The 1,4-diazabutadiene/1,2-enediamido non-innocent ligand system in the formation of iridaheteroaromatic compounds: Spectroelectrochemistry and electronic structure

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Journal of Organometallic Chemistry, 695 (7): 1052--1058 (2010)
DOI: 10.1016/j.jorganchem.2009.11.042


Oxidn. of the unambiguously characterized Ir(III)-enediamido complex IrCp*(RNCHCHNR), R = 2,6-dimethylphenyl, with six cyclically arranged p electrons was studied using EPR and UV-visible spectroelectrochem. In contrast to a corresponding iminocatecholato system reported recently by Rauchfuss et al. the two 1-electron oxidn. steps are not completely reversible, depending on the solvent. The electrochem. behavior obsd. is attributed to weakly coordinating CH2Cl2 and propylene carbonate solvents to an enhanced propensity for ligand addn.: while neutral IrCp*(RNCHCHNR) remains coordinatively unsatd. with the strongly s and p donating enediamido(2-) ligand mitigating the electron deficit, the oxidn. to the less donating radical anion ligand (RNCHCHNR)·- or even to neutral 1,4-diazabutadiene is considered to induce a strong tendency for quasi-hexacoordination in IrCp*(L)(RNCHCHNR), L = solvent, halide, substrate. The presence of excess chloride thus gives the precursor complex ion IrCp*Cl(RNCHCHNR)+ after oxidn. EPR spectroscopy of the 1-electron oxidn. intermediate IrCp*(RNCHCHNR)+ was successful only for a frozen soln. in propylene carbonate/0.1 M Bu4NPF6 which revealed an axial signal with sizeable g anisotropy. DFT calcn. results for IrCp*(RNCHCHNR)n (n = 0, 1+, 2+) confirm the available structural and spectroelectrochem. data (UV-visible, EPR). on SciFinder(R)



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