The reaction of mer-[ReIIIL(OPPh3)Cl3] 2 with PPh3 in benzene has afforded bluish violet fac-[ReIIIL(PPh3)Cl3] 1, where L is the Schiff base of pyridine-2-carbaldehyde and the substituted aniline p-XC6H4NH2 (X = H, Me, OMe or Cl). Geometrical preferences are rationalized in terms of the electronic nature of the ligands OPPh3 (σ- and π-donor), PPh3 (σ-donor and π-acceptor) and L (σ-donor and π-acceptor). The cyclic voltammetric E1/2 values of 1 lie near 0.6 V (ReIV-ReIII) and -0.6 V (ReIII-ReII). Electrooxidation of 1 at 1.0 V vs. SCE in wet acetonitrile affords yellow fac-[ReIVL′(PPh3)Cl3] 3 which is also obtainable via oxidation by dilute nitric acid (L′ is a monoanionic pyridine-2-carboxamide). Complex 3 displays ReIV-ReIII and ReV-ReIV couples near -0.2 V and 1.4 V respectively reflecting superior stabilization of the rhenium(IV) state by the amide ligand. The X-ray structures of two representative complexes of type 1 and 3 have revealed the presence of severely distorted and facially configured RePN2Cl3 coordination spheres. The average Re-Cl distance is lower by 0.06 Å in 3 due to contraction of the metal radius upon oxidation. The Re-P length is however larger by 0.1 Å in 3 signifying a weakening of Re-P back-bonding.
|Original language||English (US)|
|Number of pages||5|
|Journal||Journal of the Chemical Society - Dalton Transactions|
|State||Published - Jan 21 1999|
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