The two rare-earth-metal dialkyl complexes 1 and 2 (1, Ln = Sc; 2, Ln = Lu) were obtained via the same acid–base reaction between 1,3-bis(2-pyridylimino)isoindoline (BPI) ligand and rare-earth-metal trialkyl complexes. These complexes 1 and 2 were structurally characterized by X-ray diffraction. Both in the solid state and in the solution state, the mononuclear Sc dialkyl complex 1, containing one monoanionic tridentate C2-symmetric pincer-type BPI ligand, adopts a distorted-trigonal-bipyramidal configuration. When the Sc center of complex 1 was replaced by the larger Lu center, the intramolecular proton transfer from the isoindoline nitrogen atom to one of the imine nitrogen atoms could be observed in the tautomeric BPI ligand, which served as a monoanionic tetradentate ligand bridging two Lu centers and finally afforded the binuclear Lu dialkyl complex 2 with a cage-like symmetrical structure in the solid state. However, this binuclear Lu complex 2 could dissociate into a mononuclear structure in the solution state similar to the case for the scandium complex 1 since the same C2 symmetry was also observed in the 1H and 13C NMR spectra of the lutetium complex 2 in C6D6. In the presence of cocatalyst borate and AliBu3, these complexes 1 and 2 exhibited high activities (up to 1.9 × 106 (g of polymer)/(molLn h)) and high cis-1,4-selectivities (>99%) in the polymerization of isoprene in toluene, affording the cis-1,4-polyisoprenes with high molecular weights (Mn up to 610000 g mol–1) and narrow to moderate molecular weight distributions (Mw/Mn = 1.26–2.08).

The glass transition temperature (Tg) and density of poly-(phthalazinone ether sulfone ketone) (PPESK A) were estimated by molecular dynamic (MD) simulation. A novel poly-(phthalazinone ether sulfone ketone) (PPESK B) was constructed by introducing nitrol and amini energetic groups into PPESK A, and Tg and density were also simulated for PPESK B. The estimated Tg values of PPESK A were very close to experimental results, while for PPESK B three estimated values differed by < 5 K. The interactions between explosives and polymer binders of polymer bonded explosives (PBXs) were simulated by MD. Comparison of the cohesive energy densities (CED) and solubility parameter (δ) values of PBXs, polymer binders, and mono-explosives indicate that, upon introducing polymer binders, the CED and δ values of PBXs decreased compared with those of corresponding mono-explosives. The binding energies (Ebind) imply that 2,4,6-trinitrotoluene-based PBXs are more stable than 1,3,5-triamino-2,4,6-trinitrobenzene (TATB)-based PBXs. The mechanical properties, Young’s modulus E, shear modulus G, bulk modulus K, Poisson’s ratio γ and Cauchy pressure (C12–C44) of the PBXs were assessed. The rigidity of the PBXs was found to be lower than that of mono-explosives. All K/G values were positive, indicating that PBXs are flexible. Based on these mechanical properties results, PBXs using PPESK B as a binder are superior to those using PPESK A as a binder. Due to the low C12–C44 values of the PBXs, the ductility of the materials of the fracture surface is poorer, especially for TATB-based PBXs.

A computational study was performed on the condensation mechanism for the formation of cage hexabenzylhexaazaisowurtzitane (HBIW) from glyoxal and benzylamine. The results suggest that the intermediate 1,2-bis(benzylamino)-1,2-ethanediol is present in the reaction system, especially in the presence of acid catalyst. However, it is unfavorable for N,N′-dibenzyl-1,2-ethanediimine to be formed without the use of acid because the energy barriers for elimination of two water molecules from 1,2-bis(benzylamino)-1,2-ethanediol are 51.99 kcal mol−1 and 60.49 kcal mol−1. The acid-catalyzed water elimination reaction of 1,2-bis(benzylamino)-1,2-ethanediol decreases to 17.17 kcal mol−1, resulting in the formation of another intermediate of 1-(benzylamino)-2-(benzylimino)-ethanol. The 1-(benzylamino)-2-(benzylimino)-ethanol reacts with another 1,2-bis(benzylamino)-1,2-ethanediol to provide HBIW through four cyclization reactions.

