Multiple C-H Bond Activations Of Aromatic Compounds By Unsaturated Dirhenium Carbonyl Complexes

The background and importance of aromatic C-H bond activation by metal complexes are discussed in Chapter 1 with the help of various examples from the literature. Synthesis of the dirhenium complex Re2(CO)8(-C6H5)(-H) 1.1 is also discussed in detail. It also includes work done on C-H activation on arenes and heteroarenes by previous members of Dr. Adams’ group. The reactions of Re2(CO)8(-C6H5)(-H) with naphthalene and anthracene yielding the first multiply-CH activated arene products by the multiple oxidative-addition processes are presented in Chapter 2. The reaction of Re2(CO)8(-C6H5)(-H) with itself yielded the doubly-Re2-metalated C6H4 bridged compound Re2(CO)8(µ-H)(µ-1,µ-3- C6H4)Re2(CO)8(µ-H), 2.3. The reaction of Re2(CO)8(-C6H5)(-H) with the nonplanar molecule, corannulene, resulting in formation of Re2(CO)8(µ-H)(µ-η2-1,2-C20H9), 3.2 is reported in Chapter 3. Three new isomeric doubly-metalated corannulene products: Re2(CO)8(µ-H)(µ-η2-1,2-µ- η2-10,11-C20H8)Re2(CO)8(µ-H), 3.3, Re2(CO)8(µ-H)(µ-η2-2,1-µ-η2-10,11- C20H8)Re2(CO)8(µ-H), 3.4 and Re2(CO)8(µ-H)(µ-η2-1,2-µ-η2-11,10-C20H8)Re2(CO)8(µ- H), 3.5 were formed when compound 3.2 was allowed to react with a second equivalent of Re2(CO)8(-C6H5)(-H). The products formed from the reactions of Re2(CO)8(μ-C6H5)(μ-H) with furan and 2,5-dimethylfuran are presented in Chapter 4. Two new isomeric dirhenium compounds vii Re2(CO)8(µ-η2-2,3-C4H3O)(µ-H), 4.1 and Re2(CO)8(µ-η2-3,2-C4H3O)(µ-H), 4.2, both of which contain a bridging σ-π coordinated furyl ligand were formed by the activation of CH bonds at the α and β position of furan, respectively. Studies of C-H activations of thiophene on reaction with Re2(CO)8(-C6H5)(-H) are reported in Chapter 5. Also, the dynamic activity of Re2(CO)8(-2-SC4H3)(-H), 5.2 on the NMR timescale involving rearrangements of the bridging thienyl ligand and ring opening of thiophene molecule by C-S bond cleavage is discussed in detail. The activation of formyl C-H bond of N,N-dimethylformamide (DMF) by Re2(CO)8[μ-η2-C(H)=C(H)Bun](μ-H), 6.1 is reported in chapter 6. This reaction yielded three products, Re2(CO)8(µ-2-O=CNMe2)(µ-H), 6.2, Re2(CO)7(NHMe2)(µ-2- O=CNMe2)(µ-H), 6.3 and Re2(CO)9(NHMe2), 6.4. Compounds 6.2 and 6.3 contain a C,O- 2-bridging dimethylformamido (O=CNMe2) ligand and a bridging hydrido ligand formed by the elimination of hexene from 6.1 and the oxidative addition of the formyl C-H bond of the DMF to the dirhenium group of 6.1. Compound 6.3 contains an NHMe2 ligand formed by the decarbonylation of DMF and the transfer of the formyl hydrogen atom to the NMe2 residue. Compound 6.4 contains a similarly formed NHMe2 ligand. The investigations of synthesis and reactivity of electronically unsaturated dirhenium compounds containing bridging gold-carbene groups are described in chapter 7. Re2(CO)8[μ-Au(NHC)](μ-Ph), 7.1 and Re2(CO)8[μ-Au(NHC)]2, 7.2, were obtained from the reaction of Re2(CO)8[μ-η2-C(H)=C(H)Bun](μ-H) with MeAu(NHC), NHC = 1,3- bis(2,6-diisopropylphenyl)imidazol-2-ylidene. Conversion of compound 7.1 to the new compound Re2(CO)8[μ-Au(NHC)](μ-H), 7.3 upon reaction with hydrogen is also discussed. Addition of CO to 3 yielded the new compound Re2(CO)9[Au(NHC)](μ-H), 7.4. viii Compound 7.3 also reacts with C2H2 by an addition with insertion into the Re – H bonds to yield the compound Re2(CO)8[μ-Au(NHC)](μ-C2H3), 7.5 which contains a - coordinated, bridging C2H3 ligan

