Bio-inspired Iron Pincers

Download or read book Bio-inspired Iron Pincers written by Zhu-Lin Xie and published by . This book was released on 2019 with total page 598 pages. Available in PDF, EPUB and Kindle. Book excerpt: The enzyme [Fe]-hydrogenase catalyzes the heterolytic cleavage of H2 and hydride transfer to the substrate methenyl-tetrahydromethanopterin (methenyl-H4MPT+), a C1 carrier during the methanogenic carbon dioxide (CO2) reduction. This metalloenzyme (also called Hmd: H2-forming H4MPT dehydrogenase) plays an obligate role in the ‘nickel-free’ metabolism of CO2 to methane (CO2→CH4) in the absence of bio-available nickel ([NiFe] hydrogenase) and is the only known biological example of H2 activation by a mononuclear iron site. The active site of [Fe]-hydrogenase exhibits a distinctive array of non-proteinaceous ligands (except for Cys176), including the cis-dicarbonyl, the bidentate pyridone-acyl unit that presents a unique (to biology) organometallic Fe–C bond, a cysteine thiolate, and a substrate binding site weakly occupied by H2O in the resting state. Although computational studies of [Fe]-hydrogenase have shown that H2 splitting is achieved by metal-ligand cooperation between iron and the pyridone-oxygen, there are few synthetic models that have sufficiently investigated this process. In order to shed light on the mechanism of [Fe]-hydrogenase, we developed three families of models that mimic different aspects the enzyme active site. The first family consisted of carbamoyl thioether pincer complexes ([superscript O=] C [superscript py] NS [superscript Me]) wherein the carbamoyl group (-NH-C [superscript =O] -) mimics the acyl unit in the enzyme. The reactivities of the [superscript O=] C [superscript py] NS [superscript Me] complexes with hydride sources and strong base were investigated. The H2 activation reaction with the pentacoordinate [superscript O=] C [superscript py] NS [superscript Me] complex revealed that the fac-C, N, S arrangement is a critical factor to reactivity with H2. The second family was Schiff base [superscript py] N [superscript C=] NS [superscript H] complexes, in which a variety of iron Schiff base thiol complexes were synthesized with the non-bulky thiolate ligands and bulky thiolate ligand. The thermal stability of the complexes and the role of anionic thiolate donors in stabilizing the cis-Fe(CO)2 unit were investigated. The third family includes the carbamoyl phosphine pincer complexes ([superscript O=] C [superscript py] NP [superscript R2]), in which a phosphine donor was incorporated in place of the biomimetic sulfur donor. The phosphine donor is ideal for stabilizing Fe(II) carbonyl core, and promises the best path forward to a functional catalyst. The reactivity toward H2 activation and catalytic efficacy of the carbamoyl Fe(II) phosphine complexes were investigated