Atom Transfer Radical Reactions Research Articles

Atom‐Transfer Radical Addition Reactions Catalyzed by RuCp* Complexes: A Mechanistic Study

Kinetic and spectroscopic analyses were performed to gain information about the mechanism of atom-transfer radical reactions catalyzed by the complexes [RuCl2Cp*(PPh3)] and [RuClCp*(PPh3)2] (Cp*=pentamethylcyclopentadienyl), in the presence and in the absence of the reducing agent magnesium. The reactions of styrene with ethyl trichloroacetate, ethyl dichloroacetate, or dichloroacetonitrile were used as test reactions. The results show that for substrates with high intrinsic reactivity, such as ethyl trichloroacetate, the oxidation state of the catalyst in the resting state is +3, and that the reaction is zero-order with respect to the halogenated compound. Furthermore, the kinetic data suggest that the metal catalyst is not directly involved in the rate-limiting step of the reaction.

Microwave-Assisted Ruthenium-Catalyzed Reactions

Since the first reports on the use of microwave irradiation to accelerate organic chemical transformations, a plethora of papers has been published in this field. In most examples, microwave heating has been shown to dramatically reduce reaction times, increase product yields, and enhance product purity by reducing unwanted side reactions compared with conventional heating methods. The present contribution aims at illustrating the advantages of this technology in homogeneous catalysis by ruthenium complexes and, when data are available, at comparing microwave-heated and conventionally heated experiments. Selected examples refer to olefin metathesis, isomerization reactions, 1,3-dipolar cycloadditions, atom transfer radical reactions, transfer hydrogenation reactions, and H/D exchange reactions.

Synthesis of Fluorous Nitrogen Ligands and Their Metal Complexes as Precatalysts for Applications in Alkane, Alkene, and Alcohol Oxidation, and Atom Transfer Radical Reactions

AbstractFor Abstract see ChemInform Abstract in Full Text.

Atom-transfer radical reactions catalyzed by a coordinatively unsaturated diruthenium amidinate, [(η 5-C 5Me 5)Ru(μ 2- i-PrN [dbnd]C(Me)N i-Pr)Ru(η 5-C 5Me 5)] +

Atom-transfer radical cyclization (ATRC) and addition (ATRA) catalyzed by a coordinatively unsaturated diruthenium amidinate complex 4 , [(η 5-C 5Me 5)Ru(μ 2- i-PrN C(Me)N i-Pr)Ru(η 5-C 5Me 5)] +, are investigated, and their features are compared with those of atom-transfer radical polymerization (ATRP). As an example of ATRC, a cationic diruthenium amidinate 4 is found to exhibit excellent catalytic reactivity for the cyclization of N-allyl α-halogenated acetamides including an alkaloid skeleton at ambient temperature. A catalytic species generated in situ from a halide complex, (η 5-C 5Me 5)Ru(μ 2- i-PrN C(Me)N i-Pr)Ru(η 5-C 5Me 5)(X) [X=Cl, Br] and sodium salts of weakly coordinating anions such as NaPF 6 and NaBPh 4 also shows high catalytic activity; this actually provides a solution for a problematic instability of 4 as the practical catalyst. The in situ-generated catalyst species 4 is also active towards the intermolecular ATRA of α,α,γ-trichlorinated γ-lactam with alkenes at rt to afford the corresponding α-alkylated γ-lactams in moderate yields. Examination of ATRP of methyl methacrylate (MMA) showed that both the isolated 4 [Y=PF 6] and in situ-generated 4 [Y=PF 6] are effective for the polymerization of MMA in the presence of 2-bromoisobutylate as the initiator. Use of the isolated catalyst results in controlled polymerization at initial stage of the reaction; in contrast, the polymerization with in situ-generated catalyst produces poly(MMA) with wide molecular weight distribution. The isolated catalyst 4 is powerful for the activation of a C–Br bond of macromolecule initiators; BrCMe 2CO 2[O(CH 2) 4] n - n-Bu ( M n=3800; M w/ M n=1.2) initiated ATRP of MMA even at 25 °C to afford the poly(THF)–poly(MMA) block copolymer of M n=26,000 and M w/ M n=1.2 with the aid of 4 . The roles of the coordinatively unsaturated ruthenium species for these reactions are discussed.

Ruthenium catalysts bearing N-heterocyclic carbene ligands in atom transfer radical reactions

The catalytic activity of ruthenium- p-cymene complexes bearing N-heterocyclic carbene ligands in atom transfer radical addition (ATRA) or polymerisation (ATRP) strongly depends on the substituents of the carbene ligand, thereby providing a nice illustration of the importance of organometallic engineering and ligand fine tuning in homogeneous catalysis.

Radical-mediated imidoylation of telluroglycosides. Insertion of isonitriles into the glycosidic carbontellurium bond

Telluroglycosides react with isonitriles under photo-thermal conditions to give 1-telluroimidoylglycosides. The reaction proceeds by atom transfer radical reaction to form an imidic CTe bond, which can be substituted to a CC bond and CO bond under oxidative conditions.