Insertion hydrogen abstractions

Fig. 6. Coupling of polymer chains via (a) photoinduced hydrogen abstraction free-radical reactions and (b) nitrene insertion/addition reactions.

Tetraphenylmolybdenocene dihydride Mo(r 5-C5HPh4)CpH2 (45) was formed by addition of diphenylacetylene to MoCpL(PhC CPh)CH3 (L = P(OMe)3) (Eq. 15), presumably via an ot-hydrogen abstraction to an intermediate methylidene hydrido complex, followed by addition of two equivalents of diphenylacetylene and C — H insertion with concomitant elimination of L [57 b],... 

The chemical reactions of sulphonyl nitrenes include hydrogen abstraction, insertion into aliphatic C—H bonds, aromatic substitution , addition to olefinic double bonds, trapping reactions with suitable nucleophiles, and Wolff-type rearrangement. Hydrogen-abstraction from saturated carbon atoms is usually considered to be a reaction typical of triplet... 

Reaction of dpp-bian with Mg in THF for 30 min reflux gives complex 87 (Ar = 2,6-diisopropylphenyl) which undergoes oxidative addition via m-bond metathesis with PhC=CH to give the black alkynyl amido complex 88. The insertion reaction of 88 with Ph2CO in EtzO yields complex 89. Unexpectedly, hydrogen abstraction to give the radical anion occurs simultaneously with ketone insertion.268... 

The four hitherto known routes of the C-H insertion are shown in Scheme 1. In general, the insertion by singlet carbenes proceeds via route a in one step, whereas the reaction by triplet carbenes proceeds sequentially via route b, i.e., hydrogen abstraction followed by recombination of the radical pairs.4 Other stepwise mechanisms are hydride abstraction (route c) and proton abstraction (route d), both being followed by the recombination of ion pairs. However, extended study on routes c and d for synthetic purposes had not been done before we started, except for a few earlier studies on carbanion-promoted P C-H insertion reactions.5,6 Recent advances in transition metal-catalyzed... 

In the case of t-butyl acetate, shown in reaction 41, three successive geminal hydrogen abstractions and insertions of 303 take place a product of reductive dimerization (306) is also formed in small yield626. 

Olefinic compounds such as a-pinene (309) and /Dpi none (312) undergo hydrogen abstraction followed by rearrangement and amino-oxyl insertion (310, 313) and addition reactions (311, 314, 315), as shown in reactions 43 and 44627. Other olefinic compounds such as norbomadiene, cyclo-octene and cyclo-octa-1,5-diene gave analogous results628. 

Mechanisms [i] and [II] may occur through the recombination of unpaired electrons which are formed by the hydrogen abstraction of nitrenes, and the insertion reaction of nitrenes to C-H bonds, respectively. However, it has not been revealed in this study which C-H bond is attacked by the nitrene. 

Decomposition of 164 in ethylene, ethylene oxide, and propane mainly gave C—H insertion and hydrogen abstraction products by carbon atoms (72JA1379 77JA2627) (Scheme 44). In ethylene oxide, oxygen abstraction was also observed. 

The quenching of a triplet carbene reaction with methanol is frequently used as the standard means of probing the singlet-triplet gap. It is widely believed that singlet carbenes insert readily into the O—H bonds of methanol, while the triplet states undergo hydrogen abstraction from the C—H bonds." The behavior of diarylcar-... 

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