Synthesis and structure of bulky phosphiniminato complexes of zirconium and hafnium: Aryl groups as “non-innocent” substituents in electrophilic systems

Sterically highly hindered phosphiniminato complexes MCl₃(NCP) were prepared from MCl₄ and Li[NPC] in toluene [M = Zr or Hf; NPC = 4-Bu^tC₆H₄C(SiMe₃)P(Ph)₂NC₆H₂Me₃-2,4,6]. Reaction with methyl lithium readily affords the corresponding zirconium and hafnium trimethyl complexes. The structures of representative zirconium and hafnium complexes MX₃(NPC) (X = Cl, M = Zr, Hf; X = Me, M = Hf) were determined by X-ray diffraction. In all cases the NPC ligand acts as C-N chelate, with an additional bonding contribution from the ipso-carbon atom of the C-bound aryl substituent, which results in a η¹:η²-coordination mode. The reaction of the hafnium trimethyl complex with salts of perfluoroarylborate anions results either in the diastereoselective formation of the binuclear cation [{(NPC)HfMe₂}₂(μ-Me)]⁺ or in the formation of the mononuclear cation [(NPC)HfMe₂]⁺, depending on the molar ratio of reagents.