Salicylaldehyde compound containing an ammonium salt unit, [2-(HO)-3-tBu-5-{Bu3N+(CH2)3Si(Me2)}C6H2C(O)H][BF4 -], is prepared from which a Salen-type ligand and its cobalt(III) complex, (Salen-1)CoX (1: Salen-1 = [trans-N,N‘-bis(3-tBu-5-(Bu3N+(CH2)3Si(Me2)-salicylidene)-1,2-cyclohexanediamine)]X2; X = 2,4-dinitrophenolate), is prepared. Complex 1 shows high activity for CO2/(propylene oxide) copolymerization even at a condition of high [propylene oxide]/[catalyst] ratio and high temperature up to 90 °C, at which conditions a typical binary system of [(Salen)CoX]/[PPNCl] does not yield any copolymer. A very high TOF (up to 3500 h-1) and TON (up to 14500) are achieved, which have never been attained with other catalytic systems. The high selectivity (>84%) for the formation of copolymer over cyclic carbonate and the high molecular weight of the obtained polymers (M n = 53000−95000) are the other merits of the catalyst.
Acyclic o-phenylene-bridged bis(anilido-aldimine) compounds, o-C(6)H(4){C(6)H(2)R(2)N=CH-C(6)H(4)-(H)N(C(6)H(3)R'(2))}(2) and related 30-membered macrocyclic compounds, o-C(6)H(4){C(6)H(2)R'(2)N=CH-C(6)H(4)-(H)N-C(6)H(2)R(2)}(2) (o-C(6)H(4)) are prepared. Successive additions of Me(2)Zn and SO(2) gas to the bis(anilido-aldimine) compounds afford quantitatively dinuclear mu-methylsulfinato zinc complexes, o-C(6)H(4){(C(6)H(2)R(2)N=CH-C(6)H(4)-N(C(6)H(3)R'(2))-kappa(2)-N,N)Zn(mu-OS(O)Me)}(2) (R = iPr and R' = iPr, 29; R = Et and R' = Et, 30; R = Me and R'= Me, 31; R = Me and R' = iPr, 32; R = Et and R' = Me, 33; R = Et and R' = iPr, 34; R = iPr and R' = Et, 35) and o-C(6)H(4){C(6)H(2)R'(2)N=CH-C(6)H(4)-N-C(6)H(2)R(2)-kappa(2)-N,N)Zn(mu-OS(O)Me)}(2) (o-C(6)H(4)) (R = Et and R'= Et, 36; R = Me and R' = Me, 37; R = iPr and R' = Me, 38; R = Et and R' = Me, 39; R = Me and R'= iPr, 40). Molecular structures of 34 and 40 are confirmed by X-ray crystallography. Complexes 30-35 show high activity for cyclohexene oxide/CO(2) copolymerization at low [Zn]/[monomer] ratio (1:5600), whereas the complex of mononucleating beta-diketiminate {[(C(6)H(3)Et(2))N=C(Me)CH=C(Me)N(C(6)H(3)Et(2))]Zn(mu-OS(O)Et)}(2) shows negligible activity in the same condition. Activity is sensitive to the N-aryl ortho substituents and the highest activity is observed with 32. Turnover number up to 2980 and molecular weight (M(n)) up to 284 000 are attained with 32 at such a highly diluted condition as [Zn]/[monomer] = 1:17 400. Macrocyclic complexes 36-40 show negligible activity for copolymerization.
Salen-type ligands comprised of ethylenediamine or 1,2-cyclohexenediamine, along with an salicylaldehyde bearing a methyl substituent on its 3-position and a -[CR(CH(2)CH(2)CH(2)N(+)Bu(3))(2)] (R = H or Me) on its 5-position, unexpectedly afford cobalt(III) complexes with uncoordinated imines. In these complexes, two salen-phenoxys and two 2,4-dinitrophenolates (DNPs), which counter the quaternary ammonium cations, coordinate persistently with cobalt, while two other DNPs are fluxional between a coordinated and an uncoordinated state in THF at room temperature. The complexes of this binding mode show excellent activities in carbon dioxide/propylene oxide copolymerization (TOF, 8300-13,000 h(-1)) but with some fluctuation in induction times (1-10 h), depending on how dry the system is. The induction time is shortened (<1.0 h) and activity is increased approximately 1.5 times upon the replacement of the two fluxional DNPs with 2,4-dinitrophenol-2,4-dinitrophenolate homoconjugation ([DNP...H...DNP](-)). Imposing steric congestion either by replacing the methyl substituent on the salicylaldehyde with tert-butyl or by employing H(2)NCMe(2)CMe(2)NH(2) instead of ethylenediamine or 1,2-cyclohexenediamine results in conventional imine-coordinating complexes, which show lower activities than uncoordinated imine complexes.
