Robust and efficient transfer hydrogenation of carbonyl compounds catalyzed by NN-Mn(I) complexes.

A series of manganese(I) carbonyl complexes bearing structurally related NN- and NNN-chelating ligands have been synthesized and assessed as catalysts for transfer hydrogenation (TH). Notably, the NN-systems based on N-R functionalized 5,6,7,8-tetrahydroquinoline-8-amines, proved the most effective in the manganese-promoted conversion of acetophenone to 1-phenylethanol. In particular, the N-isopropyl derivative, Mn1, when conducted in combination with t-BuONa, was the standout performer mediating not only the reduction of acetophenone but also a range of carbonyl substrates including (hetero)aromatic-, aliphatic- and cycloalkyl-containing ketones and aldehydes with especially high values of TON (up to 17 200; TOF of 3550 h-1). These findings, obtained through a systematic variation of the N-R group of the NN ligand, are consistent with an outer-sphere mechanism for the hydrogen transfer. As a more general point, this Mn-based catalytic TH protocol offers an attractive and sustainable alternative for producing alcoholic products from carbonyl substrates.

N,N-Bis(2,4-Dibenzhydryl-6-cycloalkylphenyl)butane-2,3-diimine-Nickel Complexes as Tunable and Effective Catalysts for High-Molecular-Weight PE Elastomers.

Four examples of N,N-bis(aryl)butane-2,3-diimine-nickel(II) bromide complexes, [ArN=C(Me)-C(Me)=NAr]NiBr2 (where Ar = 2-(C5H9)-4,6-(CHPh2)2C6H2 (Ni1), Ar = 2-(C6H11)-4,6-(CHPh2)2C6H2 (Ni2), 2-(C8H15)-4,6-(CHPh2)2C6H2 (Ni3) and 2-(C12H23)-4,6-(CHPh2)2C6H2 (Ni4)), disparate in the ring size of the ortho-cycloalkyl substituents, were prepared using a straightforward one-pot synthetic method. The molecular structures of Ni2 and Ni4 highlight the variation in the steric hindrance of the ortho-cyclohexyl and -cyclododecyl rings exerted on the nickel center, respectively. By employing EtAlCl2, Et2AlCl or MAO as activators, Ni1-Ni4 displayed moderate to high activity as catalysts for ethylene polymerization, with levels falling in the order Ni2 (cyclohexyl) > Ni1 (cyclopentyl) > Ni4 (cyclododecyl) > Ni3 (cyclooctyl). Notably, cyclohexyl-containing Ni2/MAO reached a peak level of 13.2 × 106 g(PE) of (mol of Ni)-1 h-1 at 40 °C, yielding high-molecular-weight (ca. 1 million g mol-1) and highly branched polyethylene elastomers with generally narrow dispersity. The analysis of polyethylenes with 13C NMR spectroscopy revealed branching density between 73 and 104 per 1000 carbon atoms, with the run temperature and the nature of the aluminum activator being influential; selectivity for short-chain methyl branches (81.8% (EtAlCl2); 81.1% (Et2AlCl); 82.9% (MAO)) was a notable feature. The mechanical properties of these polyethylene samples measured at either 30 °C or 60 °C were also evaluated and confirmed that crystallinity (Xc) and molecular weight (Mw) were the main factors affecting tensile strength and strain at break (εb = 353-861%). In addition, the stress-strain recovery tests indicated that these polyethylenes possessed good elastic recovery (47.4-71.2%), properties that align with thermoplastic elastomers (TPEs).

Exploring fluoride effects in sterically enhanced cobalt ethylene polymerisation catalysts; a combined experimental and DFT study.

The fluoro-substituted 2,6-bis(arylimino)pyridine dichlorocobalt complexes, [2-{CMeN(2,6-(Ph2CH)2-3,4-F2C6H)}-6-(CMeNAr)C5H3N]CoCl2 (Ar = 2,6-Me2C6H3 Co1, 2,6-Et2C6H3Co2, 2,6-iPr2C6H3Co3, 2,4,6-Me3C6H2Co4, 2,6-Et-4-MeC6H2Co5), were synthesized in good yield from the corresponding unsymmetrical N,N,N'-ligands, L1-L5. Besides characterization of Co1-Co5 by FT-IR spectroscopy, 19F NMR spectroscopy and elemental analysis, the molecular structures of Co2 and Co5 were also determined highlighting the unsymmetrical nature of the terdentate ligand and the pseudo-square pyramidal geometry about the metal center. When either MAO or MMAO were employed as activators, Co1-Co5 were able to achieve a wide range of catalytic activities for ethylene polymerisation. Co5/MAO exhibited the highest activity of the study at 60 °C (7.6 × 106 g PE mol-1 (Co) h-1) which decreased to 3.3 × 106 g PE mol-1 (Co) h-1 at 80 °C. In addition, it was found that the polymerisation activity increased as the steric hindrance imparted by the ortho groups was enhanced (for MMAO: Co3 > Co5 > Co2 > Co1 > Co4), a finding that was supported by DFT calculations. Furthermore, it was shown that particularly high molecular weight polyethylene could be generated (up to 483.8 kg mol-1) when using Co5/MMAO at 30 °C, while narrow dispersities (M w/M n range: 1.8-4.7) and high linearity (T m > 131.4 °C) were a feature of all polymers produced. By comparison of Co3 with its non-fluorinated analogue using experimental data and DFT calculations, the substitution of fluorides at the meta- and para-positions was demonstrated to boost catalytic activity and improve thermal stability.

