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This study concerns the synthesis, structure and reactivity of nitrosyl complexes of ruthenium and osmium. Attempts have been made to prepare coordinatively saturated and unsaturated complexes and a study of their oxidative addition reactions bears considerable resemblance to the more familiar carbonyl complexes M(CO)3(PPh3)2. A number of interesting atom transfer reactions, generally involving oxygen, have been observed. The d8 complex RuCl(CO)(NO)(PPh3)2 results from the interaction of RuHCl(CO)(PPh3)3 with N-methyl-N-nitrosotoluene-p-sulphonamide. The labile halide ligand is readily displaced by a large range of anions and it is believed that both linear and bent nitrosyl linkages may exist for different members of this series. The structures of these complexes are discussed in the light of recent X-ray crystal structure data. Halogens and hydrogen halides add to give the familiar RuX3(NO)(PPh3)2; RuCl3(NO)(PPh2Me)2 is prepared in a direct reaction and also by phosphine exchange and 1H n.m.r. data confirm that the phosphine ligands are trans. The complexes RuX(CO)(NO)(PPh3)2 react readily with O2 to form the dioxygen complexes Ru(O2)X(NO)(PPh3)2. Halogens and hydrogen halides produce RuX3(NO)(PPh3)2. The dioxygen complexes react with SO2 and N2O4 to give sulphato and dinitrato complexes respectively. The reaction with CO results in the intramolecular oxidation of the nitrosyl group to coordinated nitrate accompanied by the incorporation of two moles of CO, i.e. RuX(NO3)(CO)2(PPh3)2 is formed. The dioxygen complexes catalytically oxidise triphenylphosphine or triphenylarsine to the respective oxides and RuX(NO)(PPh3)2 can be isolated from this cycle. Reactions of these four-coordinated complexes with O2, CO, Cl2 and NOBF4 are recorded. The dinitrosyl complex Ru(NO)2(PPh3)2 is reported from a number of syntheses, the most successful being via a ligand reaction when RuCl2(CO)2(PPh3)2 is heated with NaNO2 and Ph3P in dimethyl formamide. The P-tolyldiphenylphosphine analogue is also reported and the mono-substituted product Ru(NO)2(PPh3)[P(OPh)3] is produced in an exchange reaction between Ru(NO)2(PPh3)2 and excess triphenylphosphite. This phosphite complex reacts with Ph3P and O2 to produce Ru(O2)(NO2)(NO)PPh3)2 by an atom transfer process. Ru(NO)2(PPh3)2 reacts with the acids HY (Y = BF4, PF6, ClO4) and O2 to give the dinitrosyl cations [Ru(OH)(NO)2(PPh3)2]+Y- in which the two nitrosyl groups are structurally and electronically inequivalent. [RuCl(NO)2(PPh3)2]BF4 is reported and reactions of these dinitrosyl cations with halide ions to give RuX2(NO3)(NO)(PPh3)2, with intramolecular oxidation of the NO group, are also described. OsCl2(OH)(NO)(PPh3)2 reacts irreversibly with alcohols to form OsCl2(OR)(NO)(PPh3)2 (R = CH3, C2H5, n-C3H7, (CH3O)CH2CH2) which readily undergo hydride abstraction to form OsHCl2(NO)(PPh3)2. Sodium borohydride converts this complex to the trihydrido species OsH3(NO)(PPh3)2 and if the reaction is performed in the presence of Ph3P, OsH(NO)(PPh3)3 results. The coordinated perchlorate complex OsHCl(OClO3)(NO)(PPh3)2 results form the reaction of OsHCl2(NO)(PPh3)2 with silver perchlorate; this is readily reversed by chloride ions or the solvents CH2Cl2 and CHCl3. This perchlorato complex also arises from the reaction of OsH(CO)(NO)(PPh3)2 with HClO4 and a related tetrafluoroborato complex, OsH(OC2H5)(FBF3)(NO)(PPh3)2 by substituting HBF4. This complex reacts with Ph3P to give [OsH(OH)(NO)(PPh3)3]BF4, CO to give [Os(CO)2(NO)(PPh3)2]BF4 and LiX (X = Br, I) to give OsHX2(NO)(PPh3)2. OsHCl(OClO3)(NO)(PPh3)2 reacts with NaOH in methanol, in the presence of O2 to produce Os(O2)Cl(NO)(PPh3)2. This dioxygen complex is far less stable than the ruthenium analogue but it undergoes similar reactions. Ph3P is oxidised, SO2 and CO give sulphato and a nitratodicarbonyl complex respectively. Infra-red, 1H n.m.r., conductivity, molecular weight data and elemental analysis have been used in formulation and structural assignment.

