The Boron-Catalyzed Polymerization of Dimethylsulfoxonium Methylide. A Living Polymethylene Synthesis

Abstract

Trialkyl and aryl organoboranes catalyze the polymerization of dimethylsulfoxonium methylide (1). The product of the polymerization is a tris-polymethylene organoborane. Oxidation affords linear telechelic alpha-hydroxy polymethylene. The polymer molecular weight was found to be directly proportional to the stoichiometric ratio of ylide/borane, and polydispersities as low as 1.01-1.03 have been realized. Although oligomeric polymethylene has been the most frequent synthetic target of this method, polymeric star organoboranes with molecular weights of 1.5 million have been produced. The average turnover frequency at 120 degrees C in 1,2,4,5-tetrachlorobenzene/toluene is estimated at >6 x 10(6) g of polymethylene (mol boron)(-1) h(-1). The mechanism of the polyhomologation reaction involves initial formation of a zwitterionic organoborane.ylide complex which breaks down in a rate-limiting 1,2-alkyl group migration with concomitant expulsion of a molecule of DMSO. The reaction was found to be first order in the borane catalyst and zero order in ylide. DMSO does not interfere with the reaction. The temperature dependence of the reaction rate yielded the following activation energy parameters (toluene, DeltaH(++) = 23.2 kcal/mol, DeltaS(++) = 12.6 cal deg/mol, DeltaG(++) = 19.5 kcal/mol; THF, DeltaH(++) = 26.5 kcal/mol, DeltaS(++) = 21.5 cal deg/mol, DeltaG(++) = 20.1 kcal/mol).

Polyethylene‐Based Tadpole Copolymers

“…Polyhomologation, an organoborane initiated polymerization of dimethylsulfoxonium methylide, leading to hydroxyl-terminated polyethylene, recently developed by Shea, [34][35][36][37] is an attractive method toward well-defined PE-based polymers including cyclics. The only example of cyclic PE is given by Shea who used B-thexylborocane as initiator for the polyhomologation of dimethylsulfoxonium methylide followed by a stitching reaction to freeze the cyclic structure.…”

“…For the synthesis of (PE 546 -alkyne) 2 -b-PS 37 , a mixture of (PE 546 -OH) 2 -b-PS 37 (0.23 g, 0.012 mmol), propiolic acid (0.020 mL, 0.24 mmol), and p-toluene sulfonic acid (PTSA) (0.0050 g, 0.024 mmol) in toluene was kept refluxing by using Dean-Stark apparatus for 48-96 h. Then, the solvent was removed under reduced pressure and the polymer was precipitated in methanol and dried under vacuum (0.22 g, M n,NMR = 19.4 kg mol −1 ). Similar procedure was followed for the synthesis of (PE 813 -alkyne) 2 -b-PS 19 .…”

“…For the synthesis of (c-PE 546 )-b-PS 37 , toluene (400 mL), CuBr (0.047 g, 0.33 mmol), and N,N,N′,N′′,N′′-Pentamethyldiethylenetriamine (PMDETA) (0.070 mL, 0.33 mmol) were added to a 1 L roundbottomed flask and the solution was stirred for 1 h. In a separate flask, (PE 546 -alkyne) 2 -b-PS 37 was dissolved (M n,NMR = 19.4 kg mol −1 , 0.20 g, 0.010 mmol) in toluene (0.20 L). The solution of polymer was then added to the CuBr/PMDETA solution via a peristaltic pump at a rate of 2 mL h −1 .…”

Well-defined polyethylene-based graft terpolymers by combining nitroxide-mediated radical polymerization, polyhomologation and azide/alkyne “click” chemistry

“…The resulting star is subsequently oxidized/hydrolyzed to afford hydroxyl-end-capped linear PEs. [30][31][32][33] The hydroxylfunctionalized PE can be used directly as initiator for (ROP) [34][35] of cyclic ethers/esters or indirectly, after chemical modification, for (ATRP), [36][37][38][39] (RAFT) 40 and ring-opening metathesis polymerization (ROMP). [41][42][43] In this work, we report the synthesis of novel polyethylene-based graft terpolymers via the "grafting onto" strategy by combining NMP, polyhomologation and CuAAC "click" chemistry.…”

Reactions of organoboranes with carbanions bearing three potential leaving groups: unusual processes, products and mechanisms

“…Reactions of dimethylsulfoxonium ylides with trialkylboranes are known, but in those reactions dimethyl sulfoxide serves as a leaving group. 16 Reactions of α-chlorosulfoxides with alkyllithium reagents in the presence of alkylboronate esters result in thiophilic addition of the alkyllithium to the sulfoxide followed by elimination of sulfoxide with formation of an α-chloroalkyllithium species, which then goes on to bring about homologation of the boronate ester. 17 However, the formation of 10a appears to be more akin in nature to the formation of homologated carbonyl compounds by reactions of trialkylboranes with diazocarbonyl compounds 18 or with anions derived from α-bromocarbonyl and related compounds.…”