The recently synthesized 3-tert-butyl-5-methyl-1,2,4-triazole reacted with KBH4 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))CoNO3 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.
Carbon dioxide fixation with zinc complexes of the anionic tris(triazolyl)borate (Ttz) ligand offers biomimetic structures in a hydrophilic environment. However, the synthetic result depends greatly on the steric bulk of the Ttz ligand. Synthetic routes adapted from the synthesis of (Tp)ZnOH have been applied to bulky Ttz ligands, but side products often result because Ttz frequently forms complexes with +1 metals or cations used in the synthesis. Nonetheless, (Ttz tBu,Me )-ZnOH (1) has been successfully synthesized and crystallographically characterized, but only via the hydrolysis of the zinc (hex-(1) [a] 2495 Scheme 2. The application of synthetic routes that are known in the literature to form TpZnOH leads to different results when applied to the formation of biomimetic Ttz zinc complexes. However, zinc hydroxide complexes of Ttz can be achieved in some cases. In this Scheme M = Na, K, NMe 4 and L = Tp or Ttz of varied steric bulk (this work focuses on L = Ttz tBu,Me , Ttz iPr2 , Ttz Ph,Me ).
2496Scheme 3. Successful route to (Ttz tBu,Me )ZnOH (1) via Zn amide (6). Zn amide structure is tentatively assigned as κ 3 or κ 2 .Scheme 4. Synthesis of the zinc hydroxide (2a) and zinc carbonate (2b) complexes. Two equivalents of 2a react with CO 2 to eliminate water and form one equivalent of 2b.
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