This study concerns the synthesis, structure and reactivity of nitrosyl complexes of ruthenium and osmium. Attempts have been made to prepare coordinatively saturated and unsaturated complexes and a study of their oxidative addition reactions bears considerable resemblance to the more familiar carbonyl complexes M(CO)3(PPh3)2. A number of interesting atom transfer reactions, generally involving oxygen, have been observed. The d8 complex RuCl(CO)(NO)(PPh3)2 results from the interaction of RuHCl(CO)(PPh3)3 with N-methyl-N-nitrosotoluene-p-sulphonamide. The labile halide ligand is readily displaced by a large range of anions and it is believed that both linear and bent nitrosyl linkages may exist for different members of this series. The structures of these complexes are discussed in the light of recent X-ray crystal structure data. Halogens and hydrogen halides add to give the familiar RuX3(NO)(PPh3)2; RuCl3(NO)(PPh2Me)2 is prepared in a direct reaction and also by phosphine exchange and 1H n.m.r. data confirm that the phosphine ligands are trans. The complexes RuX(CO)(NO)(PPh3)2 react readily with O2 to form the dioxygen complexes Ru(O2)X(NO)(PPh3)2. Halogens and hydrogen halides produce RuX3(NO)(PPh3)2. The dioxygen complexes react with SO2 and N2O4 to give sulphato and dinitrato complexes respectively. The reaction with CO results in the intramolecular oxidation of the nitrosyl group to coordinated nitrate accompanied by the incorporation of two moles of CO, i.e. RuX(NO3)(CO)2(PPh3)2 is formed. The dioxygen complexes catalytically oxidise triphenylphosphine or triphenylarsine to the respective oxides and RuX(NO)(PPh3)2 can be isolated from this cycle. Reactions of these four-coordinated complexes with O2, CO, Cl2 and NOBF4 are recorded. The dinitrosyl complex Ru(NO)2(PPh3)2 is reported from a number of syntheses, the most successful being via a ligand reaction when RuCl2(CO)2(PPh3)2 is heated with NaNO2 and Ph3P in dimethyl formamide. The P-tolyldiphenylphosphine analogue is also reported and the mono-substituted product Ru(NO)2(PPh3)[P(OPh)3] is produced in an exchange reaction between Ru(NO)2(PPh3)2 and excess triphenylphosphite. This phosphite complex reacts with Ph3P and O2 to produce Ru(O2)(NO2)(NO)PPh3)2 by an atom transfer process. Ru(NO)2(PPh3)2 reacts with the acids HY (Y = BF4, PF6, ClO4) and O2 to give the dinitrosyl cations [Ru(OH)(NO)2(PPh3)2]+Y- in which the two nitrosyl groups are structurally and electronically inequivalent. [RuCl(NO)2(PPh3)2]BF4 is reported and reactions of these dinitrosyl cations with halide ions to give RuX2(NO3)(NO)(PPh3)2, with intramolecular oxidation of the NO group, are also described. OsCl2(OH)(NO)(PPh3)2 reacts irreversibly with alcohols to form OsCl2(OR)(NO)(PPh3)2 (R = CH3, C2H5, n-C3H7, (CH3O)CH2CH2) which readily undergo hydride abstraction to form OsHCl2(NO)(PPh3)2. Sodium borohydride converts this complex to the trihydrido species OsH3(NO)(PPh3)2 and if the reaction is performed in the presence of Ph3P, OsH(NO)(PPh3)3 results. The coordinated perchlorate complex OsHCl(OClO3)(NO)(PPh3)2 results form the reaction of OsHCl2(NO)(PPh3)2 with silver perchlorate; this is readily reversed by chloride ions or the solvents CH2Cl2 and CHCl3. This perchlorato complex also arises from the reaction of OsH(CO)(NO)(PPh3)2 with HClO4 and a related tetrafluoroborato complex, OsH(OC2H5)(FBF3)(NO)(PPh3)2 by substituting HBF4. This complex reacts with Ph3P to give [OsH(OH)(NO)(PPh3)3]BF4, CO to give [Os(CO)2(NO)(PPh3)2]BF4 and LiX (X = Br, I) to give OsHX2(NO)(PPh3)2. OsHCl(OClO3)(NO)(PPh3)2 reacts with NaOH in methanol, in the presence of O2 to produce Os(O2)Cl(NO)(PPh3)2. This dioxygen complex is far less stable than the ruthenium analogue but it undergoes similar reactions. Ph3P is oxidised, SO2 and CO give sulphato and a nitratodicarbonyl complex respectively. Infra-red, 1H n.m.r., conductivity, molecular weight data and elemental analysis have been used in formulation and structural assignment.

This study concerns the synthesis, structure and reactivity of nitrosyl complexes of ruthenium and osmium. Attempts have been made to prepare coordinatively saturated and unsaturated complexes and a study of their oxidative addition reactions bears considerable resemblance to the more familiar carbonyl complexes M(CO)3(PPh3)2. A number of interesting atom transfer reactions, generally involving oxygen, have been observed. The d8 complex RuCl(CO)(NO)(PPh3)2 results from the interaction of RuHCl(CO)(PPh3)3 with N-methyl-N-nitrosotoluene-p-sulphonamide. The labile halide ligand is readily displaced by a large range of anions and it is believed that both linear and bent nitrosyl linkages may exist for different members of this series. The structures of these complexes are discussed in the light of recent X-ray crystal structure data. Halogens and hydrogen halides add to give the familiar RuX3(NO)(PPh3)2; RuCl3(NO)(PPh2Me)2 is prepared in a direct reaction and also by phosphine exchange and 1H n.m.r. data confirm that the phosphine ligands are trans. The complexes RuX(CO)(NO)(PPh3)2 react readily with O2 to form the dioxygen complexes Ru(O2)X(NO)(PPh3)2. Halogens and hydrogen halides produce RuX3(NO)(PPh3)2. The dioxygen complexes react with SO2 and N2O4 to give sulphato and dinitrato complexes respectively. The reaction