Insertion rhenium-carbon bonds

Carbonyl insertions into rhenium-carbon bonds have been less studied than with manganese derivatives. Insertions of CO into rhenium-carbon bonds are more difficult than for manganese as expected from the higher BDE of the rhenium-hydrocarbyl bond with respect to the corresponding manganese-hydrocarbyl systems... 

The higher metal-carbon bond strength for a third-row metal explains the failure of rhenium to react. Carbon monoxide insertion occurs in the -cyclopentadienyl derivative of rhenium(I), Re(NO) (>7 -C5H5)Me(PMe3) ... 

The diamagnetic ylide complexes 34 have been obtained from the reaction of electron-deficient complexes [MoH(SR)3(PMePh2)] and alkynes (HC=CTol for the scheme), via the formal insertion of the latter into the Mo-P bond. The structural data show that 34 corresponds to two different resonance-stabilized ylides forms 34a (a-vinyl form) and 34b (carbene ylide form) (Scheme 17) [73]. Concerning the group 7 recent examples of cis ylide rhenium complexes 36 cis-Me-Re-Me) have been reported from the reaction of the corresponding trans cationic alkyne derivatives 35 with PR" via a nucleophilic attack of this phosphine at the alkyne carbon. 

Reaction of rhenium atoms with alkyl-substituted arenes forms dirhenium- l-arylidene compounds (2 2) (Figure 3). The products require insertion, presumably sequential, into two carbon-hydrogen bonds of the alkyl substituent. These reactions seem highly specific and require only the presence of an alkyl-substituted benzene that possesses a CH2 or CH3 substituent. Thus, co-condensation of rhenium atoms with ethylbenzene gives two isomers (see Figure 3) in which the products arise from insertion into the carbon-hydrogen bonds of the methylene or the methyl group. The product distribution in this reaction is in accord with statistical attack at all available sp3 C-H bonds. 

Either SO2 or, with the exception of rhenium and nickel, CO can be inserted in the same way into metal-carbon a bonds of the four- to seven-membered metallacycles 38 -44. - - - In each case the ring-expanded... 

The resulting reduced photoproduct acts as the catalytic intermediate for COj reduction (Figure 33). It has been suggested that carbon monoxide ligand dissociation, followed by formation of a rhenium-formate intermediate, leads to cyclic reduction of carbon dioxide to CO. Interestingly, a rhenium(I)-carboxylate complex, /ac-Re(0—C(=0)—H)(bpy)(CO)3, has been isolated as a by-product of the photosystem. The latter complex is inactive in COj reduction to CO, and hence a rhenium-formate intermediate formed by COj insertion into the hydride bond was suggested as the active intermediate for CO formation (Figure 33). 

In 2012, a rhenium-catalyzed synthesis of pyridines from y0-enamino ketones and alkynes was reported by Takai, Kuninobu, and coworkers [112]. In the presence of Re2(CO)io, with Af-acetyl / -enamino ketones and alkynes as the substrates, multisubstituted pyridines were produced in good yields and regioselectivity (Scheme 3.54). For the reaction mechanism, the reaction proceeded via insertion of alkynes into a carbon-carbon single bond of /3-enamino ketones, intramolecular nucleophilic cyclization, and elimination of acetic acid. And the presences of A-acetyl moieties are important for the reaction selectivity. 

Manganese, Tecimetinin, and Rhenium.— Photolysis of pentacarbonyltri-fluoromethylmanganese in an argon matrix at 17 K results in carbon monoxide insertion into the Mn—CFj bond. ... 

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