Deprotonated p-phenylenediamines as noninnocent ligands. Metal-to-ligand spin transfer in the ground state and ligand-to-metal charge transfer in the lowest excited state of low-spin manganese(II) complexes

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Inorganic Chemistry, 26 (21): 3596--3600 (1987)
DOI: 10.1021/ic00268a035


Neutral paramagnetic complexes between (h5-C5R5)(CO)2Mn (R = H, Me) and p-phenylenediamides(1-) were obtained via synergistic oxidative deprotonation as labile intermediates between p-phenylenediamine precursor complexes and binuclear complexes of the dehydrogenated forms of these ligands. Although the compds. must primarily be regarded as low-spin manganese(II) systems, indicating the capacity of p-phenylenediamides(1-) to stabilize metals in relatively high formal oxidn. states, the exceptional s- and p-donor capacity of deprotonated p-phenylenediamines causes facile ligand-to-metal charge transfer (LMCT). Spin delocalization is evident from reduced g factors and 55Mn EPR hyperfine coupling and, in particular, from emerging 14N and 1H superhyperfine interaction. Reprodn. of these results by HMO-McLachlan spin-d. calcns. supports the p-type metal/ligand interaction, which is also evident from apparent conformational preferences. LMCT in the lowest excited state is responsible for low-energy transitions d(SOMO) $łeftarrow$ p in the near-IR region; a correlation could be established between LMCT transition energies and the ionization potentials of the protonated ligands, i.e. the corresponding amines. The insensitivity of these transitions to changes of solvent or cyclopentadienyl substituents is a further consequence of the considerably mixed metal/ligand character of the compds. on SciFinder(R)



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