There is considerable interest in MnOH x moieties, particularly in the stepwise changes in those O–H bonds in tandem with Mn oxidation state changes. The reactivity of aquo-derived ligands, {MOH x }, is also heavily influenced by the electronic character of the other ligands. Despite the prevalence of oxygen coordination in biological systems, preparation of mononuclear Mn complexes of this type with all O-donors is rare. Herein, we report several Mn complexes with perfluoropinacolate (pin F ) 2− including the first example of a crystallographically characterized mononuclear {Mn( iii )OH} with all O-donors, K 2 [Mn(OH)(pin F ) 2 ], 3. Complex 3 is prepared via deprotonation of K[Mn(OH 2 )(pin F ) 2 ], 1, the p K a of which is estimated to be 18.3 ± 0.3. Cyclic voltammetry reveals quasi-reversible redox behavior for both 1 and 3 with an unusually large Δ E p , assigned to the Mn( iii / ii ) couple. Using the Bordwell method, the bond dissociation free energy (BDFE) of the O–H bond in {Mn( ii )–OH 2 } is estimated to be 67–70 kcal mol −1 . Complex 3 abstracts H-atoms from 1,2-diphenylhydrazine, 2,4,6-TTBP, and TEMPOH, the latter of which supports a PCET mechanism. Under basic conditions in air, the synthesis of 1 results in K 2 [Mn(OAc)(pin F ) 2 ], 2, proposed to result from the oxidation of Et 2 O to EtOAc by a reactive Mn species, followed by ester hydrolysis. Complex 3 alone does not react with Et 2 O, but addition of O 2 at low temperature effects the formation of a new chromophore proposed to be a Mn( iv ) species. The related complexes K(18C6)[Mn( iii )(pin F ) 2 ], 4, and (Me 4 N) 2 [Mn( ii )(pin F ) 2 ], 5, have also been prepared and their properties discussed in relation to complexes 1–3.
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Square-planar Co( iii ) in {O 4 } coordination: large ZFS and reactivity with ROS
Oxidation of distorted square-planar perfluoropinacolate Co compound [Co II (pin F ) 2 ] 2− , 1 , to [Co III (pin F ) 2 ] 1− , 2 , is reported. Rigidly square-planar 2 has an intermediate-spin, S = 1, ground state and very large zero-field splitting (ZFS) with D = 67.2 cm −1 ; | E | = 18.0 cm −1 , ( E / D = 0.27), g ⊥ = 2.10, g ‖ = 2.25 and χ TIP = 1950 × 10 −6 cm 3 mol −1 . This Co( iii ) species, 2 , reacts with ROS to oxidise two (pin F ) 2− ligands to form tetrahedral [Co II (Hpfa) 4 ] 2− , 3 .
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- Award ID(s):
- 1800313
- NSF-PAR ID:
- 10098367
- Date Published:
- Journal Name:
- Chemical Communications
- Volume:
- 54
- Issue:
- 85
- ISSN:
- 1359-7345
- Page Range / eLocation ID:
- 12045 to 12048
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1039/c8cc04464c