with CO results in the intramolecular oxidation of the nitrosyl group to coordinated nitrate accompanied by the incorporation of two moles of CO, i.e. RuX(NO3)(CO)2(PPh3)2 is formed. The dioxygen complexes catalytically oxidise triphenylphosphine or triphenylarsine to the respective oxides and RuX(NO)(PPh3)2 can be isolated from this cycle. Reactions of these four-coordinated complexes with O2, CO, Cl2 and NOBF4 are recorded. The dinitrosyl complex Ru(NO)2(PPh3)2 is reported from a number of syntheses, the most successful being via a ligand reaction when RuCl2(CO)2(PPh3)2 is heated with NaNO2 and Ph3P in dimethyl formamide. The P-tolyldiphenylphosphine analogue is also reported and the mono-substituted product Ru(NO)2(PPh3)[P(OPh)3] is produced in an exchange reaction between Ru(NO)2(PPh3)2 and excess triphenylphosphite. This phosphite complex reacts with Ph3P and O2 to produce Ru(O2)(NO2)(NO)PPh3)2 by an atom transfer process. Ru(NO)2(PPh3)2 reacts with the acids HY (Y = BF4, PF6, ClO4) and O2 to give the dinitrosyl cations [Ru(OH)(NO)2(PPh3)2]+Y- in which the two nitrosyl groups are structurally and electronically inequivalent. [RuCl(NO)2(PPh3)2]BF4 is reported and reactions of these dinitrosyl cations with halide ions to give RuX2(NO3)(NO)(PPh3)2, with intramolecular oxidation of the NO group, are also described. OsCl2(OH)(NO)(PPh3)2 reacts irreversibly with alcohols to form OsCl2(OR)(NO)(PPh3)2 (R = CH3, C2H5, n-C3H7, (CH3O)CH2CH2) which readily undergo hydride abstraction to form OsHCl2(NO)(PPh3)2. Sodium borohydride converts this complex to the trihydrido species OsH3(NO)(PPh3)2 and if the reaction is performed in the presence of Ph3P, OsH(NO)(PPh3)3 results. The coordinated perchlorate complex OsHCl(OClO3)(NO)(PPh3)2 results form the reaction of OsHCl2(NO)(PPh3)2 with silver perchlorate; this is readily reversed by chloride ions or the solvents CH2Cl2 and CHCl3. This perchlorato complex also arises from the reaction of OsH(CO)(NO)(PPh3)2 with HClO4 and a related tetrafluoroborato complex, OsH(OC2H5)(FBF3)(NO)(PPh3)2 by substituting HBF4. This complex reacts with Ph3P to give [OsH(OH)(NO)(PPh3)3]BF4, CO to give [Os(CO)2(NO)(PPh3)2]BF4 and LiX (X = Br, I) to give OsHX2(NO)(PPh3)2. OsHCl(OClO3)(NO)(PPh3)2 reacts with NaOH in methanol, in the presence of O2 to produce Os(O2)Cl(NO)(PPh3)2. This dioxygen complex is far less stable than the ruthenium analogue but it undergoes similar reactions. Ph3P is oxidised, SO2 and CO give sulphato and a nitratodicarbonyl complex respectively. Infra-red, 1H n.m.r., conductivity, molecular weight data and elemental analysis have been used in formulation and structural assignment.

This study concerns the synthesis, structure and reactivity of nitrosyl complexes of ruthenium and osmium. Attempts have been made to prepare coordinatively saturated and unsaturated complexes and a study of their oxidative addition reactions bears considerable resemblance to the more familiar carbonyl complexes M(CO)3(PPh3)2. A number of interesting atom transfer reactions, generally involving oxygen, have been observed. The d8 complex RuCl(CO)(NO)(PPh3)2 results from the interaction of RuHCl(CO)(PPh3)3 with N-methyl-N-nitrosotoluene-p-sulphonamide. The labile halide ligand is readily displaced by a large range of anions and it is believed that both linear and bent nitrosyl linkages may exist for different members of this series. The structures of these complexes are discussed in the light of recent X-ray crystal structure data. Halogens and hydrogen halides add to give the familiar RuX3(NO)(PPh3)2; RuCl3(NO)(PPh2Me)2 is prepared in a direct reaction and also by phosphine exchange and 1H n.m.r. data confirm that the phosphine ligands are trans. The complexes RuX(CO)(NO)(PPh3)2 react readily with O2 to form the dioxygen complexes Ru(O2)X(NO)(PPh3)2. Halogens and hydrogen halides produce RuX3(NO)(PPh3)2. The dioxygen complexes react with SO2 and N2O4 to give sulphato and dinitrato complexes respectively. The reaction with CO results in the intramolecular oxidation of the nitrosyl group to coordinated nitrate accompanied by the incorporation of two moles of CO, i.e. RuX(NO3)(CO)2(PPh3)2 is formed. The dioxygen complexes catalytically oxidise triphenylphosphine or triphenylarsine to the respective oxides and RuX(NO)(PPh3)2 can be isolated from this cycle. Reactions of these four-coordinated complexes with O2, CO, Cl2 and NOBF4 are recorded. The dinitrosyl complex Ru(NO)2(PPh3)2 is reported from a number of syntheses, the most successful being via a ligand reaction when RuCl2(CO)2(PPh3)2 is heated with NaNO2 and Ph3P in dimethyl formamide. The P-tolyldiphenylphosphine analogue is also reported and the mono-substituted product Ru(NO)2(PPh3)[P(OPh)3] is produced in an exchange reaction between Ru(NO)2(PPh3)2 and excess triphenylphosphite. This phosphite complex reacts with Ph3P and O2 to produce Ru(O2)(NO2)(NO)PPh3)2 by an atom transfer process. Ru(NO)2(PPh3)2 reacts with the acids HY (Y = BF4, PF6, ClO4) and O2 to give the dinitrosyl cations [Ru(OH)(NO)2(PPh3)2]+Y- in which the two nitrosyl groups are structurally and electronically inequivalent. [RuCl(NO)2(PPh3)2]BF4 is reported and reactions of these dinitrosyl cations with halide ions to give RuX2(NO3)(NO)(PPh3)2, with intramolecular oxidation of the NO group, are also