Ruthenium-Based Olefin Metathesis Catalysts Bearing pH-Responsive Ligands: External Control of Catalyst Solubility and Activity

Sixteen novel, Ru-based olefin metathesis catalysts bearing pH responsive ligands were synthesized. The pH-responsive groups employed with these catalysts included dimethylamino (NMe2) modified NHC ligands as well as N-donor dimethylaminopyridine (DMAP) and 3-(o-pyridyl)propylidene ligands. These pH-responsive ligands provided the means by which the solubility and/or activity profiles of the catalysts produced could be controlled via acid addition. The main goal of this dissertation was to design catalyst systems capable of performing ring opening metathesis (ROMP) and ring closing metathesis (RCM) reactions in both organic and aqueous media. In an effort to quickly gain access to new catalyst structures, a template synthesis for functionalized NHC ligand precursors was designed, in addition to other strategies, to obtain ligand precursors with ancillary NMe2 groups. Kinetic studies for the catalysts produced from these precursors showed external control of catalyst solubility was afforded via protonation of the NMe2 groups of their NHC ligands. Additionally, this protonation afforded external control of catalyst propagation rates for several catalysts. This is the first known independent external control for the propagation rates of ROMP catalysts. The incorporation of pH-responsive N-donor ligands into catalyst structures also provided the means for the external control of metathesis activity, as the protonation of these ligands resulted in an increased initiation rate based on their fast and irreversible dissociation from the metal center. The enhanced external control makes these catalysts applicable to a wide range of applications, some of which have been explored by us and/or through collaboration. Three of the catalysts designed showed remarkable metathesis activity in aqueous media. These catalysts displayed comparable RCM activity in aqueous media to a class of water-soluble catalysts reported by Grubbs et al., considered to be the most active catalyst for aqueous olefin metathesis reactions. In ROMP reactions these particular catalysts dramatically outperformed the literature catalysts, accomplishing ROMP full conversion rates within 15 minutes compared to several hours observed with the literature catalyst. These catalysts were also able to accomplish these reactions at lower catalyst loadings than ever reported with the literature catalyst, making them the most active aqueous olefin metathesis catalysts to date

Hexacoordinate Ru-based olefin metathesis catalysts with pH-responsive N-heterocyclic carbene (NHC) and N-donor ligands for ROMP reactions in non-aqueous, aqueous and emulsion conditions

Three new ruthenium alkylidene complexes (PCy3)Cl2(H2ITap)Ru=CHSPh (9), (DMAP)2Cl2(H2ITap)Ru=CHPh (11) and (DMAP)2Cl2(H2ITap)Ru=CHSPh (12) have been synthesized bearing the pH-responsive H2ITap ligand (H2ITap = 1,3-bis(2’,6’- dimethyl-4’-dimethylaminophenyl)-4,5-dihydroimidazol-2-ylidene). Catalysts 11 and 12 are additionally ligated by two pH-responsive DMAP ligands. The crystal structure was solved for complex 12 by X-ray diffraction. In organic, neutral solution, the catalysts are capable of performing standard ring-opening metathesis polymerization (ROMP) and ring closing metathesis (RCM) reactions with standard substrates. The ROMP with complex 11 is accelerated in the presence of two equiv of H3PO4, but is reduced as soon as the acid amount increased. The metathesis of phenylthiomethylidene catalysts 9 and 12 is sluggish at room temperature, but their ROMP can be dramatically accelerated at 60 °C. Complexes 11 and 12 are soluble in aqueous acid. They display the ability to perform RCM of diallylmalonic acid (DAMA), however, their conversions are very low amounting only to few turnovers before decomposition. However, both catalysts exhibit outstanding performance in the ROMP of dicyclopentadiene (DCPD) and mixtures of DCPD with cyclooctene (COE) in acidic aqueous microemulsion. With loadings as low as 180 ppm, the catalysts afforded mostly quantitative conversions of these monomers while maintaining the size and shape of the droplets throughout the polymerization process. Furthermore, the coagulate content for all experiments staye

Tetra-μ-aqua-octaaqua­bis(μ-4-chloro­pyridine-2,6-dicarboxyl­ato)bis­(4-chloro­pyridine-2,6-dicarboxyl­ato)tri­cobalt(II)disodium(I) bis­[triaqua­bis(4-chloro­pyridine-2,6-dicarboxyl­ato)cobalt(II)] hexa­hydrate

