Todd Graham - Reduction of Titanium(IV)-Phosphinimide Complexes: Routes to Ti(III) Dimers, Ti(IV)-Metallacycles, and Ti(II) Species

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  Todd W. Graham, James Kickham, Silke Courtenay, Pingrong Wei, and   Douglas W. Stephan Organometallics,   2004, 23 (13), 3309


  The redox chemistry of phosphinimide-containing group IV metal   complexes  has been investigated. Reaction of the simple   phosphinimide species  CpTi(NPR3)Cl2  (R = Me 1, i-Pr 2)   with Mg affords complexes formulated as   [CpTiCl(μ-NPR3)]2 (R = Me   3, i-Pr 4). In   contrast, CpTi(NPt-Bu3)Cl2  (5)  is reduced by Mg to a putative Ti(II)   species that can be intercepted  by a variety of reagents   including 2,3-dimethyl-1,3-butadiene,  diphenylacetylene,   phenylacetylene, bis(trimethylsilyl)acetylene,  ethylene,   and propylene to give monometallic metallacyclic complexes.   In  this fashion, the Ti(IV) metallacycles   CpTi(NPt-Bu3)(CH2C(Me)C(Me)CH2),   6,   CpTi(NPt-Bu3)(CPh)4,   7,   CpTi(NPt-Bu3)(C(Ph)CHC(Ph)CH),   8,   CpTi(NPt-Bu3)(η2-C2(SiMe3)2),   9,   CpTi(NPt-Bu3)(CH2)4,   10,   CpTi(NPt-Bu3)(CH2CHMe)2,   15, and   CpTi(NPt-Bu3)(CH2)2(CPh)2,   16, were prepared. Related intramolecular   formation of metallacycle complexes was achieved upon reduction   of   Cp‘Ti(t-Bu2(2-C6H4Ph)PN)Cl2  (Cp‘ = Cp 18, Cp* 19). The   products   [Cp‘Ti(NPtBu2(2-C6H4Ph)] (Cp‘ =   Cp 20, Cp* 21) contained   η6-interactions  between Ti and the 2-phenyl   substituent of the biphenyl unit. While    Ti(II)-phosphinimide complexes have proven difficult to handle   due to  their reactivity, an unequivocal example of a Ti(II)   species was  obtained via reduction of   Cp*Ti(NPt-Bu3)Cl2  (11) with Mg in the presence of CO, affording   the species Cp*Ti(NPt-Bu3)(CO)2  (22). X-ray data for 4,   6, 7, 9,   10, 15, and   1722 are reported.

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