Synthesis, Characterisation and Reactions of Truly Cationic NiI–Phosphine Complexes

Publisher: John Wiley & Sons Inc

E-ISSN: 1521-3765|24|4|918-927

ISSN: 0947-6539

Source: CHEMISTRY - A EUROPEAN JOURNAL, Vol.24, Iss.4, 2018-01, pp. : 918-927

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Abstract

AbstractThe recently published purely metallo‐organic NiI salt [Ni(cod)2][Al(ORF)4] (1, cod=1,5‐cyclooctadiene, RF=C(CF3)3) provides a starting point for a new synthesis strategy leading to NiI phosphine complexes, replacing cod ligands by phosphines. Clearly visible colour changes indicate reactions within minutes, while quantum chemical calculations (PBE0‐D3(BJ)/def2‐TZVPP) approve exergonic reaction enthalpies in all performed ligand exchange reactions. Hence, [Ni(dppp)2][Al(ORF)4] (2, dppp=1,3‐bis(diphenylphosphino)propane), [Ni(dppe)2][Al(ORF)4] (3, dppe=1,3‐bis(diphenyl‐phosphino)ethane), three‐coordinate [Ni(PPh3)3][Al(ORF)4] (4) and a remarkable two‐coordinate NiI phosphine complex [Ni(PtBu3)2][Al(ORF)4] (5) were characterised by single crystal X‐ray structure analysis. EPR studies were performed, confirming a nickel d9‐configuration in complexes 2, 4 and 5. This result is supported by additional magnetization measurements of 4 and 5. Further investigations by cyclic voltammetry indicate relatively high oxidation potentials for these NiI compounds between 0.7 and 1.7 V versus Fc/Fc+. Screening reactions with O2 and CO gave first insights on the reaction behaviour of the NiI phosphine complexes towards small molecules with formation of mixed phosphine‐CO‐NiI complexes and oxidation processes yielding new NiI and/or NiII derivatives. Moreover, 4 reacted with CH2Cl2 at RT to give a dimeric NiII ylide complex (4 c). As CH2Cl2 is a rather stable alkyl halide with relatively high C−Cl bond energies, 4 appears to be a suitable reagent for more general C−Cl bond activation reactions.