The title compound, [Co3Na2(C7H2ClNO4)4(H2O)12][Co(C7H2ClNO4)(H2O)3]2·6H2O, consists of a centrosymmetric dimer of [CoII(dipicCl)2]2− complex dianions [dipicCl is 4-chloro­pyridine-2,6-dicarboxyl­ate] bridged by an [Na2CoII(H2O)12]4+ tetra­cationic cluster, two independent [Co(dipicCl)(H2O)3] complexes, and six water mol­ecules of crystallization. The metals are all six-coordinate with distorted octahedral geometries. The [CoII(dipicCl)(H2O)3] complexes are neutral, with one tridentate ligand and three water molecules. The [CoII(dipicCl)2]2− complexes each have two tridentate ligands. The [Na2CoII(H2O)12]4+ cluster has a central CoII ion which is coordinated to six water molecules and lies on a crystallographic inversion center. Four of the water molecules bridge to two sodium ions, each of which have three other water molecules coordinated along with an O atom from the [CoII(dipicCl)2]2− complex. In the crystal structure, the various units are linked by O—H⋯O hydrogen bonds, forming a three-dimensional network. Two water molecules are disordered equally over two positions

CCDC 706305: Experimental Crystal Structure Determination

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.,Related Article: V.H.Rambaran, S.Balof, L.Moody, D.VanDerveer, A.A.Holden|2009|CrystEngComm|11|580|doi:10.1039/b822030

A New and Efficient Synthetic Route for the Synthesis of 3,6-Dimethylpyrazine-2,5-Dicarboxylic Acid Hydrate: Molecular Structure and Unique Supramolecular Interactions

The regioselective oxidation of 2,3,5,6,-tetramethyl pyrazine by selenium dioxide and silver nitrate resulted in the production of, 3,6-dimethylpyrazine-2,5-dicarboxylic acid hydrate in high yields. Its crystal structure, which is reported for the very first time, consists of a unique infinite three-dimensional lattice of hydrogen-bonded acid and water molecules

Tetra-\u3ci\u3eμ\u3c/i\u3e-aqua-octaaquabis(\u3ci\u3eμ\u3c/i\u3e-4-chloropyridine-2,6-dicarboxylato(bis(4-chloro-pyridine-2,6-dicarboxylato)tricobalt(II)-disodium(I) Bis[triaquabis(4-chloro-pyridine-2,6-dicarboxylato)cobalt(II)] Hexahydrate

The title compound, [Co3Na2(C72ClNO4)4(H2O)12][Co(C7H2ClNO4(H2O)3]2·6H2O, consists of a centrosymmetric dimer of [CoII(dipicCl)2]2- complex dianions [dipicCl is 4-chloro­pyridine-2,6-dicarboxyl­ate] bridged by an [Na2CoII(H2O)12]4+ tetra­cationic cluster, two independent [Co(dipicCl)(H2O)3] complexes, and six water mol­ecules of crystallization. The metals are all six-coordinate with distorted octahedral geometries. The [CoII(dipicCl)(H2O)3] complexes are neutral, with one tridentate ligand and three water molecules. The [CoII(dipicCl)2]2- complexes each have two tridentate ligands. The [Na2CoII(H2O)12]4+ cluster has a central CoII ion which is coordinated to six water molecules and lies on a crystallographic inversion center. Four of the water molecules bridge to two sodium ions, each of which have three other water molecules coordinated along with an O atom from the [CoII(dipicCl)2]2- complex. In the crystal structure, the various units are linked by O-H···O hydrogen bonds, forming a three-dimensional network. Two water molecules are disordered equally over two positions

CCDC 674276: Experimental Crystal Structure Determination

Related Article: L.Moody, S.Balof, S.Smith, V.H.Rambaran, D.VanDerveer, A.A.Holder|2008|Acta Crystallogr.,Sect.E:Struct.Rep.Online|64|m262|doi:10.1107/S1600536807067141,An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures

pH-Responsive Ruthenium-Based Olefin Metathesis Catalysts: Controlled Ring-Opening Metathesis Polymerization in Alcoholic and Aqueous Media upon Acid Addition

