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10/1/09 Research Paper Topic: N-Heterocyclic Carbene (NHC) Transition Metal Complexes as Catalysts for Selective Ionic Hydrogenation of Polar Double Bonds

10/22/09 Change of Topic because the above is too similar to my research. New Topic: Transition Metal N-Heterocyclic Carbene (NHC) Complexes in Catalytic Transfer Hydrogenation. Do you think this topic is different enough from my old topic? Basically the compounds are very similar but the processes they catalyze are different.
 * [It might be too close - do these complexes catalyze other reactions? JCB]**

Yes they do catalyze some other reactions. None of these complexes have ever been used to catalyze ionic hydrogenation (hence my research topic). There has been little done with them catalyzing transfer hydrogenation, but I believe there is enough information for me to write a paper on. Plus my research topic primarily uses Ru as the metal. For the paper I was going to specify more on the process rather than the metal, so I would be looking at complexes with Ir, Rh, Pd in addition to Ru.

11/5/09

Assignment #1 Article Summary Due 11/5/09

Article: Organometallics **2003,** 22, 1110-1114. [] =[Full Marks JCB]=
 * __ Introduction: __**
 * Recently, Ardengo-type carbenes have been looked into as potential auxillary ligands in metal catalysts because they can employee a chelating stabilization while having a large impact on the electronics of the metal. These carbenes exhibit a more potent trans effect than their phosphine and amino analogues.
 * When coordinated to Pd, the tridentate bis carbene, 2,6-bis-(1-alkylimidazolium-3-yl)pyridine salts, have been used in catalysis of C-C bond formation. These pyridine salts are not difficult to synthesize.
 * Ru analogues of the tridentate bis carbine ligand above were synthesized, characterized, and shown to be useable as catalysts for hydrogen transfer and oxidation of olefins. The only other Ru-CNC pincer complexes were synthesized very recent to this article and shown to catalyze hydrogen transfer.
 * __ Results and Discussion: __**
 * Deprotonation of 2,6-bis-(1-n-butylimidazolium-3-yl)pyridine dibromide was done with NEt3 to induce coordination to [(COD)RuCl2]n and form Ru(CNC)(CO)Br2 . The appearance of CO in the complex is believed to be from oxidative addition of CH3CHO, which is from the ethanol solvent. NEt3 is a weaker base than typically used for the carbine formation.
 * Symmetry can be seen in the NMR spectrum which supports the chelating structure. 13C and 1H NMR spectroscopy were both done.
 * Ru(CNC)(CO)Br2 structure was confirmed by X-ray diffraction. By analyzing the CO stretching frequency with IR it was determined that metal to carbine back donation is not occurring.
 * Reaction of 2.6-bis-(1-n-butylimidazolium-3-yl)pyridine dibromide with RuCl3 produced a complex identical to Ru(CNC)(CO)Br2 but without CO and Br2, which was confirmed by 13C NMR, 1H NMR, and IR. Instead the complex has two separate CNC chelating ligands. The molecular formula is [Ru(CNC)2](PF6)2.
 * The proposed structure of [Ru(CNC)2](PF6)2, theorized by spectroscopy data, was backed up with a single-crystal structure. The imidazolyl and pyridyl rings are in a plane and the bond is basically single just like in Ru(CNC)(CO)Br2.
 * Hydogen transfer from IPA to aryl and alkyl ketones was catalyzed by Ru(CNC)(CO)Br2 to produce alcohols. The highly air stable catalyst was faster at hydrogenation of aryl ketones than alkyl. The catalyst also proved to be selective of the polar carbonyl group over C=C.
 * Selective oxidative cleavage of olefins to aldehydes without by products is an important catalytic process because it avoids the use of the dangerous ozonolysis reaction. Current catalysts for this reaction have bad selectivity. The use of 1,2-diols for oxidation of olefins has not yet had a catalysts that is selective for aldehyde formation.
 * At room temperature Ru(CNC)(CO)Br2 was shown to be selective to just aldehyde formation with no side products in the oxidation of olefins. The catalysts gave better yields of aldehydes when aliphatic olefins were the substrate.
 * In catalytic experiments with [Ru(CNC)2](PF6)2, the complex was found to be poor in the hydrogen transfer and olefin oxidation reactions even under harsh conditions. NMR spectroscopy was used to show that the pincer ligands always stay coordinated to the metal making substrate activation impossible.
 * Two new Ru complexes were synthesized. The mono pincer complex Ru(CNC)(CO)Br2 was a better catalyst of olefin oxidation and transfer hydrogenation than [Ru(CNC)2](PF6)2,
 * __ Experimental Section __**
 * The procedure for synthesizing 2,6-bis-(1-n-butylimidazolium-3-yl)pyridine dibromide was from a literature source. NMR solvents used were CDCl3 and DMSO-d6 and the spectrum were taken on both 300 and 500 MHz instuments.
 * In ethanol [(COD)RuCl2], 2,6-bis-(1-n-butylimidazolium-3-yl)pyridine dibromide, and NEt3 were refluxed to produce Ru(CNC)(CO)Br2.The product was purified by column chromatography.
 * The molecular weight of Ru(CNC)(CO)Br2 was 612.39 g/mol. The complex was characterized my 1H and 13C NMR and IR spectroscopy.
 * In ethanol RuCl3.3H2O, 2,6-bis-(1-n-butylimidazolium-3-yl)pyridine dibromide, and NEt3 was refluxed to produce [Ru(CNC)2](PF6)2. Column chromatography was used to purify the compound and crystals were grown for single-crystal structure determination.
 * In addition to the single-crystal structure, [Ru(CNC)2](PF6)2 was characterized by 1H and 13C NMR and IR spectroscopy. The molecular weight of the compound was found to be 1037.89 g/mol.
 * For the hydrogen transfer catalysis the ketone, KOH, and varying amounts of Ru(CNC)(CO)Br2 were mixed. At various reaction times the yields were determined by 1H NMR.
 * In 1 mL CDCl3 Ru(CNC)(CO)Br2 and olefin were mixed and then there was further addition of water and NaIO4. At various reaction times the yields were determined by 1H NMR.
 * Single crystal structures of Ru(CNC)(CO)Br2 and [Ru(CNC)2](PF6)2 were taken with s Siemens Smart CCD diffractometer. Omega and phi angle data was obtained and the structures were determined with a variety of software packages including SHELXTL 5.1, SAINT, and SADABS.

Assignment #2**
 * 11/12/09

89-91C [|Chem Spider]  [|Wikipedia] [|MSDS] 90 C [|Wolfram Alpha] 89 C [|NIOSH]
 * __Imidazole__**
 * Melting Point**

145 C [|Chem Spider][|Wolfram Alpha][|Sigma Aldrich] [|Acros Organics][|NIOSH]
 * Flash Point**

256 C [|Wikipedia][|MSDS] [|Sigma Aldrich] 255 C [|Wolfram Alpha] 268 C [|NIOSH]
 * Boiling Point**

1.23 g/cm3 [|Wikipedia] 1.18 g/cm3 [|Wolfram Alpha] 1.0303 g/cm3 [|CRC Page 300] 1.116 g/cm3 [|Chem Spider predicted] 1.03 g/cm3 [|Alfa Aesar]
 * Density**

0.024 mmHg at 20 C [|Chem Spider predicted][|Wolfram Alpha] 0.00225 mmHg (0.3 Pa) at 20 C [|NIOSH] <1 mmHg ( 20 °C) [|Sigma Aldrich][|Chemical Book]
 * Vapor Pressure**

[Full Marks - JCB]
 * __DONE__

Term Paper Below on the Joe DePasquale Final Paper Page**