Date of Award

Spring 2021

Document Type

Open Access Dissertation

Department

Chemistry and Biochemistry

First Advisor

Richard D. Adams

Abstract

Polynuclear metal carbonyl complexes serve as the bridging model between heterogeneous catalysis and homogeneous catalysis for the activation of small molecules. Ru5(m5-C)(CO)15 has been found to exhibit superior reactivity due to its unusual polynuclear metal geometry. possibilities of interconversions of ligand bonding modes, and the formation of the electronically unsaturated metal species. C-H activation in aldehydes and azobenzene of pentaruthenium cluster complexes is described in chapters 2 and 3 respectively. The formation of new hydrocarbyl zwitterions and C – C coupling ethyne to the carbido carbon in the complex, and the alkyne insertion reactions with pentaruthenium cluster complexes are described in chapters 4, 5, and 6 respectively.

Aldehydic C-H activation of biomass derived important aldehydes such as furfural and 5-hydroxymethylfurfural by Ru5(m5-C)(CO)15 is reported in chapter 2. The reaction Ru5(m5-C)(CO)15 with furfural yielded Ru5(m5-C)(CO)14(m-h 2 -O=CC4OH3)(m-H), 2.2 which has an η2 -bridging furoyl ligand coordinated across the open edge of a Ru wingtipbridged Ru4C cluster, whereas the hydrido ligand bridges the hinge metal atoms. Similarly, the reaction Ru5(m5-C)(CO)15 with furfural yielded Ru5(m5-C)(CO)14[m-h 2 - O=CC4OH2(CH2OH)](m-H), 2.3.

The activation and coordination of azobenzene with Ru5(m5-C)(CO)15 and its derivative is discussed in chapter 3. The reaction of Ru5(m5-C)(CO)15 with azobenzene, PhN=NPh, yielded the pentaruthenium carbido cluster compound Ru5C(CO)13(C6H4N=NC6H5)(m-H), 3.4 containing a chelating ortho-metalated azobenzene ligand on one of the ruthenium atoms in a opened square-pyramidal Ru5C cluster. Compound 3.4 is electronically unsaturated and it readily adds one CO ligand at 25 ℃ to yield the electronically saturated complex Ru5C(CO)14(C6H4N=NC6H5)[m-H], 3.5. Ru5C(CO)13(m-h 2 -Ph)[m-Au(NHC)] reacts with azobenzene to yield the azobenzene complex Ru5C(CO)13(m-h 2 -PhN=NPh)(h 1 -Ph)[m-Au(NHC)], 3.6, NHC = 1,3-bis(2,6- diisopropylphenyl-imidazole-2-ylidene), which contains a novel bridging di-s-h 2 -N,N coordinated azobenzene ligand across an open edge of an Ru5C cluster. Compound 3.6 eliminated benzene and was transformed to the new compound Ru5C(CO)13(C6H4N=NC6H5)[m-Au(NHC)], 3.7 when heated to 105 ℃ for 3 h. Compound 3.7 is similar to 3.4 except that it has an Au(NHC) group in the place of the bridging hydrido ligand in 3.4. Compound 3.7 is also formally electronically unsaturated like 3.4.