Multiple C–H Bond Activations and Ring-Opening C–S Bond Cleavage of Thiophene by Dirhenium Carbonyl Complexes

The reaction of Re₂(CO)₈(μ-C₆H₅)­(μ-H) (<b>1</b>) with thiophene in CH₂Cl₂ at 40 °C yielded the new compound Re₂(CO)₈(μ-η²-SC₄H₃)­(μ-H) (<b>2</b>), which contains a bridging σ–π-coordinated thienyl ligand formed by the activation of the C–H bond at the 2 position of the thiophene. Compound <b>2</b> exhibits dynamical activity on the NMR time scale involving rearrangements of the bridging thienyl ligand. The reaction of compound <b>2</b> with a second 1 equiv of <b>1</b> at 45 °C yielded the doubly metalated product [Re₂(CO)₈(μ-H)]₂(μ-η²-2,3-μ-η²-4,5-C₄H₂S) (<b>3</b>), formed by the activation of the C–H bond at the 5 position of the thienyl ligand in <b>2</b>. Heating <b>3</b> in a hexane solvent to reflux transformed it into the ring-opened compound Re­(CO)₄[μ-η⁵-η²-SCC­(H)­C­(H)­C­(H)]­[Re­(CO)₃]­[Re₂(CO)₈(μ-H)] (<b>4</b>) by the loss of one CO ligand. Compound <b>4</b> contains a doubly metalated 1-thiapentadienyl ligand formed by the cleavage of one of the C–S bonds. When heated to reflux (125 °C) in an octane solvent in the presence of H₂O, the new compound Re­(CO)₄[η⁵-μ-η²-SC­(H)­C­(H)­C­(H)­C­(H)]­Re­(CO)₃ (<b>5</b>) was obtained by cleavage of the Re₂(CO)₈(μ-H) group from <b>4</b> with formation of the known coproduct [Re­(CO)₃(μ₃-OH)]₄. All new products were characterized by single-crystal X-ray diffraction analyses

Synthesis and Reactivity of Electronically Unsaturated Dirhenium Carbonyl Compounds Containing Bridging Gold-Carbene Groups

The electronically unsaturated compounds Re₂(CO)₈[μ-Au­(NHC)]­(μ-Ph), <b>1</b>, and Re₂(CO)₈[μ-Au­(NHC)]₂, <b>2</b>, were obtained from the reaction of Re₂(CO)₈[μ–η²-C­(H)C­(H)­Buⁿ]­(μ-H) with MeAu­(NHC), NHC = 1,3-bis­(2,6-diisopropylphenyl)­imidazol-2-ylidene. Compound <b>1</b> was converted to the new compound Re₂(CO)₈[μ-Au­(NHC)]­(μ-H), <b>3</b>, by reaction with H₂. Addition of CO to <b>3</b> yielded the new compound Re₂(CO)₉­[Au­(NHC)]­(μ-H), <b>4</b>, which contains a terminally coordinated Au­(NHC) group on one of the rhenium atoms, and the hydrido ligand was shifted to bridge the Re–Au bond. The mechanism of the formation of <b>4</b> was established by DFT computational analyses. Compound <b>3</b> also reacted with C₂H₂ by an addition with insertion into the Re–H bonds to yield the compound Re₂(CO)₈[μ-Au­(NHC)]­(μ-C₂H₃), <b>5</b>, which contains a σ–π coordinated, bridging C₂H₃ ligand. The stereochemistry of the insertion was found to proceed preferentially with a <i>cis-</i> (<i>syn-</i>) stereochemistry. Compound <b>1</b> reacted with HCl to yield Re₂(CO)₈[μ-Ph]­(μ-H), <b>6</b>, and ClAu­(NHC) by selective removal of the bridging Au­(NHC) group. All new compounds were characterized by single-crystal X-ray diffraction analyses

