G. van Koten

Bio: G. van Koten is an academic researcher from Utrecht University. The author has contributed to research in topics: Palladium & Aryl. The author has an hindex of 37, co-authored 140 publications receiving 4036 citations. Previous affiliations of G. van Koten include Centre national de la recherche scientifique & A. N. Nesmeyanov Institute of Organoelement Compounds.

Diaminoarylnickel(II) “Pincer” Complexes: Mechanistic Considerations in the Kharasch Addition Reaction, Controlled Polymerization, and Dendrimeric Transition Metal Catalysts

Abstract: It was in 1945 that researchers at the University of Chicago first reported that carbon tetrachloride could be added directly to olefinic double bonds (eq 1). This process was catalyzed by peroxides as radical initiators.1 This simple reaction is a classic example of anti-Markovnikov addition and has become known as the Kharasch addition reaction,2 in honor of its discoverer, M. S. Kharasch. In the late 1930s, Kharasch and independently Hey and Waters3 had presented a free-radical mechanism to explain this kind of addition reaction, and it is now generally accepted to occur in this manner.4 The use of the Kharasch addition is, however, often overlooked in synthetic organic chemistry although it has been employed in a number of specific syntheses. A few examples of these are shown in eqs 2-6.5-7 Both interand intramolecular Kharasch addition8 is possible.

Mechanisms of d8 organometallic reactions involving electrophiles and intramolecular assistance by nucleophiles

Abstract: The most attractive and fundamental interaction between metal centers and organic molecules that could lead to new functionalization at carbon is direct activation of the C-H bonds of hydrocarbons In particular, transition metal complexes have been used not only in pioneering studies of the synthesis or detection of complexes resulting from C-H activation, but also in cyclometalation chemistry In most of the reactions reviewed here intramolecular assistance by a nucleophile plays a major role in the mechanism and/or in the stabilization of products, and thus they are relevant also to the development of a better understanding of cyclometalation reactions This Account summarizes recent research that implicates the occurrence of electrophilic attack at the metal center in reactions leading to metal-electrophile bonding

Intramolecular Coordination in Organotin Chemistry

Abstract: Publisher Summary This chapter overviews organotin compounds containing C,Y-chelating ligands particularly, (1) structures in the solid state, (2) fluxional behavior in solution, and (3) stereochemical aspects. Attention is also given to the enhanced reactivity of tin–carbon bonds in tetraorganotin compounds as a result of intramolecular coordination. The first example of an organotin compound having C,Y-chelating ligands, i.e., bis [1, 2-bis(ethoxycarbonyl)ethyl]tin dibromide, for which the structure in the solid state was unambiguously established by an X-ray crystal structure determination. By using the steric and electronic properties of C,Y-chelating ligands, organometallic compounds that have interesting properties and special reactivities can be isolated. Special features of some of these compounds are (1) stabilization of organometallic compounds in which the metal has an unusual oxidation number, e.g., Fe(II1), Co(I1), and Ni(II1); (2) the trapping of organometallic species that are supposed to be intermediates in reactions, e.g., organoplatinum compounds in which a di-iodine molecule is coordinated end-on to platinum as a first step in oxidative-addition reactions; (3) the use of a novel organonickel compound as a catalyst in the selective Karasch addition of polyhaloalkanes to olefines; and (4) the unexpected reactivity of organocopper compounds toward acetylenes.

Palladium(II)-catalyzed C-H activation/C-C cross-coupling reactions: versatility and practicality.

Abstract: Pick your Pd partners: A number of catalytic systems have been developed for palladium-catalyzed CH activation/CC bond formation. Recent studies concerning the palladium(II)-catalyzed coupling of CH bonds with organometallic reagents through a PdII/Pd0 catalytic cycle are discussed (see scheme), and the versatility and practicality of this new mode of catalysis are presented. Unaddressed questions and the potential for development in the field are also addressed. In the past decade, palladium-catalyzed CH activation/CC bond-forming reactions have emerged as promising new catalytic transformations; however, development in this field is still at an early stage compared to the state of the art in cross-coupling reactions using aryl and alkyl halides. This Review begins with a brief introduction of four extensively investigated modes of catalysis for forming CC bonds from CH bonds: PdII/Pd0, PdII/PdIV, Pd0/PdII/PdIV, and Pd0/PdII catalysis. A more detailed discussion is then directed towards the recent development of palladium(II)-catalyzed coupling of CH bonds with organometallic reagents through a PdII/Pd0 catalytic cycle. Despite the progress made to date, improving the versatility and practicality of this new reaction remains a tremendous challenge.

Dendrimer-Encapsulated Metal Nanoparticles: Synthesis, Characterization, and Applications to Catalysis

Abstract: This Account reports the synthesis and characterization of dendrimer-encapsulated metal nanoparticles and their applications to catalysis. These materials are prepared by sequestering metal ions within dendrimers followed by chemical reduction to yield the corresponding zerovalent metal nanoparticle. The size of such particles depends on the number of metal ions initially loaded into the dendrimer. Intradendrimer hydrogenation and carbon−carbon coupling reactions in water, organic solvents, biphasic fluorous/organic solvents, and supercritical CO2 are also described.