The formation of zwitterionic, hydrocarbylonium ligands from a combination of alkynes and Me3N with pentaruthenium cluster complexes is reported in chapter 4. Reactions of the pentaruthenium cluster complexes Ru5(μ5-C)(CO)15, Ru5(μ5-C)(CO)14[μη 2 -O=C(NMe2)](μ-H), 4.6, and Ru5(μ5-C)(CO)15Cl(μ-H), 4.7 with ethyne (C2H2) in the presence of Me3NO yielded the zwitterionic complexes Ru5(μ5-C)(CO)13[μ-η2 - CHCH(NMe3)] 4.8, Ru5(μ5-C)-(CO)13[μ-η2 -O=C(NMe2)](η1 -E-CH=CH(NMe3)(μ-H) 4.9, and Ru5(μ5-C)(CO)13Cl[η1 -E-CH=CH(NMe3)](μ-H) 4.11. Each product contains a positively-charged, trimethylammonioethenyl ligand, CH=CH(+NMe3), that is derived from a 2-trimethylammonioethenide, −CH=CH(+NMe3), zwitterion that formally has a positive charge on the nitrogen atom and a negative charge on the terminal enyl carbon atom. The trimethylammonioethenyl ligand, CH=CH(+NMe3) in 4.8 is a η2 -ligand that bridges a Ru−Ru bond on a basal edge of the square-pyramidal Ru5 cluster by a combination of σ + π coordination of the ethenyl group. Compounds 4.9 and 4.11 each contain a η1 -terminally-coordinated [η1 -E-CH=CH(+NMe3)] ligand with an E stereochemistry at the C=C double bond in open Ru5 cluster complexes. Compound 4.9 was decarbonylated to yield the compound Ru5(μ5-C)(CO)12[μ-η2 -O=C(NMe2)][μ-η2 - CH=CH(NMe3)](μ-H) 4.10 containing a η2 -bridging CHCH(+NMe3) ligand. Compound 4.10 was converted back to 4.9 by the addition of CO. Two zwitterionic products, Ru5(μ5- C)(CO)14[η1 -E-CH=CH(NMe3)] 4.12 and Ru5(μ5-C)(CO)15[η1 -E-CH=CH(NMe3)] 4.13, were obtained by the addition of CO to 4.8. Compound 4.12 is an intermediate en route to 4.13. Compound 4.12 contains a terminally-coordinated η1 -E-CH=CH(+NMe3) ligand on one of the basal Ru atoms of a square-pyramidal Ru5 cluster. Compound 4.13 also contains a terminally coordinated η1 -E-CH=CH(+NMe3) ligand on the wing-tip bridging Ru atom of a butterfly Ru4C cluster. Treatment of 4.6 with methyl propiolate (HC=CCO2Me) yielded the zwitterionic complex Ru5(μ5-C)(CO)13[μ-η2 -O=C(NMe2)][η1 -E- (MeO2C)C=C(H)NMe3](μ-H) 4.14 that is structurally similar to 4.9 but contains a η1 -E- (MeO2C)C=C(H)(+NMe3) ligand. Compound 4.14 eliminated its NMe3 group to yield the compounds Ru5(μ5-C)(CO)13[μ-η2 -O=C(NMe2)][μ-η2 -(MeO2C)HC=CH] 4.15 which contains a bridging methoxycarbonyl-substituted alkenyl ligand and the known compound Ru5(μ5-C)(CO)13[μ-η2 O=C(NMe2)](HNMe2)(μ-H) 4.16.

The reactivity of a (μ5-C) carbido carbon in the pentaruthenium carbonyl cluster, Ru5(μ5-C)(CO)15 with the unsaturated molecule ethyne (C2H2) is reported in chapter 5. The thermal reaction at 48 ℃ yielded four new ethyne-bound cluster complexes, Ru5[m4-h 3 :h1 - CC(H)C(H)C(H)C(H)](CO)13(m4-h 2 :h1 :h2 :h1 -HCCH), 5.2; Ru5[m4-h 4 :h1 - CC(H)C(H)C(H)C(H)](CO)12(m4-h 2 :h1 :h2 :h1 -HCCH), 5.3; Ru5[m4-h 4 :h1 - CC(H)C(H)C(H)C(H)](CO)12(m4-h 2 :h1 :h2 :h1 -HCCH), 5.4; and Ru4(CO)11(m4- h 2 :h1 :h2 :h1 -HCCH)Ru(CO)3(C5H4), 5.5. All four compounds contain a quadruplybridging ethyne ligand coordinated to four metal atoms. Compound 5.3 has a bridging metalla-penta-1,3-dienyl ligand, RuCC(H)C(H)C(H)C(H), where two C2H2 molecules have been coupled to the carbido carbon of the cluster by forming a C – C bond. Upon carbonylation of 5.3, the bridging metalla-penta-1,3-dienyl ligand, CC(H)C(H)C(H)C(H) changes its coordination mode from h 4 :h1 to h 3 :h1 in 5.2. When 5.2 was treated with CO thermally, the bridging metalla-penta-1,3-dienyl ligand changed its coordination mode from bridging h 3 :h1 mode to a h 5-metalla-cyclopenta-1,3-dienyl ligand in 5.5. The thermal decomposition of 5.5 in presence of water yielded the known compounds: a quadruplybridged Ru4(CO)12(m4-C2H2), 5.6 and the dimer [Ru(h 5 -C5H5)(CO)2]2, 5.7.

In continuation of the study of alkynes with the pentaruthenium carbonyl cluster complex, we studied the insertion of alkynes into the Ru-phenyl bond of Ru5(m5-C)(CO)13(m-h2-Ph)[m-Au(NHC)], 6.3 in chapter 6. The reaction of C2H2 and HC2Ph with Ru5(m5-C)(CO)13(m-h2-Ph)[m-Au(NHC)], 6.3 where NHC = 1,3-bis(2,6- diisopropylphenyl-imidazol-2-ylidene) yielded the new alkenyl complexes Ru5(m5-C)(CO)13[m-h 2 -E-C(H)C(H)Ph)][m-Au(NHC)], 6.2 and Ru5C(CO)13[m-h 2 -E- C(Ph)C(H)Ph][m-Au(NHC)], 6.3 by insertion of the alkyne into the metal – carbon s-bond of the phenyl ring in 6.1.

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© 2021, Humaiara Akter

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