Reductive elimination, oxidatively induced

Since the reductive elimination involves reduction in the formal oxidation state, the reactivity of an organometallic complex may be enhanced by oxidation of the metal center, most typically by two-electron oxidation. For example, dialkylplatinum(II) complexes are fairly stable but after the oxidative addition of alkyl halides the resulting trialkylplatinum(IV) halides readily undergo C-C reductive elimination (see Section 9.5.1). On the other hand, there have been several examples where one-electron oxidation also has a pronounced effect on the rate acceleration of reductive elimination. Early instances have been documented for the complexes bearing the first-row metals (e.g., trans-NiMe(aryl)(PEt3)2 [86], cw-EeR2(bipy)2 (R = Me, Et) [87], c x-[CoR2(bipy)2]  

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More recently, reductive elimination of aryl ethers has been reported from complexes that lack the activating substituent on the palladium-bound aryl group (Equation (55)). These complexes contain sterically hindered phosphine ligands, and these results demonstrate how steric effects of the dative ligand can overcome the electronic constraints of the reaction.112,113 Reductive elimination of oxygen heterocycles upon oxidation of nickel oxametallacycles has also been reported, but yields of the organic product were lower than they were for oxidatively induced reductive eliminations of alkylamines from nickel(II) mentioned above 215-217... 

B. Paramagnetic Intermediates in Oxidatively Induced Reductive Eliminations / 291... 

Figure 31. Homolytic and concerted pathways in oxidatively induced reductive elimination reactions via open-shell intermediates.

Figure 33. Oxidatively induced reductive elimination of ethane from [Rh (Cp )Me2(L)] species followed by a comproportionation reaction between [Rh (Cp )Me2(L)] and [Rh (Cp )(solv)(L)] to form [Rh(Cp )Me(L)(solv)].

One-electron oxidation of [Pd (R)2(dmpe)] (R = Me or CH2SiMe3) in MeCN results in homolytic cleavage of the Pd—C bond with formation of alkyl radicals and [Pd (R)(dmpe)(NCMe)]" (118). The radical intermediate [Pd (R)2 (dmpe)] was not observed. The homolytic bond splitting of the Pd —R bond to yield Pd(II) and R radicals represents an oxidatively induced reductive elimination. 

An interesting oxidatively induced reductive elimination of azanickelacycles, such as 40 and 57, proceeds with l,r-diacetylferro-cenium tetrafluoroborate, which suggests that the reaction proceeds through a Ni(III) intermediate (Scheme 21). ... 

Complex 6 reacts with iodine to form heterocycle 7 [10], where it is assumed that the process of carbon-carbon bond formation is a result of oxidatively induced reductive elimination (Eq. 2). This protocol has been developed as a key step in the stoichiometric synthesis of a range of macrocycles, including interlocked 7i-conjugated macrocycles (catenanes) [10-12]. 

Scheme 23 Oxidatively induced reductive elimination of ethane from (t-Bu2bpy)PdMe2...

Iron carbonyl complexes containing 77 -alkyl-77 -allyl coordinated hydrocarbon ligands are obtained in several ways. Nucleophilic addition to cationic iron complexes containing 77 -pentadienyl ligands yields (pentenediyl)iron complexes. Oxidatively-induced reductive elimination of these complexes can be utilized as a means to generate 1,2,3-trisubstituted cyclopropanes.The reaction of cationic cycloheptadienyl complexes (Scheme 22) with appropriate nucleophiles also yields the alkyl-allyliron carbonyl complexes. Fe(CO)s also reacts with a- or /3-pincnc in refluxing dioxane (Scheme 22) to produce an alkyl-allyliron complex. Recently, 1,2- and 1,4-disubstituted [(pentadienyl)Fe(CO)3] cations were shown to react with carbon nucleophiles, such as sodium dimethylmalonate, to yield 77 77 -allyl complexes as products. 

Sato, M., and Emiko, M. (1995). Unprecedented Promoting Effect of a Ferroeenyl Group for the Oxidatively Induced Reductive Elimination in cis-Aryl(ferrocenyl acetylide)platinum(II) Complexes. Organometallics, 74,3157-3159. 

T -dienyliron cations (Scheme 4-97) (c/ Section 2.5.2.b). Oxidatively induced reductive elimination of (pentenediyl)iron complexes gives vinylcyclopropanesJ 2-226] Depending on the substitution pattern and the conditions applied in some cases the reaction proceeds with retention of the configuration, whereas sometimes inversion of the configuration at the vinylcyclopropyl carbon is observed in combination with an inversion of the configuration at the double bond. The latter has been proven by monodeuteration of the terminal vinylic carbon atom. ... 

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