High molecular weight PE elastomers through 4,4-difluorobenzhydryl substitution in symmetrical α-diimino-nickel ethylene polymerization catalysts.

The following family of N,N-diaryl-2,3-dimethyl-1,4-diazabutadienes, ArN[double bond, length as m-dash]C(Me)C(Me)[double bond, length as m-dash]NAr (Ar = 2,6-Me2-4-{CH(4-FC6H4)2}C6H2L1, 2-Me-6-Et-4-{CH(4-FC6H4)2}C6H2L2, 2,4-{CH(4-FC6H4)2}2-6-MeC6H2L3, 2,4-{CH(4-FC6H4)2}2-6-EtC6H2L4, 2,4-{CH(4-FC6H4)2}2-6-iPrC6H2L5), each incorporating para-substituted 4,4-difluorobenzhydryl groups but differing in the ortho-pairing, have been synthesized and used as precursors to their respective nickel(ii) bromide complexes, Ni1-Ni5. Compound characterization has been achieved through a combination of FT-IR, multinuclear NMR spectroscopy (1H, 13C, 19F) and elemental analysis. In addition, L1, Ni1 and Ni5 have been structurally characterized with Ni1 and Ni5 revealing similarly distorted tetrahedral geometries about nickel but with distinct differences in the steric protection offered by the ortho-substituents. All nickel complexes, under suitable activation, showed high activity for ethylene polymerization with a predilection towards forming branched high molecular weight polyethylene with narrow dispersity. Notably the most sterically bulky Ni5, under activation with either EtAlCl2, Et2AlCl or EASC, was exceptionally active (0.9-1.0 × 107 g of PE per (mol of Ni) per h) at an operating temperature of 40 °C. Furthermore, the polyethylene generated displayed molecular weights close to one million g mol-1 (M w range: 829-922 kg mol-1) with high branching densities (86-102/1000 carbons) and a selectivity for short chain branches (% Me = 94.3% (EtAlCl2), 87.2% (Et2AlCl), 87.7% (EASC)). Further analysis of the mechanical properties of the polymers produced at 40 °C and 50 °C using Ni5 highlighted the key role played by crystallinity (X c) and molecular weight (M w) on tensile strength (σ b) and elongation at break (ε b). In addition, stress-strain recovery tests reveal these high molecular weight polymers to exhibit characteristics of thermoplastic elastomers (TPEs).

Bis(imino)-6,7-dihydro-5H-quinoline-cobalt complexes as highly active catalysts for the formation of vinyl-terminated PE waxes; steps towards inhibiting deactivation pathways through targeted ligand design.

A set of five related bis(imino)-6,7-dihydro-5H-quinoline-cobalt(ii) complexes, [2-(ArN = CPh)-8-(NAr)-C9H8N]CoCl2 (Ar = 2,6-Me2C6H3Co1, 2,6-Et2C6H3Co2, 2,6-i-Pr2C6H3Co3, 2,4,6-Me3C6H2Co4, 2,6-Et2-4-MeC6H2Co5), have been synthesized in reasonable yield by the template reaction of cobalt(ii) chloride hexahydrate, 2-benzoyl-6,7-dihydro-5H-quinolin-8-one and the corresponding aniline. The molecular structures of Co1 and Co4 highlight both the differences in the two imino-carbon environments (phenyl-capped chain vs. cyclic) and also the steric properties exerted by the bulky N imine-aryl groups. On pre-treatment with either modified methylaluminoxane (MMAO) or methylaluminoxane (MAO), all complexes proved productive catalysts for the polymerization of ethylene. In particular, Co1/MAO was the most active reaching a very high level of 1.62 × 107 g PE per mol (Co) per h over a 30 minute run time. Owing to the presence of the imino-phenyl substituent, Co1-Co5 were able to exhibit good thermal stability by displaying appreciable catalytic activity at temperatures between 50 and 80 °C, generating polyethylenes with narrow dispersities (M w/M n range: 1.66-3.28). In particular, the least sterically bulky precatalysts, Co1 and Co4 formed polyethylene waxes (M w range: 1.94-5.69 kg per mol) with high levels of vinyl unsaturation as confirmed by high temperature 1H/13C NMR spectroscopy and by IR spectroscopy.