described. OsCl2(OH)(NO)(PPh3)2 reacts irreversibly with alcohols to form OsCl2(OR)(NO)(PPh3)2 (R = CH3, C2H5, n-C3H7, (CH3O)CH2CH2) which readily undergo hydride abstraction to form OsHCl2(NO)(PPh3)2. Sodium borohydride converts this complex to the trihydrido species OsH3(NO)(PPh3)2 and if the reaction is performed in the presence of Ph3P, OsH(NO)(PPh3)3 results. The coordinated perchlorate complex OsHCl(OClO3)(NO)(PPh3)2 results form the reaction of OsHCl2(NO)(PPh3)2 with silver perchlorate; this is readily reversed by chloride ions or the solvents CH2Cl2 and CHCl3. This perchlorato complex also arises from the reaction of OsH(CO)(NO)(PPh3)2 with HClO4 and a related tetrafluoroborato complex, OsH(OC2H5)(FBF3)(NO)(PPh3)2 by substituting HBF4. This complex reacts with Ph3P to give [OsH(OH)(NO)(PPh3)3]BF4, CO to give [Os(CO)2(NO)(PPh3)2]BF4 and LiX (X = Br, I) to give OsHX2(NO)(PPh3)2. OsHCl(OClO3)(NO)(PPh3)2 reacts with NaOH in methanol, in the presence of O2 to produce Os(O2)Cl(NO)(PPh3)2. This dioxygen complex is far less stable than the ruthenium analogue but it undergoes similar reactions. Ph3P is oxidised, SO2 and CO give sulphato and a nitratodicarbonyl complex respectively. Infra-red, 1H n.m.r., conductivity, molecular weight data and elemental analysis have been used in formulation and structural assignment.

This study concerns the synthesis, structure and reactivity of nitrosyl complexes of ruthenium and osmium. Attempts have been made to prepare coordinatively saturated and unsaturated complexes and a study of their oxidative addition reactions bears considerable resemblance to the more familiar carbonyl complexes M(CO)3(PPh3)2. A number of interesting atom transfer reactions, generally involving oxygen, have been observed. The d8 complex RuCl(CO)(NO)(PPh3)2 results from the interaction of RuHCl(CO)(PPh3)3 with N-methyl-N-nitrosotoluene-p-sulphonamide. The labile halide ligand is readily displaced by a large range of anions and it is believed that both linear and bent nitrosyl linkages may exist for different members of this series. The structures of these complexes are discussed in the light of recent X-ray crystal structure data. Halogens and hydrogen halides add to give the familiar RuX3(NO)(PPh3)2; RuCl3(NO)(PPh2Me)2 is prepared in a direct reaction and also by phosphine exchange and 1H n.m.r. data confirm that the phosphine ligands are trans. The complexes RuX(CO)(NO)(PPh3)2 react readily with O2 to form the dioxygen complexes Ru(O2)X(NO)(PPh3)2. Halogens and hydrogen halides produce RuX3(NO)(PPh3)2. The dioxygen complexes react with SO2 and N2O4 to give sulphato and dinitrato complexes respectively. The reaction with CO results in the intramolecular oxidation of the nitrosyl group to coordinated nitrate accompanied by the incorporation of two moles of CO, i.e. RuX(NO3)(CO)2(PPh3)2 is formed. The dioxygen complexes catalytically oxidise triphenylphosphine or triphenylarsine to the respective oxides and RuX(NO)(PPh3)2 can be isolated from this cycle. Reactions of these four-coordinated complexes with O2, CO, Cl2 and NOBF4 are recorded. The dinitrosyl complex Ru(NO)2(PPh3)2 is reported from a number of syntheses, the most successful being via a ligand reaction when RuCl2(CO)2(PPh3)2 is heated with NaNO2 and Ph3P in dimethyl formamide. The P-tolyldiphenylphosphine analogue is also reported and the mono-substituted product Ru(NO)2(PPh3)[P(OPh)3] is produced in an exchange reaction between Ru(NO)2(PPh3)2 and excess triphenylphosphite. This phosphite complex reacts with Ph3P and O2 to produce Ru(O2)(NO2)(NO)PPh3)2 by an atom transfer process. Ru(NO)2(PPh3)2 reacts with the acids HY (Y = BF4, PF6, ClO4) and O2 to give the dinitrosyl cations [Ru(OH)(NO)2(PPh3)2]+Y- in which the two nitrosyl groups are structurally and electronically inequivalent. [RuCl(NO)2(PPh3)2]BF4 is reported and reactions of these dinitrosyl cations with halide ions to give RuX2(NO3)(NO)(PPh3)2, with intramolecular oxidation of the NO group, are also described. OsCl2(OH)(NO)(PPh3)2 reacts irreversibly with alcohols to form OsCl2(OR)(NO)(PPh3)2 (R = CH3, C2H5, n-C3H7, (CH3O)CH2CH2) which readily undergo hydride abstraction to form OsHCl2(NO)(PPh3)2. Sodium borohydride converts this complex to the trihydrido species OsH3(NO)(PPh3)2 and if the reaction is performed in the presence of Ph3P, OsH(NO)(PPh3)3 results. The coordinated perchlorate complex OsHCl(OClO3)(NO)(PPh3)2 results form the reaction of OsHCl2(NO)(PPh3)2 with silver perchlorate; this is readily reversed by chloride ions or the solvents CH2Cl2 and CHCl3. This perchlorato complex also arises from the reaction of OsH(CO)(NO)(PPh3)2 with HClO4 and a related tetrafluoroborato complex, OsH(OC2H5)(FBF3)(NO)(PPh3)2 by substituting HBF4. This complex reacts with Ph3P to give [OsH(OH)(NO)(PPh3)3]BF4, CO to give [Os(CO)2(NO)(PPh3)2]BF4 and LiX (X = Br, I) to give OsHX2(NO)(PPh3)2. OsHCl(OClO3)(NO)(PPh3)2 reacts with NaOH in methanol, in the presence of O2 to produce Os(O2)Cl(NO)(PPh3)2. This dioxygen complex is far less stable than the ruthenium analogue but it undergoes similar reactions. Ph3P is oxidised, SO2 and CO give sulphato and a nitratodicarbonyl complex respectively. Infra-red, 1H n.m.r., conductivity, molecular weight data and elemental analysis have been used in formulation and structural assignment.

