Search

A laboratory experiment that uses proton nuclear magnetic resonance (NMR) and gel permeation chromatography (GPC) to investigate the transformation of monomer into polymer is described. The synthesis of polystyrene was conducted through nitroxide-mediated polymerization while GPC and NMR were used to analyze reaction-mixture aliquots. The exercise provides students with better understanding of controlled radical polymerization methods.

Remote binding of B(C6F5)3 to (PPO)PdMeL (L = pyridine or lutidine) or {(PPO)PdMe}2 ethylene polymerization catalysts that contain phosphine-arenephosphinate or phosphine-arenephosphonate ligands (PPO- = [1-PAr2-2-PR'O2-Ph]-: Ar = R' = Ph (1a); Ar = Ph, R' = OEt (1b); Ar = Ph, R' = OiPr (1c); Ar = 2-OMe-Ph, R' = OiPr (1d)) significantly increases the catalyst activity and the molecular weight of the polyethylene (PE) product. In the most favorable case, in situ conversion of (1d)PdMe(py) to the base-free adduct {1d•B(C6F5)3}PdMe increases the ethylene polymerization activity from 9.8 to 5700 kg mol-1 h-1 and the Mn of the PE product from 9030 to 99 200 Da (80 °C, 410 psi). X-ray structural data, trends in ligand lability, and comparative studies of BF3 activation suggest that these allosteric effects are primarily electronic in origin. The B(C6F5)3 binding enhances the chain growth rate (Rgrowth) by increasing the degree of positive charge on the Pd center. This effect does not result in the large increase in the chain transfer rate (Rtransfer) and concomitant reduction in PE molecular weight seen in previous studies of analogous (PO)PdRL catalysts that contain phosphine-arenesulfonate ligands, because of the operation of a dissociative chain transfer process, which is inhibited by the increased charge at Pd. [ABSTRACT FROM AUTHOR]

Arylborophosphonate cage compounds [ArPO3BAr′]nwith n= 4 or 6 were synthesized by condensation reactions ofArP(O)(OH)2and Ar′B(OH)2. (3,5-tBu2-Ph)P(O)(OH)2(1) reacts with arylboronic acids that contain electron-withdrawingsubstituents to form borophosphonate tetramers [Ar1PO3BAr2]4(Ar1= 3,5-tBu2-Ph; Ar2= o-Br-Ph, o-CF3-Ph, p-CF3-Ph, p-CHO-Ph; 3a–d) and hexamers [Ar1PO3BAr2]6(Ar2= p-CF3-Ph, p-CHO-Ph; 4c–d) in 80–93% NMR yield. For Ar2= p-CF3-Ph and p-CHO-Ph, both products wereobserved, with the tetramer being favored under dilute reaction conditionsand the hexamer favored under concentrated reaction conditions. Interconversionbetween tetramer (3cor 3d) and hexamer(4cor 4d) was observed at room temperatureand above in toluene. The phosphine phosphonic acid (2-PPh2-Ph)P(O)(OH)2(6) reacts with arylboronicacids that contain electron-withdrawing substituents to form tetramers[Ar1PO3BAr2]4(Ar1= 2-PPh2-Ph; Ar2= p-CF3-Ph, p-CHO-Ph; 7c–d) in 70–75% NMR yield. The reactions of 1or 6with (p-tolyl)B(OH)2(2f), and the reaction of 6with (o-CF3-Ph)B(OH)2(2b),yield only trace amounts of borophosphonate cage compounds and insteadafford the corresponding [ArBO]3boroxines and condensationproducts with unknown structures. [ABSTRACT FROM AUTHOR]

Themultifunctional phosphine-sulfonate-diethyl phosphonate ligand[1-(P(4-tBu-Ph)(2-PO3Et2-5-Me-Ph)-2-SO3-5-Me-Ph]−([OP-P-SO]−) was used to form complexes of type[κ2-(OP-P-SO)]PdMe(L)(L = 2,6-lutidine, 2b; L = pyridine, 2c).B(C6F5)3abstracts the Pd-bound sulfonategroup of 2band induces a switch to a phosphine-diethylphosphonate coordination mode, affording [κ2-(OP-P-SO-B(C6F5)3)]PdMe(2,6-lutidine) (3). In contrast,MgCl2binds to the sulfonate and diethyl phosphonate unitsof 2b, generating the dipalladium species [{κ2-(OP-P-SO)PdMe}2(μ-Cl)][MgCl] (4) by simple self-assembly.AgB(C6F5)4reacts with 4in the presence of THF to selectively abstract the Mg-Clto form [{κ2-(OP-P-SO)PdMe}2(μ-Cl)Mg(THF)][B(C6F5)4] (5). The ethylenepolymerization behaviors of 2b, 2c, 3, and 5are quite similar (Mn: 120–1170 Da, activity: 60–290 kg (molPd)–1h–1). All of these catalystsproduce low-molecular-weight polyethylene with predominantly internalunsaturation, but little branching. The reaction of 4with 2 equiv of AgB(C6F5)4to abstractboth chloride ions generates an active ethylene polymerization catalystthat produces linear polyethylene with a bimodal molecular weightdistribution. [ABSTRACT FROM AUTHOR]

A seriesof benzo-linked phosphine-diethyl phosphonate (P-PO) andphosphine-bis(diethyl phosphonate) (P-(PO)2) ligands andthe corresponding (P-PO)PdMe(2,6-lutidine)+and (P-(PO)2)PdMe(2,6-lutidine)+complexes were synthesized. Cationic (P-PO)PdMe(2,6-lutidine)+complexes are active for ethylene oligomerization/polymerization,with activities of 2 kg mol–1h–1for {κ2-1-PiPr2-2-P(O)(OEt)2-5-Me-Ph}PdMe(2,6-lutidine)+(3c), 125 kg mol–1h–1for {κ2-1-PPh2-2-P(O)(OEt)2-5-Me-Ph}PdMe(2,6-lutidine)+(3a), and 1470 kg mol–1h–1for {κ2-1-P(2-OMe-Ph)2-2-P(O)(OEt)2-Ph}PdMe(2,6-lutidine)+(3b). The polyethylene is highly linear, withover 80% terminal unsaturation and low (230–1890 Da) molecularweight in all cases. 3bcopolymerizes ethylene with methylacrylate, exhibiting highly selective (95%) in-chain (rather thanchain-end) acrylate incorporation. The P-(PO)2catalyst{κ2-1-P(4-tBu-Ph)(2-P(O)(OEt)2-5-Me-Ph)-2-P(O)(OEt)2-5-Me-Ph}PdMe(2,6-lutidine)+(3d) is more active for ethylene homopolymerization(2640 kg mol–1h–1), yieldinglinear, low-molecular-weight polymer (1280–1430 Da) with predominantlyinternal olefin placement. In ethylene/methyl acrylate copolymerization, 3dincorporates 2.6 mol % methyl acrylate, 60% of which isin-chain. Both 3band 3dcatalyze ethylene/acrylicacid copolymerization, albeit with low (<10 kg mol–1h–1) activities and acrylic acid incorporationup to 1.1 mol %. [ABSTRACT FROM AUTHOR]