Previous studies with the title ligand, PAP, have shown a predominance of binuclear complexes with cobalt and copper in which the ligand-to-metal ratio is 1:2. The nickel complexes produced are more varied in composition; e.g., 1:2 binuclear systems [PAPNi2X(OH)(H2O)4]X2 (X = Cl, Br); 1:1 binuclear systems [PAP2Ni2(H2O)4]X4 (X = Cl, Br), [PAP2Ni2(NCS)3]NCS, [PAP2Ni2(OH)I2]I•2H2O, [PAP2Ni2(OH)(H2O)2]X3 (X = ClO4, BF4, I); and 2:1 mononuclear systems [(PAPH)2Ni(H2O)2]X4 (X = I, BF4). Zinc forms both mononuclear, [PAPZnX2]•H2O (X = Br, I), and a 1:1 binuclear system, [PAP2Zn2Cl4]. Triple bridges are suggested between the nickel atoms in all binuclear systems involving bridging hydroxy groups. Weak antiferromagnetic exchange is observed (−J < 10 cm−1) in two binuclear nickel complexes, which is enhanced in the presence of a hydroxy bridge. Spin–spin coupling is assumed to occur via a superexchange mechanism. In all cases nickel appears to be six-coordinate while for the zinc complexes both four- and six-coordination are observed.
The reaction of 3-benzoylpyrrole and Cr(CO)6 yields only the π-complex 3-(η6-benzoyltricarbonylchromium)pyrrole, in contrast to the previously reported reaction of 2-benzoylpyrrole and Cr(CO)6 that yielded only the σ-chelate, tris(2-benzoyl-pyrrolato)chromium(III). The difference in behaviour is explained by a preference for chelate formation that is allowed by the stereochemistry of 2-benzoylpyrrole but is not allowed by the stereochemistry of 3-benzoylpyrrole.
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