<p>Automated reaction prediction has the potential to elucidate complex reaction networks for many applications in chemical engineering, including materials degradation, drug design, combustion chemistry and biomass conversion. Unlike traditional reaction mechanism elucidation methods that rely on manual setup of quantum chemistry calculations, automated reaction prediction avoids tedious trial-and-error learning processes and greatly reduces the risk of leaving out important reactions. Despite these promising advantages, the potential of automated reaction prediction as a general-purpose tool is still largely unrealized, due to high computational cost and inconsistent reaction coverage. Therefore, this dissertation develops methods to simultaneously reduce the computational cost and increase the reaction coverage. Specifically, the computational cost is reduced by the development of more efficient transition state (TS) localization workflows and fast molecular and reaction property prediction packages, while the reaction coverage is increased by a comprehensive reaction space exploration based on mathematically defined elementary reaction steps. These components are implemented in two open-source packages, one is TAFFI (Topology Automated Force-Field Interactions) component increment theory (TCIT) and the other is Yet Another Reaction Program (YARP).</p> <p><br></p> <p>The first package, TCIT, is the first component increment theory based molecular property prediction package. TCIT is based on the locality assumption, which decomposes molecular thermochemistry properties into the summation of the contributions of each subgraph. In contrast to the traditional "group" increment theory, TCIT treats each subgraph as the central atom plus its nearest and next-nearest neighboring atoms, and consistently parameterizes the contribution of each component according to purely quantum chemistry calculations. Although all parameterizations are based on quantum chemical calculations, when benchmarked against experimental data, TCIT provides more accurate predictions compared to traditional methods using the same experimental dataset for parameterization. With TCIT, the molecular properties (e.g., enthalpy of formation) and reaction properties (e.g., enthalpy of reaction) can be accurately predicted in an on-the-fly manner. The second package, YARP, is developed for automated reaction space exploration and deep reaction network prediction. By optimizing the reaction enumeration, geometry initialization, and transition state convergence algorithms that are common to many prediction methodologies, YARP (re)discovers both established and unreported reaction pathways and products while simultaneously reducing the cost of reaction characterization nearly 100-fold and increasing convergence of transition states, comparing with recent benchmarks. In addition, an updated version of YARP, YARP v2.0, further reduces the cost of reaction characterization from 100-fold to 300-fold, while increasing the reaction coverage beyond the scope of elementary reaction steps. This combination of ultra-low cost and high reaction-coverage creates opportunities to explore the reactivity of larger systems and more complex reaction networks for applications like chemical degradation, where computational cost is a bottleneck.</p> <p><br></p> <p>The power of TCIT and YARP has been demonstrated by a broad range of applications. In the first application, YARP was used to explore the reactivity of unimolecular and bimolecular reactants, comprising a total of 581 reactions involving 51 distinct reactants. The algorithm discovered all established reaction pathways, where such comparisons are possible, while also revealing a much richer reactivity landscape, including lower barrier reaction pathways and a strong dependence of reaction conformation in the apparent barriers of the reported reactions. Secondly, YARP was applied to the search for prebiotic chemical pathways, which is a long-standing puzzle that has generated a menagerie of competing hypotheses with limited experimental prospects for falsification. With YARP, the space of organic molecules that can be formed within four polar or pericyclic reactions from water and hydrogen cyanide (HCN) was comprehensively explored. A surprisingly diverse reactivity landscape was revealed within just a few steps of these simple molecules and reaction pathways to several biologically relevant molecules were discovered involving lower activation energies and fewer reaction steps compared with recently proposed alternatives. In the third application, predicting the reaction network of glucose pyrolysis, YARP generated by far the largest and most complex reaction network in the domain of biomass pyrolysis and discovered many unexpected reaction mechanisms. Further, motivated by the fact that existing reaction transition state (TS) databases are comparatively small and lack chemical diversity, YARP, together with the concept of a graphically defined model reaction, were utilized to address the data gap by comprehensively characterizing a reaction space associated with C, H, O, and N containing molecules with up to 10 heavy (non-hydrogen) atoms. The resulting dataset, namely Reaction Graph Depth 1 (RGD1) dataset, is composed of 176,992 organic reactions possessing at least one validated TS, activation energy, enthalpy of reaction, reactant and product geometries, frequencies, and atom-mapping. The RGD1 dataset represents the largest and most chemically diverse TS dataset published to date and should find immediate use in developing novel machine learning models for predicting reaction properties. In addition to exploring the molecular reaction space, YARP was also extended to explore and characterize reaction networks in heterogeneous catalysis systems. With ethylene oligomerization on silica-supported single site Ga catalysts as a model system, YARP illustrates how a comprehensive reaction network can be generated by using only graph-based rules for exploring the network and elementary constraints based on activation energy and system size for identifying network terminations. The automated reaction exploration (re)discovered the Ga-alkyl-centered Cossee-Arlman mechanism that is hypothesized to drive major product formation while also predicting several new pathways for producing alkanes and coke precursors. The diverse scope of these applications and milestone quality of many of the reaction networks produced by YARP  illustrate that automated reaction prediction is approaching a general-purpose capability.</p>

