In this Communication, the imido complex [Tp tBu,Me Co = NAd] (1) was incorrectly characterized as a paramagnetic compound with a spin ground state of S = 1. Further investigation has now revealed that this compound, like all other known Co(III) imido complexes, has a spin ground state of S = 0 and is diamagnetic at low temperatures. However, at T > 280 K, 1 undergoes a spin crossover to a thermally accessible open-shell state. All the experimental observations reported in the original Communication remain unchanged, but their interpretation is more complicated than originally realized.
Reaction of TpR,MeCo(I) dinitrogen complexes (R = iPr, tBu) with trimethylsilyl azide yields structurally characterized compounds that imply the formation of reactive intermediates of the type TpR,MeCo=NSiMe3. These cobalt imido species apparently abstract hydrogen from the 3-substituent of the Tp-ligand, leading to the formation of amido complexes accompanied by either Co-C bond formation (R = tBu) or C-C bond formation (R = iPr).
Stable terminal imido complexes of the late transition metals (Group 9 and beyond) are rare, [1] . We attribute the formation of the azide side product to the greater stability of the tert-butyl radical. Both imido complexes have been structurally characterized by X-ray diffraction; the representative molecular structure of 1 is shown in Figure 1. [3] Compound 1 is a four-coordinate molecule adopting pseudo-tetrahedral coordination of cobalt by four nitrogen ligands. Of note are the short Co(1)-N(7) bond of 1.655(2) and the Co(1)-N(7)-C(25) angle of 178.3(2), both of which are consistent with multiple bonding between cobalt and nitrogen center N(7). The parameters of the coordination by the Tp ligand (CoÀN av , 2.046(7) ; N-Co-N av , 89(1)8) are not unusual; indeed, they are a testament to the rigidity of the Tp ligand and underscore the deviation of the geometry of 1 from tetrahedral coordination.
In this Communication, the imido complex [Tp tBu,Me Co = NAd] (1) was incorrectly characterized as a paramagnetic compound with a spin ground state of S = 1. Further investigation has now revealed that this compound, like all other known Co(III) imido complexes, has a spin ground state of S = 0 and is diamagnetic at low temperatures. However, at T > 280 K, 1 undergoes a spin crossover to a thermally accessible openshell state. All the experimental observations reported in the original Communication remain unchanged, but their interpretation is more complicated than originally realized.
The use of partially quaternized, chloromethylated polystyrene as a covalent scavenger of cholate ion in aqueous media has been demonstrated. The ability of such polymers to scavenge organic anions by covalent as well as by ionic means has important implications in the areas of medicinal and environmental chemistry, which are briefly discussed.
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