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-ButC6H4C(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 CPh3+ 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.

Bulky phosphiniminates MX3(NCP) (X = Cl or Me) bind to M = Zr and Hf not only as N–C chelates but involve arene π-bonding, to give an η1:η2-coordination mode. The reaction of HfMe3(NCP) with CPh3+ gives selectively either the binuclear cation [{(NPC)HfMe2}2(μ-Me)]+ or mononuclear [(NPC)HfMe2]+, depending on the reagent ratio.Figure optionsDownload as PowerPoint slide