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Comparison of two Mn^IVMn^IV-bis-μ-oxo complexes {[Mn^IV(N₄(6-Me-DPEN))]₂(μ-O)₂}²⁺ and {[Mn^IV(N₄(6-Me-DPPN))]₂(μ-O)₂}².

ABSTRACT: The addition of tert-butyl hydro-peroxide ( ^t BuOOH) to two structurally related Mn^II complexes containing N,N-bis-(6-methyl-2-pyridyl-meth-yl)ethane-1,2-di-amine (6-Me-DPEN) and N,N-bis-(6-methyl-2-pyridyl-meth-yl)propane-1,2-di-amine (6-Me-DPPN) results in the formation of high-valent bis-oxo complexes, namely di-μ-oxido-bis-{[N,N-bis-(6-methyl-2-pyridylmeth-yl)ethane-1,2-di-amine]-manganese(II)}(Mn-Mn) bis-(tetra-phenyl-borate) dihydrate, [Mn(C₁₆H₂₂N₄)₂O₂](C₂₄H₂₀B)₂·2H₂O or {[Mn^IV(N₄(6-Me-DPEN))]₂(μ-O)₂}(2BPh₄)(2H₂O) (1) and di-μ-oxido-bis-{[N,N-bis-(6-methyl-2-pyridylmeth-yl)propane-1,3-di-amine]-manganese(II)}(Mn-Mn) bis-(tetra-phenyl-borate) diethyl ether disolvate, [Mn(C₁₇H₂₄N₄)₂O₂](C₂₄H₂₀B)₂·2C₄H₁₀O or {[Mn^IV(N₄(6-MeDPPN))]₂(μ-O)₂}(2BPh₄)(2Et₂O) (2). Complexes 1 and 2 both contain the 'diamond core' motif found previously in a number of iron, copper, and manganese high-valent bis-oxo compounds. The flexibility in the propyl linker in the ligand scaffold of 2, as compared to that of the ethyl linker in 1, results in more elongated Mn-N bonds, as one would expect. The Mn-Mn distances and Mn-O bond lengths support an Mn^IV oxidation state assignment for the Mn ions in both 1 and 2. The angles around the Mn centers are consistent with the local pseudo-octa-hedral geometry.

SUBMITTER: Coggins MK

PROVIDER: S-EPMC7336796 | biostudies-literature | 2020 Jul

REPOSITORIES: biostudies-literature

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Comparison of two MnIVMnIV-bis-μ-oxo complexes {[MnIV(N4(6-Me-DPEN))]2(μ-O)2}2+ and {[MnIV(N4(6-Me-DPPN))]2(μ-O)2}2.

Coggins Michael K MK Downing Alexandra N AN Kaminsky Werner W Kovacs Julie A JA

Acta crystallographica. Section E, Crystallographic communications 20200609 Pt 7

The addition of tert-butyl hydro-peroxide ( t BuOOH) to two structurally related MnII complexes containing N,N-bis-(6-methyl-2-pyridyl-meth-yl)ethane-1,2-di-amine (6-Me-DPEN) and N,N-bis-(6-methyl-2-pyridyl-meth-yl)propane-1,2-di-amine (6-Me-DPPN) results in the formation of high-valent bis-oxo complexes, namely di-μ-oxido-bis-{[N,N-bis-(6-methyl-2-pyridylmeth-yl)ethane-1,2-di-amine]-manganese(II)}(Mn-Mn) bis-(tetra-ph ...[more]

