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1. Leveraging Ligand Cooperativity to Accelerate C–H Activation of Alkynes Using a Tris(amido) Zirconium Complex

   https://doi.org/10.1021/acs.organomet.5c00225  

   Garcia, Nicholas A; Hernandez, George M; Roberts, Courtney C (August 2025, Organometallics)

   Early transition metal alkyl and hydride complexes have been widely explored for their propensity to faciltate C–H activation through a concerted σ-bond metathesis mechanism. Herein, we report the synthesis of a tris(amido) Zr(IV) alkyl complex 1 as a precursor of accessing a proposed transient Zr(IV)-hydride. Upon intramolecular C–H activation of a pendent methyl group, a strained cyclometalated complex 2 is obtained. Relief of ring strain and cooperative metal–ligand C–H activation provided access to Zr-acetylide complex 3, which is capable of undergoing insertion reactivity into carbonyl containing compounds, like aldehydes and ketones. Complexes 1–3 are characterized using multinuclear NMR spectroscopy, UV–vis spectroscopy, and X-ray crystallography. Newly reported electron-rich propargylic alcohols 6 and 7 are isolated and fully characterized using multinuclear NMR spectroscopy, ESI-MS, and FTIR. 

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2. Scaffold-based [Fe]-hydrogenase model: H ₂ activation initiates Fe(0)-hydride extrusion and non-biomimetic hydride transfer

   https://doi.org/10.1039/D0SC03154B  

   Kerns, Spencer A.; Seo, Junhyeok; Lynch, Vincent M.; Shearer, Jason; Goralski, Sean T.; Sullivan, Eileen R.; Rose, Michael J. (October 2021, Chemical Science)

   We report the synthesis and reactivity of a model of [Fe]-hydrogenase derived from an anthracene-based scaffold that includes the endogenous, organometallic acyl(methylene) donor. In comparison to other non-scaffolded acyl-containing complexes, the complex described herein retains molecularly well-defined chemistry upon addition of multiple equivalents of exogenous base. Clean deprotonation of the acyl(methylene) C–H bond with a phenolate base results in the formation of a dimeric motif that contains a new Fe–C(methine) bond resulting from coordination of the deprotonated methylene unit to an adjacent iron center. This effective second carbanion in the ligand framework was demonstrated to drive heterolytic H 2 activation across the Fe( ii ) center. However, this process results in reductive elimination and liberation of the ligand to extrude a lower-valent Fe–carbonyl complex. Through a series of isotopic labelling experiments, structural characterization (XRD, XAS), and spectroscopic characterization (IR, NMR, EXAFS), a mechanistic pathway is presented for H 2 /hydride-induced loss of the organometallic acyl unit ( i.e. pyCH 2 –CO → pyCH 3 +CO). The known reduced hydride species [HFe(CO) 4 ] − and [HFe 3 (CO) 11 ] − have been observed as products by 1 H/ 2 H NMR and IR spectroscopies, as well as independent syntheses of PNP[HFe(CO) 4 ]. The former species ( i.e. [HFe(CO) 4 ] − ) is deduced to be the actual hydride transfer agent in the hydride transfer reaction (nominally catalyzed by the title compound) to a biomimetic substrate ([ Tol Im](BAr F ) = fluorinated imidazolium as hydride acceptor). This work provides mechanistic insight into the reasons for lack of functional biomimetic behavior (hydride transfer) in acyl(methylene)pyridine based mimics of [Fe]-hydrogenase. 

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3. Bridging cyanides from cyanoiron metalloligands to redox-active dinitrosyl iron units

   https://doi.org/10.1039/C8DT01761A  

   Ghosh, Pokhraj; Quiroz, Manuel; Pulukkody, Randara; Bhuvanesh, Nattamai; Darensbourg, Marcetta Y. (January 2018, Dalton Transactions)

   Cyanide, as an ambidentate ligand, plays a pivotal role in providing a simple diatomic building-block motif for controlled metal aggregation (M–CN–M′). Specifically, the inherent hard–soft nature of the cyanide ligand, i.e. , hard-nitrogen and soft-carbon centers, is due to electronic handles for binding Lewis acids following the hard–soft acid–base principle. Studies by Holm and Karlin showed structural and electronic requirements for cyanide-bridged (por)Fe III –CN–Cu II/I (por = porphyrin) molecular assemblies as biomimetics for cyanide-inhibited terminal quinol oxidases and cytochrome-C oxidase. The dinitrosyliron unit (DNIU) that exists in two redox states, {Fe(NO) 2 } 9 and {Fe(NO) 2 } 10 , draws attention as an electronic analogy of Cu II and Cu I , d 9 and d 10 , respectively. In similar controlled aggregations, L-type [(η 5 -C 5 R 5 )Fe(dppe)(CN)] (dppe = diphenyl phosphinoethane; R = H and Me) have been used as N-donor, μ-cyanoiron metalloligands to stabilize the DNIU in two redox states. Two bimetallic [(η 5 -C 5 R 5 )(dppe)Fe II –CN–{Fe(NO) 2 } 9 (sIMes)][BF 4 ] complexes, Fe-1 (R = H) and Fe*-1 (R = CH 3 ), showed dissimilar Fe II CN–{Fe(NO) 2 } 9 angular bends due to the electronic donor properties of the [(η 5 -C 5 R 5 )Fe(dppe)(CN)] μ-cyanoiron metalloligand. A trimetallic [(η 5 -C 5 Me 5 )(dppe)Fe II –CN] 2 –{Fe(NO) 2 } 10 complex, Fe*-2 , engaged two bridging μ-cyanoiron metalloligands to stabilize the {Fe(NO) 2 } 10 unit. The lability of the Fe II –CN–{Fe(NO) 2 } 9/10 bond was probed by suitable X-type (Na + SPh − ) and L-type (PMe 3 ) ligands. Treatment of Fe-1 and Fe*-1 with PMe 3 accounted for a reduction-induced substitution at the DNIU, releasing [(η 5 -C 5 R 5 )Fe(dppe)(CN)] and N-heterocyclic carbene, and generating (PMe 3 ) 2 Fe(NO) 2 as the reduced {Fe(NO) 2 } 10 product. 

