Marcetta Y. Darensbourg
Just how they get naturally removed from the extended structures of minerals, transported, selectively taken up into those sites, and for what purpose(s) they exist in them, are the ultimate inspirations for the research program of Marcetta Darensbourg.
n particular, mineral deposits composed of iron sulfide are posited as the origins of the organometallic catalysts for hydrogen metabolism and for the formation of carbon-carbon bonds in the reducing atmosphere that existed on earth prior to the Great Oxygenation Event.
Overall the patterns found in these works lead through the need to understand the reactivity of transition metal hydrides in industrial catalysis, expanded to their possibilities as intermediates within the intricate mechanisms of hydrogenase enzymes—in nature.
Marcetta’s engagement with the inorganic chemistry community was early demonstrated in a symposium she and Andrea Wayda organized for the American Chemical Society in 1985.
"Remember Chicago" took on new meaning as an unexpectedly huge audience overfilled a conference room with inorganic chemists who were interested in the topic of "Experimental Organometallic Chemistry: A Practicum for Synthesis and Characterization".
The rich chemistries of anionic metal carbonyl hydrides, including possibilities of their use as hydride–transfer agents in the heterolytic (H−/H+) H2 reduction of olefins, was the next plateau on her hydrogen research landscape.
Most notable in the past two decades is the role of Mike Hall, computational chemist par excellent, whose insight into structure and bonding enriched many, many publications of his colleagues, including those of Marcetta.
The influence of colleague Arthur Martell and Paul Lindahl, and the perseverance of graduate student Dan Mills, was great towards her shift to a new career phase.
This prolific body of work commanded attention as the nucleophilicity of the cis-dithiolate sulfurs held promise for binding exogeneous electrophiles such as oxygen or metals.
We chemists in College Station recognized the connection between these observations and the possibility that Nature had developed the [NiFe]-H2ase active site to employ carbon monoxide and cyanide ligands, rather than the typical hard donor bases.
Marcetta and two respected competitors stepped into the literature with a dithiolate-bridged diiron hexacarbonyl that had certain properties matching the latter enzyme, with hardly any modification, and publishing within a few months of its structure determination.
It was an exciting time, as a large following of the [FeFe]-H2ase story was engaged by the possibility of using its principles to construct abundant metal electrocatalysts for proton reduction to hydrogen.
[7] Using 7Li nuclear magnetic resonance (NMR), the study delineates the rate-determining step of the equilibrium of the tert-butyllithium mixture, revealing that the dissociation from tetramer to dimer is key.
The findings also highlight the role of stereoconfiguration in these reactions, where tert-butyllithium exhibits a uniquely slow intermolecular exchange rate compared to other alkyl lithium compounds due to its larger size.
These include synthetic complexes featuring Fe-based organometallics species, which serve as precursor for producing iron only Hydrogenase enzyme active site.
[11] In 2020, Darensbourg et al. reported a variety of characterizations of Ni-Fe based hydrogenase species, which eventually encounter oxygen damage during their lifetime.
Studies of a [NiFeSe]-H2ase active site presented new applications for selenium in hydrogenase enzymes, as the complex exhibited a high hydrogen-processing catalytic ability and a relatively quick recovery from oxygen damage.
[12] In the beginning of 2017, Darensbourg shifted her focus to studying the metallodithiolates ligands, which act as building blocks for the synthesis of various bimetallic enzyme active sites.
[13] Darensbourg et al. reported that metallodithiolates ligands with nickel centers can increase the electron density of bonds such as Fe-S, allowing them to be cleaved easily.
[17] In expectation of spin delocalization of bimetallic derivatives upon interactions with sulfur, Darensbourg et al. performed syntheses of various sulfur-bridged multimetallic complexes.
[16] Darensbourg et al. reported that reactions of the paramagnetic (NO)Fe(N2S2) with [M(CH3CNn][BF4]2 salts forms a stairstep bond arrangement with square planar MS4 conformations.
Darensbourg et al. reported that each tri-metallic complex demonstrated similar nitrosyl stretching values in IR spectroscopy despite differences in magnetic properties.
Magnetic susceptibility and DFT calculations additionally showed that each of the {Fe(NO)}7 units exhibited antiferromatic coupling and that each N2S2 ligand engaged in a superexchange interaction with the bimetallic derivatives.
[16] Darensbourg et al. explained that the antiferromatic coupling of Fe(NO) presented new strategies for obtaining strong magnetic exchange within metallodithiolate complex through 4d and 5d orbital interactions.
Through combinations of various paramagnetic metallodithiolate donors and metal receivers, a vast collection of thiolate-bridged multimetallic complexes can be prepared with different magnetic communication strengths.
