John Miecznikowski received financial support from the following for this project: the Connecticut NASA Space Grant Alliance (Award Number P-1168), the Fairfield University Science Institute, College of Arts and Sciences Publication Fund, Fairfield University Faculty Summer Research Stipend, and National Science Foundation-Major Research Instrumentation Program (Grant Number CHE-1827854) for funds to acquire a 400 MHz NMR spectrometer. He also thanks Terence Wu (Yale University) for assistance in acquiring electrospray mass spectra. Jerry Jasinski acknowledges the National Science Foundation-Major Research Instrumentation Program (Grant Number CHE-1039027) for funds to purchase an X-ray diffractometer. Sheila Bonitatibus, Emilse Almanza, Rami Kharbouch, and Samantha Zygmont acknowledge the Hardiman Scholars Program for providing their summer research stipend.

1. Synthesis of chloro-(n3-S,S,N)-[2,6-bis(N-isopropyl-N&#8217;-methyleneimidazole-2-thione)pyridine]cobalt(II)tetrachlorocobaltate [4]
<ol>
	<li>To prepare complex 4, add 0.121 g (3.12 x 10-4 mol) of 2,6-bis(N-isopropyl-N&#8217;-methyleneimidazole-2-thione)pyridine (C19H25N5S2)6 to 15 mL of acetonitrile in a 100 mL round bottom flask. Next, to this solution, add 0.0851 g (3.58 x 10-4 mol) of cobalt chloride(II) hexahydrate (CoCl2&#183;6H2O). The reaction solution should change color from light yellow to emerald green immediately after the cobalt(II) chloride hexahydrate is added.</li>
	<li>Add a stir bar to the flask. Reflux and stir&#160;the reaction for 20 h to ensure complete reaction. Remove the solvent using a rotovap under reduced pressure.</li>
</ol>
2. Recrystallization of chloro-(n3-S,S,N)-[2,6-bis(N-isopropyl-N&#8217;-methyleneimidazole-2-thione)pyridine]cobalt(II)tetrachlorocobaltate [4] by slow vapor diffusion
<ol>
	<li>Dissolve the solute in acetonitrile (7.5 mL), filter the solution, and place the solution evenly in 1 dram vials. Fill each vial with 1.5 mL of acetonitrile solution.
	<ol>
		<li>Add cotton to cap the vials, which allows for slow vapor diffusion. Fit the cotton snugly in the opening at the top of the vial.</li>
		<li>Place the vials in a 240 mL jar containing 50 mL of diethyl ether. Close the jar with a cap.</li>
		<li>Allow the crystals to grow over a period of 1 week. 
		NOTE: Recrystallization may take longer than 1 day.</li>
	</ol>
	</li>
</ol>
3. Synthesis of chloro-(n3-S,S,N)-[2,6-bis(N-isopropyl-N&#8217;-methylenetriazole-2-thione)pyridine]cobalt(II)tetrachlorocobaltate [5]
<ol>
	<li>To prepare complex 5, add 0.183 g (4.70 x 10-4 mol) of 2,6-bis(N-isopropyl-N&#8217;-methylenetriazole-2-thione)pyridine (C17H23N7S2)6 to 15 mL of acetonitrile in a 100 mL round bottom flask. To this solution, add 0.223 g (9.37 x 10-4 mol) of cobalt chloride hexahydrate (CoCl2&#183;6H2O). The reaction solution should change color from light yellow to royal blue immediately after the cobalt(II) chloride hexahydrate is added.
	<ol>
		<li>Add a stir bar to the flask. Reflux and stir the reaction for 20 h to ensure complete reaction. Remove the solvent using a rotovap under reduced pressure.</li>
	</ol>
	</li>
</ol>
4. Recrystallization of chloro-(n3-S,S,N)-[2,6-bis(N-isopropyl-N&#8217;-methylenetriazole-2-thione)pyridine]cobalt(II)tetrachlorocobaltate [5] by slow vapor diffusion
<ol>
	<li>Dissolve the solute in acetonitrile (9.0 mL), filter the solution, and&#160;place the solution evenly in 1 dram vials. Fill each vial with 1.5 mL of acetonitrile solution.
	<ol>
		<li>Add cotton to cap the vials, which allows for slow vapor diffusion. Fit the cotton snugly in the opening at the top of the vial.</li>
		<li>Place the vials in a jar containing 50 mL of diethyl ether. Close the vial with a cap.</li>
		<li>Allow the crystals to grow over a period of 1 week. 
		NOTE: Recrystallization may take longer than 1 day.</li>
	</ol>
	</li>
</ol>
5. X-ray crystallography
<ol>
	<li>Mount a crystal of 4 on a nylon loop. Collect the data on a Rigaku Oxford Diffraction diffractometer. Here, X-ray diffraction data is collected at 173(2) K. Solve the crystal structure using Olex216 and ShelXT17 structure solution programs using direct methods. Refine the structure with the ShelXL18 refinement package using least squares minimization.</li>
	<li>Mount a crystal of 5 on a nylon loop. Collect the X-ray diffraction data on a Rigaku Oxford Diffraction diffractometer. Here, X-ray diffraction data is collected at 173(2) K. Solve the crystal structure using Olex216 and ShelXT17 structure solution programs using direct methods. Refine the structure with the ShelXL18 refinement package using least squares minimization.</li>
</ol>

