Ruthenium Olefin Metathesis Complexes: Catalyst Development and Mechanistic Studies

The field of olefin metathesis has grown to include organometallic chemists who strive to develop more efficient catalysts and to understand their mechanism of activity and decomposition, synthetic organic chemists who construct complex molecules utilizing existing catalysts and continually find challenging reactions in need of more efficient catalysts, and polymer chemists who utilize current catalysts to synthesize polymers with an ever-widening array of functional groups and structures in a controlled manner. This thesis describes the exploration of new ligands for olefin metathesis catalysts and the investigation of the model compounds of olefin metathesis reaction intermediates. Chapter 2 describes the synthesis, characterization, activity and kinetic selectivity of ruthenium olefin metathesis complexes bearing cyclic (alkyl)(amino)carbenes (CAACs). The activity of phosphine-free CAAC-ruthenium complexes is significantly affected by steric interactions. By decreasing the steric bulk of the ligand, a new catalyst with activity comparable to that of existing NHC-ruthenium (N-heterocyclic carbene) complexes has been synthesized. Additionally, these complexes exhibit unusual E/Z-diastereoselectivity and ethenolysis selectivity relative to previously studied NHC-ruthenium complexes. Chapter 3 describes the exploration of 3- and 6-membered carbenes as ligands for ruthenium olefin metathesis complexes. Stable silver-cyclopropenylidene adducts were synthesized and utilized as carbene transfer reagents in the presence of ruthenium precursors. Although good conversions were observed, isolation of cyclopropenylidene-ruthenium complexes was unsuccessful. Ruthenium complexes of 6-membered ‘borazine’-like carbenes were isolated, characterized and evaluated for ring-closing metathesis activity. Chapter 4 describes the development of a model system to study ruthenium-olefin complexes relevant to the mechanism of olefin metathesis. Upon addition of the ligand precursor 1,2-divinylbenzene to (H₂IMes)(py₂)(Cl)₂Ru=CHPh (H₂IMes = 1,3-dimesityl-4,5-dihydroimidazol-2-ylidene), two ruthenium-olefin adducts are formed. Based on ¹H NMR spectroscopy experiments and X-ray crystallographic analysis, the solution phase and solid-state structure of these complexes is assigned. Exploration of the generality of these observations through variation of the N-heterocyclic carbene ligand and the ligand precursor are also presented. Appendix 1 describes the screening of transitional-metal salts and ligands for the non-oxidative hydration of styrene. Appendix 2 describes the investigation of a prior report of intramolecular olefin hydroalkoxylation with ruthenium, copper and silver salts. Appendix 3 describes the evaluation of chiral NHCs as ligands for ruthenium and rhodium hydrosilylation catalysts. Appendix 4 describes the investigation of tin(II) halides as ligands for ruthenium olefin metathesis catalysts. Appendix 5 contains X-ray crystallographic analysis parameters of the structures presented in this thesis.</p

Ruthenium-Olefin Complexes: Effect of Ligand Variation upon Geometry

The development of a model system to study ruthenium-olefin complexes relevant to the mechanism of olefin metathesis has been reported recently. Upon addition of the ligand precursor 1,2-divinylbenzene to [RuCl2(Py)2(H2IMes)(CHPh)] (H2IMes=1,3-dimesityl-4,5-dihydroimidazol-2-ylidene), two ruthenium-olefin adducts are formed. Based on 1H NMR spectroscopy experiments and X-ray crystallographic analysis, these complexes are assigned as side-bound isomers in which the olefin and H2IMes ligands are coordinated cis to each other. Herein is reported an investigation of the generality of these observations through variation of the N-heterocyclic carbene ligand and the ligand precursor

