New Rare Earth Metal Bis(alkyl)s Bearing an Iminophosphonamido Ligand. Synthesis and Catalysis toward Highly 3,4-Selective Polymerization of Isoprene

Abstract

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.

The Origin of the MNXN Metallacycle Flexibility in the Chelate Iminophosphonamide and Amidinate Transition Metal Complexes

“…However, the chemistry of transition metal iminophosphonamides (NPN) that had been considered to be heteratomic analogs of the corresponding metal amidinates has been developing slowly. Nevertheless, in the last two decades transition metal iminophosphonamides have been reported as active catalysts for alkene polymerization (NiNPN, ZrNPN), 3,4‐selective polymerization of isoprene (rare earth NPN complexes), alkene oligomerization (CrNPN), ethene dimerization (NiNPN),[5c] cyclopropanation and aziridination (CuNPN), as well as for Tsuji–Trost cross‐coupling (PdN 2 P) Recently we have demonstrated that arene ruthenium iminophosphonamide [( p ‐cymene)RuCl{Ph 2 P(N‐ p Tol) 2 }] can efficiently reduce acetophenone under transfer hydrogenation conditions …”

Chemo‐ and stereoselective polymerization of 3‐methylenehepta‐1,6‐Diene and Its thiol‐ene modification

“…We have previously reported the cis −1,4 polymerization of the monomer MHD, showing the potential orthogonal reactivity of the two reactive sites in coordination polymerization . To obtain 1,2‐PMHD, we refer to the catalyst systems active for the 3,4‐regioselective polymerization of isoprene, which are relatively limited . In addition, we have to screen out those active for ethylene or α ‐olefin polymerization, leaving few room for choice.…”

Precisely Controlled Polymerization of Styrene and Conjugated Dienes by Group 3 Single‐Site Catalysts

“…The aminophosphinimido dialkyl scandium complex 107 Sc reported by Cui and co‐workers in combination with [PhNHMe 2 ][B(C 6 F 5 ) 4 ] and Al i Bu 3 formed the first non‐Cp‐ligated rare‐earth metal based catalytic system providing extremely high activities and 3,4‐selectivities for the IP polymerization . Sequentially, a variety of rare‐earth metal bis(alkyl) complexes 107 Lu – 116 featuring NPN ligands developed by same group also displayed highly activities and 3,4‐seletivities for IP polymerization (Figure ) .…”