Preparation of SNS Cobalt(II) Pincer Model Complexes of Liver Alcohol Dehydrogenase

This method can be used to prepare a chemical model complex of an enzyme liver alcohol dehydrogenase and to grow single crystals. The advantages of this technique are that the complex formation is facile and that the recrystallization method can be applied to the preparation of other coordination complexes. This method can provide insight into the preparation and recrystallization of inorganic coordination compounds and can be applied to any compound of interest to grow single crystals.

It takes practice to grow the single crystals. The key is to make the acetonitrile solution that contains the metal complex as concentrated as possible. To prepare complex four, add 0.121 grams of 2, 6-BIS-N-isopropyl-N’methyleneimidzole-2-thione-pyridine and 0.0851 grams of cobalt II chloride hexahydrate to a 100 milliliter round bottom flask containing 15 milliliters of acetonitrile.

The reaction should change from a light yellow color to emerald green immediately after the cobalt II chloride hexahydrate is added. Then reflux and stir the reaction for 20 hours to ensure complete reaction before using a rotovap under reduced pressure to remove the solvent. For chloro-N3-S, S, N-2, 6-BIS-N-isopropyl-N’methyleneimidzole-2-thione-pyridine cobalt II tetrachlorocobaltate recrystallization by slow vapor diffusion, dissolve the solute in 10 milliliters of acetonitrile, filer the solution, then aliquot the solution evenly between one dram vials.

Add 1.5 milliliters of fresh acetonitrile solution to each vial and snugly cap the vials with cotton. Place the vials in a 240 milliliter jar containing 50 milliliters of diethyl ether and close the jar with a cap. Then allow the crystals to grow for up to a week.

To prepare complex five, add 0.183 grams of 2, 6-BIS-N-isopropyl-N’methylenetriazole-2-thione-pyridine and 0.223 grams of cobalt II chloride hexahydrate to 15 milliliters of acetonitrile in a 100 milliliter round bottom flask. The reaction should change color from a light yellow color to royal blue immediately after the cobalt II chloride hexahydrate is added. Then reflux and stir the reaction for 20 hours to ensure complete reaction before removing the solvent using a rotovap under reduced pressure.

For chloro-N3-S, S, N-2, 6-BIS-N-isopropyl-N’methylenetriazole-2-thione-pyridine cobalt II tetrachlorocobaltate recrystallization by slow vapor diffusion, dissolve the solute in 10 milliliters of acetonitrile and filter the solution before aliquoting the solution evenly in one dram vials. Fill each vial with 1.5 milliliters of acetonitrile solution and snugly cap the vials with cotton. To grow high-quality single crystals, it’s critical that the cotton plug fits snugly within the one dram vial.

We use a little less than one cotton ball for each vial. Then place the vials in a jar containing 50 milliliters of diethyl ether, close the jar with a cap, and allow the crystals to grow for up to a week. The synthesis of complexes four and five can be successfully carried out by reacting an acetonitrile solution containing a bis-thione ligand precursor with cobalt II chloride hexahydrate.

The acquisition of single crystals of complexes four and five via slow vapor diffusion is an excellent method for growing single crystals for hard to crystallize samples. Elemental analysis of the recrystallized complexes suggests that complexes four and five are pure because the calculated percentages of carbon, hydrogen, and nitrogen are in excellent agreement with the found percentages of carbon, hydrogen, and nitrogen. In addition, ultraviolet visible spectroscopy of complexes four and five reveals that complex four exhibits three peaks in the visible region at 680, 632, and 589 nanometers, and that complex five exhibits four peaks in the visible region at 682, 613, 588, and 573 nanometers.

The most important thing to remember is that when you prepare the complex, you must add cobalt chloride hexahydrate to an acetonitrile solution that contains a ligand precursor. The recrystallization method can be applied to any organic or inorganic compound that is difficult to recrystallize. We are currently preparing cobalt II complexes that do not contain cobalt in the counter-anion and screening the complexes for their reactivity.

Be sure to conduct all of the reactions in a fume hood.