A. Sokolowski et al., METAL-CENTERED VERSUS LIGAND-CENTERED OXIDATIONS IN PHENOLATOVANADIUMAND PHENOLATOCOBALT COMPLEXES - CHARACTERIZATION OF PHENOXYLCOBALT(III) SPECIES, Inorganic chemistry, 36(17), 1997, pp. 3702-3710
The coordination chemistry of the pendent-arm macrocycles 1,4,7-tris(3
,5-dimethyl-2-hydroxybenzyl) 1,4,7-triazacyclononane, (LH3)-H-Me, rt-b
utyl-2-hydroxybenzyl)-1,4,7-triazacyolononane, (LH3)-H-BU, -methoxy-2-
hydroxybenzyl)-1,4,7-triazacyclononane, (LH3)-H-OCH3, and Tolman's lig
and rt-butyl-2-hydroxybenzyl)-1,4,7-triazacyclononane, (LH)-H-Pr, with
vanadium and cobalt(III) has been studied. The following complexes co
ntaining a fac-N3O3 donor set have been synthesized: [(LVIII)-V-Me] (1
), [(LVIV)-V-Me]PF6 (2), [((LH)-H-Me)V-V(O)]PF6 (3), [(LVIV)-V-Bu]PF6
(4), [(LVIV)-V-OCH3]PF6 (5), [(LCOIII)-C-Me] (6), [(LCoIII)-Co-Bu] (7)
, [(LCoIII)-Co-OCH3] (8). In addition, two complexes containing the (L
CoIII)-Co-Pr fragment have been prepared: [L-Pr-Co-III(acac)](ClO4) (9
) and [(LCoIII)-Co-Pr(Cl(4)cat)]. CH3CN (10), where acac(-) represents
the ligand pentane-2,4-dionate and Cl(4)cat(2-) is tetrachlorocatecho
late. Complexes 9 and 10 have been characterized by single-crystal X-r
ay crystallography: 9 crystallizes in the triclinic space group <P(1)o
ver bar> with a = 9.493(1) Angstrom, b = 9.760(1) Angstrom, c = 18.979
(2) Angstrom, alpha = 88.57(1)degrees, beta = 78.60(1)degrees, gamma =
79.24(1)degrees, V = 1693.3(3) Angstrom(3), and Z = 2; 10 crystallize
s in the monoclinic space group P2(1)/n with a = 10.184(2) Angstrom, b
= 24.860(5) Angstrom, c = 14.872(3) Angstrom, beta = 97.95(3)degrees,
V = 3729(1) Angstrom(3), and Z = 4. Electrochemically, complexes 2, 4
, and 5 can be reversibly oxidized by one electron, yielding vanadium(
V), and one-electron-reduced, affording vanadium(III) species; 3 can b
e reduced to [(LHVIV)-H-Me(O)]. These redox processes are shown to be
metal-centered. In contrast, the cyclic voltammograms of 7 and 8 displ
ay three reversible one-electron oxidations. For the monocations [7](.
+) and [8](.+), EPR and W-vis spectroscopies reveal that these are phe
noxyl-cobalt(III) species. Thus, the redox processes are ligand-center
ed, Similarly, [9](+) is reversibly oxidized to the phenoxyl-cobalt(II
I) complex [9](.2+) (S = 1/2). For 10, two reversible one-electron oxi
dation steps have been identified generating [10](.+) (S = 1/2) and [1
0](2.2+) (S = 1). It is unambiguously shown by EPR and resonance Raman
spectroscopies that [10](.+) contains a (phenolato)(semiquinonato)cob
alt(III) unit whereas in [10](2.2+) a phenoxyl(semiquinonato)cobalt(LI
I) unit prevails.