Chlorine ligand transfer

The jV-chloro-compounds were the first to be employed as radical cyclization precursors in the synthesis of pyrrolidines and piperidines, as well as fused and bridged heterocyclic skeletons [7], Aminyl and amidyl radicals were thus generated and used in intramolecular additions. Higher yields and selectivities are obtained with the metal-complexed species. Some selected examples are reported in Table 4. Generally, a typical radical chain mechanism is involved (with chlorine atom transfer from 7V-chloro-compound). In the particular case of copper-cornplexed aminyl radical cyclization, a redox chain process operates (with fast chlorine ligand transfer from cupric chloride)... 

Ligand transfer from tin(IV) to tin(II) compounds with appropriate ligands such as chlorine (d) has been used infrequently in the synthesis of stannylenes. The only reactions reported so far have been performed with oxygen as substituents at tin (see also Sect. 6.4.3). 

Arylation of activated double bonds with diazonium salts in the presence of copper catalysts is known as the Meerwin reaction. The reaction is postulated to either proceed through an organocopper intermediate or through a chlorine atom transfer from chiral CuCl complex to the a-acyl radical intermediate. Brunner and Doyle carried out the addition of mesityldiazonium tetrafluoroborate with methyl acrylate using catalytic amounts of a Cu(I)-bisoxazoline ligand complex and were able to obtain 19.5% ee for the product (data not shown) [79]. Since the mechanism of the Meerwin reaction is unclear, it is difficult to rationalize the low ee s obtained and to plan for further modifications. 

Another copper-induced reaction which may be reinterpreted in view of our mechanism is the copper-induced chlorination of ketones (64). It seems reasonable to suggest that Cu(II) bound to the ketone is oxidized to Cu(III) by C11CI2, which, in the given medium, is less stable than Cu(I). Subsequently, Cu(III) oxidizes its chlorine ligand in a double electron transfer to C1+, followed by the latter s addition to the enolic double bond. 

A recent study showed that 152 behaves mechanistically different from other catalysts in addition reactions of more activated halides 140, such as trichloroacetate to styrene [222]. After initial reduction to Ru(II), chlorine abstraction from substrates 140 is in contrast to all other ruthenium complexes not the rate limiting step (cf. Fig. 36). ESR spectroscopic investigations support this fact. The subsequent addition to styrene becomes rate limiting, while the final ligand transfer step is fast and concentration-independent. For less activated substrates 140, however, chlorine abstraction becomes rate-determining again. Moreover, the Ru(III) complex itself can enter an, albeit considerably slower Ru(III)-Ru(IV) Kharasch addition cycle, when the reaction was performed in the absence of magnesium. This cycle operates, however, for only the most easily reducible halides, such as trichloroacetate. 

Thus the first electron transfer to Pb relates to the reaction (a) in Section 7.4.3.1.1, and the second involves the oxidation of the cyclobutyl radicals either by electron transfer/deprotonation with Cu" in equation (17) or by ligand transfer of chlorine with PlAci in equation (18). When the product of a generic reaction is itself a radical cation (such as in Sections 7.4.3.1.8 and 7.4.3.1.9), an electron-transfer chain or ETC process can ensue, as in the hole-catalyzed cycloadditions and autoxidations of dienes,The electron-transfer propagation sequence for the latter is simply given as in equations (19) and (20). 

To prepare S13 by the ligand transfer reaction requires first the synthesis of the chain-like dichlorooctasulfane which is best achieved by carefully controlled chlorination of cyclo-Sg with elemental chlorine in a CS2/CCI4 mixture at 0-20 °C ... 

The proposed mechanism of the reaction involves electron transfer from an arene to a platinum(IV) compound to give an intermediate ion-radical pair, [ArH]" [Pt Clj 1 or [ArH]" lPt CU(H20r] (Scheme VII.9) (for the photochemistry of PtCU ", see, e.g., [50]). The route to this ion-radical pair may be conceived ether as an electron transfer within the 7t-complex of ArH with PtCU (VII-15) or PtCU(H20) (VII-16), or as an outer-sphere electron transfer to the excited complex of platinum(IV) with participation of a chlorine ligand (the transformation of strnctnre VII-17 into strnctures VII-18 or VII-19). Subsequent extrusion of Cl from structure VII-20 gives rise to the same ion-radical pair [ArH]" fPt Cl/ ]. 

In a recent series of articles [179-181], Seijo and Barandiaran have investigated the spectroscopy of several actinide impurities (Pa" - -, and in crystal environments. In particular, they discuss the relative position of the 5 and 5/ " 6i/ manifolds (see also chapter 7 of this book). All calculations use relativistic large-core AIMPs on the actinide centres and on the chlorine ligands. The transferability of these frozen core potentials from the neutral / elements to their cation has been discussed in Ref [182]. The crystal environment is described by the AIMP embedding cluster method. Electron and spin-orbit interactions are treated simultaneously by the three-step spin-fi e-state-shifted method detailed in section 2.2.5, using either MRCI or CASSCF/MS-CASPT2 methods in the spin-fi ee step. The active space includes the 5/ and 6d orbitals of the actinide centre, as well as the Is orbitals in order to avoid the prob-... 

The oxidation of L-tyrosine by hexachloroiridate(lV) exhibits first-order dependence on both Ir(IV) and L-tyrosine. The reaction rate increases with increase in ionic strength and decreases with increase in acidity. Dityrosine has been identified as the main product, activation parameters have been evaluated, and a mechanism has been suggested. DFT study of the oxidation of a guanine nucleotide by platinum(lV) indicated that a key step in the mechanism is electron transfer from guanine to platinum(lV). It has been shown that out of several different Pt(lV)-guanine adducts, one which is formed from replacement of an axial chlorine ligand in the platinum(lV) complex undergoes oxidation more easily. The oxidation of adenine is found to be more difficult as it involves disruption of an aromatic jt system. ... 

The reaction mechanism was proposed to involve electron transfer from the d-7i metal to ligand charge transfer excited state (MLCT transition) to the chlorinated solvent,... 

Here, M represents a transition metal atom and L a ligand. H as a ligand is given an oxidation number of — 1. If reductive, the electron pair which constitutes the bond in the sorptive, A B, is transferred to surface species if oxidative, a pair of electrons is removed from surface species. One would say that dissociative adsorption of Cl2 on a metal is oxidative if chlorine forms CP ions on the surface of the adsorbent. A dissociative adsorption would be reductive if, for example, it occurred thus (note that H2 -> 2H+ + 2ehere),... 

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