Bis-cycloheptyl-fused bis(imino)pyridine-cobalt catalysts for PE wax formation: positive effects of fluoride substitution on catalytic performance and thermal stability.

The α,α'-bis(imino)-2,3:5,6-bis(pentamethylene)pyridyl-cobalt(ii) chlorides, [2,3:5,6-{C4H8C(N(2-R1-4-R3-6-R2C6H2))}2C5HN] CoCl2 (R1 = Me, R2 = R3 = CH(p-FPh)2Co1; R1 = Et, R2 = R3 = CH(p-FPh)2Co2; R1 = i-Pr, R2 = R3 = CH(p-FPh)2Co3; R1 = Cl, R2 = R3 = CH(p-FPh)2Co4; R1 = F, R2 = R3 = CH(p-FPh)2Co5; R1 = F, R2 = R3 = CHPh2Co5'', R1 = R2 = Me, R3 = CH(p-FPh)2Co6; R1 = R3 = Me, R2 = CH(p-FPh)2Co7), have been synthesized by a one-pot template reaction of α,α'-dioxo-2,3:5,6-bis(pentamethylene)pyridine, cobalt(ii) chloride and the respective aniline in n-butanol. By contrast, the mixed cobalt(ii) chloride/acetate complex, [2,3:5,6-{C4H8C(N(2-F-4,6-(CH(p-FPh)2)2C6H2))}2C5HN]CoCl(OAc) (Co5'), was isolated when the corresponding template reaction was carried out in acetic acid. Structural characterization of Co4, Co5 and Co5'' revealed distorted square pyramidal geometries while six-coordinate Co5', incorporating a chelating acetate ligand, exhibited a distorted octahedral geometry. On activation with either MAO or MMAO, 2-fluoride-4,6-bis{di(p-fluorophenyl)methyl}-substituted Co5 showed maximum catalytic activity for ethylene polymerization at a high operating temperature of 60 °C (up to 2.1 × 107 g (PE) mol-1 (Co) h-1), producing highly linear (Tms > 121 °C), low molecular weight polyethylene waxes (Mw range: 1.5-5.0 kg mol-1) with narrow dispersity (Mw/Mn range: 1.7-2.9). End-group analysis of the waxes reveals ß-H elimination as the dominant chain transfer process.

High molecular weight polyethylenes of narrow dispersity promoted using bis(arylimino)cyclohepta[b]pyridine-cobalt catalysts ortho-substituted with benzhydryl & cycloalkyl groups.

A one-pot template strategy has been utilized to synthesize sterically enhanced bis(imino)cyclohepta[b]pyridine-cobalt(ii) chlorides, [2-{(Ar)N[double bond, length as m-dash]CMe}-9-{N(Ar)}C10H10N]CoCl2 (Ar = 2-(C5H9)-4,6-(CHPh2)2C6H2Co1, 2-(C6H11)-4,6-(CHPh2)2C6H2Co2, 2-(C8H15)-4,6-(CHPh2)2C6H2Co3, 2-(C12H23)-4,6-(CHPh2)2C6H2Co4, 2,6-(C5H9)2-4-(CHPh2)C6H2Co5). All five complexes have been characterized by a combination of FT-IR spectroscopy, elemental analysis and single crystal X-ray diffraction. The molecular structures of Co1, Co3 and Co5 highlight the substantial steric hindrance imparted by the 2-cycloalkyl-6-benzhydryl or 2,6-dicyclopentyl ortho-substitution pattern; distorted square pyramidal geometries are exhibited in each case. On activation with methylaluminoxane (MAO) or modified methylaluminoxane (MMAO), all the complexes (apart from Co4/MAO) were active ethylene polymerization catalysts (up to 3.70 × 106 g PE per mol (Co) per h for Co5/MMAO), operating effectively at temperatures between 50 °C and 60 °C, producing polyethylenes with high molecular weights (up to 589.5 kg mol-1 for Co3/MAO). Furthermore, all polymers were highly linear (Tm > 130 °C) with narrow dispersities (Mw/Mn range: 2.0-3.0). The coexistence of two chain termination pathways, ß-H elimination and transfer to aluminum, has been demonstrated using 13C/1H NMR spectroscopy.

Probing the effect of ortho-cycloalkyl ring size on activity and thermostability in cycloheptyl-fused N,N,N-iron ethylene polymerization catalysts.