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4. C(sp ³ )–H cyanation by a formal copper( iii ) cyanide complex

   https://doi.org/10.1039/d2sc06573h  

   Bower, Jamey K.; Reese, Maxwell S.; Mazin, Ilia M.; Zarnitsa, Lina M.; Cypcar, Andrew D.; Moore, Curtis E.; Sokolov, Alexander Yu.; Zhang, Shiyu (February 2023, Chemical Science)

   High-valent metal oxo complexes are prototypical intermediates for the activation and hydroxylation of alkyl C–H bonds. Substituting the oxo ligand with other functional groups offers the opportunity for additional C–H functionalization beyond C–O bond formation. However, few species aside from metal oxo complexes have been reported to both activate and functionalize alkyl C–H bonds. We herein report the first example of an isolated copper( iii ) cyanide complex (LCu III CN) and its C–H cyanation reactivity. We found that the redox potential ( E ox ) of substrates, instead of C–H bond dissociation energy, is a key determinant of the rate of PCET, suggesting an oxidative asynchronous CPET or ETPT mechanism. Among substrates with the same BDEs, those with low redox potentials transfer H atoms up to a million-fold faster. Capitalizing on this mechanistic insight, we found that LCu III CN is highly selective for cyanation of amines, which is predisposed to oxidative asynchronous or stepwise transfer of H + /e − . Our study demonstrates that the asynchronous effect of PCET is an appealing tool for controlling the selectivity of C–H functionalization. 

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5. A hemilabile manganese( i )–phenol complex and its coordination induced O–H bond weakening

   https://doi.org/10.1039/d0dt00973c  

   Kadassery, Karthika J.; Crawley, Matthew R.; MacMillan, Samantha N.; Lacy, David C. (January 2020, Dalton Transactions)

   The known compound K[( PO ) 2 Mn(CO) 2 ] ( PO = 2-((diphenylphosphino)methyl)-4,6-dimethylphenolate) (K[ 1 ]) was protonated to form the new Mn( i ) complex ( HPO )( PO )Mn(CO) 2 ( H 1 ) and was determined to have a p K a approximately equal to tetramethylguanidine (TMG). The reduction potential of K[ 1 ] was determined to be −0.58 V vs. Fc/Fc + in MeCN and allowed for an estimation of an experimental O–H bond dissociation free energy (BDFE O–H ) of 73 kcal mol −1 according to the Bordwell equation. This value is in good agreement with a corrected DFT computed BDFE O–H of 68.0 kcal mol −1 (70.3 kcal mol −1 for intramolecular H-bonded isomer). The coordination of the protonated O-atom in the solid-state H 1 was confirmed using FTIR spectroscopy and X-ray crystallography. The phenol moiety is hemilabile as evident from computation and experimental results. For instance, dissociation of the protonated O-atom in H 1 is endergonic by only a few kcal mol −1 (DFT). Furthermore, [ 1 ] − and other Mn( i ) compounds coordinated to PO and/or HPO do not react with MeCN, but H 1 reacts with MeCN to form H 1 + MeCN . Experimental evidence for the solution-bound O-atoms of H 1 was obtained from 1 H NMR and UV-vis spectroscopy and by comparing the electronic spectra of bona fide 16-e − Mn( i ) complexes such as [{ PNP }Mn(CO) 2 ] ( PNP = − N{CH 2 CH 2 (P i Pr 2 )} 2 ) and [( Me3SiOP )( PO )Mn(CO) 2 ] ( Me3Si 1 ). Compound H 1 is only meta-stable ( t 1/2 0.5–1 day) and decomposes into products consistent with homolytic O–H bond cleavage. For instance, treatment of H 1 with TEMPO resulted in formation of TEMPOH, free ligand, and [Mn II {( PO ) 2 Mn(CO) 2 } 2 ]. Together with the experimental and calculated weakened BDFE O–H , these data provide strong evidence for the coordination and hemilability of the protonated O-atom in H 1 and represents the first example of the phenolic Mn( i )–O linkage and a rare example of a “soft-homolysis” intermediate in the bond-weakening catalysis paradigm. 

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