<ol>
	<li>Holm, R. H., Kennepohl, P., Solomon, E. I. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Structural+and+Functional+Aspects+of+Metal+Sites+in+Biology.">Structural and Functional Aspects of Metal Sites in Biology.</a> Chemical Reviews. 96 (7), 2239-2314 (1996).</li><li>Ibers, J. A., Holm, R. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Modeling+coordination+sites+in+metallobiomolecules.">Modeling coordination sites in metallobiomolecules.</a> Science. 209 (4453), 223-235 (1980).</li><li>Kannan, K. K., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Crystal+structure+of+human+erythrocyte+carbonic+anhydrase+B.+Three-dimensional+structure+at+a+nominal+2.2-A+resolution.">Crystal structure of human erythrocyte carbonic anhydrase B. Three-dimensional structure at a nominal 2.2-A resolution.</a> Proceedings of the National Academy of Sciences USA. 72 (1), 51-55 (1975).</li><li>Eklund, H., Br&#228;nd&#233;n, C. I. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Structural+differences+between+apo-+and+holoenzyme+of+horse+liver+alcohol+dehydrogenase.">Structural differences between apo- and holoenzyme of horse liver alcohol dehydrogenase.</a> Journal of Biological Chemistry. 254, 3458-3461 (1979).</li><li>Miecznikowski, J. R., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Syntheses,+Characterization,+Density+Functional+Theory+Calculations+and+Activity+of+Tridentate+SNS+Zinc+Pincer+Complexes.">Syntheses, Characterization, Density Functional Theory Calculations and Activity of Tridentate SNS Zinc Pincer Complexes.</a> Inorganica Chimica Acta. 376, 515-524 (2011).</li><li>Miecznikowski, J. R., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Syntheses,+Characterization,+Density+Functional+Theory+Calculations,+and+Activity+of+Tridentate+SNS+Zinc+Pincer+Complexes+Based+on+Bis-Imidazole+or+Bis-Triazole+Precursors.">Syntheses, Characterization, Density Functional Theory Calculations, and Activity of Tridentate SNS Zinc Pincer Complexes Based on Bis-Imidazole or Bis-Triazole Precursors.</a> Inorganica Chimica Acta. 387, 25-36 (2012).</li><li>Sunderland, J. R., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Investigation+of+liver+alcohol+dehydrogenase+catalysis+using+an+NADH+biomimetic+and+comparison+with+a+synthetic+zinc+model+complex.">Investigation of liver alcohol dehydrogenase catalysis using an NADH biomimetic and comparison with a synthetic zinc model complex.</a> Polyhedron. 114, 145-151 (2016).</li><li>Miecznikowski, J. R., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Synthesis+and+characterization+of+three-+and+five-coordinate+copper(II)+complexes+based+SNS+ligand+precursors.">Synthesis and characterization of three- and five-coordinate copper(II) complexes based SNS ligand precursors.</a> Polyhedron. 80, 157-165 (2014).</li><li>Miecznikowski, J. R., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Synthesis,+Characterization,+and+Computational+Study+of+Three-Coordinate+SNS+Copper(I)+Complexes+based+on+Bis-Thione+Ligand+Precursors.">Synthesis, Characterization, and Computational Study of Three-Coordinate SNS Copper(I) Complexes based on Bis-Thione Ligand Precursors.</a> Journal of Coordination Chemistry. 67, 29-44 (2014).</li><li>Lynn, M. A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Copper(I)+SNS+Pincer+Complexes:+Impact+of+Ligand+Design+and+Solvent+Coordination+on+Conformer+Interconversion+from+Spectroscopic+and+Computational+Studies.">Copper(I) SNS Pincer Complexes: Impact of Ligand Design and Solvent Coordination on Conformer Interconversion from Spectroscopic and Computational Studies.</a> Inorganica Chimica Acta. 495, (2019).