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Thermodynamic and Kinetic Data for Adduct Formation, cis – trans Isomerization and Redox Reactions of ML 4 Complexes: A Case study with Rhodium– and Iridium–tropp Complexes in d 8 , d 9 and d 10 Valence Electron Configurations (tropp= Dibenzotropylidene Phosphanes)
Author(s) -
Breher Frank,
Rüegger Heinz,
Mlakar Marina,
Rudolph Manfred,
Deblon Stephan,
Schönberg Hartmut,
Boulmaâz Souad,
Thomaier Jörg,
Grützmacher Hansjörg
Publication year - 2004
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200305116
Subject(s) - iridium , isomerization , rhodium , adduct , chemistry , redox , kinetic energy , kinetics , photochemistry , inorganic chemistry , catalysis , organic chemistry , physics , quantum mechanics
The formation of adducts of the square‐planar 16‐electron complexes trans ‐[M(tropp ph ) 2 ] + and cis ‐[M(tropp ph ) 2 ] + (M=Rh, Ir; tropp Ph =5‐diphenylphosphanyldibenzo[a,d]cycloheptene) with acetonitrile (acn) and Cl − , and the redox chemistry of these complexes was investigated by various physical methods (NMR and UV‐visible spectroscopy, square‐wave voltammetry), in order to obtain some fundamental thermodynamic and kinetic data for these systems. A trans / cis isomerization cannot be detected for [M(tropp ph ) 2 ] + in non‐coordinating solvents. However, both isomers are connected through equilibria of the type trans ‐[M(tropp ph ) 2 ] + +L⇄[ ML(tropp ph ) 2 ] n ⇄ cis ‐[M(tropp ph ) 2 ] + +L, involving five‐coordinate intermediates [ML(tropp ph ) 2 ] n (L=acn, n =+1; L=Cl − , n =0). Values for K d ( K f ), that is, the dissociation (formation) equilibrium constant, and k d ( k f ), that is, the dissociation (formation) rate constant, were obtained. The formation reactions are fast, especially with the trans isomers ( k f >1×10 5 m −1 s −1 ). The reaction with the sterically more hindered cis isomers is at least one order of magnitude slower. The stability of the five‐coordinate complexes [ML(tropp ph ) 2 ] n increases with Ir>Rh and Cl − >acn. The dissociation reaction has a pronounced influence on the square‐wave (SW) voltammograms of trans / cis ‐[Ir(tropp ph ) 2 ] + . With the help of the thermodynamic and kinetic data independently determined by other physical means, these reactions could be simulated and allowed the setting up of a reaction sequence. Examination of the data obtained showed that the trans / cis isomerization is a process with a low activation barrier for the four‐coordinate 17‐electron complexes [M(tropp ph ) 2 ] 0 and especially that a disproportionation reaction 2 trans / cis ‐[M(tropp ph ) 2 ] 0 →[M(tropp ph ) 2 ] + +[M(tropp ph ) 2 ] − may be sufficiently fast to mask the true reactivity of the paramagnetic species, which are probably less reactive than their diamagnetic equilibrium partners.