Model Compounds of Ruthenium−Alkene Intermediates in Olefin Metathesis Reactions

The development of a model system to study ruthenium−olefin complexes relevant to the mechanism of olefin metathesis is reported. Upon addition of 1,2-divinylbenzene to (H_2IMes)(py_2)(Cl)_2Ru CHPh (H_2IMes = 1,3-dimesityl-4,5-dihydroimidazol-2-ylidene), two ruthenium−olefin adducts are formed. On the basis of ^1H NMR spectroscopy experiments and X-ray crystallographic analysis, these complexes are assigned as side-bound isomers in which the olefin and H_2IMes ligands are coordinated cis to each other. The dynamic interconversion of these two ruthenium complexes was determined to have a barrier of 19.1 ± 0.1 kcal/mol

Synthesis and reactivity of olefin metathesis catalysts bearing cyclic (alkyl) (amino) carbenes

All it's CAACed up to be! Cyclic (alkyl)(amino)carbenes (CAACs) can be used as ligands for olefin metathesis catalysis. A dramatic steric effect of the N-aryl group of the CAAC on catalyst activity was observed and utilized to develop a new catalyst with activity comparable to standard commercially available catalysts

Kinetic Selectivity of Olefin Metathesis Catalysts Bearing Cyclic (Alkyl)(Amino)Carbenes

The evaluation of ruthenium olefin metathesis catalysts 4–6 bearing cyclic (alkyl)(amino)carbenes (CAACs) in the cross-metathesis of cis-1,4-diacetoxy-2-butene (7) with allylbenzene (8) and the ethenolysis of methyl oleate (11) is reported. Relative to most NHC-substituted complexes, CAAC-substituted catalysts exhibit lower E/Z ratios (3:1 at 70% conversion) in the cross-metathesis of 7 and 8. Additionally, complexes 4–6 demonstrate good selectivity for the formation of terminal olefins versus internal olefins in the ethenolysis of 11. Indeed, complex 6 achieved 35 000 TONs, the highest recorded to date. CAAC-substituted complexes exhibit markedly different kinetic selectivity than most NHC-substituted complexes

Participation in Decision Making as a Property of Complex Adaptive Systems: Developing and Testing a Measure

Objectives. To (1) describe participation in decision-making as a systems-level property of complex adaptive systems and (2) present empirical evidence of reliability and validity of a corresponding measure. Method. Study 1 was a mail survey of a single respondent (administrators or directors of nursing) in each of 197 nursing homes. Study 2 was a field study using random, proportionally stratified sampling procedure that included 195 organizations with 3,968 respondents. Analysis. In Study 1, we analyzed the data to reduce the number of scale items and establish initial reliability and validity. In Study 2, we strengthened the psychometric test using a large sample. Results. Results demonstrated validity and reliability of the participation in decision-making instrument (PDMI) while measuring participation of workers in two distinct job categories (RNs and CNAs). We established reliability at the organizational level aggregated items scores.We established validity of the multidimensional properties using convergent and discriminant validity and confirmatory factor analysis. Conclusions. Participation in decision making, when modeled as a systems level property of organization, has multiple dimensions and is more complex than is being traditionally measured. Managers can use this model to form decision teams that maximize the depth and breadth of expertise needed and to foster connection among them

Ruthenium-based olefin metathesis catalysts bearing new N-heterocyclic carbenes

Olefin metathesis catalysts based on the L2X2Ru=CHR scaffold have contributed significantly to the expanding spectrum of olefin metathesis applications. Recent work has shown that catalysts bearing an N-heterocyclic carbene (NHC) ligand exhibit enhancecl metathesis activity over previous ruthenium-based catalysts. The synthesis and activity of olefin metathesis catalysts containing new NHC ligands will be presented

Model compounds for olefin metathesis intermediates: Synthesis and characterization of ruthenium-olefin complexes

Recent studies from our group have led to a better understanding of the mechanism of ruthenium-mediated olefin metathesis, including the dissociative nature of initiation and the influence of neutral ligands on initiation rates. However, little is known about the orientation and site of olefin binding. We have synthesized and characterized by NMR and X-ray crystallog. ruthenium-olefin complexes as model compds.; our initial results will be presented