Different nonmetallocene rare earth metal alkyl complexes such as monotropidinyl (Trop) scandium dialkyl complex (Trop)Sc(CH2SiMe3)2(THF) (1), ditropidinyl yttrium alkyl complex (Trop)2Y(CH2SiMe3)(THF) (3) as well as binuclear lutetium alkyl complex bearing one tetradentate dianionic 6-N-methyl-1,4-cycloheptadienyl (NMCH) ligand [(NMCH)Lu(CH2SiMe3)(THF)]2 (2) have been synthesized in high yields via one-pot acid–base reaction by using of the tris(trimethylsilylmethyl) rare earth metal complexes with the readily available natural product tropidine. The polymerization experiments indicate that the monotropidinyl scandium dialkyl complex 1 displays reactivity akin to that of the analogous monocyclopentadienyl scandium dialkyl complexes. In the presence of activator and a small amount of AlMe3, complex 1 exhibits similar activities (up to 1.6 × 106 g molSc–1 h–1) but higher cis-1,4-selectivities (up to 100%) than (C5H5)Sc(CH2SiMe3)2(THF) (cis-1,4-selectivity as 95%) in the isoprene polymerization, yielding the pure cis-1,4-PIPs with moderate molecular weights (Mn = 0.5–11.2 × 104 g/mol) and bimodal molecular weight distributions (Mw/Mn = 1.48–6.07). Moreover, the complex 1/[Ph3C][B(C6F5)4/AliBu3 ternary system also shows good comonomer incorporation ability in the copolymerization of isoprene and norbornene similar to the [C5Me4(SiMe3)]Sc(η3-CH2CHCH2)2/activator binary system, affording the random isoprene/norbornene copolymers with a wide range of isoprene contents around 57–91 mol % containing cis-1,4 configuration up to 88%.

A series of chiral palladium(II) and nickel(II) complexes bearing a C2-symmetric monoanionic tridentate bis(oxazoline) ligand, (R2-(S,S)-BOZ)M(X) (1–6: R = CH(CH3)2, M = Pd, X = OAc (1); R = CH(CH3)2, M = Pd, X = Cl (2); R = Ph, M = Pd, X = Cl (3); R = Ph, M = Ni, X = Cl (4); R = CH(CH3)2, M = Ni, X = Cl (5); R = CH(CH3)2, M = Pd, X = OTf (6)), have been synthesized and structurally characterized. The experimental results demonstrate that such chiral palladium(II) and nickel(II) complexes bearing C2-symmetric tridentate ligands in which the monoanionic group is located inside are effective for norbornene polymerization. In the presence of various cocatalysts such as MAO, MMAO, and activator/AlR3, these chiral palladium(II) complexes exhibit much higher activities of up to 4.8 × 108 g of PNB (mol of Pd)−1 h–1 for the vinylic polymerization of norbornene, affording insoluble polynorbornenes with high packing density. In contrast, the chiral nickel(II) complexes show relatively low activities of ca. 4.5 × 107 g of PNB (mol of Ni)−1 h–1 and produce both insoluble polynorbornenes and soluble high-molecular-weight polynorbornenes with moderate molecular weight distributions.

Methacrolein is a major degradation product of isoprene, the reaction of methacrolein with Cl atoms may play some roles in the degradation of isoprene where these species are relatively abundant. However, the energetics and kinetics of this reaction, which govern the reaction branching, are still not well understood so far. In the present study, two-dimensional potential energy surfaces were constructed to analyze the minimum energy path of the barrierless addition process between Cl and the C═C double bond of methacrolein, which reveals that the terminal addition intermediate is directly formed from the addition reaction. The terminal addition intermediate can further yield different products among which the reaction paths abstracting the aldehyde hydrogen atom and the methyl hydrogen atom are dominant reaction exits. The minimum reaction path for the direct aldehydic hydrogen atom abstraction is also obtained. The reaction kinetics was calculated by the variational transition state theory in conjunction with the master equation method. From the theoretical model we predicted that the overall rate constant of the Cl + methacrolein reaction at 297 K and atmospheric pressure is koverall = 2.3× 10–10 cm3 molecule–1 s–1, and the branching ratio of the aldehydic hydrogen abstraction is about 12%. The reaction is pressure dependent at P < 10 Torr with the high pressure limit at about 100 Torr. The calculated results could well account for the experimental observations.

