Mono-phosphacyclopentadienyl bis(tetramethylaluminate) lanthanide complexes

Abstract

Homoleptic complexes Ln(AlMe₄)₃ (Ln = La, Nd) can be straightforwardly utilized in salt metathetic exchange reactions with potassium 2,3,4,5-tetramethylphospholide (KTmp) or 3,4-dimethyl-2,5-bis(trimethylsilyl)phospholide (KDsp) affording monophosphacyclopentadienyl hydrocarbyl complexes (η⁵-PC₄Me₄)Ln(AlMe₄)₂ and [η⁵-PC₄Me₂(SiMe₃)₂]Ln(AlMe₄)₂ (Ln = La, Nd). The solid-state structures reveal distinct metal size effects as evidenced by X-ray diffraction analyses of monomeric neodymium Tmp and Dsp derivatives as well as the dimeric lanthanum Tmp complex. Dimerization is accomplished by intermolecular P → La donor contacts. Upon activation with [PhMe₂NH][B(C₆F₅)₄] the monophosphacyclopentadienyl complexes initiate the polymerization of isoprene producing 1,4-trans-polyisoprene (tPIP > 87%) with moderate activity (≈30 kg_PIP mol_Ln⁻¹ h⁻¹).