Reductive elimination binuclear

Catalytic dehalogenation cycles with a binuclear reductive elimination step have not yet been reported, but many examples are known with a single metal. The RH product eliminates easily from d8 metals (Ni(II), Pd(II)) or d6 metals (Ru(II), Rh(III)) (Eq. (25)) [196]. This reaction is believed to go by a three-center transition state [193, 194, 212] ... 

Complex XV undergoes an interesting binuclear reductive elimination reaction losing H2 upon reacting with ligands such as tertiary phosphines see Equation 6) (15), but pyridine and simple alkenes such as ethylene will not induce this reaction. 

Binuclear reductive eliminations followed by oxidative addition may also be involved in reactions such as Equation 8. 

Fig. 9. Binuclear reductive elimination. The dihydride complex, 20, passes over a low energy transition state to form a dihydrogen complex, 21. Relative energies given in kcal mol-1.

The complex (I) undergoes binuclear reductive elimination reactions induced by tertiary phosphine and other ligands (equation 2) (11). 

We suggest that binuclear reductive elimination also occurs as the initial step in reactions of (I) with methanethiol or diphenylphosphine (equation 4) (13). 

A final example of the apparent occurrence of binuclear reductive elimination is found in reactions of (I) with alkynes bearing electronegative substituents. These reactions occur as shown in equation (5)... 

Binuclear reductive elimination processes from saturated hydride complexes to yield 17-electron products have been established for electrocatalytic dihydrogen evolution systems [6, 129]. Analogous processes have been shown to occur from 19-electron hydride complexes to yield saturated products. Compounds [CpCoH(PR3)2] (R = Ph, Et, OMe) and [CpCoH(L-L)]+ (L-L = dppe, dmpe, and Ph2PCH=CHPPh2), undergo one-electron reduction processes followed by the production of H2 and the expected 18-electron Co(l) bis-phosphine products. In the presence of protons, catalytic H2 evolution was shown [25]. Although the one electron reduction process for the monophosphine derivatives is irreversible at all investigated scan rates (possibly due to phosphine decoordination from the... 

The formation of a Th(C5H5)3 complex was suggested because the subsequent thermal reaction of the photogenerated thbrium monohydride with unreacted starting hydrocarbyl complexes, gives the binuclear reductive elimination of alkane ... 

As early as 1901, Ullmann discovered the copper promoted coupling of aryl halides to biaryls, one of the first uses of transition metals in synthesis. The mechanism is still not entirely clear, but a binuclear reductive elimination of Ar—Ar from CuAr is possible. 

Oxidative addition of Mel is followed by reductive elimination. The possibility of binuclear reductive elimination is suggested from the label crossover data. 

CO2 insertion into the terminal M—C bond to give an V-OCOCH2CHCHCH2 carboxylato-allyl complex. Oxidation then leads to the coupling of the allyls by binuclear reductive elimination. 

The reaction starts by the substitution of two CO ligands by the diene to give [Fe(CO)3(T] -diene)], then continues by the substitution of a 3" CO ligand and the intramolecular oxidative addition of the endo C-H bond leading to [FeCp(CO)2H], It ends by the dimerization with formation of the Fe-Fe bond and the loss of H2. This last step is not mechanistically clear-cut, but it could be taken into account by partial decoordination of the Cp ring (from t] - to t] -), coordination of the Fe-H bond of another molecule on the vacant site and binuclear reductive elimination of H2. 

Several useful reviews have appeared. Mondal and Blake have collected thermochemical data on oxidative addition, Halpern has investigated the formation of C-H bonds by reductive elimination, while in a thought-provoking article on activation of C[5/ ]-X bonds, Chanon stresses the importance of electron transfer in oxidative addition (among other topics). In a discussion of oxidation addition and reductive elimination involving two metal centers, Halpem classifies and gives examples of three mechanisms whereby binuclear reductive elimination can occur concerted two center (77), concerted one center (78), and free-radical [(79)-(81)] reactions given in Scheme 6. 

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