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Electrochemical Investigations Give Some Insights into the Coordination Chemistry of New Stable Iridium(+1), Iridium(0), and Iridium(−1) Complexes
Author(s) -
Mlakar Marina,
Boulmaâz Souad,
Schönberg Hartmut,
Grützmacher Hansjörg
Publication year - 2003
Publication title -
electroanalysis
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.574
H-Index - 128
eISSN - 1521-4109
pISSN - 1040-0397
DOI - 10.1002/elan.200390126
Subject(s) - iridium , chemistry , redox , cyclic voltammetry , tetrahydrofuran , acetonitrile , electrochemistry , hydride , osmium , valence (chemistry) , electron transfer , infrared spectroscopy , inorganic chemistry , ruthenium , electrode , metal , catalysis , organic chemistry , solvent
The redox chemistry of the stable tetracoordinated 16 valence electron d 8 ‐[Ir +I (tropp Ph ) 2 ] + (PF 6 ) − and pentacoordinated 18 valence d 8 ‐[Ir +I (tropp Ph ) 2 Cl] complexes was investigated by cyclic voltammetry (tropp Ph =dibenzotropylidenyl phosphine). The experiments were performed using a platinum microelectrode varying scan rates (100 mV/s–10 V/s) and temperatures (− 40 to 20 °C) in tetrahydrofuran, THF, or acetonitrile, ACN, as solvents. In THF, the overall two‐electron reduction of the 16 valence electron d 8 ‐[Ir +I (tropp Ph ) 2 ] + (PF 6 ) − proceeds in two well separated slow heterogeneous electron transfer steps according to: d 8 ‐[Ir +I (tropp Ph ) 2 ] + +e − →d 9 ‐[Ir 0 (tropp Ph ) 2 ]+e − →d 10 ‐[Ir −I (tropp Ph ) 2 ] − , [ k s 1 =2.2×10 −3 cm/s for d 8 ‐Ir +I /d 9 ‐Ir 0 and k s 2 =2.0×10 −3 cm/s for d 9 ‐Ir 0 /d 10 ‐Ir −I ]. In ACN, the two redox waves merge into one “two‐electron” wave [ k s 1,2 =7.76×10 −4 cm/s for d 8 ‐Ir +I /d 9 ‐Ir 0 and d 9 ‐Ir 0 /d 10 ‐Ir −I ] most likely because the neutral [Ir 0 (tropp Ph ) 2 ] complex is destabilized. At low temperatures (ca. − 40 °C) and at high scan rates (ca. 10 V/s), the two‐electon redox process is kinetically resolved. In equilibrium with the tetracoordianted complex [Ir +I (tropp Ph ) 2 ] + are the pentacoordinated 18 valence [Ir +I (tropp Ph ) 2 L] + complexes (L=THF, ACN, Cl − ) and their electrochemical behavior was also investigated. They are irreversibly reduced at rather high negative potentials (− 1.8 to − 2.4 V) according to an ECE mechanism 1) [Ir +I (tropp Ph ) 2 (L)]+e − →[Ir 0 (tropp Ph ) 2 (L)]; 2) [Ir 0 (tropp Ph ) 2 (L)]→[Ir(tropp Ph ) 2 ]+L, iii) [Ir 0 (tropp Ph ) 2 ]+e − →[Ir −I (tropp Ph ) 2 ] − . Since all electroactive species were isolated and structurally characterized, our measurements allow for the first time a detailed insight into some fundamental aspects of the coordination chemistry of iridium complexes in unusually low formal oxidation states.