</li><li>. Web Elements Available from: <a target="_blank" href="https://www.webelements.com/zinc/atom_sizes.html">https://www.webelements.com/zinc/atom_sizes.html</a> (2019)</li><li>. Web Elements Available from: <a target="_blank" href="https://www.webelements.com/cobalt/atom_sizes.html">https://www.webelements.com/cobalt/atom_sizes.html</a> (2019)</li><li>Caballero, A., D&#237;ez-Barra, E., Jal&#243;n, F. A., Merino, S., Tejeda, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=1,1'-(pyridine-2,6-diyl)bis(3-benzyl-2,3-dihydro-1H-imidazol-2-ylidine),+a+new+multidentate+N-heterocyclic+bis-carbene+and+its+silver(I)+complex+derivative.">1,1'-(pyridine-2,6-diyl)bis(3-benzyl-2,3-dihydro-1H-imidazol-2-ylidine), a new multidentate N-heterocyclic bis-carbene and its silver(I) complex derivative.</a> Journal of Organometallic Chemistry. 617-618, 395-398 (2001).</li><li>Albrecht, M., van Koten, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Platinum+Group+Organometallics+Based+on+"Pincer"+Complexes:+Sensors,+Switches,+and+Catalysis.">Platinum Group Organometallics Based on "Pincer" Complexes: Sensors, Switches, and Catalysis.</a> Angewandte Chemie International Edition. 40 (20), 3750-3781 (2001).</li><li>Peris, E., Crabtree, R. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Key+factors+in+pincer+ligand+design.">Key factors in pincer ligand design.</a> Chemistry Society Reviews. 47, 1959-1968 (2018).</li><li>Dolomanov, O. V., Bourhis, L. J., Gildea, R. J., Howard, J. A. K., Puschmann, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+complete+structure,+solution,+refinement,+and+analysis+program.">A complete structure, solution, refinement, and analysis program.</a> Journal of Applied Crystallography. 42, 339-341 (2009).</li><li>Sheldrick, G. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Integrated+Space+Group+and+Crystal+Structure+Determination.">Integrated Space Group and Crystal Structure Determination.</a> Acta Crystallography. 71, 3-8 (2015).</li><li>Sheldrick, G. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Crystal+Structure+Refinement+with+SHELXL.">Crystal Structure Refinement with SHELXL.</a> Acta Crystallography. 71, 3-8 (2015).</li><li>Pauling, L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Metal-metal+bond+lengths+in+complexes+of+transition+metals.">Metal-metal bond lengths in complexes of transition metals.</a> Proceedings of the National Academies of the Sciences of the United States of America. 73, 4290-4293 (1976).</li><li>Trzhtsinskaya, B. V., Abramova, N. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Imidazole-2-Thiones:+Synthesis,+Structure,+Properties.">Imidazole-2-Thiones: Synthesis, Structure, Properties.</a> Sulfur Reports. 10 (4), 389 (1991).</li><li>Schneider, G., Eklund, H., Cedergren-Zeppezauer, E., Zeppezauer, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Crystal+structure+of+the+active+site+in+specifically+metal-depleted+and+cobalt+substituted+horse+liver+alcohol+dehydrogenase+derivatives.">Crystal structure of the active site in specifically metal-depleted and cobalt substituted horse liver alcohol dehydrogenase derivatives.</a> Proceedings of the National Academies of the Sciences of the United States of America. 80, 5289-5293 (1983).</li><li>Yang, L., Powell, D. R., Houser, R. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Structural+variation+in+copper(I)+complexes+with+pyridylmethylamide+ligands:+structural+analysis+with+a+new+four-coordinate+geometry+index,+&#964;4.">Structural variation in copper(I) complexes with pyridylmethylamide ligands: structural analysis with a new four-coordinate geometry index, &#964;4.</a> Dalton Transactions. , 955-964 (2007).</li></ol>

