TROPDAD: A new ligand for the synthesis of water-stable paramagnetic [16+1]-electron rhodium and iridium complexes

摘要

The new tetradentate ligand 1,4-bis(5H-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)](O3SCF3) (M = Rh, Ir). The structure of the rhodium complex was determined by X-ray analysis and points to a description of these as [M-divided by1((H)tropdad)(0)] with short C=N bonds (av 1.285 Angstrom) and a long C-C bond (1.46 Angstrom) 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-1/2(1) = -0.56V and E-1/2(1) = -0.35V, 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)(N-14) = 11.9 MHz, A(iso)(H-1) = 14.3 MHz, A(iso)(Rh-103) = -5.3 MHz; [Ir((H)tropdad)](0): A(iso)(N-14) = 11.9 MHz, A(iso)(H-1) = 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 described as [M+1((H)tropdad)(.-)] with a spin density contributions were determined. These results clearly show that the complexes [M((H)tropdad)](0) are best [16 + 1] electron configuration. [References: 29]