<div>Thermochemical processing using fast-pyrolysis technology has been used to upgrade feedstocks like biomass and natural gas and more recently studied for plastic recycling. This work aims to improve the selectivity to desired products from a pyrolysis process through better catalysts and reactor design.</div><div>Fast-pyrolysis of biomass to fuels is considered a promising technology due to the higher yields to liquid fuel products. However, the process suffers from low carbon efficiency to hydrocarbon products due to carbon losses to biochar, accounting for 25-40 wt.% of the product stream depending on the biomass type. Using a combination of inorganic free-model compounds, biomass pretreatments and mass spectrometric analyses coupled with lab-scale reactor experiments, the char contribution from the lignocellulosic components (cellulose, hemicellulose, and lignin) and mineral content was investigated. The lignocellulosic components were found to follow the order: Lignin > Hemicellulose > Cellulose. Addition of inorganic salts (K, Na and Ca) to cellobiose, a model compound for cellulose, was found to catalyze additional dehydration reactions on primary pyrolysis products (e.g., levoglucosan) to yield secondary products (e.g., 5-HMF), and produce more char. This knowledge of char formation contributors can enable optimization of the bio-refining process sequencing using process system engineering tools and thus achieve higher carbon efficiency for biomass conversion.</div><div>While biomass has been viewed as a future energy source, there is a need for a transition fuel with the lowest possible greenhouse gas (GHG) footprint. Shale gas, consisting primarily of methane, is a potential candidate due to its large availability and high hydrogen to carbon ratio. Recently, single-atom catalysts have been studied as stable and non-coking catalysts for the non-oxidative coupling of methane (NOCM) to higher hydrocarbons (like ethylene). However, lack of post reaction catalyst characterization and rigorous kinetic testing have raised questions on the stability of these materials. This work combines homogenous (Chemkin simulations, gas phase kinetics) and heterogeneous reaction kinetic studies (reaction orders, steady state kinetics), coupled with microscopy (Scanning and Transmission Electron Microscopy (SEM, TEM)) and surface characterization tools (BET, TGA, Raman spectroscopy, CO-IR spectroscopy) to understand the role of the solid materials during NOCM. Post reaction catalyst characterization using transmission electron microscopy (TEM) analysis on the spent samples (CH4 treated at 975 deg C for 3 hours) reveals that the materials containing Pt single atoms (SA) and Pt nanoparticles (NP) are found to sinter to particles approximately 5-7 nm in size. Ethylene hydrogenation experiments, a kinetic probe for surface Pt, shows initial ethane formation rates that are four orders of magnitude lower on the isolated Pt+2 sites, found on Pt SAs, when compared to the rates obtained if all the surface Pt were assumed to be metallic. These results suggest that single atoms are not the active sites. However, under same reaction conditions (50 mL min-1 CH4 flow and 975 deg C), the ethylene formation rates (in mol h-1) on the solid materials are 2-7 times higher than the empty tube rates, indicating that the surface plays a role during NOCM. Addition of incremental amounts of the solid material increases methane conversion, extrapolating to the bare tube conversion at zero loading. This indicates that the solid materials improve the NOCM performance.</div><div>Experiments with pure methane feeds indicate that the solid materials are found to deactivate due to coking on the surface, evidenced by the coke buildup observed using thermogravimetric analysis (TGA) and the initial time-on-stream kinetic results showing rapid methane deactivation. Raman spectroscopy on the spent catalysts indicate at the development of a similar graphite-like surface intermediate under steady state conditions on all the materials. When compared under the same reaction conditions (975 deg C, 60 mL min-1 Pure CH4 with 10% UHP N2 feed, space velocity = 39.6 L h-1 gcat-1), these coked surfaces show a linear dependence for the ethylene formation rate (in mol h-1 gcat-1) with the spent surface area of the material (in m2 gcat-1). This observation is irrespective of the type of the material studied (alpha Al2O3, Davisil SiO2, 1 wt.% Pt/CeO2, Graphene, Graphite, etc.). In conclusion, these results prove that the spent surface area is critical for NOCM.</div><div>Similar experimental setup was used to study the dehydrogenation of methane, ethane, and propane mixture in the gas phase. Initial experiments at 1 bar pressure and reaction temperatures ranging from 650-850 deg C revealed that ethylene and hydrogen are the main gas phase products, with methane acting as a diluting agent under these reaction conditions. These results could enable direct processing of the shale gas without the use of a conventional ethane/propane separation step. These results were further studied by the system engineers using ANSYS ChemkinPro. For practical applications, these experiments were suggested to be performed at much higher operating pressures (~30 bar) and low residence time (~0.2 s), with a quick quenching step added after the reactor to prevent change in the exit stream compositions. A new reaction system was built to experimentally validate these recommendations.</div>