The authors have nothing to disclose.

The preparation of complexes 4 and 5 is facile. The key step is to add the solid CoCl2&#183;6H2O to an acetonitrile solution that contains the respective ligand precursor. The solution turns dark green within seconds after the addition of CoCl2&#183;6H2O to form complex 4. The solution turns bright blue after the addition of CoCl2&#183;6H2O to form complex 5. To ensure complete reaction, t...

The purpose of the presented method is to prepare small-molecule analogs of LADH to further understand the catalytic activity of metalloenzymes. LADH is a dimeric enzyme that contains a cofactor-binding domain and zinc(II) metal-containing catalytic domain1. LADH, in the presence of co-factor NADH, can reduce ketones and aldehydes to their respective alcohol derivatives2. In the presence of NAD+, LADH can perform reverse catalysis of oxidation of alcohols to ketones and aldehydes2. The crystal structure of LADH&#8217;s active site shows that its zinc(II) metal center is bound to one nitrogen atom, provided by a histidine side chain and two sulfur atoms and offered by two cysteine ligands3. Further research has shown that the zinc metal center is ligated with a labile water molecule, resulting in pseudo-tetrahedral geometry around the metal center4.
We have previously reported and utilized SNS pincer ligand precursors as well as metallated the ligand precursors with ZnCl2 to form Zn(II) complexes that contain the tridentate ligand precursor5,6,7. These ligand precursors are shown in Figure 1. These zinc(II) complexes exhibited activity for the stoichiometric reduction of electron-poor aldehydes and are thus model complexes for LADH. Subsequently, the synthesis and characterization of a series of copper(I) and copper(II) complexes that contain SNS ligand precursors have been reported8,9,10.
Although LADH is a zinc(II) enzyme, we are interested in preparing cobalt(II) model complexes of LADH in order to obtain more spectroscopic information about the cobalt(II) analogs of LADH. The cobalt(II) complexes are colored, whereas the zinc(II) complexes are off-white. Since the cobalt(II) complexes are colored, ultraviolet visible spectra of the complexes can be obtained, in which information about the strength of the ligand field in cobalt(II) complexes can also be gathered. By using information from Gaussian calculations and the experimentally obtained ultra-violet visible spectra, information about the strength of the ligand field can be deduced. Cobalt(II) is a good substitute for zinc(II), since both ions have similar ionic radii and similar Lewis acidities11,12.
The presented method involves synthesizing and characterizing model complexes to attempt to mimic the natural catalytic behavior of LADH5,6. We have previously metallated a family of ligand precursors with ZnCl2 to form zinc(II) model complexes of LADH, which modeled the structure and reactivity of the zinc active site in LADH4. Through multiple experiments, these pincer ligands have proven to be robust under different environmental conditions and have remained stable with a diverse collection of attached R-groups.5,6
Tridentate ligands are preferable compared to monodentate ligands, because they have been found to be more successful with metalation due to the strong chelate effects of tridentate ligands. This observation is due to a more favored entropy of tridentate pincer ligand formation in comparison to a monodentate ligand13. Furthermore, tridentate pincer ligands are likely to prevent dimerization of the metal complexes, which is favored because dimerization is likely to slow catalytic activity of a complex14. Thus, using tridentate pincer ligands has been proven successful in organometallic chemistry in the preparation of catalytic active and robust complexes. SNS pincer complexes have been less studied than other pincer systems, as pincer complexes usually contain second and third row transition metals15.
This research on metalloenzymes can help further the understanding of their enzymatic activity, which can be applied to other areas in biology. This method of synthesizing model complexes compared to the alternative method (synthesizing the entire protein of LADH) is favorable for a number of reasons. The first advantage is that model complexes are low in molecular mass and are still capable of accurately representing catalytic activity and environmental conditions of the natural enzyme&#8217;s active site. Second, model complexes are simpler to work with and produce reliable and relatable data.
This manuscript describes the synthetic preparation and characterization of two cobalt(II) pincer model complexes of LADH. Both complexes feature a pincer ligand that contains sulfur, nitrogen, and sulfur donor atoms. The first complex (4) is based on an imidazole precursor, and the second (5) is based on a triazole precursor. The complexes show reactivity for the stoichiometry reduction of electron poor aldehydes in the presence of a hydrogen donor. These reactivity results will be reported in a subsequent manuscript.

<table><tbody><tr><td>100 mL Round Bottomed Flask</td><td>Chem Glass</td><td>CG150691</td><td>100mL Single Neck Round Bottomed Flask, 19/22 Outer Joint</td></tr><tr><td>Acetonitrile</td><td>Fisher</td><td>HB9823-4</td><td>HPLC Grade</td></tr><tr><td>Chiller for roto-vap</td><td>Lauda</td><td>L000638</td><td>Alpha RA 8</td></tr><tr><td>Cobalt Chloride hexahydrate</td><td>Acros Organics</td><td>AC423571000</td><td>Acros Organics</td></tr><tr><td>Diethyl Ether</td><td>Fisher</td><td>E-138-1</td><td>Diethyl Ether Anhydorus</td></tr><tr><td>graduated cylinder</td><td>Fisher</td><td>S63456</td><td>25 mL graduated cylinder</td></tr><tr><td>hotplate</td><td>Fisher</td><td>11-100-49SH</td><td>Isotemp Basic Stirring Hotplate</td></tr><tr><td>jars</td><td>Fisher</td><td>05-719-481</td><td>250 mL jars</td></tr><tr><td>Ligand</td><td>-----</td><td>-----</td><td>Synthezied previously by Professor Miecznikowski</td></tr><tr><td>medium cotton balls</td><td>Fisher</td><td>22-456-80</td><td>medium cotton balls</td></tr><tr><td>one dram vials</td><td>Fisher</td><td>03-339</td><td>one dram vials with TFE Lined Cap</td></tr><tr><td>pipet</td><td>Fisher</td><td>13-678-20B</td><td>5.75 inch pipets</td></tr><tr><td>pipet bulbs</td><td>Fisher</td><td>03-448-21</td><td>Fisher Brand Latex Bulb for pipet</td></tr><tr><td>recrystallizing dish for sand bath</td><td>Fisher</td><td>08-741 D</td><td>325 mL recrystallizing dish for sand bath</td></tr><tr><td>reflux condensor</td><td>Chem Glass</td><td>CG-1218-A-22</td><td>Condenser with 19/22 inner joint</td></tr><tr><td>Rotovap</td><td>Heidolph Collegiate</td><td>36000090</td><td>Brinkmann; Heidolph Collegiate Rotary Evaporator with Heidolph WB eco bath Heidolph Rotary Evaporator</td></tr><tr><td>sea sand for sandbath</td><td>Acros Organics</td><td>612355000</td><td>washed sea sand for sand bath</td></tr><tr><td>Stir bar</td><td>Fisher</td><td>07-910-23</td><td>Egg-Shaped Magnetic Stir Bar</td></tr><tr><td>Vacum grease</td><td>Fisher</td><td>14-635-5D</td><td>Dow Corning High Vacuum Grease</td></tr><tr><td>vacuum pump for rotovap</td><td>Heidolph Collegiate</td><td>36302830</td><td>Heidolph Rotovac Valve Control</td></tr></tbody></table>

preparation of sns cobalt(ii) pincer model complexes of liver alcohol dehydrogenase

