(722av) Novel Organometallic Low Energy Gap Materials and Synthetic Models of Carbon Monoxide Hydrogenase (CODH) In Biological System

Organometallic polymers combine the good physical, mechanical, and electrical properties of organic polymers with the optical, electrical, magnetic, and catalytic properties inherent to transition metals. In order to clearly understand and compare the functionality of transition metal containing materials with their organic analogues, we developed a set of conjugated transition metal containing building blocks which can be assembled into 1-D linear polymers, zig-zag polymers, and two dimensional sheet materials. Our methodology's key step is based on the alkyn-metathesis mechanism developed by Richard R. Schrock in 1980s. The introduction of metals into the conjugated organic backbones is high yield, fast, and scaleable. The energy gap of HOMO-LUMO bands can be adjusted by choosing different ligands and oxidation states of the metals. The first conjugated organometallic polymer was prepared by the polymerization of these building blocks with various organic linkers. These materials maintain the backbone's conjugation after the introduction of metal ions, unlike previous organometallic polymers. A sticking property of this type of materials is the HOMO-LUMO energy gap can be readily tuned to around or below 2.0 eV by using different ligands. Another interesting property of these types of materials is that they can be processed into mixed oxidation state materials by applying appropriate oxidants.

Furthermore, we studied the length effects of organic linkers; with shorten organic linkers, the metal centers become strong coupled. A new type of conjugated metalloyne material has been prepared by using -CºC-CºC- as the linker. These types of materials are exact analogues of polyynes, which are highly unstable, and insoluble materials at room temperature. Other applications of this metalloyne material, such as a potential proton transfer wire, will be also presented.

In addition, in earth carbon cycle, CO + H₂O → CO₂ + 2H⁺ + 2e^- plays a very important role. In biological system, there are Fe and Ni containing clusters, where this type of transformation happens. Analyzing this mechanism via chemical methods is a longstanding challenge. We used E. J. Corey's retrosynthetic analysis to separate this complex into pieces, independently synthesize each part, and assemble the complex at the last step. Dramatic progress has been achieved toward the synthesis of the complete synthetic model complex.