Mono-phosphacyclopentadienyl bis(tetramethylaluminate) lanthanide complexes.

Homoleptic complexes Ln(AlMe(4))(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 (eta(5)-PC(4)Me(4))Ln(AlMe(4))(2) and [eta(5)-PC(4)Me(2)(SiMe(3))(2)]Ln(AlMe(4))(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 [PhMe(2)NH][B(C(6)F(5))(4)] the monophosphacyclopentadienyl complexes initiate the polymerization of isoprene producing 1,4-trans-polyisoprene (tPIP > 87%) with moderate activity (approximately 30 kg(PIP) mol(Ln)(-1) h(-1)).