We report on the electrochemical alteration of a nickel(
ii
) bis-glyoximato complex into nickel-based nanoparticles at a glassy carbon electrode under acid reducing conditions. These particles show ...electrocatalytic activity towards hydrogen production at +410 mV compared to the bare glassy carbon electrode. Mechanistic insights are discussed based on DFT calculations.
Mechanistic insights into the electrochemical alteration of Ni
II
(DMGBF
2
)
2
into Ni-based nanoparticles showing electrocatalytic HER activity are provided based on experimental and theoretical studies.
We report on the electrochemical alteration of a nickel(ii) bis-glyoximato complex into nickel-based nanoparticles at a glassy carbon electrode under acid reducing conditions. These particles show ...electrocatalytic activity towards hydrogen production at +410 mV compared to the bare glassy carbon electrode. Mechanistic insights are discussed based on DFT calculations.
The mere exposure of trans-stilbene (t-St) to three types of dehydrated medium pore acid zeolites that differ by their pore diameter induces t-St spontaneous ionization in high yield. In situ diffuse ...reflectance UV–visible, EPR, and Raman spectra recorded over several months highlight the exceptional stability of the charge separated states formed in ferrierite (H-FER), H-MFI, and mordenite (H-MOR). The increase in the pore diameter from H-FER to H-MOR induces different behaviors after radical cation formation. t-St•+ is stabilized for months in the narrow pores of H-FER, whereas in the larger pore H-MFI, relatively fast electron abstraction (hole transfer) takes place from the zeolite framework to create charge transfer complexes. Pulsed EPR experiments were performed using t-St and marked D12t-St and 13C2t-St molecules to reveal the structural environment of the unpaired electrons through the assignment of the couplings with 1H, 2H, 13C, 27Al, and 29Si nuclei.
Through our bio-inspired approach toward replicating nitrous oxide reductase (N(2)Or) activity, treatment of the LMe(MAM)S-S ligand with Cu(CH3CN)(4)(OTf) (OTf = trifluoromethanesulfonate ion) leads ...to the isolation of a new dissymmetric mixed-valent (MV) dicopper(II,I) 2 center dot(H2O)(OTf)(+) containing a {Cu2S} core with labile triflate and water molecules at the copper centers. Whilst 2 center dot(H2O)(OTf)(+) is prone to ligand exchange under particular conditions, a raft of spectroscopic investigations, combined with theoretical calculations demonstrate that its structure is retained in acetone solution. Compared to our previously reported inactive parent complex 1 (Angew. Chem. Int. Ed., 2010, 49 (44), 8249-8252) featuring a symmetric and saturated coordination sphere (N and S atoms from the ligand), 2 center dot(H2O)(OTf)+ is reactive towards nitrous oxide in acetone. Spectroscopic and theoretical studies combined with kinetic measurements show that exchangeable positions are required for N2O interaction. The isolation of the final product and its characterization by X-ray crystallography as a doubly bridged (mu-thiophenolato)(mu-hydroxo) dicopper(II) species 3 center dot(mu-OH)(OTf)(2) help to support the proposed reaction pathway. Implications for N(2)Or mechanism are discussed.
The one-electron oxidation of the dianionic diamido-diphenoxo Ni(II) complexes involving H-bonding (1(2-)), or not (2(2-)), yields the corresponding Ni(III) species; the formation, stability and ...electronic structures of which are affected by the H-bonding interactions.
Due to their redox capabilities, thiols have an important role in biological oxidative/reductive processes through the formation of disulfides or their oxidation to into sulfenic, sulfinic, or ...sulfonic derivatives being also relevant for specific enzyme activities. The mechanisms of these biological pathways often involve metal ion(s). In this case, deciphering metal-assisted transformation of the S–S bond is of primary interest. This report details the reactivity of the disulfide-containing 2,6-bis(bis(pyridylmethyl)amino)methyl-4-methylmercaptophenyldisulfide (LMe(BPA)S–S) ligand with Cu(II) using different experimental conditions (anaerobic, H2O-only, H2O/O2, or O2-only). Crystallographic snapshots show the formation of tetranuclear disulfide, dinuclear sulfinate, and sulfonate complexes. Mechanistic investigations using Zn(II) as control indicate a non-metal-redox-assisted process in all cases. When present, water acts as nucleophile and attacks at the S–S bond. Under anhydrous conditions, a different pathway involving a direct O2 attack at the disulfide is proposed.
