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Chiral manganese(I) complexes that contain carbocyclic-fused 8-amino-5,6,7,8-tetrahydroquinolinyl groups that are appended with distinct para -R substituents have proven to be effective catalysts in the asymmetric transfer hydrogenation (ATH) of a wide range of ketones (48 examples). Notably, Mn2 proved to be the most productive catalyst, allowing an outstanding turnover number of 8300 with catalyst loadings as low as 0.01 mol %. Furthermore, this catalytic protocol shows considerable promise for applications in the synthesis of chiral drugs such as Lusutrombopag.

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.

Four examples of N , N -bis(aryl)butane-2,3-diimine-nickel(II) bromide complexes, [ArN=C(Me)-C(Me)=NAr]NiBr 2 (where Ar = 2-(C 5 H 9 )-4,6-(CHPh 2 ) 2 C 6 H 2 ( Ni1 ), Ar = 2-(C 6 H 11 )-4,6-(CHPh 2 ) 2 C 6 H 2 ( Ni2 ), 2-(C 8 H 15 )-4,6-(CHPh 2 ) 2 C 6 H 2 ( Ni3 ) and 2-(C 12 H 23 )-4,6-(CHPh 2 ) 2 C 6 H 2 ( 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 EtAlCl 2 , Et 2 AlCl 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 × 10 6 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 13 C 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% (EtAlCl 2 ); 81.1% (Et 2 AlCl); 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 ( X c ) and molecular weight ( M w ) were the main factors affecting tensile strength and strain at break ( ε b = 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).

The fluoro-substituted 2,6-bis(arylimino)pyridine dichlorocobalt complexes, [2-{CMeN(2,6-(Ph 2 CH) 2 -3,4-F 2 C 6 H)}-6-(CMeNAr)C 5 H 3 N]CoCl 2 (Ar = 2,6-Me 2 C 6 H 3 Co1, 2,6-Et 2 C 6 H 3 Co2, 2,6-iPr 2 C 6 H 3 Co3, 2,4,6-Me 3 C 6 H 2 Co4, 2,6-Et-4-MeC 6 H 2 Co5), were synthesized in good yield from the corresponding unsymmetrical N , N , N '-ligands, L1-L5. Besides characterization of Co1-Co5 by FT-IR spectroscopy, 19 F 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 × 10 6 g PE mol -1 (Co) h -1 ) which decreased to 3.3 × 10 6 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., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

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-Me 2 -4-{CH(4-FC 6 H 4 ) 2 }C 6 H 2 L1, 2-Me-6-Et-4-{CH(4-FC 6 H 4 ) 2 }C 6 H 2 L2, 2,4-{CH(4-FC 6 H 4 ) 2 } 2 -6-MeC 6 H 2 L3, 2,4-{CH(4-FC 6 H 4 ) 2 } 2 -6-EtC 6 H 2 L4, 2,4-{CH(4-FC 6 H 4 ) 2 } 2 -6-iPrC 6 H 2 L5), 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 ( 1 H, 13 C, 19 F) 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 EtAlCl 2 , Et 2 AlCl or EASC, was exceptionally active (0.9-1.0 × 10 7 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% (EtAlCl 2 ), 87.2% (Et 2 AlCl), 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)., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

A set of five related bis(imino)-6,7-dihydro-5 H -quinoline-cobalt(ii) complexes, [2-(ArN = CPh)-8-(NAr)-C 9 H 8 N]CoCl 2 (Ar = 2,6-Me 2 C 6 H 3 Co1, 2,6-Et 2 C 6 H 3 Co2, 2,6-i-Pr 2 C 6 H 3 Co3, 2,4,6-Me 3 C 6 H 2 Co4, 2,6-Et 2 -4-MeC 6 H 2 Co5), have been synthesized in reasonable yield by the template reaction of cobalt(ii) chloride hexahydrate, 2-benzoyl-6,7-dihydro-5 H -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 × 10 7 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 1 H/ 13 C NMR spectroscopy and by IR spectroscopy., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

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 β-H elimination as the dominant chain transfer process.

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, β-H elimination and transfer to aluminum, has been demonstrated using 13C/1H NMR spectroscopy.

The syntheses of six bis(imino)-5,6,7,8-tetrahydrocycloheptapyridine-iron(ii) chloride complexes, [2-{(Ar)NCMe}-9-{N(Ar)}C 10 H 10 N]FeCl 2 (Ar = 2-(C 5 H 9 )-6-MeC 6 H 3 Fe1, 2-(C 6 H 11 )-6-MeC 6 H 3 Fe2, 2-(C 8 H 15 )-6-MeC 6 H 3 Fe3, 2-(C 5 H 9 )-4,6-Me 2 C 6 H 2 Fe4, 2-(C 6 H 11 )-4,6-Me 2 C 6 H 2 Fe5, 2-(C 8 H 15 )-4,6-Me 2 C 6 H 3 Fe6), 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 × 10 7 g of PE per mol Fe per h for Fe5/MMAO] for ethylene polymerization forming linear polyethylene (T m '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 × 10 7 g of PE per mol Fe per h); the wide variation in polymer molecular weights (M w : 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.

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.

