Oxidative addition photoinduced

At present, high-temperature stabilization of polyolefins is still misunderstood besides, this problem presents serious difficulties. Stabilization of thermal oxidation and photoinduced destruction with the use of stabilizers in this case is inefficient, since at high temperatures these stabilizers are easily evaporated out of the polyolefin melt and decomposed with the formation of radicals capable of initiating additional kinetic chains of destruction. 

Pure cis-71 could be isolated in 65% yield and was characterized by means of x-ray structure analysis (Fe-Si 2.270(1)/2.272(1) A). This ds-conformer is exclusively formed. The formation of 71 requires a photoinduced silyl exchange followed by a decarbonylation reaction and further steps of an oxidative addition to the metal [176]. 

A review16 with 89 references is given on the excited state properties of the low valent (0 and + 1) bi- and trinuclear complexes of Pd and Pt. Physical characterization of the nature of the lowest energy excited states along with their photoinduced chemical reactivities toward oxidative additions is discussed. 

Successive hydrogen transfers within 60, followed by coordination of olefin and then H2 (an unsaturate route), constitute the catalytic cycle, while isomerization is effected through HFe(CO)3(7r-allyl) formed from 59. Loss of H2 from 60 was also considered to be photoinduced, and several hydrides, including neutral and cationic dihydrides of iridium(III) (385, 450, 451), ruthenium(II) (452) and a bis(7j-cyclopentadienyltungsten) dihydride (453), have been shown to undergo such reductive elimination of hydrogen. Photoassisted oxidative addition of H2 has also been dem-... 

Photoinduced oxidative addition of primary silane H3SiC(SiMe3)3 to [WMe(CO)3Cp ] [Eq. (24)] produced a hydridesilylene complex [W(H) = SiH(C(SiMe3)3) (CO)2Cp j (73) in 62% yield in a reaction similar to that shown in Eq. (23). An analog with the CsMe4Et ligand has been prepared similarly ... 

In summary, the triplet (do po) excited states of the d -d metal dimers [Ir(p-pz)(C0D)]2 and Pt2(pop)4 " undergo a variety of photochemical reactions. Electron transfer to one-electron quenchers such as pyridinium cations or halocarbons readily occurs with acceptors that have reduction potentials as negative as -2.0 V. With the latter reagents, net two-electron, photoinduced electron transfer yields d -d oxidative addition products. Additionally, the triplet (da pa) excited state of Pt2(pop)4 apparently is able to react by extracting a hydrogen atom from a C-H bond of an organic substrate. 

The chloromethyl complexes cis- and trans-[ Pt( PPh3)2(Cl )CH2C1 ] were synthesized by the photoinduced oxidative addition of CH2C12 to... 

ReCp(CO)2(H)(MR3) and ReCp(CO)2H2 are the products of photoinduced oxidative addition of (89) to H MR3 bonds (M = Si, Ge, Sn) (see Section 8.1.5). Photochemical activation of (89) or (90) in the presence of B2pin2 gave cis and /ran5 -ReCp (CO)2(Bpin)2, that is, oxidative addition to the B-B bond. Most remarkable, however, is the fact that further irradiation of this compound or of a mixture of (90) and B2pin2 in pentane led to regiospecific terminal C-H activation of the pentane with formation of CsHnBpin and HBpin. The mechanism of this elegant C H activation process does not seem to take place via C H activation on intermediate ReCp (CO)2.i ... 

A photoinduced oxidative addition of Bu"I and Pr I towards [Rh2(dicp)4] (dicp = 1,3-diisocyanopropane) using low-energy irradiation (553 nm) has been described, and proceeds under a nitrogen atmosphere with quantum yields of 25.2 and 22.6, respectively. Based on the kinetics measured in the presence and absence of quenchers, an electron-transfer chain mechanism has been proposed in which alkyl radicals are involved. " The same authors have also described a new methodology for the experimental determination of redox potentials and have applied this to measure the one-electron oxidation potentials of l-benzyl-l,4-dihydronicotinamide and of [Rh2(dicp)4p. ... 

There are two pathways for this reaction spontaneous thermal reactions, where AG° of the reaction is negative (thermal oxidative addition (TO A)), and photoinduced oxidative addition (POA), where A G° of the dark reaction can be either negative or positive. 

A base-stabilized dimethylsilylene iron complex (22) is reported as the product of a photoinduced oxidative addition of an aminosilane to iron pentacarbonyl (equation 52). 

Campian MV, Harris JL, Jasim N, Perutz RN, Marder TB, Whitwood AC (2006) Comparisons of photoinduced oxidative addition of B - H, B - B, and Si - H bonds at Rhodium 5-cyclopentadienyl)phosphine centers. Organometallics 25 5093... 

Oxidative addition with cleavage of H—H, C—H, and Si—H bonds requires a co-ordinatively unsaturated metal species such as four-co-ordinate / -complexes. Thus, although nucleophilic anions such as [Mn(CO)5] react readily with alkyl halides, the reaction with HSiPhg is photoinduced." Irradiation gives [Mn(CO)4]", which can then undergo oxidative addition leading to cis [MnH(SiPhs)(CO)4]-. 

In dichloroethane and methylene chloride solutions, photoinduced two-center oxidative addition of chloroalkane takes place, leading to formation of the iridium(II) coordination compound. In the case of C2H4CI2, ethylene elimination takes place [scheme (6.141)]. 

