Carbon—hydrogen activation

Co-condensation of transition metal atoms with arenes such as benzene and toluene is well known to yield bis-arene-metal compounds. However, in many cases the yields based on the metal atoms are less than 40%. Evidence that competing reactions such as carbon-hydrogen activation can occur is provided by the isolation of non-metal-containing products such as biaryl derivatives (2JL). ... 

Ghosh CK, Graham AG. Efficient and selective carbon-hydrogen activation by a tris(pyrazolyl)borate rhodium complex. J Am Chem Soc 1987 109 4726-4727. 

D. Carbon-Hydrogen Activation as Source of Allenyl Groups.. .. 73... 

Regitz, M. Reactions of carbon-hydrogen active compounds with azides. XIII. Diazo group transfer. Neuere Method. Praep. Org. Chem. 

Carbon-hydrogen activation on rhodium and iridium is well documented. The complexes Cp Rh(PMe)3(H)2 Cp Ir(PMe3)H2, and Cp Ir(CO)2 provide the best examples of C-H activation. 

Two 16-electron intermediates dominate the carbon-hydrogen activation research on iridium centers. The complex Cp Ir(CO), studied by Graham and coworkers, and the complex Cp Ir(PMe3), studied by Bergman and coworkers, activate saturated carbon-hydrogen bonds. The 16-electron carbonyl complex was generated by photolysis of Cp Ir(CO)2. ... 

The yield of Cp Ir(CO)(H)(R) was estimated as 55%. The reaction could also be effected by CpIr(CO)2 but in only 20% yield. The photochemistry of CpIr(CO)2 in several, solvents has been examined to assist in the interpretation of the carbon-hydrogen activation system. A theoretical study using nonlocal density functions was also carried out on CpIr(CO)2. A chemical route to generating [Cp Ir(CO)] by reaction of N2O on Cp Ir(CO)2 was also reported . Reaction of N2O with Cp Ir(CO)2 in cyclohexane at 125 C and 50 atm produced Cp Ir(CO)(C6Hn)(H) in 76% yield ... 

That the ethene complex was the thermodynamic product, precludes it being an intermediate en route to the carbon-hydrogen activation product (the vinyl, hydride product ). Matrix isolation studies of CpIr(C2H4)PMe3 under photolysis showed isomerization to the vinyl, hydride complex . 

A few other iridium complexes activate carbon-hydrogen bonds Cp Ir2Cl2(/i-H)2 in the presence of PPha and benzene-60% aqueous KOH-[PhCH2NEta] Cl produces a product involving carbon-phosphorus and carbon-hydrogen activation . 

Table I. Carbon-Hydrogen Activation of Hydrocarbons Using Compounds 1 and 2 as Catalysts and Iodosylbenzene as the Monooxygen Transfer Agent4...

Table m. Carbon-Hydrogen Activation of C1-C3 Hydrocarbons with a Manganese-Substituted Keggin Ion Catalyst Using t-Butyl Hydroperoxide as the Monooxygen Transfer Reagent in Benzene a... 

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