The 4,6-bis(arylimino)-1,2,3,7,8,9,10-heptahydrocyclohepta[ b ]quinoline-iron(II) chlorides (aryl = 2,6-Me 2 C 6 H 3 Fe1 ; 2,6-Et 2 C 6 H 3 Fe2 ; 2,6- i -Pr 2 C 6 H 3 Fe3 ; 2,4,6-Me 3 C 6 H 2 Fe4 ; and 2,6-Et 2 -4-Me 2 C 6 H 2 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, FeCl 2 ·4H 2 O, 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 × 10 6  g(PE) mol -1  (Fe) h -1 at 40°C (MMAO) and 9.60 × 10 6  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-Me 2 -substituted Fe1 and Fe4 proved the most active while the more sterically hindered 2,6- i -Pr 2 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., Competing Interests: The authors declare no competing financial interest., (Copyright © 2019 Zheng Wang et al.)

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-R 1 2 -4-R 2 -C 6 H 2 ))C 5 H 3 N} 2 (C 10 H 6 )]Co 2 Cl 4 (R 1 = Me, R 2 = H Co1; R 1 = Et, R 2 = H Co2; R 1 = i Pr, R 2 = H Co3; R 1 = Me, R 2 = Me Co4; R 1 = Et, R 2 = Me Co5; R 1 = CHPh 2 , R 2 = 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 × 10 7 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]CH 2 ) found to rise with the reaction temperature. By modulating the steric hindrance exerted by the ortho-R 1 substituents in the precatalyst, polyethylenes displaying a remarkably broad range of molecular weights could be obtained [from 4.52 kg mol -1 (R 1 = Me) to 246.7 kg mol -1 (R 1 = CHPh 2 )].

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-Me 2 C 9 H 6 N (Ar = 2,6-Me 2 C 6 H 3 L1, 2,6-Et 2 C 6 H 3 L2, 2,6- i Pr 2 C 6 H 3 L3, 2,4,6-Me 3 C 6 H 2 L4, 2,6-Et 2 -4-MeC 6 H 2 L5, 2,4,6- t Bu 3 C 6 H 3 L6), distinguishable by their steric and electronic profile, are described that can readily undergo complexation with cobaltous chloride to form their corresponding LCoCl 2 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 × 10 7 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 (M w ≤16.0 kg mol -1 ) and of narrow dispersity (M w /M n ≤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 β-H elimination and chain transfer to aluminum as termination pathways.

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.

A new set of five unsymmetrical N,N'-diiminoacenaphthenes, 1-[2,6-{(4-FC 6 H 4 ) 2 CH} 2 -4-NO 2 C 6 H 4 N]-2-(ArN)C 2 C 10 H 6 (Ar = 2,6-Me 2 C 6 H 3 L1, 2,6-Et 2 C 6 H 3 L2, 2,6- i Pr 2 C 6 H 3 L3, 2,4,6-Me 3 C 6 H 2 L4, 2,6-Et 2 -4-MeC 6 H 2 L5), have been synthesized and used to prepare their corresponding nickel(ii) halide complexes, LNiBr 2 (Ni1-Ni5) and LNiCl 2 (Ni6-Ni10). The molecular structures of Ni3(OH 2 ) and Ni4 reveal distorted square pyramidal and tetrahedral geometries, respectively, while the 1 H NMR spectra of all the nickel(ii) (S = 1) complexes show broad paramagnetically shifted peaks. Upon activation with either methylaluminoxane (MAO) or ethylaluminum sesquichloride (Et 3 Al 2 Cl 2 , 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 × 10 7 g PE mol -1 (Ni) h -1 at 50 °C) which produced high molecular weight plastomeric polyethylene (M w = 3.93 × 10 5 g mol -1 , T m = 70.6 °C) with narrow dispersity (M w /M n = 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 × 10 6 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.

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.

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.

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 13 C 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 27 Al 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., Competing Interests: The authors declare no conflict of interest.

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.

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).

A family of six unsymmetrical N,N'-diiminoacenaphthene-nickel(ii) bromide complexes, [1-{2,6-(Ph 2 CH) 2 -4-MeC 6 H 2 N}-2-(ArN)C 2 C 10 H 6 ]NiBr 2 (Ar = 2-(C 6 H 11 )-6-MeC 6 H 2 Ni1, 2-(C 5 H 9 )-6-MeC 6 H 2 Ni2, 2-(C 8 H 15 )-6-MeC 6 H 2 Ni3, 2-(C 6 H 11 )-4,6-Me 2 C 6 H 2 Ni4, 2-(C 5 H 9 )-4,6-Me 2 C 6 H 2 Ni5, 2-(C 8 H 15 )-4,6-Me 2 C 6 H 2 Ni6), 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 × 10 6 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 (T m 's as low as 44.2 °C) can be obtained with molecular weights in the range 2.14-6.68 × 10 5 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%).

Five examples of α,α'-bis(arylimino)-2,3:5,6-bis(pentamethylene)pyridyl-chromium(iii) chlorides (aryl = 2,6-Me 2 Ph Cr1, 2,6-Et 2 Ph Cr2, 2,6-i-Pr 2 Ph Cr3, 2,4,6-Me 3 Ph Cr4, 2,6-Et 2 -4-MePh Cr5) have been synthesized by the one-pot template reaction of α,α'-dioxo-2,3:5,6-bis(pentamethylene)pyridine, CrCl 3 ·6H 2 O and the corresponding aniline. The molecular structures of Cr1 and Cr4 reveal distorted octahedral geometries with the N,N,N-ligand adopting a mer-configuration. On activation with an aluminium alkyl co-catalyst, Cr1-Cr5 exhibited high catalytic activities in ethylene polymerization and showed outstanding thermal stability operating effectively at 80 °C with activities up to 1.49 × 10 7 g of PE (mol of Cr) -1 h -1 . Significantly, the nature of the co-catalyst employed had a dramatic effect on the molecular weight of the polymeric material obtained. For example, using diethylaluminium chloride (Et 2 AlCl) in combination with Cr4 gave high density/high molecular weight polyethylene with broad molecular weight distributions (30.9-39.3). By contrast, using modified methylaluminoxane (MMAO), strictly linear polyethylene waxes of lower molecular weight and narrow molecular weight distribution (1.6-2.0) were obtained with vinyl end-groups.

