Electron deinsertion

However, deinsertion involving two electron ligands is not a general reaction for all the hydride complexes. Indeed, the iron complex (CO)4Fe(H)SiPh3 undergoes CO replacement rather than deinsertion ... 

Insertion of S02 occurs with a wide variety of transition metal complexes, almost as commonly as CO insertion. Unlike CO, however, deinsertion of S02 (desulfination) is not common. Because S02 reacts with 18-electron complexes, the resulting coordinatively saturated insertion complex must lose a ligand to provide an open site for alkyl migration to occur. Apparently, this is a difficult process, and when it does occur, it is accompanied by substantial decomposition. 

Figure 23.8 Schematic model showing the sequence of lithium insertion-deinsertion into the carbon fiber-pyrolytic carbon composite. During reduction, once the solid electrolyte interphase (SEI) is formed, ionic lithium penetrates at first in the smallest intervals. Then it diflfiises to the largest intervals where the ions are screened by delocalized electrons through a backdonation process quasi-metaUic clusters are formed in the largest intervals. During oxidation, the opposite process occurs. (Adapted from Ref. [57].)...

Apparently, one-electron reduction of the Rh(III) species does not cause deinsertion/p-hydrogen elimination in the Rh(II) state, as observed upon further reduction to Rh(l) (irreversible le reduction wave at a 0.56 V lower potential). The Rh(ll) species (Fig. 73) was characterized by means of EPR spectroscopy. The obtained g values in frozen solution and at room temperature indicate a square-pyramidal geometry with one P atom at the apical position (Table XIV) (190). Quite similar EPR spectra and geometries were observed for the related complexes [Rh (CN)(PP3)]+, [Rh°(CN(NP3))]+, and [Rh°(C=CPh)(NP3)]+ (PP3 = P(CH2CH2PPh2)3, NP3 = N(CH2CH2PPh2)3) (191-193) (see Fig. 74 and Table XII. 

It essentially exploits the different behavior of aryl iodides bearing an ortho electron-releasing group and bromides containing an electron-withdrawing substituent in the attack to palladium(O) (followed by norbornene insertion) and palladiiun(II) (followed by norbornene deinsertion). 

Behind the interest manifested in binuclear complexes stands the expectation that they will display fundamentally new modes of reactivity. Naturally, we also expect that they can show the patterns of reactivity known for mononuclear complexes. These include Lewis base associ-ation/dissociation, Lewis acid association/dissociation, ligand migration (insertion/deinsertion), oxidative addition/reductive elimination, and oxidative ligand coupling/reductive ligand uncoupling, as well as electron-transfer. While these reaction patterns do occur with binuclear... 

The series of reactions above is a simple catalytic cycle for the water gas shift reaction, CO + H2O CO2 + H2. (a) What is the oxidation state of rhodium in each complex in the cycle (b) Indicate whether each complex is a sixteen- or eighteen-electron complex, (c) Which of these classes of reactions does each step of the cycle illustrate addition, elimination, oxidative addition, reductive elimination, insertion, or deinsertion ... 

The influence of the electronics on the rate of the migratory deinsertion was measured with para-substituted benzoylrhodium(III) complexes (Scheme 1.52) [68]. An electron-deficient aryl group migrated faster than an electron-rich one. The rate of the migratory deinsertion was also affected by the spectator ligand migratory deinsertion of the chloride complex was faster than that of the bromide complex. 

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