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A Pyrazolate‐Bridged Bis(pentadentate) Ligand and Its Dinuclear Ruthenium Complex
Author(s) -
Sander Anett C.,
Schober Anne,
Dechert Sebastian,
Meyer Franc
Publication year - 2015
Publication title -
european journal of inorganic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 1434-1948
DOI - 10.1002/ejic.201500469
Subject(s) - chemistry , ruthenium , cerium , electron paramagnetic resonance , ligand (biochemistry) , medicinal chemistry , cyclic voltammetry , triflic acid , catalysis , crystallography , stereochemistry , electrochemistry , inorganic chemistry , photochemistry , organic chemistry , biochemistry , physics , electrode , nuclear magnetic resonance , receptor
A new bis(pentadentate) pyrazole‐bridged proligand HL bis5 providing two {N 5 } binding pockets and its diruthenium complex [L bis5 Ru 2 (MeCN) 2 ](PF 6 ) 3 ( 1 ) have been synthesized, and the structure of 1 has been elucidated by X‐ray diffraction. The two exogenous MeCN ligands in 1 are both directed into the central pocket created by the two metal ion compartments and interfere with each other, which leads to some distortion of the dimetallic framework. According to an Eyring analysis of variable‐temperature NMR spectroscopic data, interconversion of the resulting enantiomeric forms is rapid with a free activation energy of Δ G ≠ = 43.7 kJ mol –1 at 298 K (Δ H ≠ = 30.8 kJ mol –1 , Δ S ≠ = –43.2 J mol –1 K –1 ). Cyclic voltammetry of 1 shows two sequential reversible oxidations at ca. 0.85 and 1.25 V (vs. SCE), and the mixed‐valent Ru III Ru II species has been characterized by spectroelectrochemistry, UV/Vis/NIR and EPR spectroscopy. Complex 1 was found to be a poor catalyst for water oxidation: under standard conditions [triflic acid, pH 1, using cerium(IV) ammonium nitrate as oxidant] rapid degradation by oxidative ligand fragmentation at its benzylic‐type CH 2 groups was observed.