In the mononuclear title complex, [CuI(C 2 H 3 N)(C 26 H 24 N 2 )], the Cu I ion has a distorted tetra-hedral coordination environment, defined by two N atoms of the chelating 2-(naphthalen-1-yl)-6-[(2,4,6-tri-methyl-phen-yl)imino]-pyridine ligand, one N atom of an aceto-nitrile ligand and one iodide ligand. Within the complex, there are weak intra-molecular C-H⋯N hydrogen bonds, while weak inter-molecular C-H⋯I inter-actions between complex mol-ecules, help to facilitate a three-dimensional network.

Five examples of selectively fluorinated unsymmetrical diiminoacenaphthylenes, 1-[2,6-{(4-FC 6 H 4 ) 2 CH} 2 -4-FC 6 H 4 N]-2-(ArN) C 2 C 10 H 6 (Ar = 2,6-Me 2 C 6 H 3 L1, 2,6-Et 2 C 6 H 3 L2, 2,6-iPr 2 C 6 H 3 L3, 2,4,6-Me 3 C 6 H 2 L4, 2,6-Et 2 -4-MeC 6 H 2 L5), have been synthesized and used to prepare their corresponding nickel(ii) halide complexes, LNiBr 2 (Ni1-Ni5) and LNiCl 2 (Ni6-Ni10). Both 1 H and 19 F NMR spectroscopy techniques have been employed to characterize paramagnetic Ni1-Ni10; an inequivalent fluorine environment is a feature of the tetrahedral complexes in solution. Upon activation with relatively low ratios (ca. 600 equiv.) of ethylaluminum sesquichloride (Et 3 Al 2 Cl 2 , EASC), all the nickel complexes displayed high activities toward ethylene polymerization at 30 °C with precatalyst Ni4 the standout performer at 2.20 × 10 7 g of PE per mol of Ni per h, producing highly branched polyethylenes. In comparison with related diiminoacenaphthylene-nickel catalysts, these current systems, incorporating a high fluorine content on one N-aryl group, display superior productivity. In addition, the molecular structures of Ni2 and Ni4 are reported and the active catalyst is probed using 19 F NMR spectroscopy.

Correction for 'Resonance Raman spectroscopy as an in situ probe for monitoring catalytic events in a Ru-porphyrin mediated amination reaction' by Paolo Zardi et al., Analyst, 2016, 141, 3050-3058.

Resonance Raman microspectroscopy has been widely used to study the structure and dynamics of porphyrins and metal complexes containing the porphyrin ligand. Here, we have demonstrated that the same technique can be adapted to examine the mechanism of a homogeneously-catalysed reaction mediated by a transition-metal-porphyrin complex. Previously it has been challenging to study this type of reaction using in situ spectroscopic monitoring due to the low stability of the reaction intermediates and elevated-temperature conditions. We have made a straightforward modification to the sample stage on a microscope for time-lapsed Raman microspectroscopy from reaction mixtures in these media. The allylic amination of unsaturated hydrocarbons by aryl azides, which can be catalysed by a ruthenium-porphyrin complex, has been used as an illustrative example of the methodology. The mechanism of this particular reaction has been studied previously using density-functional theory and kinetic approaches. The Raman measurements support the mechanism proposed in the earlier publications by providing the first experimental verification of a precursor reaction complex between the aryl azide and the ruthenium metal ion, and evidence for the formation of a mono-imido intermediate complex under conditions of high concentration of the reactant olefin.

The 2-(2′-aniline)-6-imine-pyridines, 2-(C6H4-2′-NH2)-6-(CMe=NAr)C5H3N (Ar = 4-i-PrC6H4 (HL1a), 2,6-i-Pr2C6H3 (HL1b)), have been synthesised via sequential Stille cross-coupling, deprotection and condensation steps from 6-tributylstannyl-2-(2-methyl-1,3-dioxolan-2-yl)pyridine and 2-bromonitrobenzene. The palladium(II) acetate N,N,N-pincer complexes, [{2-(C6H4-2′-NH)-6-(CMe=NAr)C5H3N}Pd(OAc)] (Ar = 4-i-PrC6H4 (1a), 2,6-i-Pr2C6H3 (1b)), can be prepared by reacting HL1 with Pd(OAc)2 or, in the case of 1a, more conveniently by the template reaction of ketone 2-(C6H4-2′-NH2)-6-(CMe=O)C5H3N, Pd(OAc)2 and 4-isopropylaniline; ready conversion of 1 to their chloride analogues, [{2-(C6H4-2′-NH)-6-(CMe=NAr)C5H3N}PdCl] (Ar = 4-i-PrC6H4 (2a), 2,6-i-Pr2C6H3 (2b)), has been demonstrated. The phenyl-containing complexes, [{2-(C6H4-2′-NH)-6-(CMe=NAr)C5H3N}PdPh] (Ar = 4-i-PrC6H4 (3a), 2,6-i-Pr2C6H3 (3b)), can be obtained by treating HL1 with (PPh3)2PdPh(Br) in the presence of NaH or with regard to 3a, by the salt elimination reaction of 2a with phenyllithium. Reaction of 2a with silver tetrafluoroborate or triflate in the presence of acetonitrile allows access to cationic [{2-(C6H4-2′-NH)-6-(CMe=N(4-i-PrC6H4)C5H3N}Pd(NCMe)][X] (X = BF4 (4), X = O3SCF3 (5)), respectively; the pyridine analogue of 5, [{2-(C6H4-2′-NH)-6-(CMe=N(4-i-PrC6H4)C5H3N}Pd(NC5H5)][O3SCF3] (5′), is also reported. Oxidation of phenyl-containing 3a with one equivalent of 1-chloromethyl-4-fluoro-1,4-diazoniabicyclo[2.2.2]octane bis(tetrafluoroborate) (Selectfluor™) in acetonitrile at low temperature leads to a new palladium species that slowly decomposes to give 4 and biphenyl; biphenyl formation is also observed upon reaction of 3a with XeF2. However, no such oxidatively induced coupling occurs when using 3b. Single crystal X-ray diffraction studies have been performed on HL1b, 1a, 1b, 2a, 2b, 3a, 3b and 5′.

