Intramolecular transfer reaction complexes

A new process developed by Institut Francais du Petrole produces butene-1 (1-butene) by dimerizing ethylene.A homogeneous catalyst system based on a titanium complex is used. The reaction is a concerted coupling of two molecules on a titanium atom, affording a titanium (IV) cyclic compound, which then decomposes to butene-1 by an intramolecular (3-hydrogen transfer reaction. ... 

Disiloxane, tetramesityl-, 3,206 Disproportionation iridium catalysts, 4,1159 Dissolution nuclear fuels, 6, 927 Distannene, 3,217 Distannoxane, 1,3-dichloro-, 3,207 Distibine, tetraphenyl-, 2,1008 Distibines, 2,1008 Disulfido ligands metal complexes, 2,531-540, 553 bonding, 2, 539 electron transfer, 2, 537 intramolecular redox reactions, 2,537 reactions, 2, 537... 

The elementary electrochemical reactions differ by the degree of their complexity. The simplest class of reactions is represented by the outer-sphere electron transfer reactions. An example of this type is the electron transfer reactions of complex ions. The electron transfer here does not result in a change of the composition of the reactants. Even a change in the intramolecular structure (inner-sphere reorganization) may be neglected in many cases. The only result of the electron transfer is then the change in the outer-sphere solvation of the reactants. The microscopic mechanism of this type of reaction is very close to that for the outer-sphere electron transfer in the bulk solution. Therefore, the latter is worth considering first. 

The interconversion between different spin states is closely related to the intersystem crossing process in excited states of transition-metal complexes. Hence, much of the interest in the rates of spin-state transitions arises from their relevance to a better understanding of intersystem crossing phenomena. The spin-state change can alternatively be described as an intramolecular electron transfer reaction [34], Therefore, rates of spin-state transitions may be employed to assess the effect of spin multiplicity changes on electron transfer rates. These aspects have been covered in some detail elsewhere [30]. 

An important contribution to silylium ion chemistry has been made by the group of Muller, who very recently published a series of papers describing the synthesis of intramolecularly stabilized silylium ions as well as silyl-substituted vinyl cations and arenium ions by the classical hydride transfer reactions with PhjC TPEPB in benzene. Thus, the transient 7-silanorbornadien-7-ylium ion 8 was stabilized and isolated in the form of its nitrile complex [8(N=C-CD3)]+ TPFPB (Scheme 2.15), whereas the free 8 was unstable and possibly rearranged at room temperature into the highly reactive [PhSi /tetraphenylnaphthalene] complex. ... 

An expression of the type in Eq. (29) has been rederived recently in Ref. 13 for outer-sphere electron transfer reactions with unchanged intramolecular structure of the complexes where essentially the following expression for the effective outer-sphere reorganization energy Ers was used ... 

The systems that we investigated in collaboration with others involved intermolecular and intramolecular electron-transfer reactions between ruthenium complexes and cytochrome c. We also studied a series of intermolecular reactions between chelated cobalt complexes and cytochrome c. A variety of high-pressure experimental techniques, including stopped-flow, flash-photolysis, pulse-radiolysis, and voltammetry, were employed in these investigations. As the following presentation shows, a remarkably good agreement was found between the volume data obtained with the aid of these different techniques, which clearly demonstrates the complementarity of these methods for the study of electron-transfer processes. 

Interestingly, reaction of alkynyl disilane 14 with trityl cation did not result in the formation of stable vinyl cations. Obviously, the formation of the four-membered disilacyclobutane ring is unfavorable. Similarly, treatment of alkyne 15 with the pre-formed triethylsilylarenium ion 1 derived from toluene did not give the expected intramolecular transfer of the silylium ion to the triple bond. Instead, only a complex product mixture was obtained. 

The effect of ring substituents on the rate constants, deuterium kinetic isotope effects and Arrhenius parameters for ene-additions of acetone to 1,1-diphenylsilane have been explained in terms of a mechanism involving fast, reversible formation of a zwitterionic silene-ketone complex, followed by a rate-limiting proton transfer between the a-carbonyl and silenic carbon. A study of the thermal and Lewis acid-catalysed intramolecular ene reactions of allenylsilanes with a variety of... 

Electron-transfer and intramolecular redox reactions (related to 82 complexes). The redox behavior of 82 complexes is of particular interest because it can probably provide a foundation for understanding the course of reactions involved in relevant enzymes and catalysts (especially hydrodesulfurization catalysts). Intramolecular redox reactions related to type la 82 ligands can be summarized as follows ... 

The enantiopure tricarbonyl(dienal)iron complex 61 suitably transfers chirality in the piperidine ring formation. Condensation to the Schiff base is followed by the intramolecular Mannich reaction catalyzed with p-TSA. The piperidine was converted to dienomycin C (62) in five additional steps <99EJOC1517>. 

A variety of linkage isomer pairs have been produced from somewhat more complex ligands, such as substituted pyridines and benzoic acids, for example (5a) and (5b).77,78 These complexes have been employed in detailed studies of inner-sphere electron transfer reactions in order to assess the importance of the nature and orientation of the bridge between redox centres on intramolecular electron transfer rates.77-80... 

Intramolecular electron transfer from Ru(II) to Fe(III) in (NH3)3Ru(II) (His-33)cyt(Fe(III)) induced by pulse-radiolysis reduction of Ru(III) in the (NH3)5Ru(III) (His-33)cyt(Fe(III)) complex were investigated [84]. The results obtained differ from those of refs. 77-80 where flash photolysis was used to study the similar electron transfer reaction. It was found [84] that, over the temperature range 276-317 K the rate of electron transfer from Ru(II) to Fe(III) is weakly temperature dependent with EA 3.3 kcal mol 1. At 298 K the value of kt = 53 2 s"1. The small differences in the temperature dependence of the electron tunneling rate in ruthenium-modified cytochrome c reported in refs. 77-80 and 84 was explained [84] by the different experimental conditions used in these two studies. 

Intramolecular photoinduced electron transfer reactions of homonaphthoquinones are also made possible by the presence of Mg(C104)2 in MeCN [212]. As shown in Scheme 27, the photoexcitation of 10 in the presence of Mg2 + results in intramolecular electron transfer due to the complexation of Mg2 + with the semiquinone anion moiety, which can accelerate the photoinduced electron transfer and at the same time may retard the back electron transfer [212], No reaction occurred in the absence of Mg2+ or in the dark at ordinary temperature [212], The generated radical ion I undergoes ring... 

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