Chemical model complexes are prepared to represent the active site of an enzyme. In this protocol, a family of tridentate pincer ligand precursors (each possessing two sulfur and one nitrogen donor atom functionalities (SNS) and based on bis-imidazole or bis-triazole compounds) are metallated with CoCl2&#183;6H2O to afford tridentate SNS pincer cobalt(II) complexes. Preparation of the cobalt(II) model complexes for liver alcohol dehydrogenase is facile. Based on a quick color change upon adding the CoCl2&#183;6H2O to acetonitrile solution that contains the ligand precursor, the complex forms rapidly. Formation of the metal complex is complete after allowing the solution to reflux overnight. These cobalt(II) complexes serve as models for the zinc active site in liver alcohol dehydrogenase (LADH). The complexes are characterized using single crystal X-ray diffraction, electrospray mass spectrometry, ultra-violet visible spectroscopy, and elemental analysis. To accurately determine the structure of the complex, its single crystal structure must be determined. Single crystals of the complexes that are suitable for X-ray diffraction are then grown via slow vapor diffusion of diethyl ether into an acetonitrile solution that contains the cobalt(II) complex. For high quality crystals, recrystallization typically takes place over a 1 week period, or longer. The method can be applied to the preparation of other model coordination complexes and can be used in undergraduate teaching laboratories. Finally, it is believed that others may find this recrystallization method to obtain single crystals beneficial to their research.

Synthesis 
The syntheses of complexes 4 and 5 were successfully carried out by reacting an acetonitrile solution containing a bis-thione ligand precursor with cobalt (II) chloride hexahydrate (Figure 2). This reaction occurred at a reflux temperature in the presence of air. In general, complexes 4 and 5 were observed to be soluble in acetonitrile, dimethyl sulfoxide, dichloromethane, and methanol. Compl...

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Preparation of SNS CobaltII Pincer Model Complexes of Liver Alcohol Dehydrogenase

The preparation of SNS pincer cobalt(II) model complexes of liver alcohol dehydrogenase is presented here. The complexes can be prepared by reacting the ligand precursor with CoCl2&#183;6H2O and can then be recrystallized by allowing diethyl ether to slowly diffuse into an acetonitrile solution that contains the cobalt complex.

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

Chemical model complexes are prepared to represent the active site of an enzyme. In this protocol, a family of tridentate pincer ligand precursors (each ...

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7.0K Views.  Fairfield University. Deze methode kan worden gebruikt om een chemisch model complex van een enzym lever alcohol dehydrogenase voor te bereiden en om enkele kristallen groeien. De voordelen van deze techniek zijn dat de complexe formatie facile is en dat de herkristallisatiemethode kan worden toegepast op de voorbereiding van andere coördinatiecomplexen. Deze methode kan inzicht geven in de voorbereiding en herkristallisatie van anorganische coördinatieverbindingen en kan worden toegepast op elke verbinding van ...

Video: Preparation of SNS CobaltII Pincer Model Complexes of Liver Alcohol Dehydrogenase

Preparation and Use of Carbonyl-decorated Carbenes in the Activation of White Phosphorus

Here we present a protocol for the synthesis of two distinct carbonyl-decorated carbenes. Both carbenes can be prepared using nearly identical procedures in multi-gram scale quantities. The goal of this manuscript is to clearly detail how to handle and prepare these unique carbenes such that a synthetic chemist of any skill level can work with them. The two carbenes described are a diamidocarbene (DAC, carbene 1) and a monoamidoaminocarbene (MAAC 2). These carbenes are highly electron-deficient and as such display reactivity profiles that are atypical of more traditional N-heterocyclic carbenes. Additionally, these two carbenes only differ in their electrophilic character and not their steric parameters, making them ideal for studying how carbene electronics influence reactivity. To demonstrate this phenomenon, we are also describing the activation of white phosphorus (P4) using these carbenes. Depending on the carbene used, two very different phosphorus-containing compounds can be isolated. When the DAC 1 is used, a tris(phosphaalkenyl)phosphane can be isolated as the exclusive product. Remarkably however, when MAAC 2 is added to P4 under identical reaction conditions, an unexpected carbene-supported P8&#160;allotrope of phosphorus is isolated exclusively. Mechanistic studies demonstrate that this carbene-supported P8allotrope forms via a [2+2] cycloaddition dimerization of a transient diphosphene which has been trapped by treatment with 2,3-dimethyl-1,3-butadiene.