The syntheses of six bis(imino)-5,6,7,8-tetrahydrocycloheptapyridine-iron(ii) chloride complexes, [2-{(Ar)NCMe}-9-{N(Ar)}C10H10N]FeCl2 (Ar = 2-(C5H9)-6-MeC6H3Fe1, 2-(C6H11)-6-MeC6H3Fe2, 2-(C8H15)-6-MeC6H3Fe3, 2-(C5H9)-4,6-Me2C6H2Fe4, 2-(C6H11)-4,6-Me2C6H2Fe5, 2-(C8H15)-4,6-Me2C6H3Fe6), are reported in which the ring size of the ortho-cycloalkyl group has been varied as has the type of para-substituent. The molecular structures of Fe3 and Fe6 reveal square pyramidal geometries at iron while the ortho-cyclooctyl rings adopt boat-chair conformations. On treatment with either methylaluminoxane (MAO) or modified methylaluminoxane (MMAO), all six complexes showed optimal activities at 80 °C [up to 1.9 × 107 g of PE per mol Fe per h for Fe5/MMAO] for ethylene polymerization forming linear polyethylene (Tm's > 126 °C). Notably, the catalytic activities showed a marked correlation with the ring size of the ortho-cycloalkyl substituent: cyclohexyl (Fe2 and Fe5) > cyclooctyl (Fe3 and Fe6) > cyclopentyl (Fe1 and Fe4) for either para-substituent, H or Me. Furthermore, this family of iron catalysts exhibited remarkable thermostability by remaining highly active even at temperatures as high as 100 °C (1.1 × 107 g of PE per mol Fe per h); the wide variation in polymer molecular weights (Mw: 2.4-166 kg mol-1), influenced through choice of precatalyst and co-catalyst as well as by temperature and pressure, further highlights the versatility of these catalysts.

Steric and electronic modulation of iron catalysts as a route to remarkably high molecular weight linear polyethylenes.

Five structurally related bis(arylimino)pyridine-iron(ii) chloride complexes, [2-[CMeN{2,6-{(4-FC6H4)2CH}2-4-NO2}]-6-(CMeNAr)C5H3N]FeCl2 (Ar = 2,6-Me2C6H3Fe1, 2,6-Et2C6H3Fe2, 2,6-i-Pr2C6H3Fe3, 2,4,6-Me3C6H2Fe4, and 2,6-Et2-4-MeC6H2Fe5), incorporating one N-2,6-bis{di(4-fluorophenyl)methyl}-4-nitrophenyl group and one distinct N-aryl group, have been prepared in good yield through the interaction of the corresponding free ligands (L1-L5) with FeCl2·4H2O. All ferrous complexes were paramagnetic which was manifested by broad and highly shifted peaks in their 1H NMR spectra. The marked steric imbalance imposed by the two inequivalent N-aryl groups was a key feature highlighted in the molecular structures of representative complexes Fe1 and Fe2. Upon activation with either MAO or MMAO, Fe1-Fe5 all exhibited high activities for ethylene polymerization with good thermal stability [activities as high as 1.58 × 107 g (PE) mol-1 (Fe) h-1 at 60 °C], affording especially high molecular weight linear polyethylenes (3.92 × 105 g mol-1 at 70 °C; Tm > 130 °C). To the best of our knowledge, the molecular weights of the polyethylenes produced by the current class of iron catalysts exceed the highest values reported for related bis(imino)pyridine-iron catalysts to date; changes in the ortho-R1 substitution pattern offered some additional fine control of the molecular weight. Moreover, the nature of the aluminoxane co-catalyst employed had a noticeable effect on the polymer end group composition. When using MAO, unsaturated polymers containing both vinyl and n-propyl end groups were evident, whereas with MMAO, fully saturated polymers were generated containing both isobutyl and n-propyl end groups.

gem-Dimethyl-substituted bis(imino)dihydroquinolines as thermally stable supports for highly active cobalt catalysts that produce linear PE waxes.

Six types of 2,8-bis(imino)-7,7-dimethyl-5,6-dihydroquinoline, 2-(ArN[double bond, length as m-dash]CMe)-8-(ArN)-7,7-Me2C9H6N (Ar = 2,6-Me2C6H3L1, 2,6-Et2C6H3L2, 2,6-iPr2C6H3L3, 2,4,6-Me3C6H2L4, 2,6-Et2-4-MeC6H2L5, 2,4,6-tBu3C6H3L6), distinguishable by their steric and electronic profile, are described that can readily undergo complexation with cobaltous chloride to form their corresponding LCoCl2 chelates, Co1-Co6. The molecular structures of Co2 and Co3 reveal square pyramidal geometries with ring puckering a feature of the gem-dimethyl section of their unsymmetrical N,N,N'-ligands. On activation with either methylaluminoxane (MAO) or modified methylaluminoxane (MMAO), all the cobalt complexes exhibited exceptionally high activities for ethylene polymerization with levels reaching up to 1.19 × 107 g PE per mol (Co) per h for mesityl-containing Co4. Significantly, these catalysts exhibited good thermal stability by displaying their optimal performance at temperatures up to 70 °C whilst also maintaining appreciable catalytic lifetimes. With the exception of that obtained using the most sterically hindered Co6 (2,4,6-t-butyl), the polyethylenes are of low molecular weight (Mw≤16.0 kg mol-1) and of narrow dispersity (Mw/Mn≤3.4). Moreover, end-group analysis of these highly linear polymer waxes reveals evidence for unsaturated as well as various levels of fully saturated materials highlighting the role of both ß-H elimination and chain transfer to aluminum as termination pathways.