The syntheses of two families of sterically tuneable O,N,N pro-ligands are reported, namely the 2-(phenyl-2'-ol)-6-imine-pyridines, 2-(C6H4-2'-OH),6-(CMe=NAr)C5H3N [Ar = 4-i-PrC6H4 (HL1(a)), 2,6-i-Pr2C6H3 (HL1(b))] and the 2-(phenyl-2'-ol)-6-(amino-prop-2-yl)pyridines, 2-(C6H4-2'-OH),6-(CMe2NHAr)C5H3N [Ar = 4-i-PrC6H4 (HL2(a)), 2,6-i-Pr2C6H3 (HL2(b))], using straightforward synthetic approaches and in reasonable overall yields. Interaction of HL1(a/c) and HL2(a/b) with palladium(II) acetate affords the O,N,N-pincer complexes, [{2-(C6H4-2'-O)-6-(CMe=NAr)C5H3N}Pd(OAc)] (Ar = 4-i-PrC6H4 (1a), 2,6-i-Pr2C6H3 (1b)) and [{2-(C6H4-2'-O)-6-(CMe2NHAr)C5H3N}Pd(OAc)] (Ar = 4-i-PrC6H4 (2a), 2,6-i-Pr2C6H3 (2b)), which can be readily converted to their chloride derivatives, [{2-(C6H4-2'-O)-6-(CMe=NAr)C5H3N}PdCl] (Ar = 4-i-PrC6H4 (3a), 2,6-i-Pr2C6H3 (3b)) and [{2-(C6H4-2'-O)-6-(CMe2NHAr)C5H3N}PdCl] (Ar = 4-i-PrC6H4 (4a), 2,6-i-Pr2C6H3 (4b)), respectively, on reaction with an aqueous sodium chloride solution. Treating each of 3a, 3b, 4a and 4b with two equivalents of di-p-tolyliodonium triflate at 100 °C in a toluene/acetonitrile mixture affords varying amounts of 4-chlorotoluene along with the 4-iodotoluene by-product with the conversions highly dependent on the steric and backbone properties of the pincer complex employed (viz. 4a > 3a > 4b > 3b); notably, the least sterically bulky and most flexible amine-containing 4a reaches 90% conversion to 4-chlorotoluene in 15 h as opposed to 17% for imine-containing 3b. In the case of 3a, the inorganic palladium species recovered from the reaction has been identified as the Pd(II) salt [{2-(C6H4-2'-O)-6-(CMe=N(4-i-PrC6H4)C5H3N}Pd(NCMe)][O3SCF3] (5a), which was independently prepared by the reaction of 3a with silver triflate in acetonitrile. Single crystal X-ray structures are reported for HL1(a), HL2(a), 1a, 1b, 2a, 2b, 3a and 5a.

The 2-(3-biphenyl-2-ol)-6-iminepyridines, 2-(3-C12H8-2-OH)-6-(CH=NAr)C5H3N (Ar = 2,6-i-Pr2C6H3 (L1a-H), 2,4,6-Me3C6H2 (L1b-H)), have been prepared in high yield via sequential Suzuki coupling, deprotection and condensation reactions from 2-methoxybiphenyl-3-ylboronic acid and 2-bromo-6-formylpyridine. Treatment of L1-H with Pd(OAc)2 or (MeCN)2PdCl2 results in deprotonation of L1-H to afford the discrete square planar ONN-chelates, [{2-(3-C12H8-2-O)-6-(CHNAr)C5H3N}Pd(OAc)] (Ar = 2,6-i-Pr2C6H3 (1a), 2,4,6-Me3C6H2 (1b)) and [{2-(3-C12H8-2-O)-6-(CH=NAr)C5H3N}PdCl] (Ar = 2,6-i-Pr2C6H3 (2a), 2,4,6-Me3C6H2 (2b)), in good yield, respectively; conversion of 1 to 2 using aqueous sodium chloride has been demonstrated. Selective reduction of the imino unit in L1-H with LiAlH4 proceeds smoothly to yield the 2-(3-biphenyl-2-ol)-6-(methylamine)pyridines, 2-(3-C12H8-2-OH)-6-(CH2-NHAr)C5H3N (Ar = 2,6-i-Pr2C6H3 (L2a-H), 2,4,6-Me3C6H2 (L2b-H)), which on reaction with Pd(OAc)2 give [{2-(3-C12H8-2-O)-6-(CH2-NHAr)C5H3N}Pd(OAc)] (Ar = 2,6-i-Pr2C6H3 (3a), 2,4,6-Me3C6H2 (3b)). Depending on the temperature of the reaction, the oxidised aldimine products 1a or 1b can also be observed as a competitive side-product during the formation of 3a or 3b. Similarly, ketimine-containing, [{2-(3-C12H8-2-O)-6-(CMe=N(2,6-i-Pr2C6H3))C5H3N}Pd(OAc)] (5), can be detected during the preparation of chiral [{2-(3-C12H8-2-O)-6-(CMeH-NH(2,6-i-Pr2C6H3))C5H3N}Pd(OAc)] (4) from 2-(3-C12H8-2-OH)-6-(CH2-NH(2,6-i-Pr2C6H3))C5H3N (L3-H) and Pd(OAc)2. Complexes 3a, 3b and 4 all exist as dimeric species in the solid state in which two anti-aligned square planar monomers are held together by two intermolecular NH(amine)···O(phenolate) interactions resulting in palladium–palladium separations of between 3.141–3.284 Å. The structurally related chloride-containing dimeric assemblies, [{2-(3-C12H8-2-O)-6-(CH2-NHAr)C5H3N)}PdCl] (Ar = 2,6-i-Pr2C6H3 (6a), 2,4,6-Me3C6H2 (6b)), can also be isolated on treatment of 3 with aqueous sodium chloride or by reaction of L3-H with (MeCN)2PdCl2. Single crystal X-ray diffraction studies have been performed on L1a-H, L3-H, 1a, 1b, 2a, 2b, 3a, 3b, 4, 6a and 6b.

