Sterically Bulky Tris(triazolyl)borate Ligands as Water-Soluble Analogues of Tris(pyrazolyl)borate Finith E. Jernigan, III, ² Nathan A. Sieracki, ‡ Michael T. Taylor, ² Aaron S. Jenkins, ² Sharon E. Engel, ‡ Brittany W. Rowe, ² Fernando A. Jove ´, § Glenn P. A. Yap, § Elizabeth T. Papish,* ,² and Gregory M. Ferrence* ,‡ Department of Chemistry, Salisbury UniVersity, Salisbury, Maryland 21801, Department of Chemistry, Illinois State UniVersity, Normal, Illinois 61790, and Department of Chemistry, UniVersity of Delaware, Newark, Delaware 19716 Received September 25, 2006 The recently synthesized 3-tert-butyl-5-methyl-1,2,4-triazole reacted with KBH 4 to give the new potassium tris(3-tert-butyl-5-methyl- 1,2,4-triazolyl)borate K(Ttz tBu,Me ) ligand. Ttz tBu,Me formed a four- coordinate (Ttz tBu,Me )CoCl complex and five-coordinate (Ttz tBu,Me )CoNO 3 and (Ttz tBu,Me )ZnOAc complexes. When these complexes were compared to their Tp tBu,Me analogues, it was found that Ttz tBu,Me resulted in negligible steric differences. K(Ttz tBu,Me ) is more water-soluble than K(Tp tBu,Me ), so bulky tris(triazolyl)borate ligands should lead to functional models for enzyme active sites in an aqueous environment and the creation of water-soluble analogues of Tp catalysts. The chemistry of scorpionate-supported transition-metal complexes has been the subject of intense research with in excess of 2000 papers published on poly(pyrazolyl)borate complexes spanning over 70 elements of the periodic table. 1 The Cambridge Structural Database (CSD) includes data for over 2900 crystal structures of tris(pyrazolyl)borate (Tp) metal complexes, 2 with many bulky derivatives. In stark contrast, only 25 tris(triazolyl)borate (Ttz) metal complexes are reported in the CSD, 3,4 consisting predominantly of unsubstituted triazoles and just three tris(3,5-dimethyltriaz- olyl)borate complexes. 4 Thus far, no examples of sterically demanding triazolylborate ligands have been reported. This is particularly significant given that bulky Tp ligands have been found to be well suited for the isolation of low- coordinate metal complexes of importance to the disparate areas of nonaqueous lanthanide chemistry and biomimetic transition-metal chemistry. Those with tert-butyl groups attached to the pyrazolyl 3 positions have been referred to as tetrahedral enforcers. 5 The tris(3-tert-butyl-5-methylpyra- zolyl)borate ligand readily stabilizes five-coordinate and even putatively four-coordinate divalent lanthanide complexes. 6 Of the many tripod-zinc complexes employed to model zinc enzymes, those with appropriately substituted Tp ligands have received considerable attention. 7 With these features in mind, our groups independently became interested in examining the analogous chemistry using the tris(3-tert-butyl-5-methyl-1,2,4-triazolyl)borate (Ttz tBu,Me ) ligand. The change from Tp to Ttz ligands should result in negligible steric, but potentially significant, elec- tronic differences. Subtle changes in the supporting ligand environment commonly leads to a substantive difference in the chemistry of corresponding lanthanide complexes. 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