R. A. Faltynek and M. S. Wrighton, /. Amer. Chem. Soc., 1978, 100, 2701. Photoinduced substitution and oxidative-addition reactions of pentacarbonyl manganesef—1) and tetra-car nyl(triphenylphosphine)manganese(—1). 

Since the zerovalent complex Pd(PPh3)3 undergoes photoinduced oxidative addition with chlorobenzene, dimeric palladium(O) complexes are also expected to undergo such reactions. An additional feature of the dimers, however, is the presence of two metal centers that can undergo such a two-electron addition. An example of such a double addition is found in the photoreaction between... 

Isomerization and polymerization reactions of alkenes and alkynes are to be expected because both the MLCT and LMCT excited states have diradical character. Both the tetracyanoethylene and dicyanoacetylene 7r-complexes of Pt(PPh3>2 undergo a photoinduced intramolecular oxidative addition reaction to give the cyano vinyl and cyano acetylide complexes of platinum(II) respectively ... 

In a few cases alkyl complexes can be synthesized by the photoaddition of dichloromethane or chloroform to a low-valent transition metal complex, but the usual products from these halogen abstraction reactions are the dichloro complexes. Photoinduced oxidative addition reactions are not always the result of the generation of an excited state that is more reactive than the ground state. An alternative photochemical pathway can involve the initial dissociation of a ligand to generate a coordinately unsaturated intermediate, which is then activated toward oxidative addition of the substrate. An example of such a reaction is... 

Intramolecular photoinduced oxidative addition reactions can also occur. For example, when the platinum(0) complex Pt(C2H4)(PPh3)2 is photolyzed at 280 nm, the product is a cyclometalated platinum(II) complex formed by intramolecular oxidative addition of the ortho carbon-hydrogen bond, followed by ethylene insertion into the intmnediate platinum(II) hydride ... 

The photoinduced oxidation addition to [Rh2(jit-dicp)4] (dicp = 1,3-diisocyanopropane) of n-butyl iodide in MeCN yields chiefly [n-BuRh(/t-dicp)4RhI] . High quantum yields, the fact that the reaction is inhibited by reagents such as benzoquinone and oxygen, and the formation of 1-butanol and butyraldehyde in the latter case, indicate a radical-chain process (116) and (ll ) ... 

Morishima et al. [75, 76] have shown a remarkable effect of the polyelectrolyte surface potential on photoinduced ET in the laser photolysis of APh-x (8) and QPh-x (12) with viologens as electron acceptors. Decay profiles for the SPV (14) radical anion (SPV- ) generated by the photoinduced ET following a 347.1-nm laser excitation were monitored at 602 nm (Fig. 13) [75], For APh-9, the SPV- transient absorption persisted for several hundred microseconds after the laser pulse. The second-order rate constant (kb) for the back ET from SPV- to the oxidized Phen residue (Phen+) was estimated to be 8.7 x 107 M 1 s-1 for the APh-9-SPV system. For the monomer model system (AM(15)-SPV), on the other hand, kb was 2.8 x 109 M-1 s-1. This marked retardation of the back ET in the APh-9-SPV system is attributed to the electrostatic repulsion of SPV- by the electric field on the molecular surface of APh-9. The addition of NaCl decreases the electrostatic interaction. In fact, it increased the back ET rate. For example, at NaCl concentrations of 0.025 and 0.2 M, the value of kb increased to 2.5 x 108 and... 

In addition, the rate of Oz reduction, forming 02 by electron, is of importance in preventing carrier recombination during photocatalytic processes utilizing semiconductor particles. 02 formation may be the slowest step in the reaction sequence for the oxidation of organic molecules by OH radicals or directly by positive holes. Cluster deposition of noble metals such as Pt, Pd, and Ag on semiconductor surfaces has been demonstrated to accelerate their formation because the noble metal clusters of appropriate loading or size can effectively trap the photoinduced electrons [200]. Therefore, the addition of a noble metal to a semiconductor is considered as an effective method of semiconductor surface modification to improve the separation efficiency of photoinduced electron and hole pairs. 

Highly efficient and stereoselective addition of tertiary amines to electron-deficient alkenes is used by Pete et al. for the synthesis of necine bases [26,27], The photoinduced electron transfer of tertiary amines like Af-methylpyrrolidine to aromatic ketone sensitizers yield regiospecifically only one of the possible radical species which then adds diastereospecifically to (5I )-5-menthyloxy-2-(5//)-furanone as an electron-poor alkene. For the synthesis of pyrrazolidine alkaloids in approximately 30% overall yield, the group uses a second PET step for the oxidative demethylation of the pyrrolidine. The resulting secondary amine react spontaneously to the lactam by intramolecular aminolysis of the lactone (Scheme 20) [26,27]. 

Photoinduced oxidation of Cjq has been achieved by electron transfer from excited to a strong electron acceptor such as p-chloranil [72, 73], p-benzoquinone [73], tetracyano-p-quinodimethane (TCNQ) or tetracyanoethylene (TONE). This electron transfer proceeds efficiently only by addition of promoters such as Sc(OTf)3 or triflic acid, both of which strongly enhance the electron-transfer process [72, 73]. Another possibility to produce the cation is the electron transfer from to the singlet excited state of a strong electron acceptor such as N-methylacridinium hexafluorophosphate (NMA ) [74, 75], triphenylpyriliumtetrafluoroborate (TPP" )... 

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