1,5-Naphthyl-linked bis(imino)pyridines as binucleating scaffolds for dicobalt ethylene oligo-/polymerization catalysts: exploring temperature and steric effects.

Six examples of dinuclear bis(imino)pyridine-cobalt(ii) complexes, [1,5-{2-(CMe[double bond, length as m-dash]N)-6-(CMe[double bond, length as m-dash]N(2,6-R12-4-R2-C6H2))C5H3N}2(C10H6)]Co2Cl4 (R1 = Me, R2 = H Co1; R1 = Et, R2 = H Co2; R1 = iPr, R2 = H Co3; R1 = Me, R2 = Me Co4; R1 = Et, R2 = Me Co5; R1 = CHPh2, R2 = Me Co6), have been prepared from the corresponding bis(tridentate) compartmental ligands (L1-L6) in reasonable yields. The molecular structures of Co3 and Co5 revealed two N,N,N-cobalt dichloride units to adopt anti-positions about the 1,5-naphthyl linking unit, with each cobalt center exhibiting a distorted trigonal bipyramidal geometry. On activation with either MAO or MMAO, Co1-Co6 were shown to promote both polymerization and oligomerization of ethylene with high overall activities (up to 1.03 × 107 gPE per·mol(Co) per·h for Co1/MAO at 70 °C). Curiously, on increasing the reaction temperature a larger proportion of polymer was noted, while at lower temperature an enhanced selectivity for oligomer was seen. In general, the oligomeric products displayed Schulz-Flory distributions with high selectivities for α-olefins (>99%). On the other hand, the highly linear polymers displayed narrow dispersities and comprised both fully saturated and unsaturated chain ends with the vinyl content (-CH[double bond, length as m-dash]CH2) found to rise with the reaction temperature. By modulating the steric hindrance exerted by the ortho-R1 substituents in the precatalyst, polyethylenes displaying a remarkably broad range of molecular weights could be obtained [from 4.52 kg mol-1 (R1 = Me) to 246.7 kg mol-1 (R1 = CHPh2)].

Bis(imino)pyridines fused with 6- and 7-membered carbocylic rings as N,N,N-scaffolds for cobalt ethylene polymerization catalysts.

The unsymmetrical diketone, 1,2,3,7,8,9,10-heptahydrocyclohepta[b]quinoline-4,6-dione, based on a central pyridine unit fused by both 6- and 7-membered rings, has been synthesized via a sequence of reactions including ruthenium-catalyzed coupling cyclization. Templating this diketone with a mixture of cobalt(ii) chloride hexahydrate and the corresponding aniline in acetic acid at reflux afforded five examples of carbocyclic-fused bis(arylimino)pyridine-cobalt(ii) chlorides (aryl = 2,6-Me2Ph Co1, 2,6-Et2Ph Co2, 2,6-i-Pr2Ph Co3, 2,4,6-Me3Ph Co4, 4-Me-2,6-Et2Ph Co5) in good yield. All cobalt complexes have been fully characterized including by 1H NMR spectroscopy which reveals broad but assignable paramagnetically shifted peaks. The molecular structures of Co1, Co3 and Co4 highlight the inequivalency of the two fused rings with the cobalt center adopting a distorted trigonal bipyramidal geometry. Treatment of Co1-Co5 with MAO gave highly active catalysts (up to 5.03 × 106 g PE mol-1 (Co) h-1 at 40 °C, with Co4 > Co5 > Co1 > Co2 > Co3) for ethylene polymerization generating strictly linear vinyl-terminated polymers with low molecular weights (Mw range: 1.53-22.77 kg mol-1). By comparison, polymerizations conducted using Co1-Co5/MMAO were less active and displayed a lower selectivity for unsaturated polymers. Common to both MAO and MMAO, the most sterically hindered precatalyst Co3 gave the highest molecular weight polymer of the series (up to 22.77 kg mol-1) but exhibited the lowest activity.

Plastomeric-like polyethylenes achievable using thermally robust N,N'-nickel catalysts appended with electron withdrawing difluorobenzhydryl and nitro groups.