Bidentate N,N-pyridylimine or N,N-pyridylamine donors are effective chelating ligands for regiospecific C-H activation at the peri-(C(8))-position of a naphthyl ring on reaction with palladium(ii) acetate; DFT calculations show N,N-chelates bias the cyclopalladation towards 6-membered ring products.

The first neutral, [IrClF(2)(NHC)(COD)] and [IrClF(2)(CO)(2)(NHC)] (NHC = IMes, IPr), and cationic, [IrF(2)py(IMes)(COD)][BF(4)] and [IrF(2)L(CO)(2)(NHC)][BF(4)] (NHC = IMes, L = PPh(2)Et, PPh(2)CCPh, py; NHC = IPr, L = py), NHC iridium(III) fluoride complexes, have been synthesised by the xenon difluoride oxidation of iridium(I) substrates. The stereochemistries of these iridium(III) complexes have been confirmed by multinuclear NMR spectroscopy in solution and no examples of fluoride-trans-NHC arrangements were observed. Throughout, CO was found to be a better co-ligand for the stabilisation of the iridium(III) fluoride complexes than COD. Attempts to generate neutral trifluoroiridium(III) complexes, [IrF(3)(CO)(NHC)], via the ligand substitution reaction of [IrF(3)(CO)(3)] with the free NHCs were unsuccessful.

The bis(imino)quaterpyridine, 6,6'''-{(2,4,6-i-Pr(3)C(6)H(2))N=CMe}(2)-2,2':6',2'':6'',2'''-C(20)H(12)N(4) (L(tripp)), can be prepared in good yield by the condensation reaction of 6,6'''-bis(acetyl)quaterpyridine with 2,4,6-triisopropylaniline; the 2,6-diisopropylphenyl derivative 6,6'''-{(2,6-i-Pr(2)C(6)H(3))N=CMe}(2)-2,2':6',2'':6'',2'''-C(20)H(12)N(4) (L(dipp)) is also reported. Reactions of L(tripp) with 2.5 equivalents of MX(2) (MX(2) = CoCl(2), CoBr(2), (DME)(2)NiCl(2) and FeCl(2)) in n-butanol at 100 degrees C overnight results in self-assembly to form the paramagnetic salts [(L(tripp))M(2)X(3)](2)[MX(4)] [M = Co, X = Cl (1a); M = Co, X = Br (1b); M = Ni, X = Cl (2); M = Fe X = Cl (3)] in moderate yield. The molecular structures of the acetonitrile/water adducts 1a(NCMe)(2), 1b(NCMe)(OH(2)) and 2(NCMe)(4) reveal that L(tripp) acts as a bis(tridentate) ligand that can support a range of structural motifs for the cationic units including [(L(tripp))CoCl(mu-Cl)CoCl(NCMe)](+), [(L(tripp))CoBr(2)CoBr(OH(2))(NCMe)](+), [(L(tripp))CoBr(mu-Br)CoBr)](+) and [(L(tripp))NiCl(NCMe)(mu-Cl)NiCl(NCMe)](+). On activation with MAO (methylaluminoxane), 1-3 show modest activities for ethylene oligomerisation (1a/MAO approximately 1b/MAO > 2/MAO) or are inactive (3/MAO). Notably, the two cobalt systems (1a/MAO, 1b/MAO) afford highly linear alpha-olefins while the nickel system (2/MAO) yields methyl-branched waxes composed of mostly internal unsaturation along with lower levels of alpha-olefins. In addition to 1a(NCMe)(2), 1b(NCMe)(2)(OH(2)) and 2(NCMe)(3), a single crystal X-ray determination has been performed on the structurally related salt [(L(tripp))Ni(2)Br(3)(OH(2))(2)][Br] (4).

