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.

https://www.pnas.org/content/pnas/104/17/6908.full.pdf

Agostic interactions in transition metal compounds

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.

Coordination−Insertion Copolymerization of Fundamental Polar Monomers

3.1. The Reaction 3381 3.2. The Catalysts and the Carbene Source 3381 3.3. Achievements 3383 3.4. Selectivity and Mechanistic Considerations 3386 3.5. Future Development 3386 4. C-H Bond Functionalization by Nitrene Insertion 3387 4.1. The Reaction 3387 4.2. The Catalysts and the Nitrene Sources 3387 4.3. Development and Mechanistic Considerations 3388 4.4. Future Development 3389 5. C-H Bond Oxidations 3389 5.1. The Reaction and the Catalysts 3389 5.2. Development and Perspective 3390 6. Conclusions 3393 7. Acknowledgments 3393 8. References 3393

Coinage metal catalyzed C-H bond functionalization of hydrocarbons.

More than 50 years have passed since Ziegler and Natta shared the Nobel Prize in Chemistry for their discovery of olefin polymerization catalysts. The field of metal-catalysed polymerization has since matured, in no small part owing to the development of several high-performance catalysts. Although polymerization research has in many ways been driven by catalyst development, this has often occurred as a result of trial and error discovery of a promising motif, followed by extensive tuning of the steric and electronic properties of the ligand(s) present in the lead complex. Recently, some alternative design strategies have emerged that afforded new classes of olefin polymerization catalysts. This Perspective highlights recently designed catalyst motifs and the novel reactivity patterns they enable. Special attention is given to methods specifically designed for the copolymerization of ethylene with polar-functionalized co-monomers — challenging reactions that showcase these creatively designed catalyst motifs. The development of high-performance olefin polymerization catalysts is a major driving force in polyolefin studies. This Perspective discusses some alternative strategies for catalyst design — strategies in which existing systems are tuned beyond merely modifying the electronic and steric properties.

Designing catalysts for olefin polymerization and copolymerization: beyond electronic and steric tuning

http://www.paginaspersonales.unam.mx/files/996/Publica_20120530220609.pdf

Ethylene oligomerization, homopolymerization and copolymerization by iron and cobalt catalysts with 2,6-(bis-organylimino)pyridyl ligands

The synthesis of a series of (α-diimine)NiR2 (R = Et, nPr) complexes via Grignard alkylation of the corresponding (α-diimine)NiBr2 precursors is presented. Protonation of these species by the oxonium acid [H(OEt2)2]+[BAr‘4]- at low temperatures yields cationic Ni(II) β-agostic alkyl complexes which model relevant intermediates present in nickel-catalyzed olefin polymerization reactions. The highly dynamic nature of these agostic alkyl cations is quantitatively addressed using NMR line broadening techniques. Trapping of these complexes with ethylene provides cationic Ni alkyl ethylene species, which are used to determine rates of ethylene insertion into primary and secondary carbon centers. The Ni agostic alkyl cations are also trapped by CH3CN and Me2S to yield Ni(R)(L)+ (L = CH3CN, Me2S) complexes, and the dynamic behavior of these species in the presence of varied [L] is discussed. The kinetic data obtained from these experiments are used to present an overall picture of the ethylene polymerization mech...

Mechanistic Studies of Nickel(II) Alkyl Agostic Cations and Alkyl Ethylene Complexes: Investigations of Chain Propagation and Isomerization in (α-diimine)Ni(II)-Catalyzed Ethylene Polymerization

