With the goal of generating anionic analogues to MN2S2
Visible‐light capture activates a thermodynamically inert CoIII−CF3bond for direct C−H trifluoromethylation of arenes and heteroarenes. New trifluoromethylcobalt(III) complexes supported by a redox‐active [OCO] pincer ligand were prepared. Coordinating solvents, such as MeCN, afford green, quasi‐octahedral [(SOCO)CoIII(CF3)(MeCN)2] (
- Award ID(s):
- 1464852
- NSF-PAR ID:
- 10049469
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Angewandte Chemie International Edition
- Volume:
- 57
- Issue:
- 5
- ISSN:
- 1433-7851
- Page Range / eLocation ID:
- p. 1311-1315
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract ⋅ Mn(CO)3Br we introduced metallodithiolate ligands, MN2S22−prepared from the Cys‐X‐Cys biomimetic, ema4−ligand (ema=N,N′‐ethylenebis(mercaptoacetamide); M=NiII, [VIV≡O]2+and FeIII) to Mn(CO)5Br. An unexpected, remarkably stable dimanganese product, (H2N2(CH2C=O(μ‐S))2)[Mn(CO)3]2resulted from loss of M originally residing in the N2S24−pocket, replaced by protonation at the amido nitrogens, generating H2ema2−. Accordingly, the ema ligand has switched its coordination mode from an N2S24−cavity holding a single metal, to a binucleating H2ema2−with bridging sulfurs and carboxamide oxygens within Mn‐μ‐S‐CH2‐C‐O, 5‐membered rings. In situ metal‐templating by zinc ions gives quantitative yields of the Mn2product. By computational studies we compared the conformations of “linear” ema4−to ema4−frozen in the “tight‐loop” around single metals, and to the “looser” fold possible for H2ema2−that is the optimal arrangement for binucleation. XRD molecular structures show extensive H‐bonding at the amido‐nitrogen protons in the solid state. -
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Abstract With the goal of generating anionic analogues to MN2S2
⋅ Mn(CO)3Br we introduced metallodithiolate ligands, MN2S22−prepared from the Cys‐X‐Cys biomimetic, ema4−ligand (ema=N,N′‐ethylenebis(mercaptoacetamide); M=NiII, [VIV≡O]2+and FeIII) to Mn(CO)5Br. An unexpected, remarkably stable dimanganese product, (H2N2(CH2C=O(μ‐S))2)[Mn(CO)3]2resulted from loss of M originally residing in the N2S24−pocket, replaced by protonation at the amido nitrogens, generating H2ema2−. Accordingly, the ema ligand has switched its coordination mode from an N2S24−cavity holding a single metal, to a binucleating H2ema2−with bridging sulfurs and carboxamide oxygens within Mn‐μ‐S‐CH2‐C‐O, 5‐membered rings. In situ metal‐templating by zinc ions gives quantitative yields of the Mn2product. By computational studies we compared the conformations of “linear” ema4−to ema4−frozen in the “tight‐loop” around single metals, and to the “looser” fold possible for H2ema2−that is the optimal arrangement for binucleation. XRD molecular structures show extensive H‐bonding at the amido‐nitrogen protons in the solid state. -
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.more » « less
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Abstract Reactivities of non‐heme iron(IV)‐oxo complexes are mostly controlled by the ligands. Complexes with tetradentate ligands such as [(TPA)FeO]2+(TPA=tris(2‐pyridylmethyl)amine) belong to the most reactive ones. Here, we show a fine‐tuning of the reactivity of [(TPA)FeO]2+by an additional ligand X (X=CH3CN, CF3SO3−, ArI, and ArIO; ArI=2‐(
t BuSO2)C6H4I) attached in solution and reveal a thus far unknown role of the ArIO oxidant. The HAT reactivity of [(TPA)FeO(X)]+/2+decreases in the order of X: ArIO > MeCN > ArI ≈ TfO−. Hence, ArIO is not just a mere oxidant of the iron(II) complex, but it can also increase the reactivity of the iron(IV)‐oxo complex as a labile ligand. The detected HAT reactivities of the [(TPA)FeO(X)]+/2+complexes correlate with the Fe=O and FeO−H stretching vibrations of the reactants and the respective products as determined by infrared photodissociation spectroscopy. Hence, the most reactive [(TPA)FeO(ArIO)]2+adduct in the series has the weakest Fe=O bond and forms the strongest FeO−H bond in the HAT reaction.