<p>Various organic reactions, including important synthetic reactions involving C–C, C–N, and C–O bond formation as well as reactions of biomolecules, are known to be accelerated when the reagents are present in confined volumes such as sprayed or levitated microdroplets or thin films. This phenomenon of reaction acceleration and the key role of interfaces played in it are of intrinsic interest and potentially of practical value as a simple, rapid method of performing small-scale synthesis. This dissertation has three focusing subtopics in the field of reaction acceleration: (1) application of reaction acceleration in levitated droplets and mass spectrometry to accelerate the reaction-analysis workflow of forced degradation of pharmaceuticals at small scale; (2) fundamental understanding of mechanisms of accelerated reactions at air/solution interfaces; (3) discovery the use of glass particles as a `green' heterogeneous catalysts in solutions and systematical study of solid(glass)/solution interfacial reaction acceleration as a superbase for synthesis and degradation using high-throughput screening.</p><p><br></p><p>Reaction acceleration in confined volumes could enhance analytical methods in industrial chemistry. Forced degradation is critical to probe the stabilities and chemical reactivities of therapeutics. Typically performed in bulk followed by LC-MS analysis, this traditional workflow of reaction/analysis sequence usually requires several days to form and measure desirable amount of degradants. I developed a new method to study chemical degradation in a shorter time frame in order to speed up both drug discovery and the drug development process. Using the Leidenfrost effect, I was able to study, over the course of seconds, degradation in levitated microdroplets over a metal dice. This two-minute reaction/analysis workflow allows major degradation pathways of both small molecules and therapeutic peptides to be studied. The reactions studied include deamidation, disulfide bond cleavage, ether cleavage, dehydration, hydrolysis, and oxidation. The method uses microdroplets as nano-reactors and only require a minimal amount of therapeutics per stress condition and the desirable amount of degradant can be readily generated in seconds by adjusting the droplet levitation time, which is highly advantageous both in the discovery and development phase. Built on my research, microdroplets can potentially be applied in therapeutics discovery and development to rapidly screen stability of therapeutics and to screen the effects of excipients in enhancing formulation stabilities.</p><p><br></p><p>My research also advanced the fundamental understanding of reaction acceleration by disentangles the factors controlling reaction rates in microdroplet reactions using constant-volume levitated droplets and Katritzky transamination as a model. The large surface-to-volume ratios of these systems results in a major contribution from reactions at the air/solution interface where reaction rates are increased. Systems with higher surface-active reactants are subject to greater acceleration, particularly at lower concentrations and higher surface-to-volume ratios. These results highlight the key role that air/solution air/solution interfaces play in Katritzky reaction acceleration. They are also consistent with the view that reaction increased rate constant is at least in part due to limited solvation of reagents at the interface.</p><p><br></p><p><br></p><p>While reaction acceleration at air/solution interfaces has been well known in microdroplets, reaction acceleration at solid/solution interfaces appears to be a new phenomenon. The Katritzky reaction in bulk solution at room temperature is accelerated significantly by the surface of a glass container compared to a plastic container. Remarkably, the reaction rate is increased by more than two orders of magnitude upon the addition of glass particles with the rate increasing linearly with increasing amounts of glass. A similar phenomenon is observed when glass particles are added to levitated droplets, where large acceleration factors are seen. Evidence shows that glass acts as a ‘green’ heterogeneous catalyst: it participates as a base in the deprotonation step and is recovered unchanged from the reaction mixture. </p><p><br></p><p>Subsequent to this study, we have systematically explored the solid/solution interfacial acceleration phenomena using our latest generation of a high-throughput screening system which is capable of screening thousands of organic reactions in a single day. Using desorption electrospray ionization mass spectrometry (DESI-MS) for automated analysis, we have found that glass promotes not only organic reactions without organic catalysts but also reactions of biomolecules without enzymes. Such reactions include Knoevenagel condensation, imine formation, elimination of hydrogen halide, ester hydrolysis and/or transesterification of acetylcholine and phospholipids, as well as oxidation of glutathione. Glass has been used as a general `green' and powerful heterogeneous catalyst.</p>

<p dir="ltr">Zeolites are microporous crystalline aluminosilicates that are widely used as catalysts for upgrading hydrocarbons and oxygenates to higher value chemicals and fuels. The substitution of tetrahedral Si⁴⁺ with Al³⁺ in a charge-neutral silica framework ([SiO_4/2]) generates anionic centers ([AlO_4/2]^-), which charge-compensate Brønsted acid protons (H⁺) that serve as active sites for catalysis. Brønsted acid sites in aluminosilicates of diverse topologies have similar acid strength, but can be located within varying intracrystalline (or internal) microporous environments (0.4‒2 nm diameter) or at extracrystalline (or external) surfaces and mesoporous environments (>2 nm diameter); yet, catalytic diversity exists, <i>even</i> for a fixed zeolite framework topology, because micropores impose constraints on molecular access to and from intracrystalline active sites and provide van der Waals contacts that influence the stabilities of reactive intermediates and transition states. Tailoring the material properties of a given zeolite framework for targeted catalytic applications requires strategies to design both the bulk crystallite properties (e.g., morphology, active site density) that influence intracrystalline diffusion and the secondary environments that surround active sites and influence intrinsic kinetics, and further necessitates molecular-level insights to elucidate the influences of bulk and active site properties on catalysis. In this work, we provide synthetic and post-synthetic strategies to respectively tune active site environments within varying micropore voids and at external surfaces of zeolites, and develop gas-phase toluene methylation and liquid-phase mesitylene benzylation as probe reactions to quantify the catalytic consequences of active site environments on aromatic alkylation catalysis.