J. Appl. Cryst.の発刊に際して

1. Advantages of Chemical Redox Agents 878 2. Disadvantages of Chemical Redox Agents 879 C. Potentials in Nonaqueous Solvents 879 D. Reversible vs Irreversible ET Reagents 879 E. Categorization of Reagent Strength 881 II. Oxidants 881 A. Inorganic 881 1. Metal and Metal Complex Oxidants 881 2. Main Group Oxidants 887 B. Organic 891 1. Radical Cations 891 2. Carbocations 893 3. Cyanocarbons and Related Electron-Rich Compounds 894

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Chemical Redox Agents for Organometallic Chemistry

Once considered the 'holy grail' of organometallic chemistry, synthetically useful reactions employing C-H bond activation have increasingly been developed and applied to natural product and drug synthesis over the past decade. The ubiquity and relative low cost of hydrocarbons makes C-H bond functionalization an attractive alternative to classical C-C bond forming reactions such as cross-coupling, which require organohalides and organometallic reagents. In addition to providing an atom economical alternative to standard cross - coupling strategies, C-H bond functionalization also reduces the production of toxic by-products, thereby contributing to the growing field of reactions with decreased environmental impact. In the area of C-C bond forming reactions that proceed via a C-H activation mechanism, rhodium catalysts stand out for their functional group tolerance and wide range of synthetic utility. Over the course of the last decade, many Rh-catalyzed methods for heteroatom-directed C-H bond functionalization have been reported and will be the focus of this review. Material appearing in the literature prior to 2001 has been reviewed previously and will only be introduced as background when necessary. The synthesis of complex molecules from relatively simple precursors has long been a goal for many organic chemists. The ability to selectively functionalize a molecule with minimal pre-activation can streamline syntheses and expand the opportunities to explore the utility of complex molecules in areas ranging from the pharmaceutical industry to materials science. Indeed, the issue of selectivity is paramount in the development of all C-H bond functionalization methods. Several groups have developed elegant approaches towards achieving selectivity in molecules that possess many sterically and electronically similar C-H bonds. Many of these approaches are discussed in detail in the accompanying articles in this special issue of Chemical Reviews. One approach that has seen widespread success involves the use of a proximal heteroatom that serves as a directing group for the selective functionalization of a specific C-H bond. In a survey of examples of heteroatom-directed Rh catalysis, two mechanistically distinct reaction pathways are revealed. In one case, the heteroatom acts as a chelator to bind the Rh catalyst, facilitating reactivity at a proximal site. In this case, the formation of a five-membered metallacycle provides a favorable driving force in inducing reactivity at the desired location. In the other case, the heteroatom initially coordinates the Rh catalyst and then acts to stabilize the formation of a metal-carbon bond at a proximal site. A true test of the utility of a synthetic method is in its application to the synthesis of natural products or complex molecules. Several groups have demonstrated the applicability of C-H bond functionalization reactions towards complex molecule synthesis. Target-oriented synthesis provides a platform to test the effectiveness of a method in unique chemical and steric environments. In this respect, Rh-catalyzed methods for C-H bond functionalization stand out, with several syntheses being described in the literature that utilize C-H bond functionalization in a key step. These syntheses are highlighted following the discussion of the method they employ.

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Rhodium-Catalyzed C-C Bond Formation via Heteroatom-Directed C-H Bond Activation

Late-metal catalysts for ethylene homo- and copolymerization.

N-Heterocyclic Carbenes in Late Transition Metal Catalysis

This paper describes the synthesis of base-free (C5R5)2Zr(OtBu)+ cations, the direct observation of nonchelated alkene and alkyne adducts of these cations, and studies of the thermodynamic and dynamic properties of these novel species. Reaction of (Cp‘ = C5H4Me) with tert-butyl alcohol followed by [Ph3C][B(C6F5)4] in benzene yields [ ][B(C6F5)4] (1), which exists as solvent adducts in C6D5Cl and CD2Cl2 solutions. Addition of ligands L (L = ethylene, propylene, propyne, 2-butyne, CO, phenylacetylene, allene, 1-hexene, cis-2-butene) to 1 in CD2Cl2 at −89 °C results in reversible formation of adducts. NMR data for (4) indicate that the propylene coordinates unsymmetrically and is polarized with positive charge buildup at Cint. Equilibrium constants, defined by Keq = [Zr−L][1]-1[L]-1, vary in the order CO > propyne > 2-butyne > phenylacetylene > ethylene > allene > propylene > 1-hexene > cis-2-butene > vinyl chloride. Loss of L from to give 1 appears to proceed via associative displacement by CD2Cl2 in most c...

Coordination of alkenes and alkynes to a cationic d0 zirconocene alkoxide complex

A process of preparing in high yield ansa-metallocene complexes and rac-ansa-metallocene complexes by reacting an ansa-bis-cyclopentadiene compound with a metal amide complex.

https://ir.uiowa.edu/cgi/viewcontent.cgi?article=1159&context=patents

Synthesis of ANSA-metallocene catalysts

Zirconium-mediated reactions of carbon monoxide and alkynes. Insertion chemistry of cationic Zr(IV) .eta.2-acyl and alkenyl complexes

On etudie les reactions sans precedent de (C 5 H 5 ) 2 Zr[Ru(CO) 2 (C 5 H 5 )] 2 avec des coordinats ajoutes (ethylene, PMe 3 , etc) qui conduisent a l'expulsion de (C 5 H 5 )Ru(CO) 2 H et formation de produits C 5 H 4 Zr ou intermediaires

Ligand-induced reactions of a directly bonded early-late transition metal complex involving reversible cleavage of a zirconium-ruthenium bond with expulsion of a ruthenium hydride

Richard F. Jordan

Papers

Coordination of alkenes and alkynes to a cationic d0 zirconocene alkoxide complex

Synthesis of ANSA-metallocene catalysts

Zirconium-mediated reactions of carbon monoxide and alkynes. Insertion chemistry of cationic Zr(IV) .eta.2-acyl and alkenyl complexes

Ligand-induced reactions of a directly bonded early-late transition metal complex involving reversible cleavage of a zirconium-ruthenium bond with expulsion of a ruthenium hydride

Formation of novel ansa-carborane-alkoxide complexes by carbonylation of (C5Me5)(η5-C2B9H 11)TiMe