Mechanistic Studies of Pd(II)−α-Diimine-Catalyzed Olefin Polymerizations1
30 Jun 2000-Journal of the American Chemical Society (American Chemical Society)-Vol. 122, Iss: 28, pp 6686-6700
TL;DR: In this article, mechanistic studies of olefin polymerizations catalyzed by aryl-substituted α-diimine−Pd(II) complexes are presented.
Abstract: Mechanistic studies of olefin polymerizations catalyzed by aryl-substituted α-diimine−Pd(II) complexes are presented. Syntheses of several cationic catalyst precursors, [(N∧N)Pd(CH3)(OEt2)]BAr‘4 (N∧N = aryl-substituted α-diimine, Ar‘ = 3,5-(CF3)2C6H3), are described. X-ray structural analyses of [ArNC(H)C(H)NAr]Pd(CH3)(Cl) and [ArNC(Me)C(Me)NAr]Pd(CH3)2 (Ar = 2,6-(iPr)2C6H3) illustrate that o-aryl substituents crowd axial sites in these square planar complexes. Low-temperature NMR studies show that the alkyl olefin complexes, (N∧N)Pd(R)(olefin)+, are the catalyst resting states and that the barriers to migratory insertions lie in the range 17−19 kcal/mol. Following migratory insertion, the cationic palladium alkyl complexes (N∧N)Pd(alkyl)+ formed are β-agostic species which exhibit facile metal migration along the chain (“chain walking”) via β-hydride elimination/readdition reactions. Model studies using palladium−n-propyl and −isopropyl systems provide mechanistic details of this process, which is respon...
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TL;DR: The graph below shows the progression of monoanionic and non-monoanionic ligands through the history of synthesis, as well as some of the properties that have been identified since the discovery of R-Diimine.
Abstract: B. Anionic Ligands 302 IX. Group 9 Catalysts 302 X. Group 10 Catalysts 303 A. Neutral Ligands 303 1. R-Diimine and Related Ligands 303 2. Other Neutral Nitrogen-Based Ligands 304 3. Chelating Phosphorus-Based Ligands 304 B. Monoanionic Ligands 305 1. [PO] Chelates 305 2. [NO] Chelates 306 3. Other Monoanionic Ligands 306 4. Carbon-Based Ligands 306 XI. Group 11 Catalysts 307 XII. Group 12 Catalysts 307 XIII. Group 13 Catalysts 307 XIV. Summary and Outlook 308 XV. Glossary 308 XVI. References 308
2,369 citations
TL;DR: The impact of agostic interactions (i.e., 3-center–2-electron MHC bonds) on the structures and reactivity of organotransition metal compounds is reviewed.
Abstract: The impact of agostic interactions (i.e., 3-center-2-electron M-H-C bonds) on the structures and reactivity of organotransition metal compounds is reviewed.
878 citations
TL;DR: Akifumi Nakamura’s research interests include synthetic organic chemistry, organometallic chemistry, computational chemistry, and polymer chemistry.
Abstract: numerous polyethylene or polypropylene compounds have been synthesized by metal-catalyzed coordination-insertion polymerization. On the other hand, organometallic catalysts * To whom correspondence should be addressed. E-mail: nozaki@chembio.t.utokyo.ac.jp. Akifumi Nakamura (left) was born in 1984 in Kanagawa, Japan. He received his B.S. degree in 2007 and M.S. degree in 2009 from the University of Tokyo under the guidance of Professor Kyoko Nozaki. During that time he joined Professor Keiji Morokuma’s group at Kyoto University as a visiting student. In 2009, he started his Ph.D. study at the University of Tokyo under the guidance of Professor Kyoko Nozaki. He is also a research fellow of the Japan Society for the Promotion of Science. His research interests include synthetic organic chemistry, organometallic chemistry, computational chemistry, and polymer chemistry.
690 citations
511 citations
TL;DR: The aim of this review was to establish ana-C2v-Ligated Catalysts as a stand-alone database of Lanthanide Complexes with a focus on the latter stages of their development in the second half of the 1990s.