Here, we present a protocol for the synthesis of two carbonyl-decorated carbenes. The protocol makes these interesting compounds readily available to chemists of all skill levels. In addition to the synthesis of these two carbenes, their use in the activation of white phosphorus is also described.

Here we present a protocol for the synthesis of two distinct carbonyl-decorated carbenes. Both carbenes can be prepared using nearly identical procedures ...

Hydrolysis of a Ni-Schiff-Base Complex Using Conditions Suitable for Retention of Acid-labile Protecting Groups

Unnatural amino acids, amino acids containing side-chain functionalities not commonly seen in nature, are increasingly found in synthetic peptide sequences. Synthesis of some unnatural amino acids often includes the use of a precursor consisting of a Schiff-base stabilized by a nickel cation. Unnatural side-chains can be installed on an amino acid backbone found in this Schiff-base complex. The resulting unnatural amino acid can then be isolated from this complex using hydrolysis of the Schiff-base, typically by employing reflux in strongly acidic solution. These highly acidic conditions may remove acid-labile side-chain protecting groups necessary for the unnatural amino acids to be used in microwave-assisted solid-phase peptide synthesis. In this work, we present an efficient hydrolysis and subsequent Fmoc protection of an amino acid isolated from a Ni-Schiff base complex. Hydrolysis conditions presented in this work are suitable for retention of acid-labile side-chain protecting groups and may be adaptable to a variety of unnatural amino acid substrates.

Here, we present an efficient hydrolysis and subsequent Fmoc protection of an amino acid isolated from a Ni-Schiff-base complex. Hydrolysis conditions presented here are suitable for use when retention of acid-labile side-chain protecting groups is required. This technique may be adaptable to a variety of unnatural amino acid substrates.

Unnatural amino acids, amino acids containing side-chain functionalities not commonly seen in nature, are increasingly found in synthetic peptide ...

Biochemistry

The Synthesis, Characterization and Reactivity of a Series of Ruthenium N-triphosPh Complexes

Herein we report the synthesis of a tridentate phosphine ligand N(CH2PPh2)3 (N-triphosPh) (1) via a phosphorus based Mannich reaction of the hydroxylmethylene phosphine precursor with ammonia in methanol under a nitrogen atmosphere. The N-triphosPh ligand precipitates from the solution after approximately 1 hr of reflux and can be isolated analytically pure via simple cannula filtration procedure under nitrogen. Reaction of the N-triphosPh ligand with [Ru3(CO)12] under reflux affords a deep red solution that show evolution of CO gas on ligand complexation. Orange crystals of the complex [Ru(CO)2{N(CH2PPh2)3}-&#954;3P] (2) were isolated on cooling to RT. The 31P{1H} NMR spectrum showed a characteristic single peak at lower frequency compared to the free ligand. Reaction of a toluene solution of complex 2 with oxygen resulted in the instantaneous precipitation of the carbonate complex [Ru(CO3)(CO){N(CH2PPh2)3}-&#954;3P] (3) as an air stable orange solid. Subsequent hydrogenation of 3 under 15 bar of hydrogen in a high-pressure reactor gave the dihydride complex [RuH2(CO){N(CH2PPh2)3}-&#954;3P] (4), which was fully characterized by X-ray crystallography and NMR spectroscopy. Complexes 3 and 4 are potentially useful catalyst precursors for a range of hydrogenation reactions, including biomass-derived products such as levulinic acid (LA). Complex 4 was found to cleanly react with LA in the presence of the proton source additive NH4PF6 to give [Ru(CO){N(CH2PPh2)3}-&#954;3P{CH3CO(CH2)2CO2H}-&#954;2O](PF6) (6).

The Synthesis, Characterization and Reactivity of a Series of Ruthenium N-triphosPh Complexes

Ruthenium phosphine complexes are widely used for homogeneous catalytic reactions such as hydrogenations. The synthesis of a series of novel tridentate ruthenium complexes bearing the N-triphos ligand N(CH2PPh2)3 is reported. Additionally, the stoichiometric reaction of a dihydride Ru&#8211;N-triphos complex with levulinic acid is described.

Herein we report the synthesis of a tridentate phosphine ligand N(CH2PPh2)3 (N-triphosPh) (1) via a phosphorus based Mannich reaction of the ...

Detection and Recovery of Palladium, Gold and Cobalt Metals from the Urban Mine Using Novel Sensors/Adsorbents Designated with Nanoscale Wagon-wheel-shaped Pores

Developing low-cost, efficient processes for recovering and recycling palladium, gold and cobalt metals from urban mine remains a significant challenge in industrialized countries. Here, the development of optical mesosensors/adsorbents (MSAs) for efficient recognition and selective recovery of Pd(II), Au(III), and Co(II) from urban mine was achieved. A simple, general method for preparing MSAs based on using high-order mesoporous monolithic scaffolds was described. Hierarchical cubic Ia3d wagon-wheel-shaped MSAs were fabricated by anchoring chelating agents (colorants) into three-dimensional pores and micrometric particle surfaces of the mesoporous monolithic scaffolds. Findings show, for the first time, evidence of controlled optical recognition of Pd(II), Au(III), and Co(II) ions and a highly selective system for recovery of Pd(II) ions (up to ~95%) in ores and industrial wastes. Furthermore, the controlled assessment processes described herein involve evaluation of intrinsic properties (e.g., visual signal change, long-term stability, adsorption efficiency, extraordinary sensitivity, selectivity, and reusability); thus, expensive, sophisticated instruments are not required. Results show evidence that MSAs will attract worldwide attention as a promising technological means of recovering and recycling palladium, gold and cobalt metals.