The (13)C NMR characterization of the 2,2'- and the 4,4'-hexaarylbiimidazoles is reported for the first time as resulting from the recombination of the radical pairs produced upon irradiation of the ...1,2'-dimer, without any isolation processes, directly in a 500 MHz NMR spectrometer coupled with in situ laser irradiation.
Deprotonation of 1-arylimidazoles (aryl = mesityl (Mes), 2,6-diisopropylphenyl (Dipp)), with
n
-butyl lithium afforded the corresponding derivatives (1-aryl-1
H
-imidazol-2-yl)lithium (
1a
, Ar = ...Mes;
1b
, Ar = Dipp) in good yield. Reaction of
1a
with 0.5 equiv. of Ir(cod)(μ-Cl)
2
yielded two geometrical isomers of a doubly C2,N3-bridged dinuclear complex Ir(cod){μ-C
3
H
2
N
2
(Mes)-κC2,κN3}
2
(
3
),
3
H-H
, a head-to-head (H-H) isomer of
C
S
symmetry, and
3
H-T
, the thermodynamically preferred head-to-tail (H-T) isomer of
C
2
symmetry. The metallated carbon of the 4 electron donor anionic bridging ligands has some carbene character, reminiscent of the situation in N-metallated protic NHC complexes. Displacement of cod ligands from
3
H-H
and
3
H-T
afforded the tetracarbonyl complexes Ir(CO)
2
{μ-C
3
H
2
N
2
(Mes)-κC2,κN3}
2
4
H-H
and
4
H-T
, respectively. The reaction with PMe
3
, which gave only one complex, Ir(CO)(PMe
3
){μ-C
3
H
2
N
2
(Mes)-κC2,κN3}
2
(
5
), demonstrates that the isomerization of the central core Irμ-C
3
H
2
N
2
(Mes)-κC2,κN3
2
Ir from H-H to H-T on going from
4
H-H
to
5
is readily triggered by phosphine substitution under mild conditions. Oxidative-addition of MeI to
5
afforded the formally metal-metal bonded d
7
-d
7
complex Ir
2
(CO)
2
(PMe
3
)
2
(Me)I{μ-C
3
H
2
N
2
(Mes)-κC2,κN3}
2
(
6
). The blue Ir(C
2
H
4
)
2
{μ-C
3
H
2
N
2
(Mes)-κC2,κN3}
2
(
7
) and purple Rh(C
2
H
4
)
2
{μ-C
3
H
2
N
2
(Dipp)-κC2,κN3}
2
(
9
) tetraethylene complexes were also obtained with only a H-T arrangement of the bridging ligands. Although only modestly efficient in alkane dehydrogenation, complex
7
was found to be a more active pre-catalyst than
3
H-T
,
4
H-T
and
5
, probably because of the favorable lability of the ethylene ligands. From cyclic voltammetry, exhaustive coulometry and spectroelectrochemistry studies, it was concluded that
3
H-T
undergoes a metal-based one electron oxidation to generate the mixed-valent Ir(
i
)/Ir(
ii
) system. The energy of the intervalence band for the orange dirhodium complex Rh(cod){μ-C
3
H
2
N
2
(Mes)-κC2,κN3}
2
(
8
) is shifted toward lower energies in comparison with
3
H-T
, reflecting the decrease of the energy with the intermetallic distance. It was concluded from the EPR study that the Ir and Rh centres contribute substantially to the experimental magnetic anisotropy and thus to the singly occupied molecular orbital (SOMO) in the mixed-valent Ir(
i
)/Ir(
ii
) and Rh(
i
)/Rh(
ii
) systems. The molecular structures of
3
H-H
,
3
H-T
,
8
and
9
have been determined by X-ray diffraction.
In doubly C,N-bridged dinuclear complexes with 1-arylimidazolide ligands, the Ir head-to-head isomer can be thermally converted to the head-to-tail isomer.
