摘要:
The first crystallographically characterized neutral square-planar complex of cobalt in an oxidation state higher than 2+, Co(eta-4-1), is reported. Structural data for this new class of compounds indicate that the macrocycle in Co(eta-4-1) is[GRAPHICS]noninnocent; however, EPR data in toluene at 5.9 K (S = 1/2; g1 = 2.558, g2 = 2.170, g3 = 2.017; A2 almost-equal-to 15 G) show that the metal center is the primary residence site of the unpaired electron. Co(eta-4-1) is a stable, yet potent, oxidant which is soluble in benzene and slightly soluble in pentane. The Co(eta-4-1)/[Co(III)(eta-4-1)]- couple is reversible and found at 0.550 V vs Fc+/Fc in CH2Cl2 (ca. 1.26 V vs NHE). Co(eta-4-1) slowly oxidized water, yielding H[Co(III)(eta-4-1)], which may also be prepared by the reaction of [Co(III)(eta-4-1)]- with HBF4. Both the redox and the acid/base chemistries of [Co(III)(eta-4-1)]- are reversible. Electrochemical and EPR data are also presented for Co(eta-4-2) and Co(eta-4-3).