Because of the importance and extensive use of palladium, gold and cobalt metals in high-technology equipment, their recovery and recycling constitute an important industrial challenge. The metal recovery system described herein is a simple, low-cost means for the effective detection, removal, and recovery of these metals from the urban mine.

Developing low-cost, efficient processes for recovering and recycling palladium, gold and cobalt metals from urban mine remains a significant challenge in ...

Engineering

Developing Photosensitizer-Cobaloxime Hybrids for Solar-Driven H2 Production in Aqueous Aerobic Conditions

Developing photocatalytic H2 production devices is the one of the key steps for constructing a global H2-based renewable energy infrastructure. A number of photoactive assemblies have emerged where a photosensitizer and cobaloxime-based H2 production catalysts work in tandem to convert light energy into the H-H chemical bonds. However, the long-term instability of these assemblies and the need for hazardous proton sources have limited their usage. Here, in this work, we have integrated a stilbene-based organic dye into the periphery of a cobaloxime core via a distinct axial pyridine linkage. This strategy allowed us to develop a photosensitizer-catalyst hybrid structure with the same molecular framework. In this article, we have explained the detailed procedure of the synthesis of this hybrid molecule in addition to its comprehensive chemical characterization. The structural and optical studies have exhibited an intense electronic interaction between the cobaloxime core and the organic photosensitizer. The cobaloxime was active for H2 production even in the presence of water as the proton source. Here, we have developed a simple airtight system connected with an online H2 detector for the investigation of the photocatalytic activity by this hybrid complex. This photosensitizer-catalyst dyad present in the experimental setup continuously produced H2 once it was exposed in the natural sunlight. This photocatalytic H2 production by the hybrid complex was observed in aqueous/organic mixture media in the presence of a sacrificial electron donor under complete aerobic conditions. Thus, this photocatalysis measurement system along with the photosensitizer-catalyst dyad provide valuable insight for the development of next generation photocatalytic H2 production devices.

Developing Photosensitizer-Cobaloxime Hybrids for Solar-Driven H2 Production in Aqueous Aerobic Conditions

We have directly incorporated a stilbene-based organic dye into a cobaloxime core to generate a photosensitizer-catalyst dyad for photocatalytic H2 production. We have also developed a simple experimental setup for evaluating the light-driven H2 production by photocatalytic assemblies.

Developing photocatalytic H2 production devices is the one of the key steps for constructing a global H2-based renewable energy infrastructure. A number ...

Synthesis of Metal Nanoparticles Supported on Carbon Nanotube with Doped Co and N Atoms and its Catalytic Applications in Hydrogen Production

A method for facile synthesis of nanostructured catalysts supported on carbon nanotubes with atomically dispersed cobalt and nitrogen dopant is presented herein. The novel strategy is based on a facile one-pot pyrolysis treatment of cobalt (II) acetylacetonate and nitrogen-rich organic precursors under Ar atmosphere at 800 &#176;C, resulting in the formation of Co- and N- co-doped carbon nanotube with earthworm-like morphology. The obtained catalyst was found to have a high density of defect sites, as confirmed by Raman spectroscopy. Here, cobalt (II) nanoparticles were stabilized on the atomically dispersed cobalt- and nitrogen-doped carbon nanotubes. The catalyst was confirmed to be effective in the catalytic hydrolysis of ammonia borane, in which the turnover frequency was 5.87 mol H2&#183;molCo-1&#183;min-1, and the specific hydrogen generation rate was determined to be 2447 mL H2&#183;gCo-1&#183;min-1. A synergistic function between the Co nanoparticle and the doped carbon nanotubes was proposed for the first time in the catalytic hydrolysis of ammonia borane reaction under a mild condition. The resulting hydrogen production with its high energy density and minimal refueling time could be suitable for future development as energy sources for mobile and stationary applications such as road trucks and forklifts in transport and logistics.

Here, we present a protocol to synthesize Co nanoparticles supported on carbon nanotubes with Co- and N- dopants for hydrogen productions.

A method for facile synthesis of nanostructured catalysts supported on carbon nanotubes with atomically dispersed cobalt and nitrogen dopant is presented ...

