Reductive insertion

The intention of this section is to discuss some aspects of the chemistry of metal complexes in solution which are related to the conversion of carbon monoxide and hydrogen to organic products. In order to provide a framework for the initial part of the discussion, we have adopted the simple reduction/insertion sequence shown in Eq. (2). 

Reductive insertion Z (leaving group) Permutational interconversion... 

The palladium catalysed reductive insertion of acetylenes is also viable through the use of formate ions as hydride equivalent (c.f 3.24.), The ring closure of /V-acetylenic-2-iodoanilines gave the corresponding 3-alkylideneindolines in a selective manner (3.27.), demonstrating that the... 

The mechanism for the reductive insertion is not known since the corresponding neutral nido-carborane is also produced, it would seem to involve the THF solvent. 

In path (a) a sequence of reduction-insertion-reduction gives Ci. C2 and C3 products, whereas in path (b) the selective formation of cthene is explained by juj-methylene-bridged species. 

The M-NR2 bond is labile and Nb and Ta dialkylamides M(NR2)5 (12) are valuable starting materials (Scheme 2). They can easily undergo substitution or Insertion reactions. Insertion of CO2, CS2, and COS in M(NR2)5 has been observed, giving dialkylcarbamates, dithiocarbamates, or monothiocarbamate derivatives, respectively. In the case of niobium, the insertion of CS2 is accompanied by reduction. Insertion of CO2 is catalyzed by amines resulting from adventitious hydrolysis. Monodentate as well as bidentate carbamato... 

In the absence of tertiary amines, osmium tetroxide reacts with alkenes via 1,3-dipolar addition to generate a monomeric Os(VI) ester such as 252,352 where L is a ligand that can be a solvent molecule or an added substrate such as pyridine. Sharpless et al. proposed that hydroxylation proceeds by an allowed [2-1-2]- cycloaddition reaction, producing an Os(VII) intermediate, followed by reductive insertion of the Os—C bond into an Os=0 bond.353 This complex can be decomposed in aqueous or alcoholic solution, but the hydrolysis is... 

Reductive insertion. Isoxazolidines give perhydrooxazines by IrClj-catalyzed insertion of CO into the N-0 bond. Interestingly, perhydrooxazin-2-ones are obtained by changing the catalyst to [RhfcodlCllj. 

The reaction mechanism of the osmium-catalyzed dihydroxylation was intensely discussed. Boseken [31] proposed already in 1922 that the reaction proceeds via a thermally allowed concerted (3-1-2) cycloaddition reaction, while Sharpless suggested the formation of a metallaoxetane intermediate via a reversible (2-1-2) cycloaddition, followed by irreversible reductive insertion of the Os-C bond into an Os=0 bond leading to the monoglycolate ester [2] (Scheme 3). 

The reductive insertion of a silyl group into the N-N bond and migration of a phenyl group from the silicon to a nitrogen atom which occurred are both unprecedented so far. 

Originally, this referred specifically to layered structures that can undergo insertion of ions or molecules between the van der Waals gaps, but is now commonly used for any structure that undergoes topotactic insertion reactions. For Li-ion battery materials, it refers specifically to compounds that undergo reductive insertion of lithium ions, such as graphite (used as an anode) or LiCo02 (used as a cathode). 

The second class of sol-gels contains redox-active metal oxides, such as tungsten oxide, vanadium pentoxide, manganese oxide, and other transition metal oxides. Moreover, many n-type semiconductors such as zinc oxide, barium titanate, and titanium dioxide can be used in this class (113). The structures of these gels are sensitive to the pH and oxidation state of the precursors. Many redox-active sol-gels exhibit electrochromism (different oxidation states exhibit different colors, allowing spectroscopic determination of redox states). These gels can also accommodate the reductive insertion of lithium and other moieties. 

Structurally authenticated complexes have been reported with bonds between group 2 and main group metals (Figure 2.4), prepared using reductive insertion, salt elimination, and Lewis acid-base pairing routes. Importantly, strontium- and barium-Main group metal bonded complexes are included in this cohort. Recall that electron-precise bonds between strontium or barium and a TM have yet to be structurally authenticated. 

Scheme 3.13 Reductive insertion of lanthanoids Sm, Eu, and Yb into Ga-Ga bonds.

Polarization curve of Ag in 1M NaOH with peaks A1 and A2 of formation of AgjO and AgO, respectively, and peaks Cl and C2 for their reduction. Insert shows the initiation of oxide formation at potentials negative to peak A"l. (From Hecht, D. et al.. Surf. Sci., 365,263,1996.)... 

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