High oxidation state multiple metal-carbon bonds.

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.

Metallabenzenes are analogues of benzene in which one of the benzene CH groups has been formally replaced by a transition metal and its ancillary ligands. This article summarises some of the important recent highlights of metallabenzene chemistry including the synthesis of the first platinabenzene, the synthesis of the first metallanaphthalene (an iridanaphthalene) and the development of new synthetic routes to metallabenzenes. The results of a number of theoretical studies that provide important insights into the nature and reactivity of metallabenzenes are discussed and in the concluding section some of the immediate goals and challenges in this field are identified.

Metallabenzenes and metallabenzenoids

An overview of modeling studies in HDS, HDN and HDO catalysis

The concept of aromaticity was initially introduced in chemistry to account for the stability, reactivity, molecular structures, and other properties of many unsaturated organic compounds. Despite that, it has been extended to other species with mobile electrons including saturated systems, transition structures, and even inorganic molecules. In this review, we focus on the aromaticity of a particular family of organometallic compounds known as metallabenzenes, which are characterized by the formal replacement of a CH group in benzene by an isolobal transition metal fragment. In addition, aromaticity of related compounds such as heterometallabenzenes is considered as well. To this end, we shall describe herein the insight gained by the available experimental data as well as by the application of the state-of-the-art computational methods developed as descriptors for aromaticity together with a critical evaluation of their performance to quantitatively estimate the strength of aromaticity of these systems.

Aromaticity of metallabenzenes and related compounds

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

Pyridine degradation intermediates as models for hydrodenitrogenation catalysis : preparation and properties of a metallapyridine complex

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

Paula M. Briggs

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

Pyridine degradation intermediates as models for hydrodenitrogenation catalysis : preparation and properties of a metallapyridine complex

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

Isolation and characterization of a monomeric metallapyridine complex: Models for pyridine hydrodenitrogenation intermediates

Unusual alkylidene ligands: Synthesis and structure of the cyclopentadienylidene complex [(η5-C5H5)Ta(NEt2) 2(=C5H4)]