Coordination Chemistry Complexes

Source: Laboratory of Dr. Neal Abrams &#8212; SUNY College of Environmental Science and Forestry
Transition metals are found everywhere from vitamin supplements to electroplating baths. Transition metals also make up the pigments in many paints and compose all minerals. Typically, transition metals are found in the cationic form since they readily oxidize, or lose electrons, and are surrounded by electron donors called ligands. These ligands do not form ionic or covalent bonds with the metal center, rather they take on a third type of bond known as coordinate-covalent. The coordinate-covalent bond between a ligand and a metal is dynamic, meaning that ligands are continuously exchanging and re-coordinating around the metal center. The identities of both the metal and the ligand dictates which ligands will bond preferentially over another. In addition, color and magnetic properties are also due to the types of complexes that are formed. The coordination compounds that form are analyzed using a variety of instruments and tools. This experiment explores why so many complexes are possible and uses a spectrochemical (color and chemical) method to help identify the type of coordination complex that forms.

Metal-Ligand Coordination Complex

Source: Laboratory of Dr. Neal Abrams &#8212; SUNY College of Environmental Science and Forestry
Transition metals are found everywhere from vitamin ...

JoVE Science Education

General Chemistry

Structure Of Ferrocene

Source: Tamara M. Powers, Department of Chemistry, Texas A&#38;M University&#160;
In 1951, Kealy and Pauson reported to Nature the synthesis of a new organometallic compound, ferrocene.1&#160;In their original report, Pauson suggested a structure for ferrocene in which the iron is singly bonded (sigma bonds) to one carbon atom of each cyclopentadiene ligand (Figure 1, Structure I).1,2,3&#160;This initial report led to wide-spread interest in the structure of ferrocene, and many leading scientists participated in the structure elucidation of this interesting new molecule. Wilkinson and Woodward were quick to suggest an alternative formulization where the iron is &#34;sandwiched&#34; between two cyclopentadiene ligands, with equal binding to all 10 carbon atoms (Figure 1, Structure II).4&#160;Here, we will synthesize ferrocene and decide, based on experimental data (IR and 1H NMR), which of these structures is observed. In addition, we will study the electrochemistry of ferrocene by collecting a cyclic voltammogram. In the course of this experiment, we introduce the 18-electron rule and discuss valence electron counting for transition metal complexes.
<img alt="Figure 1" src="/files/ftp_upload/10347/10347fig1v2.jpg" /> 
Figure 1. Two proposed structures of ferrocene.

Structure Determination of Ferrocene-an Organometallic Complex

Source: Tamara M. Powers, Department of Chemistry, Texas A&#38;M University&#160;
In 1951, Kealy and Pauson reported to Nature the synthesis of a new ...

Inorganic Chemistry

Molecular Orbital (MO) Theory

Source: Tamara M. Powers, Department of Chemistry, Texas A&#38;M University
This protocol serves as a guide in the synthesis of two metal complexes featuring the ligand 1,1&#39;-bis(diphenylphosphino)ferrocene (dppf): M(dppf)Cl2, where M = Ni or Pd. While both of these transition metal complexes are 4-coordinate, they exhibit different geometries at the metal center. Using molecular orbital (MO) theory in conjunction with 1H NMR and Evans method, we will determine the geometry of these two compounds.

Molecular Orbital MO Theory: Predicting Geometry of Transition Metal Complexes

Source: Tamara M. Powers, Department of Chemistry, Texas A&#38;M University
This protocol serves as a guide in the synthesis of two metal complexes ...

Synthesis of an Oxygen-Carrying Cobalt(II) Complex

Source: Deepika Das, Tamara M. Powers, Department of Chemistry, Texas A&#38;M University
Bioinorganic chemistry is the field of study that investigates the role that metals play in biology. Approximately half of all proteins contain metals and it is estimated that up to one third of all proteins rely on metal-containing active sites to function. Proteins that feature metals, called metalloproteins, play a vital role in a variety of cell functions that are necessary for life. Metalloproteins have intrigued and inspired synthetic inorganic chemists for decades, and many research groups have dedicated their programs to modeling the chemistry of metal-containing active sites in proteins through the study of coordination compounds.
The transport of O2 is a vital process for living organisms. O2-transport metalloproteins are responsible for binding, transporting, and releasing oxygen, which can then be used for life processes such as respiration. The oxygen-carrying cobalt coordination complex, [N,N&#39;-bis(salicylaldehyde)ethylenediimino]cobalt(II) [Co(salen)]2&#160;has been studied extensively to gain understanding about how metal complexes reversibly bind O2.1
In this experiment, we will synthesize [Co(salen)]2 and study its reversible reaction with O2 in the presence of dimethylsulfoxide (DMSO). First, we will quantify the amount of O2 consumed upon exposure of [Co(salen)]2 to DMSO. We will then visually observe the release of O2 from the [Co(salen)]2-O2 adduct by exposing the solid to CHCl3.

Synthesis of an Oxygen-Carrying [Cosalen]2 Complex

Source: Deepika Das, Tamara M. Powers, Department of Chemistry, Texas A&#38;M University
Bioinorganic chemistry is the field of study that investigates ...

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

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