Deprotonation of 1-arylimidazoles (aryl = mesityl (Mes), 2,6-diisopropylphenyl (Dipp)), with n-butyl lithium afforded the corresponding derivatives (1-aryl-1H-imidazol-2-yl)lithium (1a, Ar = Mes; 1b, ...Ar = Dipp) in good yield. Reaction of 1a with 0.5 equiv. of Ir(cod)( mu -Cl) sub(2) yielded two geometrical isomers of a doubly C2,N3-bridged dinuclear complex Ir(cod){ mu -C sub(3)H sub(2)N sub(2)(Mes)- Kappa C2, Kappa N3} sub(2) (3), 3 sub(H-H), a head-to-head (H-H) isomer of C sub(S) symmetry, and 3 sub(H-T), the thermodynamically preferred head-to-tail (H-T) isomer of C sub(2) symmetry. The metallated carbon of the 4 electron donor anionic bridging ligands has some carbene character, reminiscent of the situation in N-metallated protic NHC complexes. Displacement of cod ligands from 3 sub(H-H) and 3 sub(H-T) afforded the tetracarbonyl complexes Ir(CO) sub(2){ mu -C sub(3)H sub(2)N sub(2)(Mes)- Kappa C2, Kappa N3} sub(2)4 sub(H-H) and 4 sub(H-T), respectively. The reaction with PMe sub(3), which gave only one complex, Ir(CO)(PMe sub(3)){ mu -C sub(3)H sub(2)N sub(2)(Mes)- Kappa C2, Kappa N3} sub(2) (5), demonstrates that the isomerization of the central core Ir mu -C sub(3)H sub(2)N sub(2)(Mes)- Kappa C2, Kappa N3 sub(2)Ir from H-H to H-T on going from 4 sub(H-H) to 5 is readily triggered by phosphine substitution under mild conditions. Oxidative-addition of MeI to 5 afforded the formally metal-metal bonded d super(7)-d super(7) complex Ir sub(2)(CO) sub(2)(PMe sub(3)) sub(2)(Me)I{ mu -C sub( 3)H sub(2)N sub(2)(Mes) - Kappa C2, Kappa N3} sub(2) (6). The blue Ir(C sub(2)H sub(4)) sub(2 ){ mu -C sub(3)H sub(2)N sub(2)(Mes)- Kappa C2, Kappa N3} sub(2) (7) and purple Rh(C sub(2)H sub(4)) sub(2 ){ mu -C sub(3)H sub(2)N sub(2)(Dipp)- Kappa C2, Kappa N3} sub(2) (9) tetraethylene complexes were also obtained with only a H-T arrangement of the bridging ligands. Although only modestly efficient in alkane dehydrogenation, complex 7 was found to be a more active pre-catalyst than 3 sub(H-T), 4 sub(H-T) and 5, probably because of the favorable lability of the ethylene ligands. From cyclic voltammetry, exhaustive coulometry and spectroelectrochemistry studies, it was concluded that 3 sub(H-T) undergoes a metal-based one electron oxidation to generate the mixed-valent Ir(i)/Ir(ii) system. The energy of the intervalence band for the orange dirhodium complex Rh(cod){ mu -C sub(3)H sub(2)N sub(2)(Mes)- Kappa C2, Kappa N3} sub(2) (8) is shifted toward lower energies in comparison with 3 sub(H-T), reflecting the decrease of the energy with the intermetallic distance. It was concluded from the EPR study that the Ir and Rh centres contribute substantially to the experimental magnetic anisotropy and thus to the singly occupied molecular orbital (SOMO) in the mixed-valent Ir(i)/Ir(ii) and Rh(i)/Rh(ii) systems. The molecular structures of 3 sub(H-H), 3 sub(H-T), 8 and 9 have been determined by X-ray diffraction.
Hydrogen production through water splitting is one of the most promising solutions for the storage of renewable energy. NiFe hydrogenases are organometallic enzymes containing nickel and iron centers ...that catalyze hydrogen evolution with performances that rival those of platinum. These enzymes provide inspiration for the design of new molecular catalysts that do not require precious metals. However, all heterodinuclear NiFe models reported so far do not reproduce the Ni-centered reactivity found at the active site of NiFe hydrogenases. Here we report a structural and functional NiFe mimic that displays reactivity at the Ni site. This is shown by the detection of two catalytic intermediates that reproduce structural and electronic features of the Ni-L and Ni-R states of the enzyme during catalytic turnover. Under electrocatalytic conditions, this mimic displays high rates for H
2
evolution (second order rate constant of 2.5 10
4
M
-1
s
-1
; turnover frequency of 225 s
-1
at 10 mM H
+
concentration) from mildly acidic solutions.
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