|Title||Investigations directed at catalytic carbon-carbon and carbon-oxygen bond formation via C-H bond activation|
|Publication Type||Journal Article|
|Year of Publication||2007|
|Authors||Blackmore, IJ, Semiao, CJ, Buschhaus, MSA, Patrick, BO, Legzdins, P|
potential catalytic cycle for the formation of new C-C and C-O linkages from hydrocarbon feedstocks and readily available olefin and ketone substrates mediated by Cp’M(NO)(L) (M = Mo, W; Cp’ = Cp*, Cp; L = Lewis base) fragments has been investigated. The cycle is based on three steps: (1) oxidative addition of the hydrocarbon substrate to the metal center, (2) subsequent hydrometalation of the olefin or the ketone, and (3) final reductive elimination of the coupled product. Of the various Cp’M(NO)(L) groups examined, the Cp*W(NO)(PPh3) fragment has been found to be the best candidate for mediating these catalytic steps since it is not prone to form unreactive Cp*W(NO)(PPh3)2 as are some of the other fragments that readily decompose to 18e Cp’M(NO)L-2 complexes. Hence, Cp*W(NO)(PPh3) has been utilized to determine if the oxidative addition and hydrometalation steps can occur sequentially under one-pot experimental conditions. However, olefins are too pi-acidic and readily form stable 18e Cp*W(NO)(PPh3)(eta(2)-olefin) adducts, which prevent oxidative addition of the hydrocarbon substrate to the tungsten center. Similarly, benzophenone, Ph2CO, and diisopropyl ketone, (Pr2CO)-Pr-i, also form 1:1 eta(2) -C=O adducts with the pi-basic tungsten center in the 16e fragment. Nevertheless, oxidative addition and hydrometalation do occur sequentially to form the desired aryl alkoxide complex, Cp*W(NO)(OCHi-Pr-2))(Ph), in addition to the Cp*W(NO)(eta(2) -(OCPr2)-Pr-i)(PPh3) adduct, when benzene and diisopropyl ketone are employed as the two substrates. The solid-state molecular structures of cis-Cp*W(NO)[eta(2)-(CH2-NMe)P(NMe2)(2)](H), Cp*W(NO)((OCHPr2)-Pr-i)(Ph), and Cp*W(NO)(eta(2)-(OCPr2)-Pr-i)(PPh3) have been established by single-crystal X-ray crystallographic analyses.
|URL||<Go to ISI>://000249559900008|