Treatment of tetranuclear [RuF(-F)(CO)3]4 (1) with the free N-heterocyclic carbenes (NHCs), IMes (1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene) and IPr (1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene), followed by work-up in carbon tetrachloride leads to fluoride-bridge cleavage in 1 and the formation of the mononuclear octahedral complexes cis,cis,trans-[RuF2(CO)2(NHC)2] [NHC = IMes (2a), IPr (2b)], respectively. Complexes 2a and 2b can also be obtained by interaction of 1 with the corresponding imidazolium chloride, [-N(Ar)CHN(Ar)CHCH-]Cl (Ar = 2,4,6-Me3C6H2, 2,6-i-Pr2C6H3), in the presence of KOtBu. However, extension of this latter base-assisted approach to [-N(Ar)CHN(Ar)CHCH-]Cl (Ar = 2,6-Me2C6H3, 2,4,6-i-Pr3C6H2) results in halide exchange with the work-up solvent (CCl4) to generate cis,cis,trans-[RuCl2(CO)2(IMe)2] (3) and dinuclear [RuCl(mu-Cl)(CO)2(ITPr)]2 (4), respectively. Reaction of 2a with gaseous BF3 in dichloromethane and subsequent carbonylation affords in high yield monocationic [Ru(FBF3)(CO)3(IMes)2](BF4) (5), while with 2b, BF3 addition alone results in solvent exchange to yield dinuclear monocationic [Ru2(mu-Cl)3(CO)4(IPr)2](BF4)/(F) (6). Conversely, interaction of 2a and 2b with BF3.OEt2 in acetonitrile furnishes dicationic cis,cis,trans-[Ru(CO)2(NCMe)2(NHC)2](BF4)2 [NHC = IMes (7a), IPr (7b)]; in the case of 7a carbonylation gives [Ru(CO)4(IMes)2](B2F7)2 (8). Single crystal X-ray structures are presented for 3, 4, 5, 6 and 8.

Two new sterically demanding bis(imino)bipyridine ligands, 6,6'-{(2,6-i-Pr(2)C(6)H(3))N=R}(2)C(10)H(6)N(2) (R = H (L1), Me (L2)), have been prepared in high yield by the condensation reaction of 2,6-diisopropylaniline with 6,6'-(O=R)(2)C(10)H(6)N(2) (R = H, Me). Palladium(0)-mediated cross coupling of 2-(Bu(3)Sn)-6-{C(Me)OCH(2)CH(2)O}C(5)H(3)N with 2-Br-6-{C(Me)OCH(2)CH(2)O}C(5)H(3)N, followed by an acid-mediated deprotection, has been employed as an efficient route to the precursor 6,6'-bis(acetyl)-2,2'-bipyridine. Reaction of aldimino L1 with two equivalents of MX(2) [MX(2) = ZnCl(2), NiCl(2) or (DME)NiBr(2)] in n-BuOH at elevated temperature gives the five-coordinate mononuclear complexes [(L1)MX(2)] (M = Zn, X = Cl 1; M = Ni, X = Cl 2a; M = Ni, X = Br 2b) as the sole products, in which one imine group is bound and the other uncoordinated (endo-exo). In the case of diamagnetic 1, VT (1)H NMR spectroscopy reveals a fast exchange process operating between the two possible forms of the endo-exo isomer which is likely to proceed via an exo-exo intermediate (DeltaH(double dagger)(interconversion) = 35.6 +/- 1.5 kJ mol(-1), DeltaG(double dagger)(298) = 47.4 +/- 3.3 kJ mol(-1)). In contrast, treatment of ketimino L2 with MCl(2) (MCl(2) = ZnCl(2) or NiCl(2)) affords bimetallic [(L2)Zn(2)Cl(4)] (4) and the six-coordinate monometallic species [(L2)NiCl(2)] (5), respectively; in 4, L2 adopts a bis(bidentate) bonding mode (endo-endo) while in 5 it acts as tetradentate ligand (endo-endo). Prolonged standing of 1 in chlorinated solvents results in partial hydrolysis and the formation of the 6-imino-6'-formyl-2,2'-bipyridine zinc complex, [(6-{(2,6-i-Pr(2)C(6)H(3))N=Me)-6'-(CH=)C(10)H(6)N(2))ZnCl(2)] (3) (endo-imine, exo-formyl). Single crystal X-ray structures are reported for L1,1 , 2a, 3, 4 and 5.

A series of chiral dizinc complexes of the type [(2,6-{ArN=C(Me)C5H3N}2C6H3O)Zn2(micro-Cl)Cl2] [Ar=2,6-i-Pr2C6H3 (), 2,6-Me2C6H3 (), 2,4,6-Me3-C6H2 (), 2,4-Me2C6H3 ()] can be conveniently prepared in good yield by the template reaction of 2,6-{O=C(Me)C5H3N}2C6H3OH with an excess of the corresponding aniline and two equivalents of zinc dichloride in n-BuOH at elevated temperature. Alternatively, the pro-ligands, 2,6-{(ArN=C(Me)C5H3N}2C6H3OH [Ar=2,6-i-Pr2C6H3 (L1-H), 2,6-Me2C6H3 (L2-H), 2,4,6-Me3C6H2 (L3-H), 2,4-Me2C6H3 (L4-H)], can be isolated and then treated with two equivalents of zinc dichloride to afford . Interaction of with two equivalents of NaOAc in the presence of TlBF4 gives the diacetate-bridged salt [(L1)Zn2(micro-OAc)2](BF4) () while with Nadbm (dbm=dibenzoylmethanato) the bis(dbm)-chelated salt [(L1)Zn2(dbm)2](BF4) () is obtained. Hydrolysis occurs on reaction of with TlOEt to furnish [(L1)Zn2(micro-OH)Cl2] () as the only isolable product. Conversely, reaction of with Tlhp (hp=2-pyridonate) affords the neutral bis(pyridonate)-bridged trimetallic complex [(L1)Zn3(micro-hp)2Cl3] () as the major product along with as the minor one. Complex and mixtures of / act as modest activators for the ring-opening polymerisation of epsilon-caprolactone. Single crystal X-ray diffraction studies have been performed on , , , , and reveal Zn...Zn separations in the range: 3.069(4)-4.649(6) A.