PMID: 32695449

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Project description:The asymmetric unit of the title compound, [{Sn(C4H9)2(C6H5COO)}2O]2, consists of two half molecules, completed by application of inversion symmetry. Both mol-ecules adopt a ladder structure typical for this class of dimeric tetra-organodistannoxane di-carboxyl-ates characterized by a centrosymmetric four-membered (Sn-O)2 ring of rhomboidal shape that is extended on both sides by folded six-membered Sn-O-C rings. To a first approximation, both kinds of Sn atoms (Sn i and Sn o ) are trigonal-bipyramidally coordinated. The bond angles between the n-butyl groups are widened [135.64 (7)-146.20 (7)°] in comparison with an ideal trigonal bipyramid. Sn-O bond lengths within the {R2SnO3} coordination sphere depend strongly on the position of the corresponding O atom - axial (ax) or equatorial (eq) - as well as on the functionality of the carboxyl-ate groups which exhibit μ2 (-COO i ) and μ1 (-COO o ) coordination modes, respectively. In summary, the following sequence of distances [mean values] is found: d(Sn o -Oμ3) eq [2.024 (2) Å] < d(Sn i -Oμ3) eq [2.044 (2) Å] < d(Sn i -Oμ3) ax [2.158 (6) Å] < d(Sn o -Oμ1-carb) ax [2.182 (6) Å] < d(Sn i -Oμ2-carb) ax [2.250 (2) Å] ≃ d(Sn o -Oμ2-carb) ax [2.247 (12) Å]. The n-butyl groups adopt an anti-anti conformation with exception of two disordered outer n-butyl groups of the second mol-ecule which exhibit gauche-anti and anti-gauche conformations. Weak intra-molecular Sn⋯O inter-actions between the different O atoms of the outer carboxyl groups with the inner, as well as outer, Sn atoms give rise to a strongly distorted octa-hedral coordination at these Sn atoms. Inter-molecular inter-actions between the individual mol-ecules are restricted to van der Waals and O⋯H-C inter-actions of which a nearly linear very short C-H⋯O contact between the H atom of the phenyl group of one of the mol-ecules with the outer non-coordinating C=O group of the other molecule is the most prominent. It gives rise to a chain-like arrangement of the mol-ecules along [111]. The two n-butyl groups attached to the outer Sn atom of one mol-ecule are disordered over two sets of sites with occupancies of 0.806 (3)/0.194 (3) and 0.702 (3)/0.298 (3).

Project description:The thermodynamic properties of structurally similar Mn(III) and Mn(IV) complexes have been reinvestigated to understand their reactivity with substrates having C-H bonds. The complexes have the general formula [MnH(3)buea(O)](n-), where [H(3)buea](3-) is the tripodal ligand, tris[(N'-tert-butylureaylato)-N-ethylene]aminato. These complexes are unique because of the intramolecular hydrogen-bonding (H-bond) network surrounding the Mn-oxo units. The redox potentials for the Mn(III/IV)(O) couple was incorrectly assigned in earlier reports: the corrected value is -1.0 V vs Cp(2)Fe(+)/Cp(2)Fe in DMSO, while the Mn(IV/V)(O) process is -0.076 under the same conditions. The oxo ligand in the Mn(III)(O) complexes is basic with a pK(a) of 28.3; the basicity of the terminal oxo ligand in the Mn(IV)(O) complex is estimated to be approximately 15. These values were used to re-evalulate the O-H bond dissociation energy (BDE(OH)) of the corresponding Mn(II/III)-OH complexes: BDE(OH) values of 89 and 77 kcal/mol were determined for [Mn(III)H(3)buea(OH)](-) and [Mn(II)H(3)buea(OH)](2-), respectively. Both Mn(O) complexes react with 9,10-dihydroanthracene (DHA) to produce anthracene in nearly quantitative yields. This is surprising based on the low redox potiental of the complexes, suggesting the basicity of the oxo ligand is a major contributor to the observed reactivity. In contrast to the thermodynamic results, a comparative kinetic investigation found that the Mn(III)(O) complex reacts nearly 20 times faster than the Mn(IV)(O) complex. Activation parameters, determined from an Eyring analysis, found that the entropy of activation is significantly different between the two systems (DeltaDeltaS(++) = -35 eu, where DeltaDeltaS(++) = DeltaS(++)(Mn(IV)(O)) - DeltaS(++)(Mn(III)(O)). This unusual kinetic behavior can be explained in the context of the basicity of the oxo ligands that leads to different mechanisms: for [Mn(III)H(3)buea(O)](2-) a proton transfer-electron transfer mechanism is proposed, whereas for [Mn(IV)H(3)buea(O)](-) a hydrogen-atom transfer pathway is likely.

Dataset Information

Comparison of two Mn^IVMn^IV-bis-μ-oxo complexes {[Mn^IV(N₄(6-Me-DPEN))]₂(μ-O)₂}²⁺ and {[Mn^IV(N₄(6-Me-DPPN))]₂(μ-O)₂}².

Publications

Comparison of two Mn<sup>IV</sup>Mn<sup>IV</sup>-bis-μ-oxo complexes {[Mn<sup>IV</sup>(N<sub>4</sub>(6-Me-DPEN))]<sub>2</sub>(μ-O)<sub>2</sub>}<sup>2+</sup> and {[Mn<sup>IV</sup>(N<sub>4</sub>(6-Me-DPPN))]<sub>2</sub>(μ-O)<sub>2</sub>}<sup>2</sup>.

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