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

摘要

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(mu-NPR_3)]_2 (R=Me 3,i-Pr 4).In contrast,CpTi(NPt-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-l,3-butadiene,diphenylacetylene,phenyl-acetylene,bis(trimethylsilyl)acetylene,ethylene,and propylene to give monometallic met-allacyclic complexes.In this fashion,the Ti(IV) metallacycles CpTi(NPt-Bu_3)(CH_2C(Me)-C(Me)CH_2),6,CpTi(NPt-Bu_3)(CPh)4,7,CpTi(NP~*-Bu_3)(C(Ph)CHC(Ph)CH),8,CpTi(NP~*-Bu_3)-(eta~2-C_2(SiMe_3)_2),9,CpTi(NP~*-Bu_3)(CH_2)_4,10,CpTi(NPt-Bu_3)(CH_2CHMe)_2,15,and CpTi(NPt-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_6H_4Ph)PN)Cl_2 (Cp'=Cp 18,Cp~* 19).The products [Cp'Ti(NPtBu_2(2-C_6H_4Ph)) (Cp'=Cp 20,Cp~* 21) contained eta~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(NPt-Bu_3)Cl_2 (11) with Mg in the presence of CO,affording the species Cp~*Ti(NPt-Bu_3)(CO)_2 (22).X-ray data for 4,6,7,9,10,15,and 17-22 are reported.