Bis(imino)diphenylamido rare-earth metal dialkyl complexes [o-(2,6-iPr2-C6H3–NC–C6H4)2–N]Ln(CH2SiMe3)2 (1: Ln = Sc; 2: Ln = Lu; 3: Ln = Y) have been synthesized in good yields and structurally characterized by elemental analysis, NMR spectroscopy, and single-crystal X-ray diffraction studies. They serve as highly efficient single-component catalysts both for the living ring-opening ε-caprolactone polymerization and random copolymerization with γ-butyrolactone, with the activity being dependent on the steric hindrance around the metal center, yielding high molecular weight PCLs or P(CL-co-BL)s with narrow molecular weight distributions.

•The mechanism and kinetics of the HNCO + CN reaction has been carefully studied.•The C–N addition channel is as important as the previously considered hydrogen abstraction channel.•The C–N addition channel is found to be the dominant channel at T > 273 K.•The hydrogen abstraction channel is only competitive at T < 273 K.The mechanism for the HNCO + CN reaction was investigated by considering the possible channels of the C atom and N atom of the CN radical attacking the H, N, C, and O atoms of HNCO based on the B3LYP/6-311+G(2d,p) method; and the CCSD/6-31+G(d,p) method was adopted to optimize the geometries of stationary points of the main paths for further kinetics calculation. The energies of all the stationary points were refined with an accurate multilevel method. The energetically most favorable channel for the HNCO + CN reaction was predicted to be the addition reaction of the C atom of CN radical to the N atom of HNCO, producing the HNCN + CO (P2) products, which is different from most of the HNCO-radical reactions in which the hydrogen abstraction channel is dominant. The thermal rate constants were calculated using the conventional transition state theory with Eckart tunneling correction. The results showed that the C–N addition channel (HNCO + CN → HNCN + CO) is dominant at T > 273 K, whereas the hydrogen abstraction channel is more competitive at T < 273 K. As compared to the previously over-estimated temperature independent reaction rate constant of 2.5 × 10−11 cm3 molecule−1 s−1, the calculated rate constants of the C–N addition channel and the hydrogen abstraction channel are positively temperature dependent, and are only 7.22 × 10−16 and 5.34 × 10−16 cm3 molecule−1 s−1 at 298 K, respectively.Graphical abstract

A series of half-sandwich fluorenyl (Flu′) scandium dialkyl complexes Flu′Sc(CH2SiMe3)2(THF)n (1, Flu′ = C13H9, n = 1; 2, Flu′ = 2,7-tBu2C13H7, n = 1; 3, Flu′ = 9-SiMe3C13H8, n = 1; 4, Flu′ = 2,7-tBu2-9-SiMe3C13H6, n = 1; 5, Flu′ = 9-CH2CH2NMe2C13H8, n = 0; 6, Flu′ = 2,7-tBu2-9-CH2CH2NMe2C13H6, n = 0) have been synthesized and structurally characterized. In comparison with the well-known cyclopentadienyl-ligated scandium catalyst system [(C5Me4SiMe3)Sc(CH2SiMe3)2(THF)]/[Ph3C][B(C6F5)4], the analogous combinations of the fluorenyl-ligated, THF-containing complexes 1–4 with [Ph3C][B(C6F5)4] show relatively low activities, albeit with similar syndioselectivities for styrene polymerization and styrene–ethylene copolymerization. However, on treatment with 15 equiv of AliBu3, the 1–4/[Ph3C][B(C6F5)4] combinations show a dramatic increase in catalytic activity without changes in the stereoselectivity. In contrast, the combinations of complexes 5 and 6, which have an amino group attached to the fluorenyl ring and intramolecularly bonded to the metal center, exhibit very low activity, no matter whether or not AliBu3 is present, affording syndiotactic polystyrenes with broad molecular weight distributions. The DFT calculations of the activation mechanism by using the representative catalysts suggest that AliBu3 can capture the THF molecule from the catalyst precursors 1–4 at first,and then the new, THF-free cationic half-sandwich scandium active species [Flu′Sc(CH2SiMe3)][B(C6F5)4] with less steric hindrance around the metal center is generated in the presence of an activator such as [Ph3C][B(C6F5)4]. The DFT calculations on the syndioselectivity of styrene (co)polymerization catalyzed by [Flu′Sc(CH2SiMe3)][B(C6F5)4] have also been carried out, thus shedding new light on the mechanistic aspects of the (co)polymerization processes.