Abstract: 1.3. Scope of Review 5161 2. Methacrylate Polymerization 5161 2.1. Lanthanide Complexes 5161 2.1.1. Nonbridged Lanthanocenes 5161 2.1.2. ansa-Lanthanocenes 5164 2.1.3. Half-Lanthanocenes 5166 2.1.4. Non-lanthanocenes 5166 2.2. Group 4 Metallocenes 5170 2.2.1. Nonbridged Catalysts 5170 2.2.2. ansa-C2v-Ligated Catalysts 5173 2.2.3. ansa-C2-Ligated Catalysts 5173 2.2.4. ansa-C1-Ligated Catalysts 5176 2.2.5. ansa-Cs-Ligated Catalysts 5177 2.2.6. Constrained Geometry Catalysts 5178 2.2.7. Half-Metallocene Catalysts 5180 2.2.8. Supported Catalysts 5180 2.3. Other Metallocene Catalysts 5180 2.4. Nonmetallocene Catalysts 5181 2.4.1. Group 1 and 2 Catalysts 5181 2.4.2. Group 13 Catalysts 5183 2.4.3. Group 14 Catalysts 5186 2.4.4. Transition-Metal Catalysts 5187 3. Acrylate Polymerization 5188 3.1. Lanthanocenes 5188 3.2. Group 4 Metallocenes 5189 3.3. Nonmetallocenes 5190 4. Acrylamide and Methacrylamide Polymerization 5191 4.1. Acrylamides 5191 4.2. Methacrylamides 5192 4.3. Asymmetric Polymerization 5193 5. Acrylonitrile and Vinyl Ketone Polymerization 5196 5.1. Acrylonitrile 5196 5.2. Vinyl Ketones 5196 6. Copolymerization 5197 6.1. Polar-Nonpolar Block Copolymers 5197 6.2. Polar-Nonpolar Random Copolymers 5199 6.3. Polar-Polar Copolymers 5204 7. Ion-Pairing Polymerization 5206 8. Summary and Outlook 5208 9. Acknowledgments 5208 10. References 5208
460 citations
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TL;DR: This procedure provides a nonhazardous alternative to distillations and vacuum transfers and does not require undue supervision or cooling, yet allows for the rapid collection of large quantities of extremely pure solvents on demand.
2,663 citations
TL;DR: A family of catalysts has been developed whose members are tolerant of both heteroatoms and less pure starting materials, and which produce high-molecular-weight polyethylene, polymerize functionalized olefins, and require no cocatalyst.
Abstract: More than half of the 170 million metric tons of polymers produced each year are polyolefins. Current technology uses highly active cationic catalysts, which suffer from an inability to tolerate heteroatoms such as oxygen, nitrogen, and sulfur. These systems require scrupulously clean starting materials and activating cocatalysts. A family of catalysts has been developed whose members are tolerant of both heteroatoms and less pure starting materials. These heteroatom-tolerant neutral late transition metal complexes are in fact highly active systems that produce high-molecular-weight polyethylene, polymerize functionalized olefins, and require no cocatalyst.
999 citations
TL;DR: In this article, the effects of reaction conditions and catalyst structure on the copolymerization reaction were rationalized, and the effect of the acrylate comonomer at the ends of branches as −CH2CH2C(O)OMe groups was analyzed.
Abstract: Mechanistic aspects of palladium-catalyzed insertion copolymerizations of ethylene and α-olefins with methyl acrylate to give high molar mass polymers are described. Complexes [(N∧N)Pd(CH2)3C(O)OMe]BAr‘4 (2) or [(N∧N)Pd(CH3)(L)]BAr‘4 (1: L = OEt2; 3: L ⋮ NCMe; 4: L ⋮ NCAr‘) (N∧N ≡ ArNC(R)−C(R)NAr, e.g., Ar ⋮ 2,6-C6H3(i-Pr)2, R ⋮ H (a), Me (b); Ar‘ ⋮ 3,5-C6H3(CF3)2) with bulky substituted α-diimine ligands were used as catalyst precursors. The copolymers are highly branched, the acrylate comonomer being incorporated predominantly at the ends of branches as −CH2CH2C(O)OMe groups. The effects of reaction conditions and catalyst structure on the copolymerization reaction are rationalized. Low-temperature NMR studies show that migratory insertion in the η2-methyl acrylate (MA) complex [(N∧N)PdMe{H2CCHC(O)OMe}]+ (5) occurs to give initially the 2,1-insertion product [(N∧N)PdCH(CH2CH3)C(O)OMe]+ (6), which rearranges stepwise to yield 2 as the final product upon warming to −20 °C. Activation parameters (ΔH⧧ = ...
857 citations
TL;DR: A review of nickel-catalyzed reactions can be found in this article, where some mechanistic aspects are also dealt with, such as cyclic and linear oligomerization and polymerization reactions of monoenes and dienes.
Abstract: The efficiency and future development of the chemical industry are closely linked to catalysis. It has been estimated, for example, that 60 to 70% of all industrial chemicals have involved the use of a catalyst at some point during their manufacture. In the past two decades the share of the market credited to homogeneous transition metal catalysis increasead to 10–15%. Besides cobalt, which is used mainly in hydroformylation reactions, nickel is the most frequently used metal. Many carbon–carbon bond formation reactions can be carried out with high selectivity if catalyzed by organonickel complexes. Such reactions include, inter alia, carbonylation reactions, cyclic and linear oligomerization and polymerization reactions of monoenes and dienes, and hydrocyanation reactions. It was Reppe and Wilke who pioneered and shaped the field of homogeneous nickel catalysis. Great impetus was also given to the development of organonickel chemistry by Wilke and his students. Research in this area has contributed immensely towards an understanding of the reactions involved in catalysis.—This review is primarily concerned with nickel-catalyzed reactions which are of interest both preparatively and industrially; some mechanistic aspects are also dealt with.
537 citations