A new set of five unsymmetrical N,N'-diiminoacenaphthenes, 1-[2,6-{(4-FC6H4)2CH}2-4-NO2C6H4N]-2-(ArN)C2C10H6 (Ar = 2,6-Me2C6H3L1, 2,6-Et2C6H3L2, 2,6-iPr2C6H3L3, 2,4,6-Me3C6H2L4, 2,6-Et2-4-MeC6H2L5), have been synthesized and used to prepare their corresponding nickel(ii) halide complexes, LNiBr2 (Ni1-Ni5) and LNiCl2 (Ni6-Ni10). The molecular structures of Ni3(OH2) and Ni4 reveal distorted square pyramidal and tetrahedral geometries, respectively, while the 1H NMR spectra of all the nickel(ii) (S = 1) complexes show broad paramagnetically shifted peaks. Upon activation with either methylaluminoxane (MAO) or ethylaluminum sesquichloride (Et3Al2Cl2, EASC), Ni1-Ni10 displayed very high activities for ethylene polymerization with the optimal performance being observed using 2,6-dimethyl-containing Ni1 in combination with EASC (1.66 × 107 g PE mol-1 (Ni) h-1 at 50 °C) which produced high molecular weight plastomeric polyethylene (Mw = 3.93 × 105 g mol-1, Tm = 70.6 °C) with narrow dispersity (Mw/Mn = 2.97). Moreover, Ni1/EASC showed good thermal stability by operating effectively at an industrially relevant 80 °C with a level of activity (6.01 × 106 g of PE mol-1 (Ni) h-1) that exceeds previously disclosed N,N'-nickel catalysts under comparable reaction conditions. This improved thermal stability and activity has been ascribed to the combined effects imparted by the para-nitro and fluoride-substituted benzhydryl ortho-substituents.

Fusing Carbocycles of Inequivalent Ring Size to a Bis(imino)pyridine-Iron Ethylene Polymerization Catalyst: Distinctive Effects on Activity, PE Molecular Weight, and Dispersity.

The 4,6-bis(arylimino)-1,2,3,7,8,9,10-heptahydrocyclohepta[b]quinoline-iron(II) chlorides (aryl = 2,6-Me2C6H3 Fe1; 2,6-Et2C6H3 Fe2; 2,6-i-Pr2C6H3 Fe3; 2,4,6-Me3C6H2 Fe4; and 2,6-Et2-4-Me2C6H2 Fe5) have been prepared in good yield by a straightforward one-pot reaction of 2,3,7,8,9,10-hexahydro-1H-cyclohepta[b]quinoline-4,6-dione, FeCl2·4H2O, and the appropriate aniline in acetic acid. All ferrous complexes have been characterized by elemental analysis and FT-IR spectroscopy. In addition, the structure of Fe3 has been determined by single crystal X-ray diffraction, which showed the iron center to adopt a distorted square pyramidal geometry with the saturated sections of the fused six- and seven-membered carbocycles to be cis-configured. In combination with either MAO or MMAO, Fe1-Fe5 exhibited exceptionally high activities for ethylene polymerization (up to 15.86 × 106 g(PE) mol-1 (Fe) h-1 at 40°C (MMAO) and 9.60 × 106 g(PE) mol-1 (Fe) h-1 at 60°C (MAO)) and produced highly linear polyethylene (HLPE, T m ≥ 128°C) with a wide range in molecular weights; in general, the MMAO-promoted polymerizations were more active. Irrespective of the cocatalyst employed, the 2,6-Me2-substituted Fe1 and Fe4 proved the most active while the more sterically hindered 2,6-i-Pr2 Fe3 the least but afforded the highest molecular weight polyethylene (M w : 65.6-72.6 kg mol-1). Multinuclear NMR spectroscopic analysis of the polymer formed using Fe4/MMAO at 40°C showed a preference for fully saturated chain ends with a broad bimodal distribution a feature of the GPC trace (M w/M n = 13.4). By contrast, using Fe4/MAO at 60°C a vinyl-terminated polymer of lower molecular weight (M w = 14.2 kg mol-1) was identified that exhibited a unimodal distribution (M w/M n = 3.8). Moreover, the amount of aluminoxane cocatalyst employed, temperature, and run time were also found to be influential on the modality of the polymer.

Cycloheptyl-fused N,N,N'-chromium catalysts with selectivity for vinyl-terminated polyethylene waxes: thermal optimization and polymer functionalization.

