Nucleophilic versus Electrophilic Reactivity of Bioinspired Superoxido Nickel(II) Complexes.

The formation and detailed spectroscopic characterization of the first biuret-containing monoanionic superoxido-NiII intermediate [LNiO2 ]- as the Li salt [2; L=MeN[C(=O)NAr)2 ; Ar=2,6-iPr2 C6 H3 )] is reported. It results from oxidation of the corresponding [Li(thf)3 ]2 [LNiII Br2 ] complex M with excess H2 O2 in the presence of Et3 N. The [LNiO2 ]- core of 2 shows an unprecedented nucleophilic reactivity in the oxidative deformylation of aldehydes, in stark contrast to the electrophilic character of the previously reported neutral Nacnac-containing superoxido-NiII complex 1, [L'NiO2 ] (L'=CH(CMeNAr)2 ). According to density-functional theory (DFT) calculations, the remarkably different behaviour of 1 versus 2 can be attributed to their different charges and a two-state reactivity, in which a doublet ground state and a nearby spin-polarized doublet excited-state both contribute in 1 but not in 2. The unexpected nucleophilicity of the superoxido-NiII core of 2 suggests that such a reactivity may also play a role in catalytic cycles of Ni-containing oxygenases and oxidases.

Biomimetic [2Fe-2S] clusters with extensively delocalized mixed-valence iron centers.

A complete series of biomimetic [2Fe-2S] clusters, [(L(Dep) Fe)2 (µ-S)2 ] (3, L(Dep) =CH[CMeN(2,6-Et2 C6 H3 )]2 ), [(L(Dep) Fe)2 (µ-S)2 K] (4), [(L(Dep) Fe)2 (µ-S)2 ][Bu4 N] (5, Bu=n-butyl), and [(L(Dep) Fe)2 (µ-S)2 K2 ] (6), could be synthesized and characterized. The all-ferric [2Fe-2S] cluster 3 is readily accessible through the reaction of [(L(Dep) Fe)2 (µ-H)2 ] (2) with elemental sulfur. The chemical reduction of 3 with one molar equivalent of elemental potassium affords the contact ion pair K(+) [2Fe-2S](-) (4) as a one-dimensional coordination polymer, which in turn reacts with [Bu4 N]Cl to afford the separate ion pair [Bu4 N](+) [2Fe-2S](-) (5). Further reduction of 4 with potassium furnishes the super-reduced all-ferrous [2Fe-2S] cluster 6. Remarkably, complexes 4 and 5 are [2Fe-2S] clusters with extensively delocalized Fe(2+) Fe(3+) pairs as evidenced by (57) Fe Mössbauer, X-ray absorption and emission spectroscopy (XAS, XES) and in accordance with DFT calculations.

Reductive cleavage of P4 by iron(I) centres: synthesis and structural characterisation of Fe2(P2)2 complexes with two bridging P2(2-) ligands.

The selective transformation of white phosphorus with a ß-diketiminato iron(I) toluene complex under mild reaction conditions is reported which furnishes a new dinuclear iron(III) Fe2(P2)2 complex with two bridging P2(2-) ligands. Its reduction with potassium results in the formation of the first delocalised mixed-valent bis-diphosphido iron(II,III) complex which is isostructural with the neutral Fe2P4 precursor.