
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Research Interests
Organopalladium Research
Over the years we have discovered a wide range of useful new synthetic organic reactions that are catalyzed by palladium and we have explored their scope and limitations. A wide variety of different Pd catalyst systems have been developed during the course of that work. Palladium is exceptionally useful as a catalyst, because it (1) possesses relatively low toxicity, (2) very efficiently catalyzes a wide range of reactions under very mild reaction conditions, and (3) can be readily adapted to industrial scale reactions. In fact, some of the Larock methodology is in use by major pharmaceutical companies. We have recently discovered some very unusual rearrangements during the course of these organopalladium reactions in which the palladium migrates from one carbon to another through space. These unique processes appear to be very general and are currently being examined mechanistically. Their synthetic potential is also being determined. We have also recently observed that we can carry out Pd-catalyzed annulations on arynes, like benzyne, suggesting that we should be able to extend all of our earlier work on the annulation of alkynes to arynes.
Aryne Chemistry
The Larock group has recently discovered a number of very interesting and synthetically useful reactions of arynes, like benzyne. The arynes can be easily generated under very mild reaction conditions from o-(trimethylsilyl)aryl triflates and CsF. Reaction with amines, sulfonamides and carboxylic acids give the corresponding N- and O-arylated products in excellent yields. Novel C-N and S-N insertion products have been observed with trifluoroacetanilides and trifluoromethanesulfinamides. These arynes undergo facile annulation chemistry. For example, o-hydroxybenzoate esters react with these arynes to give xanthones. Finally, we have observed that they undergo facile Pd-catalyzed annulation by o-halobenzaldehydes to give fluorenones and react with o-halobiaryls to give triphenylene derivatives.
Polymer Research
The Larock group at Iowa State University have discovered that a remarkable range of exciting new rubber, adhesive, elastomeric and plastic materials can be made by the cationic polymerization and copolymerization of regular, LoSat and conjugated soybean oils with a number of readily available, commercial comonomers, including styrene and divinylbenzene. Bioplastics from a range of other biological oils, including corn, tung, and fish oils have also been prepared using this technology. In addition to thermophysical and mechanical properties comparable to petroleum-based polymers, these new soybean oil-containing materials possess even more valuable properties, such as good damping and shape memory properties. Damping materials are capable of reducing unwanted noise and preventing vibration fatigue failure. Good shape memory materials can be formed into desired, persistent shapes by altering the temperature of the material.
We have recently discovered that excellent bioplastics can be prepared by the thermal and free radical copolymerization of natural oils and a range of new comonomers. We can also prepare stronger materials by making composites and nanocomposites of these exciting new bioplastics.
With the tremendous commercial importance of the plastics industry, it is obvious that the replacement of petroleum-based plastics with useful new bioplastics from inexpensive, renewable agricultural materials, like soybean and corn oils, will have a tremendous impact economically, environmentally and energy-wise. These soy and corn oil materials have a very bright future, since soybean and corn oils are (1) readily available in large quantities from a renewable natural resource, (2) cheaper than most petroleum-based monomers used in the plastics industry right now, (3) likely to produce new rubbers, elastomers and plastics that more readily biodegrade in landfills than the present, virtually indestructible, petroleum-based plastics, and (4) likely to provide thermal, mechanical and physical properties not presently available in commercial plastics. The technology being developed is remarkably simple and widely used in the polymer industry today, so there should be little opposition in the polymer industry to switching to these new materials once the advantages of using the soy plastics are seen.
Current research plans include (1) improvements in the current processes, (2) examination of a wide range of other naturally-occurring oils and commercially available monomers, (3) exploration of other polymerization processes, (4) development of a wide range of elastomers, (5) study of a wide range of biocomposites and nanocomposites using commercial and agricultural fillers, and (6) examination of these materials in various industrial applications.
