Perfectly Alternating and Regioselective Copolymerization of Carbonyl Sulfide and Epoxides by Metal‐Free Lewis Pairs

Abstract

The preparation of perfectly alternating and regioslective copolymers derived from the copolymerization of carbonyl sulfide (COS) and epoxides by metal-free Lewis pair catalysts composed of a Lewis base (amidine, guanidine, or quaternary onium salts) and a Lewis acid (triethyl borane) is described. Colorless and highly transparent copolymers of poly(monothiocarbonate) were successfully obtained with over 99 % tail-to-head content and high molecular weight (up to 92.5 kg mol ). In most instances, oxygen-sulfur exchange reactions (O/S ERs), which would generate random thiocarbonate and carbonate units, were effectively suppressed. The turnover frequencies (TOF) of these Lewis pair catalyzed processes were as high as 119 h at ambient temperature.

Ring‐opening of Epoxides Mediated by Frustrated Lewis Pairs

“…The molecular structure of 3a is unambiguously established by single-crystal X-ray diffraction analysis (Figure 3, bottom) [24] and shows that the ring-opened 2-methyloxirane gives rise to Scheme3.Relative wB97X-D/6-31G(d,p) Gibbs free energies (in kcal mol À1 )for the conversion of 1 into 2a-c (only the methyl-substituted species a are shown;hydrogen atoms are omitted for clarity). (17),C22ÀC23 1.538(2),C 23ÀO1 1.403(2), C23ÀC24 1.532(2), O1ÀB1 1.519(2), C1ÀP1 1.7956 (19);P1-C22-C23 118.56 (12), C22-C23-O1 107.67 (15), C23-O1-B1119.77 (14).…”

“…31 P{ 1 H}, 11 B{ 1 H} spectra were recorded on aB ruker Avance4 00 and externally referenced (85 % H 3 PO 4 and BF 3 ·OEt 2 ,r espectively). 19 FNMR spectra were recorded on aB ruker Avance2 50 and externally referenced (CFCl 3 ). The 1 H and 13 Cr esonance signals were attributed by means of 2D HSQC and HMBC experiments.…”

“…Reactionof1 with propylene sulfide (left) and molecular structure of 6 (right;ellipsoids are setat5 0% probability,h ydrogen atoms are omitted for clarity). Selectedb ond lengths []and angles [8]f or 6:P1 ÀS1 2.0280(5), S1ÀB1 2.1117 (19), B1ÀC1 1.670(2),C1 ÀP1 1.7875 (16); P1-S1-B1 75.48(5), S1-B1-C1 95.45(10), B1-C1-P19 4.23(10), C1-P1-S1 94.83(6);S 1-P1-C1-B1 0.92 (11). m-C 6 H 5 ), 7.09 (t, 3 J H,H = 7.5 Hz, 2H; m-C 6 H 5 ), 7.02 (t, 3 J H,H = 7.2 Hz, 1H; p-C 6 H 5 ), 6.92 (t, 3…”

“…Furthermore, a cationic aluminium phosphine complex was shown to ring‐open propylene oxide . Zhang, Darensbourg and co‐workers extended this concept to catalytic ring‐opening reactions, thereby developing the copolymerization of carbonyl sulfide and epoxides catalyzed by metal‐free Lewis pairs . To further advance this field, a better mechanistic understanding of these ring‐opening processes is desirable, which will aid in the development of more active and selective metal‐free catalysts.…”

“…[18] Zhang, Darensbourg and co-workers extended this concept to catalytic ring-opening reactions, thereby developing the copolymerization of carbonyl sulfide and epoxides catalyzed by metal-free Lewis pairs. [19] To furthera dvance this field, ab etter mechanistic un- derstanding of these ring-openingp rocesses is desirable, which will aid in the development of more active and selective metal-free catalysts. Hence, we envisioned to examinethe reactions of metal-free FLPs with epoxides, and study these reactions mechanistically by employing intramolecular FLPs.…”