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

The redox chemistry of phosphinimide-containing group IV metal complexes has been investigated. Reaction of the simple phosphinimide species CpTi(NPR 3 )Cl 2 (R = Me 1, i -Pr 2 ) with Mg affords complexes formulated as [CpTiCl(μ-NPR 3 )] 2 (R = Me 3, i- Pr 4 ). In contrast, CpTi(NP t -Bu 3 )Cl 2 ( 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(NP t- Bu 3 )(CH 2 C(Me)C(Me)CH 2 ), 6, CpTi(NP t- Bu 3 )(CPh) 4, 7, CpTi(NP t- Bu 3 )(C(Ph)CHC(Ph)CH), 8, CpTi(NP t- Bu 3 )(η 2 -C 2 (SiMe 3 ) 2 ), 9, CpTi(NP t- Bu 3 )(CH 2 ) 4, 10, CpTi(NP t- Bu 3 )(CH 2 CHMe) 2, 15, and CpTi(NP t- Bu 3 )(CH 2 ) 2 (CPh) 2, 16, were prepared. Related intramolecular formation of metallacycle complexes was achieved upon reduction of Cp‘Ti( t- Bu 2 (2-C 6 H 4 Ph)PN)Cl 2 (Cp‘ = Cp 18, Cp* 19 ). The products [Cp‘Ti(NPtBu 2 (2-C 6 H 4 Ph)] (Cp‘ = Cp 20, Cp* 21 ) contained η 6 -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(NP t- Bu 3 )Cl 2 ( 11 ) with Mg in the presence of CO, affording the species Cp*Ti(NP t- Bu 3 )(CO) 2 ( 22 ). X-ray data for 4, 6, 7, 9, 10, 15, and 17 − 22 are reported.