Five chromium(iii) chloride complexes, [2-{(Ar)N[double bond, length as m-dash]CMe}-9-{N(Ar)}C10H10N]CrCl3 (Ar = 2,6-Me2C6H3Cr1, 2,6-Et2C6H3Cr2, 2,6-i-Pr2C6H3Cr3, 2,4,6-Me3C6H2Cr4, 2,6-Et2-4-MeC6H2Cr5), each chelated by a sterically and electronically different cycloheptyl-fused N,N,N'-bis(imino)pyridine, have been synthesized by the reactions of CrCl3(THF)3 with the corresponding ligand (L1/L1'-L5/L5'). The molecular structure of Cr2 highlights both the steric properties exerted by the inequivalent N-2,6-ethylphenyl groups and the puckering of the fused cycloheptyl ring; a distorted octahedral geometry is conferred about the metal center. On activation with methylaluminoxane (MAO) or modified MAO (MMAO), Cr1-Cr5 displayed their optimal activity for ethylene polymerization at temperatures between 70 and 80 °C with the least sterically demanding Cr1 proving the most productive (1.44 × 107 g (PE) per mol (Cr) per h). The polyethylenes formed are of low molecular weight (Mw range: 0.66-3.56 kg mol-1) with narrow molecular weight distributions and display high levels of end-group unsaturation. Furthermore, the amenability of these vinyl-terminated polyethylenes to undergo functionalization via epoxidation has been demonstrated.

Ligand and solvent control of selectivity in the C-H activation of a pyridylimine-substituted 1-naphthalene; a combined synthetic and computational study.

The pyridylimine-substituted 1-naphthalenes, 2-(1-C10H7)-6-{CR[double bond, length as m-dash]N(2,6-i-Pr2C6H3)}C5H3N (R = Me HLMe, H HLH), react with Na2[PdCl4] in acetic acid at elevated temperature to afford either ortho-C-Hnaphthyl activated (LMe)PdCl (2ortho) or the unactivated adduct (HLH)PdCl2 (1b). Alternatively, 1b and its ketimine analogue (HLMe)PdCl2 (1a), can be prepared by treating (MeCN)2PdCl2 with either HLMe or HLH in chloroform at room temperature. Regio-selective ortho-C-H activation to form 2ortho can also be initiated by the thermolysis of 1a in acetic acid, while no reaction occurs under similar conditions with 1b. Interestingly, the C-H activation of HLMe to give 2ortho is found to be reversible with 100% deuteration of the peri-site occurring on reacting Na2[PdCl4] with HLMe in acetic acid-d4. By contrast, heating 1a in toluene gives a 55 : 45 mixture of 2ortho and its peri-activated isomer 2peri. Pure 2peri can, however, be obtained either from (LMe)PdOAc (3peri) by OAc/Cl exchange or by the sequential reactions of 1a with firstly silver acetate then with aqueous sodium chloride. Intriguingly, a peri to ortho interconversion occurs on heating 2peri in acetic acid to give 2ortho. DFT calculations have been used to investigate the C-H activation steps and it is found that in acetic acid ortho-C-H activation is kinetically and thermodynamically favoured but peri-CH activation is kinetically accessible (ΔΔG‡ = 2.4 kcal mol-1). By contrast in toluene, the reaction appears to be irreversible with the difference in barrier height for ortho- and peri-C-H activation being very small within the error of the method (ΔΔG‡ = 0.7 kcal mol-1), findings that are in agreement with the empirically observed product distribution for 2ortho and 2peri. Single crystal X-ray structures are reported for 1a, 1b, 2ortho and 2peri.

An air and moisture tolerant iminotrihydroquinoline-ruthenium(ii) catalyst for the transfer hydrogenation of ketones.

Reaction of 8-amino-5,6,7,8-tetrahydroquinoline with RuCl2(PPh3)3 at room temperature affords the ruthenium(ii) chelate (8-NH2-C9H10N)RuCl2(PPh3)2 (E), in which the two triphenylphosphine ligands are disposed mutually cis. By contrast, when the reaction is performed at reflux ligand oxidation/dehydrogenation occurs along with cis-trans reorganization of the triphenylphosphines to form the 8-imino-5,6,7-trihydroquinoline-ruthenium(ii) complex, (8-NH-C9H9N)RuCl2(PPh3)2 (F). Complex F can also be obtained in higher yield by heating a solution of E alone to reflux. Comparison of their molecular structures highlights the superior binding properties of the bidentate imine ligand in F over its amine-containing counterpart in E. Both complexes are highly effective in the transfer hydrogenation of a wide range of alkyl-, aryl- and cycloalkyl-containing ketones affording their corresponding secondary alcohols with loadings of as low as 0.1 mol%. Significantly, F can deliver excellent conversions even in bench quality 2-propanol in reaction vessels open to the air, whereas the catalytic efficiency of E is diminished by the presence of air but only operates efficiently under inert conditions.

Methylene-bridged bimetallic bis(imino)pyridine-cobaltous chlorides as precatalysts for vinyl-terminated polyethylene waxes.

