Oxidation of [Con(dacoda)(H20)] (dacoda = 1,5-diazacyclooctane-7V,7V-diacetate) with Pb02 in the presence of 1 equiv of S032' affords the classically five-coordinate Co(III) complex K[Co,n(dacoda)(S03)]-5H20 (3), which contains a three-center, two-electron Co"HC (agostic) interaction in the sixth coordination position. 3 crystallizes in the monoclinic space group P2Jc with a = 7.500 (2) A, 6 = 16.5469 (15) A, c = 30.978 (4) A, ß = 89.91 (2)e, V = 3844 (1) A3, with Z = 8, and a final unweighted R value of 0.051. The structural and spectroscopic results indicate that a weak agostic interaction exists between the Co center and the C(2)-H(2a) bond. The agostic Co(l)-H(2a) and Co(l)-C(2) distances were found to be 2.31 (5) and 2.531 (4) A, respectively. ,3C NMR studies reveal that the agostic C(2)-H(2a) group shows only a slightly reduced coupling constant, /(13C-'H) = 122 Hz, versus the value of 129 Hz observed for similar methylene C-H groups within the metal complex. The ligand field parameter, Dq, of the "agostic ligand" is calculated to be only ~600 cm"1, reflecting the weakness of the agostic interaction. The weakness of the Co"HC interaction and the reason for the surprising stability of 3 in aqueous solution are attributed to the strong trans influence of the sulfite ligand. However, this complex can be deprotonated in methanol to form the Co-alkyl complex [Com-(dacoda-C( 2))(H20)], where dacoda-C(2) refers to dacoda coordinated in a quinquedentate fashion with the C(2) carbon of the daco portion of the ligand directly bonded to the cobalt center. These results demonstrate the activation of a C-H bond via electrophilic attack of Co(lII) in a relative simple but sterically constrained molecule, which may be inherent to C-H activation

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A series of octahedral cobalt(III) complexes involving tetradentate diaminedicarboxylic acid chelating agents was prepared: [Co(Am)(Lig)] + where Am = ethylenediamine and Lig = ethylenediamine-N,N'-diacetate (EDDA), N,N'-dimethylethylenediamine-N,N'-d¡acetate (DMEDDA), and N,N'-diethylethylenediamine-N,N'-diacetate (DEEDDA); and where Lig = Contribution from the Department op Chemistry,

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