Three [CuII(L) (BF)]+ complexes, where L is tris(2-pyridylmethyl)amine (TPA) (1), bis(2-pyridylmethyl)amine (BPA) (2) or bis(2-benzimidazolylmethyl)amine (BBA) (3), and BF is benzoylformate, have been synthesized as structural models for the active site of α-keto acid-dependent enzymes. Single crystals of 1 (P21/n, a=11.3332(1), b=9.0159(1), c=40.2883(1) Å, Z=4, V=4114.62(6) Å3) were obtained and subjected to X-ray diffraction analysis. Complex 1 has a mononuclear trigonal bipyramidal Cu(II) center with a monodentate BF occupying an axial position. The solid structure of 1 appears to be maintained in solution as probed by IR, Vis, NMR and EPR spectroscopy. Spectroscopic studies of 2 and 3 with tridentate ligands replacing the tetradentate TPA ligand suggest a square pyramidal Cu(II) center in these two complexes, and the BF is proposed to bind in a bidentate manner via its two carboxylate oxygen atoms. The fact that the α-keto carbonyl is not involved in binding to the Cu(II) center suggests that it is not crucial for the formation of Cu(II)-BF complexes. This conclusion supports the working model proposed for the metal site in Cu-TfdA (Cu-substituted 2,4-dichlorophenoxyacetate/α-ketoglutarate dioxygenase) and its interaction with the cofactor α-ketoglutarate.
Bibliographical noteFunding Information:
This work was supported by a grant from the National Institutes of Health (GM-33162). We thank Dr Victor G. Young, Jr. for his work on the X-ray structure of \[C u (TPA) (BF) \]B Ph4+ The Varian NMR spectrometers and the Siemens SMART system were purchased with grants from the National Science Foundation.
- Copper complexes
- Crystal structures
- α-Keto acid complexes