A novel catalyst composed of neodymium (III) isopropoxide [Nd(OiPr) 3 ] and methylaluminoxane (MAO) was examined in isoprene polymerization. The Nd(OiPr) 3 -MAO catalyst proved to be highly effective in heptane even at low [Al]/[Nd] ratios (ca. 30) to give polyisoprene that possessed high cis-1,4 stereoregularity (Ͼ ca. 90%), a high number-average molecular weight (M n ϳ10 5 ), and relatively narrow molecular weight distributions (M w /M n ϭ 1.9 -2.8). The catalyst activity increased with an increasing [Al]/[Nd] ratio from 10 to 80 as well as temperature of aging and polymerization from 0 to 60°C. The polymerization proceeded in the first order with respect to the monomer concentration. Aliphatic solvents (heptane and cyclohexane) achieved a higher yield and M n of polymer than toluene as a solvent. The M w /M n ratio remained around 2.0, and the gel permeation chromatographic curve was always unimodal, indicating that this system is homogeneous and involves a single active site. The microstructure of polyisoprene was determined by IR, 1 H NMR, and 13 C NMR. The cis-1,4 contents of the final polymers stayed in the range of 90 -92%, regardless of reaction conditions, indicating the high stability of stereospecificity of the catalyst.

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Newrareearthmetalbis(alkyl)complexes[(NPN Ph )Ln(CH 2 SiMe 3 ) 2 (THF)](NPN Ph :N(Ph)PPh 2 dNC 6 H 2 Me 3 -2,4,6; Ln ) Sc (3a), Ln ) Y (3b), Ln ) Lu (3c)) and [(NPN Py )Sc(CH 2 SiMe 3 ) 2 (THF)] (NPN Py ) N(Py)PPh 2 dNC 6 H 2 Me 3 -2,4,6) (3d)) have been prepared via protonolysis reaction between rare earth metal tris(alkyl)s and the corresponding iminophosphonamines. Complexes 3a-d are analogous monomers of THF solvate. Each metal ion coordinates to a η 2 -chelated NPN ligand and two cis-located alkyl groups, adopting tetrahedron geometry. The scandium complex [(NPN Ph )Sc(CH 2 SiMe 3 ) 2 (THF)] in combination with [PhNHMe 2 ][B(C 6 F 5 ) 4 ] and AliBu 3 forms the first non-Cp-ligated rare earth metal based catalyst system to provide extremely high activity and 3,4-selectivity for the polymerization of isoprene. The resultant high molecular weight polymer (M n ) 99 × 10 4 ) with narrow molecular weight distribution (PDI ) 1.55) has a 3,4-regularity up to 94.7% (Tp ) -40°C, toluene, 2 h, 100% yield). The complexes 3b and 3c, with a larger ionic radius, are less regioselective, and 3d, with an electron-donating pyridyl moiety, is inert. The probable initiation species and mechanistic scenario are also presented.