Synthesis and Reactivity of Electronically Unsaturated Dirhenium Carbonyl Compounds Containing Bridging Gold-Carbene Groups

The electronically unsaturated compounds Re₂(CO)₈[μ-Au­(NHC)]­(μ-Ph), <b>1</b>, and Re₂(CO)₈[μ-Au­(NHC)]₂, <b>2</b>, were obtained from the reaction of Re₂(CO)₈[μ–η²-C­(H)C­(H)­Buⁿ]­(μ-H) with MeAu­(NHC), NHC = 1,3-bis­(2,6-diisopropylphenyl)­imidazol-2-ylidene. Compound <b>1</b> was converted to the new compound Re₂(CO)₈[μ-Au­(NHC)]­(μ-H), <b>3</b>, by reaction with H₂. Addition of CO to <b>3</b> yielded the new compound Re₂(CO)₉­[Au­(NHC)]­(μ-H), <b>4</b>, which contains a terminally coordinated Au­(NHC) group on one of the rhenium atoms, and the hydrido ligand was shifted to bridge the Re–Au bond. The mechanism of the formation of <b>4</b> was established by DFT computational analyses. Compound <b>3</b> also reacted with C₂H₂ by an addition with insertion into the Re–H bonds to yield the compound Re₂(CO)₈[μ-Au­(NHC)]­(μ-C₂H₃), <b>5</b>, which contains a σ–π coordinated, bridging C₂H₃ ligand. The stereochemistry of the insertion was found to proceed preferentially with a <i>cis-</i> (<i>syn-</i>) stereochemistry. Compound <b>1</b> reacted with HCl to yield Re₂(CO)₈[μ-Ph]­(μ-H), <b>6</b>, and ClAu­(NHC) by selective removal of the bridging Au­(NHC) group. All new compounds were characterized by single-crystal X-ray diffraction analyses

Biostimulation of Anaerobic Digestion Using Iron Oxide Nanoparticles (IONPs) for Increasing Biogas Production from Cattle Manure

The effect of synthesised IONPs employing a nontoxic leaf extract of Azadirachta indica as a reducing, capping, and stabilizing agent for increasing biogas and methane output from cattle manure during anaerobic digestion (AD) was investigated in this study. Furthermore, the UV-visible spectra examination of the synthesized nanoparticles revealed a high peak at 432 nm. Using a transmission electron microscope, the average particle size of IONPs observed was 30–80 nm, with irregular, ultra-small, semi-spherical shapes that were slightly aggregated and well-distributed. IONPs had a polydisparity index (PDI) of 219 nm and a zeta potential of −27.0 mV. A set of six bio-digesters were fabricated and tested to see how varying concentrations of IONPs (9, 12, 15, 18, and 21 mg/L) influenced biogas, methane output, and effluent chemical composition from AD at mesophilic temperatures (35 ± 2 °C). With 18 mg/L IONPs, the maximum specific biogas and methane production were 136.74 L/g of volatile solids (VS) and 64.5%, respectively, compared to the control (p < 0.05), which provided only 107.09 L/g and 51.4%, respectively. Biogas and methane production increased by 27.6% and 25.4%, respectively using 18 mg/L IONPs as compared to control. In all treatments, the pH of the effluent was increased, while total volatile fatty acids, total solids, volatile solids, organic carbon content, and dehydrogenase activity decreased. Total solid degradation was highest (43.1%) in cattle manure + 18 mg/L IONPs (T5). According to the results, the IONPs enhanced the yield of biogas and methane when compared with controls