Terpolymerizations of CO 2 /propylene oxide (PO)/cyclohexene oxide (CHO), CO 2 /PO/1-hexene oxide (HO), and CO 2 /PO/1-butene oxide (BO) were carried out without the formation of cyclic carbonates and ether linkages with a cobalt(III) complex of a Salen-type ligand tethered by four quaternary ammonium salts (1). The activities were excellent, in the range of (0.62-1.6) Â 10 6 g/mol-Co (TOF, 4400-14 000 h -1 ). In all three of terpolymerizations, the data for the PO mole fractions in the feed (f PO ) and the polymers (F PO ) fit the Fineman-Ross plot well to determine the monomer reactivity ratios. The linear dependencies of the T g 's of the polymers on the mole fractions of the third monomers (F CHO , F HO , and F BO ) were observed with the relationships of "T g (°C) = 81 Â F CHO þ 40", "T g (°C) = -62 Â F HO þ 38", and "T g (°C) = -27 Â F BO þ 38", respectively. The decomposition temperature of the resin increased when the third monomer was employed. The GPC data indicated that the polymer chains grew in an immortal passion from four 2,4-dinitrophenolates as well as the two 2,4-dinitrophenols in 1. High molecular weights (M n ) above 200 000 were attainable because of the high activities.
Regioselective partial hydrogenation of tricyclopentadiene (TCPD) was achieved with a high turnover number of 10 000 by catalysis with a N-heterocyclic carbene-palladium complex. Copolymerization of ethylene and the partially hydrogenated product, dihydrotricyclopentadiene (HTCPD), was realized using a catalytic system of [8-The copolymer was unambiguously characterized through the analysis of one-and two-dimensional NMR spectra. The monomer reactivity ratios, r ethylene and r HTCPD , determined through the Fineman-Ross plot, were 2.8 and 0.025, respectively, indicating negligible successive insertion of two HTCPD. A nearly alternating copolymer with a HTCPD content of 45 mol % was obtained with a satisfactory activity (4.7 Â 10 6 g/(mol Ti h)), of which T g was 177 °C, significantly higher than that of norbornene/ethylene copolymer at the same cycloolefin content. Tensile stress-strain curves indicated that the brittleness observed for a high-T g norbornene/ethylene copolymer was relieved to show some ductile property for the HTCPD/ethylene copolymer of the same level of high T g .
A cobalt(III) complex (1) of a salcy-type ligand tethering 4 quaternary ammonium salts, which is thought to act as a highly active catalyst for CO2/propylene oxide (PO) copolymerization, also shows high activity (TOF, 25,900 h(-1); TON, 518,000; 2.72 kg polymer per g cat) and selectivity (>98%) for CO2/ethylene oxide (EO) copolymerization that results in high-molecular-weight polymers (M(n), 200,000-300,000) that have strictly alternating repeating units. The related cobalt(III) complexes 11-14 were prepared through variations of the ligand framework of 1 by replacing the trans-1,2-diaminocyclohexane unit with 2,2-dimethyl-1,3-propanediamine, trans-1,2-diaminocyclopentane, or 1,1'-binaphthyl-2,2'-diamine or by replacing the aldimine bond with ketimine. These ligand frameworks are thought to favour the formation of the cis-β configuration in complexation, and the formation of the cis-β configuration in 11-14 was confirmed through NMR studies or X-ray crystallographic studies of model complexes not bearing the quaternary ammonium salts. Complexes 11, 13, and 14, which adopt the cis-β configuration even in DMSO did not show any activity for CO2/PO copolymerization. Complex 12, which was constructed with trans-1,2-diaminocyclopentane and fluctuated in DMSO between the coordination and de-coordination of the acetate ligand as observed for 1, showed fairly high activity (TOF, 12,400 h(-1)). This fluctuating behaviour may play a role in polymerization. However, complex 12 did not compete with 1 in terms of activity, selectivity, and the catalyst cost.
Anion exchange of BF(4)(-) occurs by stirring a cobalt(III) complex of salen-type ligand tethered by four quaternary ammonium BF(4)(-) salts over a slurry of NaX in CH(2)Cl(2), affording a complex containing four X's per cobalt (X = 2,4,5-trichlorophenolate, 6; X = 4-nitrophenolate, 10; X = 2,4-dichlorophenolate, 12). The (1)H and (13)C NMR spectra are in agreement with an unusual imine uncoordinated structure. The two salen-phenoxys and the two X's persistently coordinate with cobalt(III) to form a square planar cobaltate complex while the other two X's scramble through coordination and decoordination to the axial sites of the square plane. Another form of the complex (X = 2,4,5-trichlorophenolate, 14; X = 4-nitrophenolate, 15; X = 2,4-dichlorophenolate, 16) is also prepared, in which the scrambling two X's in 6, 10, or 12 are replaced with the corresponding [X...H...X](-) homoconjugate. These complexes, which adopt an unusual imine uncoordinated structure, are excellent catalysts for CO(2)/propylene oxide copolymerization (turnover frequency (TOF), 8300-16,000 h(-1)). In all cases, the complex containing the homoconjugate [X...H...X](-) shows higher activity than the corresponding phenol-free complex. Among the prepared complexes, 4-nitrophenol-4-nitrophenolate homoconjugate complex 15 showed the best performance (TOF, 16,000 h(-1); selectivity, 98%; M(n), 273,000), allowing for replacement of the explosive 2,4-dinitrophenolate complex.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.