In the crystal structure of the title compound, [RuF(2)(C(26)H(24)P(2))(2)].2CHCl(3), the Ru atom lies on a centre of symmetry with a trans arrangement of the F atoms. A H...F contact (2.249 A) suggests weak intramolecular hydrogen bonding. The solvent molecules exhibit hydrogen bonding with the F atoms (H...F = 1.91 A).

The reaction between carbonyl fluoride and [Ir(COD)(PPh(3))(2)]BF(4) (COD is cycloocta-1,5-diene) in dichloromethane solution affords the novel title iridium salt, [IrCl(2)(C(18)H(15)P)(2)(CO)(2)]BF(4). The cation lies across a twofold rotation axis in the space group P2(1)2(1)2 and its structure confirms the presence in a cis relationship of two metal-bound chlorides, while the phosphine ligands occupy a trans pair of sites. The anion also lies across a twofold rotation axis, and the F atoms are disordered over two sets of sites.

Two new bulky aryl-bridged pyridyl-imine compartmental (pro)ligands, 2,6-{(2,6-i-Pr(2)C6H3)N=C(Me)C5H3N}2C6H3Y (Y = H L1, OH L2-H), have been prepared in moderate to good overall yields via a Stille-type cross-coupling approach. The molecular structure of L2-H reveals a transoid configuration within the pyridyl-imine units with a hydrogen-bonding interaction maintaining the phenol coplanar with one of the adjacent pyridine rings. The interaction of 2 equiv of MX2 with L1 in n-BuOH at 110 degrees C gives the binuclear complexes, [(L1)M2X4] (M = Fe, X = Cl (1a); M = Co, X = Cl (1b); M = Ni, X = Br (1c); M = Zn, X = Cl (1d)), in which the metal centers adopt distorted tetrahedral geometries and occupy the two pyridyl-imine cavities in L1. In contrast, deprotonation of L2-H occurs upon reaction with 2 equiv of MX2 to afford the phenolate-bridged species [(L2)M2(mu-X)X2] (M = Fe, X = Cl (2a); M = Co, X = Cl (2b); M = Ni, X = Br (2c); M = Zn, X = Cl (2d)). 1H NMR studies of diamagnetic 1d and 2d reveal that the limited rotation of the N-aryl groups in 1d is further impeded in 2d by steric interactions imparted by the two closely located N-aryl groups. Partial displacement of the bridging bromide in 2c results upon its treatment with acetonitrile to afford [(L2)Ni2Br3(NCMe)] [2c(MeCN)]; no such reaction occurs for 2a, 2b, or 2d. Upon activation with excess methylalumoxane (MAO), 1b, 1c, 2b, and 2c show some activity for alkene oligomerization forming low molecular-weight materials with methyl-branched products predominating for the nickel systems. Single-crystal X-ray diffraction studies have been performed on L2-H, 1c, 2b, 2c, 2c(NCMe), and 2d.

The bis(imino)terpyridine ligands, 6,6''-{(2,6-i-Pr2C6H3)N=CR}2-2,2':6',2''-C15H9N3 (R = H L1, Me L2), have been prepared in high yield from the condensation reaction of the corresponding carbonyl compound with two equivalents of 2,6-diisopropylaniline. The molecular structure of L2 reveals a transoid relationship between the imino and pyridyl nitrogen groups throughout the ligand framework. Treatment of aldimine-containing L1 with one equivalent or an excess of MX2 in n-BuOH at 110 degrees C gives the mononuclear five-coordinate complexes, [(L1)MX2] (M = Fe, X = Cl 1a; M = Ni, X = Br 1b; M = Zn, X = Cl 1c), in which the metal centre occupies the terpyridine cavity and the imino groups pendant. Conversely, reaction of ketimine-containing L2 with excess MX2 in n-BuOH at 110 degrees C affords the binuclear complexes, [(L2)M2X4] (M = Fe, X = Cl 3a; M = Ni, X = Br 3b; M = Zn, X = Cl 3c), in which one metal centre occupies a bidentate pyridylimine cavity while the other a tridentate bipyridylimine cavity. 1H NMR studies on diamagnetic 3c suggests a fluxional process is operational at ambient temperature in which the central pyridine ring undergoes an exchange between metal coordination. Under less forcing conditions (room temperature in dichloromethane), the monometallic counterpart of 1b [(L2)NiBr2] (2b) has been isolated which can be converted to 3b by addition of one equivalent of (DME)NiBr2 (DME = 1,2-dimethoxyethane) in n-BuOH at 110 degrees C. Quantum mechanical calculations (DFT) have been performed on [(L1)ZnCl2] and [(L2)ZnCl2] for different monometallic conformations and show that 1a is the energetically preferred structure for L1 while there is evidence for dynamic behaviour in L2-containing species leading to bimetallic formation. Single-crystal X-ray diffraction studies have been performed on 1a, 1b, 1c, 2b, 3a, 3b(H2O) and 3c.

