Bis(alkyl) rare-earth complexes supported by a new tridentate amidinate ligand with a pendant diphenylphosphine oxide group. Synthesis, structures and catalytic activity in isoprene polymerization

Abstract

A new tridentate amidine 2-[Ph2P(O)]C6H4NHC(tBu)[double bond, length as m-dash]N(2,6-Me2C6H3) (1) bearing a side chain pendant Ph2P[double bond, length as m-dash]O group was synthesized and proved to be a suitable ligand for coordination to rare-earths ions. Bis(alkyl) complexes {2-[Ph2P(O)]C6H4NC(tBu)N(2,6-Me2C6H3)}Ln(CH2SiMe3)2(THF)n (Ln = Y, n = 1 (3), Ln = Er, n = 1 (4), Ln = Lu, n = 0 (5)) were prepared using alkane elimination reactions of and Ln(CH2SiMe3)3(THF)2 (Ln = Y, Er, Lu) in hexane and were isolated in 50, 70 and 75% yields respectively. The X-ray studies revealed that complexes 2-5 feature intramolecular coordination of P[double bond, length as m-dash]O groups to metal ions. The lutetium complex 5 proved to be rather stable: at 20 °C its half-life time is 1155 h, while for the yttrium analogue the half-life time was found to be 63 h. Complexes 3-5 were evaluated as precatalysts for isoprene polymerization. The systems Ln/borate/AliBu3 (Ln = 3-5, borate = [PhNHMe2][B(C6F5)4], [Ph3C][B(C6F5)4]) turned out to be highly efficient in isoprene polymerization and enable complete conversion of 1000-10,000 equivalents of monomer into polymer at 20 °C within 0.5-2.5 h affording polyisoprenes with a very high content of 1,4-cis units (up to 96.6%) and from narrow (1.49) to moderate (3.54) polydispersities. A comparative study of catalytic performance of the related bis(alkyl) yttrium complexes supported by amidinate ligands of different denticities and structures [tBuC(N-2,6iPr2C6H4)2](-), [tBuC(N-2,6-iPr2C6H4)(N-2-MeOC6H4)](-) and {2-[Ph2P(O)]C6H4NC(tBu)N(2,6-Me2C6H3)}(-) demonstrated that the introduction of a pendant donor group (2-MeOC6H4 or Ph2P(O)) into a side chain of amidinate scaffolds results in a significant increase in catalytic activity. The amidinate ligand bearing a Ph2P(O)-group provides a high isoprene polymerization rate along with excellent control over regio- and stereoselectivities and allows us to obtain polyisoprenes with a reasonable molecular weight distribution.

Metal Complexes as Catalysts/Moderators for Polymerization Reactions

“…), affording the corresponding polymeric materials with good transand cis-1,4-selectivity (≈ 96%), respectively. [22][23] A series of rare-earth metal complexes of bis-and tris(pyrazolyl)-based ligands were developed for applications in polymerization reactions (2.7-2.10, Figure 2.3). While complexes 2.7, activated with MAO, exhibited only moderate activities in ethylene polymerization, 24 the other heteroscorpionate bis(pyrazolyl)-based complexes (2.8-2.9) and the tris(pyrazolyl)borate complex 2.10 showed high activities (up to 3.2 x 10 6 g mol -1 h -1 atm -1 ) when activated with MAO and [Ph3C][B(C6F5)4], respectively.…”

N,N,N-Tris(diphenylphosphorylmethyl)amine

“…Phosphine oxides act as ligands for stabilizing oxophilic metal ions via complex formation. Many complexes of phosphine oxides stabilizing lanthanide and actinide ions have been described (some recent examples are: Baulin et al, 2015;Bowden et al, 2015;Dong et al, 2015;Hasegawa et al, 2015;Hirai et al, 2015Hirai et al, , 2016Tolpygin et al, 2015;Yanagisawa et al, 2015). Tripodal ligands form a pocket in which the metal can be embedded via spherical coordination and therefore create a shielded pocket contributing to an even greater stabilization of the complexes (see: Cecconi et al, 2000Cecconi et al, , 2001aFu et al, 2011;Li et al, 2010;Somov & Chausov, 2014, 2015Somov et al, , 2016.…”

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

“…Recently we demonstrated that the bis(alkyl) complexes {2-[Ph 2 P(O)]C 6 H 4 NC(tBu)N(2,6-Me 2 C 6 H 3 )}Ln-(CH 2 SiMe 3 ) 2 (THF) n (Ln = Y, n = 1; Ln = Er, n = 1; Ln = Lu, n = 0) coordinated by a tridentate amidinate ligand with a pendant Ph 2 PO group form ternary catalytic systems (Ln/ borate/10AliBu 3 ) which enable highly stereoselective (up to 96.6% cis-1,4) isoprene polymerization. 24 Nd, La) revealed a significant effect of the "actor group" on the activity and selectivity of the catalytic system as well as on the molecular weight distribution of the obtained polyisoprenes. 25 In order to develop new, efficient catalytic systems for isoprene polymerization based on complexes of lanthanides featuring large ionic radii (La, Nd, Sm), we focused on the synthesis of bis(tetramethylaluminate) complexes supported by the tridentate amidinate ligands {2-[Ph…”