Vinyl acetate (VA) and vinyl trifluoroacetate (VAf) react with [(N∧N)Pd(Me)(L)][X] (M = Pd, Ni, (N∧N) = N,N‘-1,2-acenaphthylenediylidene bis(2,6-dimethyl aniline), Arf = 3,5-trifluoromethyl phenyl, L = ArfCN, Et2O; X = B(Arf)4-, SbF6-) to form π-adducts 3 and 5 at −40 °C. Binding affinities relative to ethylene have been determined. Migratory insertion occurs in a 2,1 fashion (ΔG⧧ = 19.4 kcal/mol, 0 °C for VA, and 17.4 kcal/mol, −40 °C for VAf) to yield five-membered chelate complexes [(N∧N)Pd(κ2-CH(Et)(OC(O)CH3))]+, 4, and [(N∧N)Pd(κ2-CH(Et)(OC(O)CF3))]+, 6. When VA is added to [(N∧N)Ni(CH3)]+, an equilibrium mixture of an η2 olefin complex, 8c, and a κ-oxygen complex, 8o, results. Insertion occurs from the η2 olefin complex, 8c (ΔG⧧ = 15.5 kcal/mol, −51 °C), in both a 2,1 and a 1,2 fashion to generate a mixture of five- and six-membered chelates, 92,1 and 91,2. VAf inserts into the Ni−CH3 bond (−80 °C) to form a five-membered chelate with no detectable intermediate. Thermolysis of the Pd chelates result...

Reactions of vinyl acetate and vinyl trifluoroacetate with cationic diimine Pd(II) and Ni(II) alkyl complexes: identification of problems connected with copolymerizations of these monomers with ethylene.

Ni(II)-Catalyzed Polymerization of trans-2-Butene

Copolymerizations of ethylene with vinyltrialkoxysilanes using cationic (α-diimine)Ni(Me)(CH3CN)+ complexes 4a,b/B(C6F5)3 yield high molecular weight copolymers exhibiting highly branched to nearly linear backbones depending on reaction conditions and catalyst choice. Polymerizations are first-order in ethylene pressure and inverse-order in silane concentration. Microstructural analysis of the copolymers reveals both in-chain and chain-end incorporation of −Si(OR)3 groups whose ratios depend on temperature and ethylene pressure. Detailed low-temperature NMR spectroscopic investigations show that well-defined complex 3b (α-diimine)Ni(Me)(OEt2)+ reacts rapidly at −60 °C with vinyltrialkoxysilanes via both 2,1 and 1,2 insertion pathways to yield 4- and 5-membered chelates, respectively. Such chelates are the major catalyst resting states but are in rapid equilibrium with ethylene-opened chelates, (α-diimine)Ni(R)(C2H4)+ complexes, the species responsible for chain growth. Chelate rearrangement via β-silyl el...

Nickel-Catalyzed Copolymerization of Ethylene and Vinyltrialkoxysilanes: Catalytic Production of Cross-Linkable Polyethylene and Elucidation of the Chain-Growth Mechanism

Laboratorio de Catalisis Homogenea, Departamento de Quimica y Ciencia de los Materiales, Unidad Asociada al CSIC, Campus de El Carmen s/n, Universidad de Huelva, 21007-Huelva, Spain; Department of Chemistry and Biochemistry, University of Delaware, Newark, Delaware 19716; Department of Chemistry, University of North Carolina, Chapel Hill, CB3290, Chapel Hill, North Carolina 27599; and Universitat Konstanz, Fachbereich Chemie, 78457 Konstanz, Germany

/pdf/controlled-copper-catalyzed-functionalization-of-polyolefins-4ssdl4e9sl.pdf

Mark D. Leatherman

Papers

Mechanistic Studies of Nickel(II) Alkyl Agostic Cations and Alkyl Ethylene Complexes: Investigations of Chain Propagation and Isomerization in (α-diimine)Ni(II)-Catalyzed Ethylene Polymerization

Reactions of vinyl acetate and vinyl trifluoroacetate with cationic diimine Pd(II) and Ni(II) alkyl complexes: identification of problems connected with copolymerizations of these monomers with ethylene.

Ni(II)-Catalyzed Polymerization of trans-2-Butene

Nickel-Catalyzed Copolymerization of Ethylene and Vinyltrialkoxysilanes: Catalytic Production of Cross-Linkable Polyethylene and Elucidation of the Chain-Growth Mechanism

Controlled, Copper-Catalyzed Functionalization of Polyolefins