The new hexacoordinate catalysts (PCy3)(DMAP)2Cl2Ru═CH(p-C6H4)CH2NMe2 (7) and (PCy3)(DMAP)2Cl2Ru═CH(p-C6H4)N(CH3)2 (8) have been synthesized via exchange of a PCy3 ligand for two DMAP ligands from their (PCy3)2Ru precursors 4 and 5 in a one-step reaction in high yield. The catalysts promoted controlled ROMP of two cationic exo-7-oxanorbornene derivatives under homogeneous conditions in various acidic protic media, including acidic aqueous media. Very low polydispersities were accomplished in TFE/0.1 M HClaq. (1:1 v/v) with PDIs as low as 1.05

Hexacoordinate Ru-Based Olefin Metathesis Catalysts with pH-Responsive N-Heterocyclic Carbene (NHC) and N-Donor Ligands for ROMP Reactions in Non-Aqueous, Aqueous and Emulsion Conditions

Three new ruthenium alkylidene complexes (PCy3)Cl2(H2ITap)Ru=CHSPh (9), (DMAP)2Cl2(H2ITap)Ru=CHPh (11) and (DMAP)2Cl2(H2ITap)Ru=CHSPh (12) have been synthesized bearing the pH-responsive H2ITap ligand (H2ITap = 1,3-bis(2’,6’-dimethyl-4’-dimethylaminophenyl)-4,5-dihydroimidazol-2-ylidene). Catalysts 11 and 12 are additionally ligated by two pH-responsive DMAP ligands. The crystal structure was solved for complex 12 by X-ray diffraction. In organic, neutral solution, the catalysts are capable of performing standard ring-opening metathesis polymerization (ROMP) and ring closing metathesis (RCM) reactions with standard substrates. The ROMP with complex 11 is accelerated in the presence of two equiv of H3PO4, but is reduced as soon as the acid amount increased. The metathesis of phenylthiomethylidene catalysts 9 and 12 is sluggish at room temperature, but their ROMP can be dramatically accelerated at 60 °C. Complexes 11 and 12 are soluble in aqueous acid. They display the ability to perform RCM of diallylmalonic acid (DAMA), however, their conversions are very low amounting only to few turnovers before decomposition. However, both catalysts exhibit outstanding performance in the ROMP of dicyclopentadiene (DCPD) and mixtures of DCPD with cyclooctene (COE) in acidic aqueous microemulsion. With loadings as low as 180 ppm, the catalysts afforded mostly quantitative conversions of these monomers while maintaining the size and shape of the droplets throughout the polymerization process. Furthermore, the coagulate content for all experiments staye

Hexacoordinate Ru-Based Olefin Metathesis Catalysts with pH-Responsive N-Heterocyclic Carbene (NHC) and N-Donor Ligands for ROMP Reactions in Non-Aqueous, Aqueous and Emulsion Conditions

Three new ruthenium alkylidene complexes (PCy3)Cl2(H2ITap)Ru=CHSPh (9), (DMAP)2Cl2(H2ITap)Ru=CHPh (11) and (DMAP)2Cl2(H2ITap)Ru=CHSPh (12) have been synthesized bearing the pH-responsive H2ITap ligand (H2ITap = 1,3-bis(2’,6’-dimethyl-4’-dimethylaminophenyl)-4,5-dihydroimidazol-2-ylidene). Catalysts 11 and 12 are additionally ligated by two pH-responsive DMAP ligands. The crystal structure was solved for complex 12 by X-ray diffraction. In organic, neutral solution, the catalysts are capable of performing standard ring-opening metathesis polymerization (ROMP) and ring closing metathesis (RCM) reactions with standard substrates. The ROMP with complex 11 is accelerated in the presence of two equiv of H3PO4, but is reduced as soon as the acid amount increased. The metathesis of phenylthiomethylidene catalysts 9 and 12 is sluggish at room temperature, but their ROMP can be dramatically accelerated at 60 °C. Complexes 11 and 12 are soluble in aqueous acid. They display the ability to perform RCM of diallylmalonic acid (DAMA), however, their conversions are very low amounting only to few turnovers before decomposition. However, both catalysts exhibit outstanding performance in the ROMP of dicyclopentadiene (DCPD) and mixtures of DCPD with cyclooctene (COE) in acidic aqueous microemulsion. With loadings as low as 180 ppm, the catalysts afforded mostly quantitative conversions of these monomers while maintaining the size and shape of the droplets throughout the polymerization process. Furthermore, the coagulate content for all experiments stayed \u3c2%. This represents an unprecedented efficiency in emulsion ROMP based on hydrophilic ruthenium alkylidene complexes