A series of chiral mononuclear dialkyl complexes [(S,S)-BOPA]Ln(CH2SiMe3)2 (1, 2) (BOPA = (S,S)-bis(oxazolinylphenyl)amido; Ln = Sc (1); Ln = Lu (2)) and binuclear alkyl complexes [ο-(S)-OPA–C6H4–(CH2SiMe3)C═N–CH(iPr)CH2–O]Ln(CH2SiMe3)}2 (3,4) (OPA = (oxazolinylphenyl)amine; Ln = Y (3); Ln = Tm (4)) have been synthesized in moderate yields via one-pot acid–base reactions by use of the tris(trimethylsilylmethyl) rare earth metal complexes with the chiral tridentate (S,S)-bis(oxazolinylphenyl)amine ligand. In the presence of activator with or without a small amount of AliBu3, the dialkyl complexes 1 and 2 exhibit very high activities (up to 6.8 × 105 g molLn–1 h–1) and trans-1,4-selectivity (up to 100%) in the quasi-living polymerization of isoprene, yielding the trans-1,4-PIPs with moderate molecular weights (Mn = (0.2–1.0) × 105 g/mol) and narrow molecular weight distributions (Mw/Mn = 1.02–2.66).

Treatment of rare earth metal trialkyl complexes Ln(CH2SiMe3)3(THF)2 (Ln = Sc, Lu, and Y) with 1 equiv of α-diimine ligands 2,6-R2C6H3N═CH−CH═NC6H3R2-2,6 (R = iPr, Me) affords straightforwardly monoanionic iminoamido rare earth metal dialkyl complexes [2,6-R2C6H3N−CH2−C(CH2SiMe3)═NC6H3R2-2,6]Ln(CH2SiMe3)2(THF) (1: Ln = Sc, R = iPr; 2: Ln = Lu, R = iPr; 3: Ln = Y, R = iPr; 4: Ln = Sc, R = Me; 5: Ln = Lu, R = Me; 6: Ln = Y, R = Me) in 65−85% isolated yields. X-ray analyses show these complexes have decreasing steric hindrance in the coordination spheres of the metal centers in the order 1 > 2 > 3 > 4 > 5 > 6. A mechanism involving intramolecular alkyl and hydrogen migration is supported on the basis of DFT calculations to account for ligand alkylation. Activated by [Ph3C][B(C6F5)4], all of these iminoamido rare earth metal dialkyl complexes are active for living polymerization of isoprene, with activity and selectivity being significantly dependent on the steric hindrance around the metal center to yield homopolyisoprene materials with different microstructures and compositions. The sterically crowded complexes 1−3 give a mixture of 3,4- and trans-1,4-polyisoprenes (3,4-selectivities: 48−82%, trans-1,4-selectivities: 50−17%), whereas the less sterically demanding complexes 4−6 show high 3,4-selectivities (3,4-selectivities: 90−100%). In the presence of 2 equiv of AliBu3, the complexes 1−6/activator systems exhibit higher activities and 3,4-selectivities in the living polymerization of isoprene. A similar structure−reactivity relationship in polymerization catalysis can be also observed in these ternary systems. A possible mechanism of the isoprene polymerization processes is proposed on the basis of the DFT calculations.

Bis(imino)diphenylamido rare-earth metal dialkyl complexes [o-(2,6-iPr2-C6H3–NC–C6H4)2–N]Ln(CH2SiMe3)2 (1: Ln = Sc; 2: Ln = Lu; 3: Ln = Y) have been synthesized in good yields and structurally characterized by elemental analysis, NMR spectroscopy, and single-crystal X-ray diffraction studies. They serve as highly efficient single-component catalysts both for the living ring-opening ε-caprolactone polymerization and random copolymerization with γ-butyrolactone, with the activity being dependent on the steric hindrance around the metal center, yielding high molecular weight PCLs or P(CL-co-BL)s with narrow molecular weight distributions.