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1. Iron Olefin Metathesis: Unlocking Reactivity and Mechanistic Insights

   https://doi.org/10.1021/jacs.4c04356  

   Lincoln, Zachary S; Iluc, Vlad M (June 2024, Journal of the American Chemical Society)

   Olefin metathesis catalyzed by iron complexes has garnered substantial interest due to iron’s abundance and nontoxicity relative to ruthenium, yet its full potential remains untapped, largely because of the propensity of iron carbenes to undergo cyclopropanation instead of cycloreversion from a metallacycle intermediate. In this report, we elucidate the reactions of [{PC(sp2)P}Fe(L)(N2)], ([PC(sp2)P] = bis[2-(diisopropylphosphino)phenyl]methylene) with strained olefins, unveiling their capability to yield metathesis-related products. Our investigations led to the isolation of a structurally characterized metallacyclobutane during the reaction with norbornadiene derivatives, ultimately leading to a ring-opened iron alkylidene. These findings provide compelling evidence that iron complexes adhere to the Chauvin olefin metathesis mechanism. 

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2. Catalytic behavior of hexaphenyldisiloxane in the synthesis of pyrite FeS ₂

   https://doi.org/10.1039/D0CC03397A  

   Todd, Paul K.; Martinolich, Andrew J.; Neilson, James R. (August 2020, Chemical Communications)

   null (Ed.)

   Functional small molecules afford opportunities to direct solid-state inorganic reactions at low temperatures. Here, we use catalytic amounts of organosilicon molecules to influence the metathesis reaction: FeCl 2 + Na 2 S 2 → 2NaCl + FeS 2 . Specifically, hexaphenyldisiloxane ((C 6 H 5 ) 6 Si 2 O) is shown to increase pyrite yields in metathesis reactions performed at 150 °C. In situ synchrotron X-ray diffraction (SXRD) paired with differential scanning calorimetry (DSC) reveals that diffusion-limited intermediates are circumvented in the presence of (C 6 H 5 ) 6 Si 2 O. Control reactions suggest that the observed change in the reaction pathway is imparted by the Si–O functional group. 1 H NMR supports catalytic behavior, as (C 6 H 5 ) 6 Si 2 O is unchanged ex post facto . Taken together, we hypothesize that the polar Si–O functional group coordinates to iron chloride species when NaCl and Na 2 S 4 form, forming an unidentified, transient intermediate. Further exploration of targeted small molecules in these metathesis reaction provides new strategies in controlling inorganic materials synthesis at low-temperatures. 

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3. Exploring the Formation of Copper–Ruthenium Bimetallic Complexes in Olefin Metathesis

   https://doi.org/10.1021/acs.organomet.3c00338  

   Almuzaini, Hanan N; Slebodnick, Carla; Schulz, Michael D (December 2023, Organometallics)

   Copper(I) halides are often added to olefin metathesis reactions to inhibit catalyst degradation, control product isomerization, enhance catalyst activation, or facilitate catalyst dimerization. In each of these examples, the copper salt is presumed to operate as an independent species, separate from the ruthenium center. We have discovered, however, that certain copper salts can form complexes with the ruthenium catalyst itself, forming hetero-bimetallic copper-ruthenium olefin metathesis catalysts. We confirmed the formation of two complexes through single-crystal X-ray crystallography and NMR spectroscopy. The crystal structure revealed the presence of a four-member ring containing ruthenium, carbon, copper, and chlorine or bromine. The hetero-bimetallic catalyst displayed higher latency and lower activity in the ring-opening metathesis polymerization (ROMP) of norbornene compared to analogous monometallic catalysts. For example, norbornene polymerization catalyzed by the monometallic complex reached 80 % conversion after 4 h, but only 12% conversion when catalyzed by the hetero-bimetallic copper-ruthenium complex under the same conditions. Conversion increased to 63 % when the temperature increased to 50 °C for 1 h, indicating that the bimetallic complex retains activity but requires a higher temperature to activate. The formation of these copper-ruthenium bimetallic complexes suggests the possibility of multi-metallic olefin metathesis catalysts, potentially with different activity and properties than their traditional monometallic counterparts. 

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4. Carbon–Carbon Bond Formation Mediated by an Iron(0)–Olefin Pincer Complex

   https://doi.org/10.1055/a-2615-1768  

   Lincoln, Zachary S; Hoffbauer, Melissa R; Iluc, Vlad M (July 2025, Synthesis)

   Abstract C–H functionalization is a highly appealing strategy for accessing complex molecular structures. Herein, we show that π-tethered pincer ligands can engage in C–H activation when coordinated to iron. These reactions result in C(sp2)–C(sp2) bond formation through oxidative coupling and β-hydride elimination/reductive elimination pathways with alkynes and isocyanides. 

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5. Alternative Reactivity of Leucine 5-Hydroxylase Using an Olefin-Containing Substrate to Construct a Substituted Piperidine Ring.

   https://doi.org/10.1021/acs.biochem.0c00289  

   Cha, L.; Milikisiyants, S.; Davidson, M.; Xue, S.; Smirnova, T. I.; Smirnov, A. I.; Guo, Y.; Chang, W.-c. (May 2020, Biochemistry)

   Booker, S (Ed.)

   Applying enzymatic reactions to produce useful molecules is a central focus of chemical biology. Iron and 2-oxoglutarate (Fe/2OG) enzymes are found in all kingdoms of life and catalyze a broad array of oxidative transformations. Herein, we demonstrate that the activity of an Fe/2OG enzyme can be redirected when changing the targeted carbon hybridization from sp3 to sp2. During leucine 5-hydroxylase catalysis, installation of an olefin group onto the substrate redirects the Fe(IV)−oxo species reactivity from hydroxylation to asymmetric epoxidation. The resulting epoxide subsequently undergoes intramolecular cyclization to form the substituted piperidine, 2S,5S-hydroxypipecolic acid. 

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