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TROPDAD: A New Ligand for the Synthesis of Water‐Stable Paramagnetic [16+1]‐Electron Rhodium and Iridium Complexes
Author(s) -
Breher Frank,
Böhler Carsten,
Frison Gilles,
Harmer Jeffrey,
Liesum Lorenz,
Schweiger Arthur,
Grützmacher Hansjörg
Publication year - 2003
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.200204700
Subject(s) - rhodium , chemistry , electron paramagnetic resonance , ligand (biochemistry) , iridium , cationic polymerization , crystallography , moiety , paramagnetism , hyperfine structure , stereochemistry , nuclear magnetic resonance , polymer chemistry , organic chemistry , catalysis , biochemistry , physics , receptor , quantum mechanics
The new tetradentate ligand 1,4‐bis(5 H ‐dibenzo[ a , d ]cyclohepten‐5‐yl)‐1,4‐diazabuta‐1,3‐diene ( H tropdad) allows the syntheses of the 16‐electron cationic rhodium complexes [M( H tropdad)](O 3 SCF 3 ) (M=Rh, Ir). The structure of the rhodium complex was determined by X‐ray analysis and points to a description of these as [M +1 ( H tropdad) 0 ] with short CN bonds (av 1.285 Å) and a long CC bond (1.46 Å) in the diazabutadiene (dad) moiety, that is the M→dad charge‐transfer is negligible. Both [Rh( H tropdad)] + and [Ir( H tropdad)] + are reduced at very low potentials ( E 1 1/2 = −0.56 V and E 1 1/2 =−0.35 V, respectively) which allowed the quantitative synthesis of the neutral paramagnetic complexes [M( H tropdad)] 0 (M=Rh, Ir) by reacting the cationic precursor complexes simply with zinc powder. The [M( H tropdad)] 0 complexes are stable against protic reagents in organic solvents. Continuous wave and pulse EPR spectroscopy was used to characterize the paramagnetic species and the hyperfine coupling constants were determined: [Rh( H tropdad)] 0 : A iso ( 14 N)=11.9 MHz, A iso ( 1 H)=14.3 MHz, A iso ( 103 Rh)= −5.3 MHz; [Ir( H tropdad)] 0 : A iso ( 14 N)=11.9 MHz, A iso ( 1 H)=14.3 MHz. In combination with DFT calculations, the experimentally determined g and hyperfine matrices could be orientated within the molecular frame and the dominant spin density contributions were determined. These results clearly show that the complexes [M( H tropdad)] 0 are best described as [M +1 ( H tropdad) .− ] with a [16+1] electron configuration.