Highly Stereoregular 1,3-Butadiene and Isoprene Polymers through Monoalkyl-N-Aryl-Substituted Iminopyridine Iron Complex-Based Catalysts: Synthesis and Characterization

Abstract

Some novel monoalkyl-N-aryl-substituted iminopyridine iron chloride complexes, differing in the nature of the substituent at the iminic carbon and at the ortho position of the aryl ring, were synthesized and characterized. For one of them, single crystals were obtained, which allowed for the determination of its crystalline structure, in which the iron center is coordinated to the chlorides and to the two nitrogen atoms of the ligand. The coordination around iron is distorted tetrahedral, a coordination mode rarely identified for FeCl2 adducts with bidentate nitrogen ligands. All the complexes were used, in combination with methylaluminoxane, for the polymerization of 1,3-butadiene and isoprene, providing syndiotactic 1,2 poly­(1,3-butadiene)­s and poly­(isoprene)­s with a predominantly cis-1,4/3,4 alternating structure, in which short cis-1,4 sequences of three or five units, whose length depends on the nature of the ligand on the iron atom, are present. A detailed NMR characterization (1H-, 13C-, and 2D experiments) of the resultant poly­(isoprene)­s is reported, and a tentative scheme for the formation of the novel isoprene polymers is proposed.

Fe‐based catalyst with diphenylphosphite as donor for stereopolymerization of butadiene, isoprene, and myrcene

“…The microstructures of the polymers were determined by FT-IR (Bruker, Alpha II) and NMR spectroscopy (Bruker AV-400 spectrometer, 400 MHz for 1 H NMR and S C H E M E 1 The N,N-bidentate iron complexes reported for diene polymerization 100.6 MHz for 13 C NMR in CDCl 3 or o-C 6 D 4 Cl 2 ). The number average-molecular weights (M n ) and molecular weight distributions (Ð) of polymers were measured at 30 C by gel permeation chromatography (PL-2000) using tetrahydrofuran eluent or 150 C by HLC-8321GPC/HT using 1,2,4-C 6 H 3 Cl 3 at a flow rate of 1.0 ml min À1 .…”

“…Trans-1,4 (967 cm À1 ), however, is invisible. Assignments to the olefin protons using 1 H NMR and 13 C NMR are also illustrated in Figure 2. The 1,2 ratio and the pentad (rrrr) denoting syndiotactic stereoregularity can be determined by the Equation 1 and 2, respectively.…”

“…Al i-Bu 3 and AlEt 3 activated catalysts are of essentially 1,2 syndiotactic selectivity, and the regio-and stereoregularity are much higher than most iron catalysts supported with nitrogen ligand. [3][4][5][6][7][8][9][10][11][12][13][14][15] For example, 59.1% to 92.8% of 1,2 regioselectivity with 75.3% to 95.1% syndiotacticity index for Al i-Bu 3 (run 1-5, Table 1), and 73.8% to 75.6% regioselectivity with 51.3% regularity for AlEt 3 (run 6-8, Table 1). Elevating the feeding has a slightly beneficial effect on the selectivity.…”

“…We have also examined the thermal stability the formed catalyst by varying the polymerization temperature from 5 to 80 C. The polymerization activity is prominent at elevated temperature, superior to iron counterpart supported by N,N-type ligand. [13][14][15] Majority of butadiene (82.1%) is converted to polymer at 80 C in 1 h (run 14, Table 1), whereas only 45.3% of monomer is polymerized at 28 C in 4 h (run 13, Table 1). Particularly, the 1,2-syndiotactic selectivity is survived at 80 C, and the resultant polybutadiene is incorporated at 83.3% of 1,2 units with 89.3% syndiotactic configuration.…”

“…These catalysts were very active in diene polymerizations under ambient temperature, providing binary cis-1,4/3,4, trans-1,4/3,4 polyisoprene, cis-1,4/1,2 (major) polybutadiene, as well as polymyrcene in some cases. [12][13][14][15] Over the past decades, there are significant progresses in stereoselective polymerization of butadiene promoted by iron, [16][17][18][19][20][21][22] cobalt, 23 chromium 24,25 and molydenium catalyts [26][27][28] with phosphine, phosphate or phosphite as an additive or ligand. Preceding this work, [16][17][18][19][20][21][22] we have reported phosphate and phosphite are efficient additives for iron catalyzed 1,2 stereopolymerization of butadiene.…”