Historic overview Carbon–hydrogen bond activation

cobalt-catalyzed c-h activation

in 1969, a.e. shilov reported potassium tetrachloroplatinate induced isotope scrambling between methane , heavy water. pathway proposed involve binding of methane pt(ii). in 1972, shilov group able produce methanol , methyl chloride in similar reaction involving stoichiometric amount of potassium tetrachloroplatinate, catalytic potassium hexachloroplatinate, methane , water. due fact shilov worked , published in soviet union during cold war era, work largely ignored western scientists. so-called shilov system today 1 of few true catalytic systems alkane functionalizations.

in cases, discoveries in c-h activation being made in conjunction of cross coupling. in 1969, yuzo fujiwara reported synthesis of (e)-1,2-diphenylethene benzene , styrene pd(oac)2 , cu(oac)2, procedure similar of cross coupling. on category of oxidative addition, m. l. h. green in 1970 reported on photochemical insertion of tungsten (as cp2wh2 complex) in benzene c–h bond , george m. whitesides in 1979 first carry out intramolecular aliphatic c–h activation

fujiwara s palladium- , copper-catalyzed c-h functionalization

the next breakthrough reported independently 2 research groups in 1982. r. g. bergman reported first transition metal-mediated intermolecular c–h activation of unactivated , saturated hydrocarbons oxidative addition. using photochemical approach, photolysis of cp*ir(pme3)h2, cp* pentamethylcyclopentadienyl ligand, led coordinatively unsaturated species cp*ir(pme3) reacted via oxidative addition cyclohexane , neopentane form corresponding hydridoalkyl complexes, cp*ir(pme3)hr, r = cyclohexyl , neopentyl, respectively. w.a.g. graham found same hydrocarbons react cp*ir(co)2 upon irradiation afford related alkylhydrido complexes cp*ir(co)hr, r = cyclohexyl , neopentyl, respectively. in latter example, reaction presumed proceed via oxidative addition of alkane 16-electron iridium(i) intermediate, cp*ir(co), formed irradiation of cp*ir(co)2.

c–h activation bergman et al. (left) , graham et al.

the selective activation , functionalization of alkane c–h bonds reported using tungsten complex outfitted pentamethylcyclopentadienyl, nitrosyl, allyl , neopentyl ligands, cp*w(no)(η-allyl)(ch2cme3).

in 1 example involving system, alkane pentane selectively converted halocarbon 1-iodopentane. transformation achieved via thermoloysis of cp*w(no)(η-allyl)(ch2cme3) in pentane @ room temperature, resulting in elimination of neopentane pseudo-first-order process, generating undetectable electronically , sterically unsaturated 16-electron intermediate coordinated η-butadiene ligand. subsequent intermolecular activation of pentane solvent molecule yields 18-electron complex possessing n-pentyl ligand. in separate step, reaction iodine @ −60 °c liberates 1-iodopentane complex.

arene c–h bonds readily activated metal complexes, illustrated directed ortho metalation. n,n-dimethylbenzylamine in cyclometalation readily many transition metals:

one manifestation murai olefin coupling.




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