ABSTRACT
We report on the synthesis, redox, electronic, and catalytic behavior of two new cobalt(iii) complexes, namely [CoIII(L1)MeOH] (1) and [CoIII(L2)MeOH] (2). These species contain nitro-rich, phenolate-based pentadentate ligands and present dramatically distinct properties associated with the position in which the -NO2 substituents are installed. Species 1 displays nitro-substituted phenolates, and exhibits irreversible redox response and negligible catalytic activity, whereas 2 has fuctionalized phenylene moieties, shows much improved redox reversibility and catalytic proton reduction activity at low overpotentials. A concerted experimental and theoretical approach sheds some light on these drastic differences.
ABSTRACT
The new pentadentate 3d9 complex [CuII(LN2Py3)](PF6)2 (1) based on a nitrogen-rich framework acts as an electrocatalyst toward dihydrogen production from water. This species is active at pHs 7 and 2.5 yielding respective TON3h values of 1670 and 3900. Comparison of the molecular structure of 1 with that of the reduced [CuI(LN2Py3)]PF6 (2) evidences elongated Cu-N bond lengths resulting from an increased electron density around the 3d10 CuI center. The absence of nanoparticulate formation indicates that molecular mechanisms prevail at both pHs. Furthermore, experimental and DFT data support that distinct mechanisms are operative: while the metal center plays a key role at pH 7, one dangling pyridine moiety gets protonated at pH 2.5 and becomes actively involved in a relay mechanism. In both cases the CuIII-H- intermediate seems to be bypassed by PCET processes.
ABSTRACT
The bimetallic catalyst [CoII2 (L1 )(bpy)2 ]ClO4 (1), in which L1 is an [NN'2 O2 ] fused ligand, efficiently reduced H+ to H2 in CH3 CN in the presence of 100â equiv of HOAc with a turnover number of 18 and a Faradaic efficiency of 94 % after 3â h of bulk electrolysis at -1.6â V (vs. Ag/AgCl). This observation allowed the proposal that this bimetallic cooperativity is associated with distance, angle, and orbital alignment of the two Co centers, as promoted by the unique Co-Namido -Co environment offered by L1 . Experimental results revealed that the parent [CoII CoII ] complex undergoes two successive metal-based 1â e- reductions to generate the catalytically active species [CoI CoI ], and DFT calculations suggested that addition of a proton to one CoI triggers a cooperative 1â e- transfer by each of these CoI centers. This 2â e- transfer is an alternative route to generate a more reactive [CoII (CoII -H- )] hydride, thus avoiding the CoIII -H- required in monometallic species. This [CoII (CoII -H- )] species then accepts another H+ to release H2 .
ABSTRACT
The pyridine-rich complex [NiII(LN2Py3)(MeCN)](ClO4)2 (1) acts as an efficient electro- and photocatalyst in the generation of H2 from water. Observed TONs reach 1050 for electrocatalysis and a remarkable 3500 for photocatalysis. Experimental and DFT data support the ligand-reduced [NiILË] as the catalytically active species, contrasting with the [CoIL] observed for cobalt catalysts.
ABSTRACT
Amphiphilic five-coordinate iron(III) complexes with {N2 O2 Cl} and {N2 O3 } coordination spheres are studied to elucidate the roles of electronic structure on the mechanisms for current rectification. The presence of an apical chlorido or phenolato ligand plays a crucial role, and the [Fe(III) {N2 O2 Cl}] species supports an asymmetric mechanism while its [Fe(III) {N2 O3 }] counterpart seems to allow for unimolecular mechanism. The effects of electron-donating and electron-withdrawing substituents in the ligand frameworks are also considered.
ABSTRACT
The complex molecule of the title compound, [Rh2{N(C6H5)COCH3}4(C8H7N)2], exhibits inversion symmetry. The four acetamidate ligands bridging the dirhodium core are arranged in a 2,2-trans manner with two N atoms and two O atoms coordinating to each Rh(II) atom trans to one another. The Neq-Rh-Rh-Oeq torsion angles on the acetamidate bridge vary between -4.07â (5) and -6.78â (7)°. The axial nitrile ligands complete the distorted octa-hedral coordination sphere of each Rh(II) atom and show a nonlinear coordination with Rh-N-C bond angles of 151.6â (3) and 152.5â (3)°. The bond lengths of the two nitrile triple bonds are 1.133â (5) and 1.137â (5)â Å.
ABSTRACT
In the title compound, [Rh2(C8H8NO)4(C8H7N)], the four acetamidate ligands bridging the dirhodium core are arranged in a 2,2-trans manner. One Rh(II) atom is five-coordinate, in a distorted pyramidal geometry, while the other is six-coord-in-ate, with a disorted octa-hedral geometry. For the six-coord-inate Rh(II) atom, the axial nitrile ligand shows a non-linear Rh-nitrile coordination with an Rh-N-C bond angle of 166.4â (4)° and a nitrile N-C bond length of 1.138â (6)â Å. Each unique Rh(II) atom is coordinated by a trans pair of N atoms and a trans pair of O atoms from the four acetamide ligands. The Neq-Rh-Rh-Oeq torsion angles on the acetamide bridge varies between 12.55â (11) and 14.04â (8)°. In the crystal, the 3-methyl-benzo-nitrile ring shows a π-π inter-action with an inversion-related equivalent [inter-planar spacing = 3.360â (6)â Å]. A phenyl ring on one of the acetamide ligands also has a face-to-face π-π inter-action with an inversion-related equivalent [inter-planar spacing = 3.416â (5)â Å].
ABSTRACT
The title structure, [Rh2(C11H14NO)4(C7H5N)2], contains a dinuclear Rh complex of point symmetry -4 with an Rh-Rh unit and two benzonitrile ligands located in special positions along the twofold axis passing through -4. Four symmetry-equivalent mesitylacetamidate ligands bridge the Rh-Rh unit. Thus, each Rh(II) atom has an approximately octa-hedral coordination by one Rh [Rh-Rh = 2.4290â (6)â Å], two acetamidate O atoms trans to each other [Rh-O = 2.044â (3)â Å], two acetamidate N atoms trans to each other [Rh-N = 2.091â (4)â Å], and a benzonitrile N atom trans to Rh [Rh-N = 2.222â (3)â Å]. The structure is held together by weak van der Waals forces.
