Insertion reactions single bond insertions

The advantages of this method of carbene synthesis are that reaction can be carried out in neutral solution, and that reaction yields are often dramatically improved. Thus, although reactions of dihalocarbenes generally do not give rise to products corresponding to single bond insertion, Seyferth has reported insertion of phenyl (trihalomethyl) mercury-generated carbenes into... 

REACTIONS OF SILYLENES 4.1. Insertion into Single Bonds... 

The chemistry of ketenes is dominated by their high reactivity most of them are not stable under normal conditions, many exist only as transient species. Nucleophilic attack at the -carbon, [2 + 2] cycloadditions, and ketene insertion into single bonds are the most important and widely used reactions of such compounds. 

The formation of toluene in the reaction of diazomethane with benzene (8-3) brings us to the second characteristic reaction of carbenes, namely insertion into single bonds, in this case into an sp -C —H bond. Here again prehistoric examples (i.e., investigations before 1950) of Buchner and Meerwein are known (Buchner and Schulze, 1910 Buchner and Scholtenhammer, 1920 Meerwein et al., 1942), as well as early systematic work by Doering s group after 1950. 

Another reaction of singlet carbenes is insertion into single bonds, as shown in equation 5.40. 

Across single bonds (insertion reactions) The insertion reaction of isocyanates into substrates A-B seems to involve a stepwise process. The insertion product either forms a single... 

Across single bonds (insertion reactions) The addition of isothiocyanates across the polar single bond in dimethylaminobis-(trifluoromethyl)borane affords the switter ionic four-membered ring cycloadducts 78 . ... 

By performing excellent model reactions [144], Grubbs and his co-workers demonstrated direct olefin insertion into an M-C bond. Thus, complex 115 was treated with AlEtCl2 to give complex 116, whose decomposition afforded methylcyclopentane. Under the same conditions, the polymerization of ethylene took place. In this way, the insertion of a-olefins into a Ti-C single bond in a model Ziegler-Natta catalyst system was directly observed (Eq. 9). 

In two separate reactions, a new carbon-carbon double bond was created by the insertion of a heteroallene into the Al-C-Al bonds of a spirocyclic dimethylaluminum bis(iminophosphorano)methandiide compound (Figure 2(b)).47 In both compounds, the C-C bond is shorter than a single bond but longer than a typical double bond, indicating delocalization within the interesting bicyclic ring systems. 

Table 5. Post-HF activation barriers for the insertion reaction of ethene into the Zr-CH3 bond of the HjSifCpEZrCH species. All the reported insertion barriers were obtained through single point calculations on the MP2 geometries of Tables 3 and 4 (corresponding to run 3 in this Table). In the valence calculations the Is orbitals on the C atoms, the orbitals up to 2p on the Si atom and up to the 3d on the Zr atom where not included in the active orbitals space. In the full MP2 calculations all occupied orbitals were correlated.

In 1956, Doering et al. reported that methylene (CH2) inserted into the C H bonds of pentane, 2,3-dimethylbutane, and cyclohexene with no discrimination (other than statistical) between chemically different sites CH2 was classed as the most indiscriminate reagent known in organic chemistry. Doering and Kirmse also demonstrated that the C—H insertion reactions of CH2 in solution were direct, single barrier concerted processes with transition states that could be represented as 27 (Fig. 7.12). In particular, they did not proceed via initial H abstraction to give radical pair intermediates that subsequently recombined. (Triplet carbene C H insertions, however, do follow abstraction-recombination, radical pair mechanisms, as demonstrated in classic experiments of Closs and Closs and Roth (see Chapter 9 in this volume). 

Insertion reactions of silylene into a number of single bonds have been observed. The bonds include Si—O, Si N, Si H, Si halogen, strained C O, Si Si, O—H, N—H, and C—H (intramolecular only). Insertion into an X H bond can be initiated by the formation of silaylide (50) with the donation of a pair of electrons from a heteroatom X to form a bond to a divalent sihcon atom (Scheme 14.26). 

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