Phosphine-functionalized amidinate ligated rare-earth metal complexes for highly 3,4-selective living polymerization of 1,3-conjugated dienes.

A series of rare-earth metal bis(alkyl) complexes have been prepared via protonolysis reactions of tris(aminobenzyl) complexes (Ln(CH 2 C 6 H 4 N(Me) 2 - o ) 3 ) with phosphine-functionalized amidinated ligands ( Dipp NCN(CH 2 ) n PPh 2 , n = 2 (L1-H) and n = 3 (L2-H)). The X-ray diffraction of P2-Sc ( Dipp NCN(CH 2 ) 3 PPh 2 Sc(CH 2 C 6 H 4 N(Me) 2 - o ) 2 ) showed the un-coordination of the diphenylphosphine group due to the inherent saturation of the central metal ion. In conjunction with [Ph 3 C][B(C 6 F 5 ) 4 ], all the rare-earth metal complexes showed a high catalytic activity for the polymerization of 1,3-conjugated dienes (isoprene, β-myrcene and β-farnesene), affording highly 3,4-regular polymers (up to 100% 3,4-) with high molecular weight and narrow molecular weight distribution. After the abstraction of the alkyl moiety -CH 2 C 6 H 4 N(Me) 2 - o of P1-Sc by [Ph 3 C][B(C 6 F 5 ) 4 ], the species with the coordination of the diphenylphosphine group to the central metal probably formed, as shown in the 31 P NMR spectra and DFT calculation results, and it might serve as the true active species in the 3,4-selective polymerization of 1,3-conjugated dienes.