</p><p dir="ltr">The MFI framework (orthorhombic phase) consists of 12 crystallographic distinct tetrahedral-sites and 26 unique framework oxygen atoms located around channels (~0.55 nm diameter) or channel intersections (~0.70 nm diameter). The synthesis of MFI zeolites using the conventional tetra-<i>n</i>-propylammonium (TPA⁺) organic structure directing agent (OSDA) is known to place framework Al and their attendant H⁺ sites within the larger intersection environments, because electrostatic interactions are favorable between such locations of [AlO_4/2]^- and the quaternary N⁺ center in TPA⁺ that becomes positioned rigidly within channel intersections during crystallization. The methylation of toluene by dimethyl ether (DME; 403 K) on MFI-TPA zeolites of fixed active site densities (~2 Al per unit cell) result in <i>ortho</i>-xylene (<i>o</i>-X; ~65%) as the major product over <i>para</i>-xylene (<i>p</i>-X; ~27%) and <i>meta</i>-xylene (<i>m</i>-X; ~8%). In contrast, toluene methylation on MFI zeolites (~2 Al per unit cell) synthesized using non-conventional OSDAs, such as ethylenediamine (EDA) or 1,4-diazabicyclo[2.2.2]octane (DABCO), predominantly forms <i>p</i>-X (~75%) over <i>o</i>-X (~23%) and <i>m</i>-X (~2%). Within the subsets of MFI-TPA and MFI-EDA/DABCO zeolites, measured xylene formation rates and isomer selectivities are independent of crystallite sizes (0.1‒13 µm), toluene conversions (0.02‒2.0%) and external H⁺ content (up to 9% external H⁺ per total Al), indicating negligible effects of diffusion-enhanced secondary xylene isomerization reactions at intracrystalline or extracrystalline domains. The invariance of xylene isomer selectivity with reactant pressures (0.2‒9 kPa toluene, 25‒66 kPa DME) or methylating agent (1‒4 kPa methanol) indicate that differences in reactivity of toluene to form each xylene isomer reflects differences in the stabilities of their respective kinetically relevant transition states that share the same reactive intermediate. Measured xylene isomer formation rate constants and rate constant ratios, obtained from mechanism-derived rate expressions and interpreted using transition state theory formalisms, are used alongside density functional theory (DFT) calculations to reveal that intersection void environments (~0.70 nm diameter) similarly stabilize all three xylene transition states over unconfined surfaces (>2 nm diameter) without altering the established aromatic substitution patterns, while channel void environments (~0.55 nm diameter) preferentially destabilize bulkier <i>o</i>-X and <i>m</i>-X transition states thereby resulting in high intrinsic <i>p</i>-X selectivity. DFT calculations reveal that the ability of protonated DABCO complexes to reorient within MFI intersections and participate in additional hydrogen-bonding interactions with anionic Al centers during synthesis, facilitates the placement of Al in smaller channel environments that are less favored by TPA⁺. These molecular-level details, enabled by combining synthesis, characterization, kinetics and DFT, establish a mechanistic link between OSDA structure, active site placement and transition state stability, and provide active site design strategies orthogonal to crystallite design approaches that rely on complex reaction-diffusion phenomena.</p><p dir="ltr">For various reactions including toluene methylation at higher reaction temperatures (573‒773 K) and toluene conversions (>10%), extracrystalline H⁺ sites in MFI zeolites are reported to influence reactivity, selectivity, and deactivation behavior during catalysis in undesired ways. Post-synthetic chemical treatments to passivate external H⁺ sites on MFI zeolites result in unintended (but not always undesirable) changes to bulk structural properties and Al and H⁺ contents. The number of extracrystalline H⁺ sites is difficult to quantify using conventional spectroscopic or titrimetric methods, especially when present in dilute amounts on samples whose surfaces have been passivated. The systematic treatment of MFI zeolites (2.4, 5.7 and 7.1 Al per unit cell) using ammonium hexafluorosilicate (AHFS) at varying treatment duration times, AHFS concentrations and number of successive treatments resulted in MFI zeolites that retain their bulk structural properties and total Al and H⁺ contents, except for one parent MFI sample containing a significant amount of non-framework Al species. The benzylation of mesitylene by dibenzyl ether (363 K) occurs exclusively at external H⁺ sites because the bulky 1,3,5-trimethyl-2-benzylbenzene product is sterically prevented from forming at intracrystalline H⁺ sites. The intrinsic zero-order rate constant (per external H⁺) for mesitylene benzylation is extracted from rate measurements (per total Al) on a suite of untreated MFI samples with known amounts of external H⁺ sites (1‒15% external H⁺ per total Al) quantified using bulky 2,6-di-<i>tert</i>-butylpyridine base titrants. Measured zero-order rate constants on AHFS-treated MFI zeolites are used to quantify the extent to which AHFS treatments passivate external H⁺ sites, revealing efficacies that depend on the specific treatment conditions and the parent sample used. The developed kinetic methods demonstrate the utility of catalytic probes, when compared to stoichiometric probes based on spectroscopic or titration methods, in amplifying and quantifying dilute concentrations of external H⁺ sites on zeolites. The methods enable comparisons of the efficacy of various post-synthetic passivation strategies and permit rigorous assessments of the influence of external H⁺ during acid catalysis.</p><p dir="ltr">Overall, this work provides (post-)synthetic strategies to tune active site environments within intracrystalline micropores or at extracrystalline surfaces and develops quantitative kinetic probes that enable a molecular-level understanding of catalytic consequences of active site environments on aromatic alkylation reactions. Taken together, the methodology and findings of this study have broader implications in zeolite catalyst design for selectively upgrading traditional fossil feedstocks (crude oil and shale gas) and emerging feedstocks (biomass and waste plastics).</p>