Four examples of phenol-substituted methylene-bridged bis(imino)pyridines, CH(C6H4-4-OH){2'-(4-C6H2-2,6-R22N[double bond, length as m-dash]CMe)-6'-(2'',6''-R12C6H3N[double bond, length as m-dash]CMe)C5H3N}2 [R1 = R2 = Me L1, R1 = R2 = Et L2, R1 = Et, R2 = Me L3, R1 = iPr, R2 = Me L4], have been synthesized and fully characterized. Treatment of L1-L4 with two equivalents of cobaltous chloride affords the bimetallic complexes, [(L)Co2Cl4] (L = L1Co1, L2Co2, L3Co3, L4Co4), in good yield. The molecular structure of Co1 shows the two metal centers to be separated by a distance of 13.339 Å with each cobalt displaying a distorted trigonal bipyramidal geometry. On activation with either MAO or MMAO, Co1-Co4 exhibited high activities for ethylene polymerization (up to 1.46 × 107 g(PE) mol-1(Co) h-1 at 50 °C) with their relative values influenced by the steric properties of the N-aryl groups: Co1 > Co3 > Co4 > Co2. Highly linear polyethylenes incorporating high degrees of vinyl end-groups are a feature of all the materials produced with the molecular weights of the MAO-promoted systems (Mw range = 2-8 kg mol-1) generally higher than seen with MMAO (Mw range = 1-3 kg mol-1), while the distributions using MMAO are narrower (PDI < 2.0).

Bimetallic Aluminum 5,6-Dihydro-7,7-dimethyl quinolin-8-olates as Pro-Initiators for the ROP of ε-CL; Probing the Nuclearity of the Active Initiator.

Six examples of aluminum 5,6-dihydro-7,7-dimethylquinolin-8-olates, [{2-R¹-7,7-Me2-8-R²C9H6N-8-O}AlR³2]2 (R¹ = R² = H, R³ = Me C1; R¹ = R² = H, R³ = Et C2; R¹ = R² = H, R³ = i-Bu C3; R¹ = Cl, R² = H, R³ = Me C4; R¹ = H, R² = R³ = Me C5; R¹ = Cl, R² = R³ = Me C6), have been prepared by treating the corresponding pro-ligand (L1⁻L4) with either AlMe3, AlEt3 or Al(i-Bu)3. All complexes have been characterized by ¹H and 13C NMR spectroscopy and in the case of C1 and C4 by single crystal X-ray diffraction; dimeric species are a feature of their molecular structures. In the presence of PhCH2OH (BnOH), C1⁻C6 displayed good control and efficiency for the ROP of ε-CL with almost 100% conversion achievable in 10 min at 90 °C; the chloro-substituted C4 and C6 notably exhibited the lowest activity of the series. However, in the absence of BnOH, C1 showed only low activity with 15% conversion achieved in 30 min forming a linear polymer capped with either a methyl or a L1 group. By contrast, when one or more equivalents of BnOH was employed in combination with C1, the resulting catalyst was not only more active but gave linear polymers capped with BnO end-groups. By using ¹H and 27Al NMR spectroscopy to monitor solutions of C1, C1/BnOH and C1/BnOH/10 ε-CL over a range of temperatures, some support for a monomeric species being the active initiator at the operational temperature is presented.

ortho-Cycloalkyl substituted N,N'-diaryliminoacenaphthene-Ni(ii) catalysts for polyethylene elastomers; exploring ring size and temperature effects.

A family of six unsymmetrical N,N'-diiminoacenaphthene-nickel(ii) bromide complexes, [1-{2,6-(Ph2CH)2-4-MeC6H2N}-2-(ArN)C2C10H6]NiBr2 (Ar = 2-(C6H11)-6-MeC6H2Ni1, 2-(C5H9)-6-MeC6H2Ni2, 2-(C8H15)-6-MeC6H2Ni3, 2-(C6H11)-4,6-Me2C6H2Ni4, 2-(C5H9)-4,6-Me2C6H2Ni5, 2-(C8H15)-4,6-Me2C6H2Ni6), each bearing one ring-size variable 4-R-2-methyl-6-cycloalkyl-substituted N-aryl group and one N'-4-methyl-2,6-dibenzhydrylphenyl group, have been prepared and fully characterized. The molecular structures of Ni1, Ni2, Ni3 and Ni5 reveal distorted tetrahedral geometries with different degrees of steric protection imparted by the two inequivalent N-aryl groups. On activation with either EASC or MMAO, all the precatalysts are highly active (up to 17.45 × 106 g PE mol-1 (Ni) h-1) for ethylene polymerization at 20-50 °C with their activities correlating with the type of cycloalkyl ortho-substituent: cyclooctyl (Ni6, Ni3) > the cyclopentyl (Ni5, Ni2) > cyclohexyl (Ni4, Ni1) for either R = H or Me. Moderately branched to hyperbranched polyethylenes (Tm's as low as 44.2 °C) can be obtained with molecular weights in the range 2.14-6.68 × 105 g mol-1 with the branching content enhanced by the temperature of the polymerization. Dynamic mechanical analysis (DMA) and monotonic tensile stress-strain tests have been employed on the polyethylene samples and reveal the more branched materials to show good elastic recovery properties (up to 75.5%).