E. Solari et al., GEOMETRICAL ISOMERISM AND REDOX BEHAVIOR IN ZIRCONIUM-SCHIFF BASE COMPLEXES - THE FORMATION OF C-C BONDS FUNCTIONING AS 2-ELECTRON RESERVOIRS, Journal of the Chemical Society. Dalton transactions, (17), 1997, pp. 2903-2910
Two model compounds have been used for exploring the ligand-based redo
x chemistry of zirconium-Schiff base complexes, namely [Zr(salophen)Cl
-2(thf)] 1 and [Zr(salophen)(2)] 2 [salophen = N,N'-bis(salicylidene)-
o-phenylenediamine dianion, thf = tetrahydrofuran]. The latter occurs
in two thermally non-interconvertible isomeric forms, 2A and 2B. Both
contain eight-co-ordinate zirconium in a dodecahedral, 2A, and in a sq
uare-antiprismatic environment, 2B. The reduction of 1 with either Na
or Mg led to the isolation of [Zr2LL'(2)](L'=thf 3 or pyridine 4). The
centrosymmetric dinucleating octaanionic ligand L, which contains two
-fold coupled salophen units joined by two C-C bonds, arises from the
intermolecular reductive coupling of four imino groups belonging to tw
o Zr(salophen) units. In an attempt to perform intramolecularly the sa
me transformation; complexes 2A and 2B were reduced with sodium. Both
isomers gave complex [ZrL''Na-4(dme)(4)] 5 (dme=1,2-dimethoxyethane) c
ontaining a novel form of an hydrogenated coupled salophen ligand, L''
, where the two salophen units are joined by a single C-C bond. The C-
C bonds in the ligand L have been exploited as two-electron reservoirs
in the reaction of 3 with PhlCl(2), and 9,10-phenanthrenequinone. In
this reaction the original salophen moiety is restored in its original
form and the Zr(salophen) moiety present in 3 behaves as a source of
masked zirconium(II).