Cyclometalated titanium and zirconium complexes stabilised by a new silylmethylene-linked tetradentate triamidophosphine

Abstract

The silylmethylene-linked triamidophosphine P(CH₂SiMe₂NHPh)₃ was isolated in form of its tri-lithium salt Li₃[P(CH₂SiMe₂NPh)₃]·2.5Et₂O (1·2.5Et₂O) and employed for the synthesis of titanium and zirconium complexes. Starting from 1·2.5Et₂O, the chlorido complexes [κ⁴-N,N,N,P-PN₃]MCl (4-M, M = Ti, Zr) were prepared and examined with respect to alkylation. Upon reaction of 4-Ti with (trimethylsilyl)methyl lithium, intra-ligand cyclometalation at one of the ortho-N-phenyl positions was observed and the resulting thermally stable titanazetidine [κ⁵-N,N,N,P,C-N₂P(NC)]Ti (5-Ti) isolated. Similarly, the related zirconazetidine [κ⁵-N,N,N,P,C-N₂P(NC)]Zr(THF) (5-Zr) was isolated upon reaction of 4-Zr with Bn₂Mg(THF)₂. Using LiCH₂PMe₂ as alkyl transfer reagent, both complexes 4-M were converted to the corresponding phosphametallacyclopropanes [κ⁴-N,N,N,P-PN₃]M(κ²-C,P-CH₂PMe₂) (7-M, M = Ti, Zr). Upon gentle heating, complexes 7-M were cleanly converted to the cyclometalated species 5-M and trimethylphosphine. These results are discussed in the context of related amidophosphine and triamidoamine complexes.