Metalloradical Compounds with 1,2-Dipivaloylhydrazido Ligands: Electron Transfer and Alkylation/Protonation Effects
, , , , , und .
European Journal of Inorganic Chemistry 2019 (21): 2639--2647 (2019)

Under oxidative conditions the complexes M(bpy)2Cl2, M = Ru or Os, react with 1,2-dipivaloylhydrazine H2L = tBuC(O)-NH-NH-C(O)-tBu to yield the paramagnetic compds. M(L)(bpy)2(PF6) 1(PF6), M = Ru and 2(PF6), M = Os. Crystal structures of 1(ClO4) and 2(PF6) reveal an NNCO chelate coordination of L with d(NN) $\approx$ 1.39 \AA. EPR spectroscopy suggests a metal/ligand mixed situation for the unpaired electron, with 29 \% (Ru, 1+) or 46 \% (Os, 2+) metal spin contribution according to DFT calcns. Both complex cations exhibit reversible one-electron oxidn. and redn. (Kc $\approx$ 1019 for 1+ and 1012 for 2+) which could also be monitored by IR (nCO) and UV/Vis-NIR spectroelectrochem. These data confirm a metal/ligand orbital mixing MII(L·-) $łeftrightarrow$ MIII(L2-), with the osmium analog favoring the latter alternative. Reaction of Ru(bpy)2Cl2 under non-oxidizing conditions yields the intermediate (1H)(PF6) which could be oxidatively deprotonated to 1+ or methylated to (1Me)(PF6), both identified by 1H and 13C NMR. While oxidn. of (1H)+ proceeds irreversibly due to proton loss, the reversible spectroelectrochem. oxidn. of (1Me)+ suggests a metal-based process RuII(LMe-) $\rightarrow$ RuIII(LMe-). The results reveal that not only dinuclear complexes of 1,2-diacylhydrazido ligands but also mononuclear analogs are distinguished by remarkably variable metal/ligand mixed contributions to the frontier orbitals. on SciFinder(R)
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