Alkylation of (ArNHCH2CH2){(2-C5H4N)CH2}NH with RX [RX = MeI, 4-CH2=CH(C6H4)CH2Cl) and (2-C5H5N)CH2Cl] in the presence of base has allowed access to the sterically demanding multidentate nitrogen donor ligands, {(2,4,6-Me3C6H2)NHCH2CH2}{(2-C5H4N)CH2}NMe (L1), {(2,6-Me3C6H3)NHCH2CH2}{(2-C5H4N)CH2}NCH2(C6H4)-4-CH=CH2 (L2) and (ArNHCH2CH2){(2-C5H4N)CH2}2N (Ar = 2,4-Me2C6H3 L3a, 2,6-Me2C6H3 L3b) in moderate yield. L3 can also be prepared in higher yield by the reaction of (NH2CH2CH2){(2-C5H4N)CH2}2N with the corresponding aryl bromide in the presence of base and a palladium(0) catalyst. Treatment of L1 or L2 with MCl2 [MCl2 = CoCl2.6H2O or FeCl2(THF)1.5] in THF affords the high spin complexes [(L1)MCl2](M = Co 1a, Fe 1b) and [(L2)MCl2](M = Co 2a, Fe 2b) in good yield, respectively; the molecular structure of reveals a five-coordinate metal centre with bound in a facial fashion. The six-coordinate complexes, [(L3a)MCl2](M = Co 3a, Fe 3b, Mn 3c) are accessible on treatment of tripodal L3a with MCl2. In contrast, the reaction with the more sterically encumbered leads to the pseudo-five-coordinate species [(L3b)MCl2](M = Co 4a, Fe 4b) and, in the case of manganese, dimeric [(L3b)MnCl(mu-Cl)]2 (4c); in 4a and 4b the aryl-substituted amine arm forms a partial interaction with the metal centre while in 4c the arm is pendant. The single crystal X-ray structures of , 1a, 3b.MeCN, 3c.MeCN, 4b.MeCN and 4c are described as are the solution state properties of 3b and 4b.

The aryl-substituted N-picolylethylenediamine and diethylenetriamine ligands, (ArNHCH(2)CH(2))[(2-C(5)H(4)N)CH(2)]NH and (ArNHCH(2)CH(2))(2)NH (Ar = 2,6-Me(2)C(6)H(3), 2,4,6-Me(3)C(6)H(2)), have been prepared by employing palladium-catalysed N-C(aryl) coupling reactions of the corresponding primary amines with aryl bromide. Treatment of MCl(2) with (ArNHCH(2)CH(2))[(2-C(5)H(4)N)CH(2)]NH affords [[(ArNHCH(2)CH(2))((2-C(5)H(4)N)CH(2))NH]CoCl(2)](Ar = 2,6-Me(2)C(6)H(3) 1a; 2,4,6-Me(3)C(6)H(2)) 1b and [[(ArNHCH(2)CH(2))((2-C(5)H(4)N)CH(2))NH]FeCl(2)](n)(n= 1, Ar = 2,6-Me(2)C(6)H(3) 2a; n= 2, 2,4,6-Me(3)C(6)H(2) 2b) in high yield. The X-ray structures of 1a and 1b are isostructural and reveal the metal centres to adopt distorted trigonal bipyramidal geometries with the N,N,N-chelates adopting fac-structures. A facial coordination mode of the ligand is also observed in bimetallic 2b, however, in 2a the N,N,N-chelate adopts a mer-configuration with the metal centre adopting a geometry best described as square pyramidal. Solution studies indicate that mer-fac isomerisation is a facile process for these systems at room temperature. Quantum mechanical calculations (DFT) have been performed on 1a and 2a, in which the ligands employed are identical, and show the fac- to be marginally more stable than the mer-configuration for cobalt (1a) while for iron (2a) the converse is evident. Reaction of (ArNHCH(2)CH(2))(2)NH with CoCl(2) gave the five-coordinate complexes [[(ArNHCH(2)CH(2))(2)NH]CoCl(2)](Ar = 2,6-Me(2)C(6)H(3) 3a, 2,4,6-Me(3)C(6)H(2) 3b), in which the ligand adopts a mer-configuration; no reaction occurred with FeCl(2). All complexes 1-3 act as modest ethylene oligomerisation catalysts on activation with excess methylaluminoxane (MAO); the iron systems giving linear alpha-olefins while the cobalt systems give mixtures of linear and branched products.

A series of bis(imino)pyridyliron and -cobalt complexes [[2,6-(CR=NAr)2C5H3N]MX2] (R=H, Me; M=Fe, Co; X=Cl, Br) 8-16 containing imino-aryl rings (Ar) with at least one small ortho substituent, as well as Ar=biphenyl and Ar=naphthyl, has been synthesised. Crystallographic analyses of complexes 9 (Ar = 2,3-dimethylphenyl), 13 and 14 (Ar= biphenyl; X= Cl or Br, respectively) reveal a distorted trigonal-bipyramidal geometry in the solid state. These complexes, in combination with methyl aluminoxane (MAO), are active catalysts for the oligomerisation of ethylene, yielding >99% linear alpha-olefin mixtures that follow a Schulz-Flory distribution. Iron ketimine (R = Me) precatalysts give the highest activities and a greater alpha-value than their aldimine (R = H) analogues. Cobalt precatalysts follow a similar trend, though their activities are almost two orders of magnitude lower than those of the corresponding iron catalysts. Ethylene pressure studies on cobalt precatalyst 15 reveal a first-order dependence on ethylene for both the rate of propagation and the rate of chain transfer, and a pressure independence of the alpha value.