Alkyl(amino)- and Alkyl(chloro)phosphanyl-Substituted Cyclopentadienyl Complexes of Titanium and Zirconium

Abstract

Phosphanyl-substituted cyclopentadienes of the type [RnCp−PR(NR1R2/Cl)] (1−22) (R = Alk, Ar; R1, R2 = H, Alk, Ar, SiR3; RnCp = tBuCp, Me4Cp, Ind, Me6Ind, Flu) can be synthesised by reaction of alkyldichlorophosphanes and alkyl(amino)chlorophosphanes with alkali metal cyclopentadienides. The method used is a general one and provides high isolated yields of the target compounds. The phosphanylcyclopentadienes can easily be deprotonated by strong bases (e.g. nBuLi, PhCH2K, Ph2CHK) and the potassium salts [RnCp−PR(NR1R2)]K (25−28) are efficiently transmetallated by Me3SnCl. A subsequent reaction with TiCl4(L)2 and ZrCl4(L)2 (L = THF, tetrahydrothiophene, Me3P) affords new half-sandwich complexes [{Me4Cp−PtBu(NEt2)}TiCl3] (36), [{Me4Cp−PtBu(NEt2)}TiCl3] (37) and [{tBuCp−PtBu(NEt2)}TiCl3] (38) in moderate yields. The reaction of [tBuCp−PtBu(Cl)] (6) with TiCl4 in the presence of Et3N at low temperature yields the half-sandwich complex [{tBuCp−PtBu(Cl)}TiCl3] (39) quantitatively; [(Cp−PtBu(Cl)]2CMe2] (11) reacts similarly and gives, dependent on the reagent ratio, either the homobimetallic derivative [{(Cp−PtBu(Cl)2CMe2}{TiCl3}2] (40) (1:2 ratio) or the ansa complex [{(Cp−PtBu(Cl)]2CMe2}TiCl2] (41) (1:1 ratio). The scope of this reaction could not be extended to sterically more demanding cyclopentadienyl derivatives. Treatment of [{tBuCp−PtBu(Cl)}TiCl3] (39) by LiN(H)tBu in the presence of Et3N leads to the formation of the constrained geometry complex [{tBuCp−PtBu(NtBu)}TiCl2] (42) in a high yield. All synthesised compounds were characterised by NMR spectroscopy, mass spectrometry and elemental analyses. The crystal structures of the ligand precursor [Me6Ind−PtBu(NHtBu)] (15) and that of [{Me4Cp−PtBu(NEt2)}TiCl3] (36) have been determined by X-ray diffractometry. The complexes described in this work are active in the MAO-mediated polymerisation of ethylene.