Bis(tetramethylaluminate) Lanthanide Complexes Supported by Amidinate Ligands with a Pendant Ph₂P═X (X = O, S) Group: Application in Isoprene Polymerization

Abstract

A series of bis­(tetramethylaluminate) lanthanide complexes {2-[Ph2PX]­C6H4NC­(tBu)­N­(2,6-Me2C6H3)}­Ln­(AlMe4)2 (X = O, Ln = La (1); X = O, Ln = Nd (2); X = O, Ln = Sm (3); X = S, Ln = La (4); X = S, Ln = Nd (5)) coordinated by tridentate amidinate ligands bearing a hard (PO) or soft (PS) donor group were synthesized in 82, 71, 54, 77, and 69% yields, respectively. An X-ray analysis revealed that complexes 1–5 feature an intramolecular coordination of the Ph2PX group to the metal ion and both AlMe4 fragments coordinate to the metal center in a κ2 fashion. The binary systems containing Nd complexes 2 and 5 in combination with [Ph3C]­[B­(C6F5)4] (TB) or [PhNHMe2]­[B­(C6F5)4] (HNB) have high catalytic activity in isoprene polymerization. The activity of 5 containing a soft Lewis base (PS) in the presence of both TB and HNB was much higher in comparison to that of 2 bearing a hard PO group. For the ternary systems 1–5/TB,HNB/nAlR3 (AliBu3, n = 10; AliBu2H, n = 1; AlMe3, n = 10; toluene, room temperature) record reaction rates were observed for neodymium complex 5: in combination with TB, HNB, and AliBu3 it enables quantitative polymerization of 1000 equiv of monomer within 5 min. The effect of the nature of the pendant donor group (hard PO vs soft PS) on the catalytic activity of the ternary systems is clearly manifested only in the case of neodymium complexes 2 and 5: the systems based on complex 5 have much higher activity in comparison to 2. The systems 4/TB,HNB/10AliBu3 and 5/TB/10AliBu3 provide the best stereoselectivities and enable formation of polyisoprene with 73.9–77.4% content of cis-1,4-units. These systems allow for the synthesis of polyisoprenes with a rather narrow polydispersity (M w/M n = 1.17–1.83).

Sc and Y bis(alkyl) complexes supported by bidentate and tridentate amidinate ligands. Synthesis, structure and catalytic activity in polymerization of isoprene and 1-heptene

“…In a series of recent publications, it was demonstrated that bidentate and tridentate amidinate ligands bearing various pendant donor groups 2-MeOC 6 H 4 , 17 NC 9 H 6 , 18 2-[Ph 2 P(X)]C 6 H 4 (X = O, S, NPh, N(2,6-Me 2 C 6 H 3 )), 19 (N 2 C 3 H 2 )(C 6 H 2 Me 3 -2,4,6) 20 in the side chain, can be successfully employed as a suitable coordination environment for the synthesis of isolable mono, bis(alkyl), tetramethylaluminate and borohydrido complexes of large rare-earth metals. At the same time, a number of these bis(alkyl) complexes make it possible to polymerize isoprene at a high rate and regulate the stereoselectivity of the process depending on the nature of the ligand ( cis -1,4 up to 98.5%, 19 a , b trans -1,4 up to 84.8% 19 b or 3,4 up to 99.3% 20 ).…”

Syntheses of Group 5 Amide Amidinates and Their Reactions with Water: Different Reactivities of Nb(V) and Ta(V) Complexes

“…Early transition metal amidinate complexes have been shown to be catalysts (or precatalysts) for a number of chemical reactions. − In addition, complexes with all N-containing ligands including those with amidinates have been used as precursors to microelectronic materials − such as metal oxides. We reported earlier reactions of M­(NMe 2 ) 5 (M = Nb, Ta) with H 2 O, yielding oxo-bridged cage complexes [M­(μ 3 -O)­(Me 2 N) 3 ] 4 (Scheme ; M = Nb, 1 ; Ta, 2 ) with elimination of HNMe 2 .…”