The organometallic chemistry of late transition metals in high oxidation states has been of considerable interest because of its relevance to certain catalytic reactions. [1][2][3][4] Organonickel compounds in the formal oxidation state + 4 have been obtained by the oxidation of decamethylnickelocene [5] and in a trinickelacarborane complex.[6] The first examples of octahedral diorganonickel(iv) compounds containing sbonded methyl and acylphenolato ligands were reported only recently.[7] The occurrence of tetracoordinate organonickel(iv) intermediates has been proposed in some cases, [8] but there are no previous reports of the isolation of a tetrahedral nickel(iv) compound containing s-bonded organic ligands. Herein we report the preparation of a tris(1-norbornyl)nickelate(ii) complex and its oxidation, which results in the formation of a diamagnetic pseudotetrahedral triorganonickel(iv) compound. The tetrakis(1-norbornyl) compounds of the first-row metals, with the exception of nickel, are rare examples of high oxidation state homoleptic transition-metal alkyl complexes with extraordinarily high stability.[9]Previously, we prepared several 1-norbonyl complexes of Ni II , which include the nickelate(ii) salt Li[CpNi(1-nor) 2 ] (Cp = C 5 H 5 ), starting from nickelocene.[10] For the preparation of the tris(1-norbornyl)nickel(ii) complex anion we now started from the pale blue compound [nBu 4 N] 2 [Ni IIBr 4 ] (1). The reaction of 1 with three equivalents of 1-norbornyllithium (2) in THF at À60 8C gave a blue-green solution of the anionic complex 3 (Scheme 1). The reaction with four equivalents of 2 also produced 3 and not the tetrakis(1-norbonyl)nickel(ii) complex, as was demonstrated by a subsequent transformation. Note that all previously reported nickel complexes of the type Li 2 [Ni II

The excited-state dynamics of five derivatives of the GFP-chromophore, which differ by the position and nature of their substituents, has been investigated in solvents of various viscosity and polarity and in rigid media using femtosecond-resolved spectroscopy. In polar solvents of low viscosity, like acetonitrile or methanol, the fluorescence decays of all compounds are multiexponential, with average lifetimes of the order of a few picoseconds, whereas in rigid matrices (polymer films and low temperature glasses), they are single exponential with lifetimes of the order of a few nanoseconds and fluorescence quantum yields close to unity. Global analysis of the fluorescence decays recorded at several wavelengths and of the transient absorption spectra reveals the presence of several excited-state populations with slightly different fluorescence and absorption spectra and with distinct lifetimes. These populations are attributed to the existence of multiple ground-state conformers. From the analysis of the dependence of the excited-state dynamics on the solvent and on the nature of the substituents, it follows that the nonradiative deactivation of all these excited chromophores involves an intramolecular coordinate with large amplitude motion. However, depending on the solvent and substituent, additional channels, namely, inter-and intramolecular hydrogen bond assisted nonradiative deactivation, are operative. This allows tuning of the excited-state lifetime of the chromophore. Finally, an ultrafast photoinduced intramolecular charge transfer is observed in polar solvents with one derivative bearing a dimethylaminophenyl substituent.

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