Investigations Directed at Catalytic Carbon−Carbon and Carbon−Oxygen Bond Formation via C−H Bond Activation

A 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)L2 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 π-acidic and readily form stable 18e
Cp*W(NO)(PPh3)(η2-olefin) adducts, which prevent oxidative addition of the hydrocarbon substrate to
the tungsten center. Similarly, benzophenone, Ph2CO, and diisopropyl ketone, iPr2CO, also form 1:1
η2-CO adducts with the π-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)(OCHiPr2)(Ph), in addition to the Cp*W(NO)(η2-OCiPr2)(PPh3) adduct, when benzene and diisopropyl ketone
are employed as the two substrates. The solid-state molecular structures of cis-Cp*W(NO)[η2-(CH2NMe)P(NMe2)2](H), Cp*W(NO)(OCHiPr2)(Ph), and Cp*W(NO)(η2-OCiPr2)(PPh3) have been established
by single-crystal X-ray crystallographic analyses.