One of the most exciting developments in the areas of catalysis, organometallic chemistry, and polymer science in recent years has been the intense exploration and commercialization of new polymerization technologies based on single-site and metallocene coordination olefin polymerization catalysts.1 The vast number of specifically designed/synthesized transition metal complexes (catalyst precursors) and main-group organometallic compounds (cocatalysts) allows unprecedented control over polymer microstructure, the generation of new polymer architectures, and the development of new polymerization reactions. Commercialization of new generations of single-site and metallocene catalyst-based technologies has provided the multibillion pound per year polyolefins industry with the ability to deliver a wide range of new and innovative olefin-based polymers having improved properties.2-4 The intense industrial activity in the field and the challenges to our basic understanding that have come to light have in turn 1391 Chem. Rev. 2000, 100, 1391−1434

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Cocatalysts for Metal-Catalyzed Olefin Polymerization: Activators, Activation Processes, and Structure−Activity Relationships

Advances in the chemistry of tetrahydroquinolines.

Novel catalysts for advanced hydroprocessing: transition metal phosphides

Kunbing Ouyang,†,‡ Wei Hao,† Wen-Xiong Zhang,*,†,§ and Zhenfeng Xi† †Beijing National Laboratory for Molecular Sciences (BNLMS), Key Laboratory of Bioorganic Chemistry and Molecular Engineering of the Ministry of Education, College of Chemistry, Peking University, Beijing 100871, China ‡Institute of Chemistry, Chinese Academy of Sciences (CAS), Beijing 100190, China State Key Laboratory of Elemento-Organic Chemistry, Nankai University, Tianjin 300071, China

Transition-Metal-Catalyzed Cleavage of C-N Single Bonds.

A high level of hydrodenitrogenation (HDN) is required to achieve a desirable conversion of other hydroprocessing reactions. This results from a strong adsorption of nitrogen‐containing compounds on catalytic sites that slows down the hydrogen activation process and hinders the adsorption of other reactants. Studies on model compounds and real feeds indicate that less than 50 ppm of nitrogen in the feed can poison catalytic sites. Kinetic studies determined adsorption constants of various nitrogen‐containing compounds and concluded that at least four different catalytic sites are required to interpret experimental observations in contrast with a dual site site≅concept, which only considered two sites. The advancements in experimental techniques allowed identification of products formed during very early stages of hydrodenitrogenation. These results confirmed that the removal of the amino group from saturated amines, as the last step in hydrodenitrogenation, is governed by the type of carbon to which the a...

Hydrodenitrogenation of Petroleum

The reaction of the {eta}{sup 2}(N,C)-pyridine complex with LiBEt{sub 3}H affords the C-N bond scission product (2). The reactions of (1) with carbon nucleophiles RLi or RMgX provide the alkyl derivatives [R = Me (3), Et (4), {sup n}Pr (5), {sup n}Bu (6), and CH{sub 2}SiMe{sub 3} (7)]. Kinetic and mechanistic studies of the 3 {yields} 8 rearrangement reveal that methyl migration is strictly intramolecular. The reactions of this model system delineate one process by which heterocyclic C-N bonds are cleaved and offer new insight as to how nitrogen heterocycles may be further degraded after C-N bond cleavage in hydrodenitrogenation catalysis. 74 refs., 7 figs., 5 tabs.

Carbon-Nitrogen Bond Cleavage in an .eta.2(N,C)-Pyridine Complex Induced by Intramolecular Metal-to-Ligand Alkyl Migration: Models for Hydrodenitrogenation Catalysis

The catalytic removal of sulfur and nitrogen from petroleum feedstocks and coal-derived liquids is essential to preclude the poisoning of hydrocracking and reforming catalysts and to reduce emissions of their oxides. Industrial hydrodenitrogenation (HDN) is typically effected over sulfided CoMo/Al{sub 2}O{sub 3} or NiMo/Al{sub 2}O{sub 3} under conditions which remove nitrogen as NH{sub 3}. The nitrogen-containing compounds which are most difficult to process are the aromatic heterocycles such as pyridine, quinoline, and indole derivatives. One central question in HDN catalysis which remains unresolved concerns how the strong C-N bonds in these heterocycles are cleaved. Herein the authors provide evidence for an {eta}{sup 1}(N){r_arrow}{eta}{sup 2}(N,C) bonding rearrangement in model HDN substrates and demonstrate that nucleophilic attack of an {eta}{sup 2}(N,C)-pyridine results in facile, regioselective C-N bond cleavage. 17 refs., 3 figs.

Regioselective carbon-nitrogen bond cleavage in an .eta.2(N,C)-coordinated pyridine and an .eta.1(N) .fwdarw. .eta.2(N,C) bonding rearrangment in coordinated quinoline: models for hydrodenitrogenation catalysis

Early-transition-metal-mediated [2+2+2] cycloadditions: formation and fragmentation of a reactive metallacyclopentadiene and its direct conversion to .eta.6-arene and .eta.2-pyridine complexes of tantalum

Homogeneous models for hydrodenitrogenation catalysis

Mechanistic Aspects of Carbon-Nitrogen Bond Cleavage in an .eta.2(N,C)-Pyridine Complex: Intimate Details of Metal to Ligand Aryl Migrations and Their Relevance to Hydrodenitrogenation Catalysis

Steven D. Gray

Papers

Carbon-Nitrogen Bond Cleavage in an .eta.2(N,C)-Pyridine Complex Induced by Intramolecular Metal-to-Ligand Alkyl Migration: Models for Hydrodenitrogenation Catalysis

Regioselective carbon-nitrogen bond cleavage in an .eta.2(N,C)-coordinated pyridine and an .eta.1(N) .fwdarw. .eta.2(N,C) bonding rearrangment in coordinated quinoline: models for hydrodenitrogenation catalysis

Early-transition-metal-mediated [2+2+2] cycloadditions: formation and fragmentation of a reactive metallacyclopentadiene and its direct conversion to .eta.6-arene and .eta.2-pyridine complexes of tantalum

Homogeneous models for hydrodenitrogenation catalysis

Mechanistic Aspects of Carbon-Nitrogen Bond Cleavage in an .eta.2(N,C)-Pyridine Complex: Intimate Details of Metal to Ligand Aryl Migrations and Their Relevance to Hydrodenitrogenation Catalysis