Thermally stable and highly active cobalt precatalysts for vinyl ‐ polyethylenes with narrow polydispersities : integrating fused ‐ ring and imino ‐ carbon protection into ligand design

A series of [2-(1-aryliminobenzylidene)-9-arylimino-5,6,7,8-tetrahydrocyclohepta[b]pyridyl]cobalt chlorides (aryl = 2,6-Me2Ph (Co1), 2,6-Et2Ph (Co2), 2,6-i-Pr2Ph (Co3), 2,4,6-Me3Ph (Co4), and 4-Me-2,6-Et2Ph (Co5)), incorporating a fused seven-membered ring and an imino C-phenyl group, was synthesized and characterized. Upon activation with methylaluminoxane (MAO) or modified methylaluminoxane (MMAO), Co1–Co5 all showed high activities toward ethylene polymerization with the Co4/MAO system showing the highest activity (8.65 × 106 g(PE) mol−1(Co) h−1). Significantly, these systems exhibited good thermal stability (up to 80 °C) as well as long catalytic lifetimes. The polyethylenes obtained all contained vinyl end-groups as well as narrow polydispersities. These phenyl-modified cobalt precatalysts provide a functional system for generating a unique class of vinyl-polyethylenes due to their ease of preparation, high catalytic activities and thermally stable polymerization.


Introduction
The search for late-transition metal catalysts for ethylene polymerization is an area of keen current interest to both academic and industrial researchers. 1In comparison to traditional Ziegler-Natta systems, a key advantage of latetransition metal catalysts is their ready tunability through straightforward ligand modification, which makes for easier and better control of the properties of the resultant polymers. 2he last twenty years or so have seen a host of developments in the field, 3,4 with two key milestones identifiable, viz., the αdiimine Ni(II) and Pd(II) catalysts 5 and the bis(imino)pyridine Fe(II) and Co(II) catalysts. 6So far, there have been numerous studies dedicated to modifying the bis(imino)pyridine ligand framework, especially on varying the imino N-aryl group. 6By contrast, less research activity has been focused on changing substituents linked to the imino carbon atom. 7owever, one drawback of the bis(imino)pyridine systems (e.g., A, Scheme 1) is their susceptibility to catalyst deactivation at higher operating temperatures.This may, in part, be attributed to degradation pathways involving alkylation reactions of the catalyst by the alkylaluminium cocatalyst. 8Alternatively, the imino C-methyl groups can undergo deprotonation chemistry, providing a further route for catalyst deactivation.8a,9 To circumvent these unwanted side reactions, the introduction of a phenyl group at the imino carbon atom presents a potential means of inhibiting these pathways which in turn may improve the thermal stability of the catalyst.Scheme 1. Ligand frameworks for active cobalt complex pre-catalysts Elsewhere, our group has previously found that the fused ring-size plays a crucial role in controlling the catalytic activity and the properties of the resultant polyethylenes.Indeed cobalt catalysts based on a 2-(1-(arylimino)ethyl)-8-arylimino-5,6,7-trihydroquinolyl ligand set (B, Scheme 1), incorporating a six-membered ring, exhibit much higher activities and better thermal stability than the prototypical 2,6-bis(imino)pyridyl This journal is © The Royal Society of Chemistry 20xx Please do not adjust margins Please do not adjust margins Scheme 2. Synthesis of organic compounds and their cobalt(II) complexes cobalt complexes (A). 10 On the other hand, contraction of the ring to a five-membered cyclopentane ring (C, Scheme 1), leads to much lower activities in ethylene polymerization; 11 an observation that can be attributed to inefficient imine-N coordination to the cobalt.Significantly however, the sevenmembered ring system (D, Scheme 1) exhibits the highest activity among these cobalt systems, the longest catalyst lifetime and displays reasonable thermal stability. 12ubsequent work has seen the development of alternative ligand sets incorporating two fused rings namely α,α'dibenzylidene-2,3:5,6-bis(pentamethylene)pyridine 13 (E, Scheme 1), their cobalt derivatives display high activity in ethylene polymerization. 13erein, we are concerned with the synthesis of a new family of cobalt(II) chloride precatalysts bearing the unsymmetrical tridentate ligands of 2-(1aryliminobenzylidene)-9-arylimino-5,6,7,8-tetrahydrocyclo hepta[b]pyridines (F, Scheme 1), in which a single fused seven-membered ring and an imino C-phenyl group are incorporated into the ligand design.Five distinct members of the family are targeted in which the aryl substitution pattern has been systematically varied (aryl = 2,6-Me 2 Ph, 2,6-Et 2 Ph, 2,6-i-Pr 2 Ph, 2,4,6-Me 3 Ph, 4-Me-2,6-Et 2 Ph); full characterization of all the complexes and organic precursor compounds are given.Moreover, a comprehensive ethylene polymerization screen is reported using both MAO and MMAO at different temperatures and pressures with a view to highlighting any effects of the ligand design on precatalyst performance and, above all, thermal stability of the catalyst itself.Furthermore, the resultant polyethylenes have been shown to contain vinyl chain-ends with narrow polydispersities, such materials 14 are in high demand as new comonomers for long-chain branched polymers and coating materials.

Synthesis and characterization of the cobalt complexes.
As in previous work, 13 we attempted to prepare the free bisimino 2-(1-aryliminobenzylidene)-9-arylimino-5,6,7,8-tetra hydrocyclohepta[b]pyridine compounds, by condensation of diketone 5 with the corresponding aniline.However, these compounds were not stable and the yields were poor.Therefore, in order to avoid excessive consumption of 5 and maximize the yield, a one-pot template methodology was applied to synthesize the cobalt complexes based on approaches described in the literature. 19The template reaction of 5, corresponding aniline and cobalt dichloride were carried out in boiling acetic acid for 6 hours to afford, after work-up, Please do not adjust margins Please do not adjust margins revealed stretching frequencies for the C=N bond in the range of 1608~1571 cm -1 , characteristic of bound iminonitrogen atoms; no absorption corresponding to a complexed C=O bond or free diketone (5) was apparent.Additionally, the elemental analysis data confirmed the formulae of all the cobalt complexes.C( 12)C( 13 The Co3 complex was also the subject of a single crystal Xray diffraction study.Single crystals suitable for the study were grown by layering diethyl ether onto a solution of the complex in a methanol/dichloromethane mixture.The molecular structure is shown in Figure 1; selected bond lengths and angles of Co3 are tabulated in Table 1.The coordination geometry of Co3 can be best described as distorted square-pyramidal, which is similar to related N,N,NCoCl 2 structures reported elsewhere. 10,12The basal plane is formed by the N pyridyl atom, two N imino atoms and one chloride atom (Cl1), while the other chloride Cl2 occupies the apical position.There is a deviation of 0.071 Å for Cl1 away from the basal plane.Since the cycloheptyl ring is more flexible than the cyclohexyl ring (see B, Scheme 1), an improved coordination between cobalt and N3 results.However, this has the consequent effect that sp 3

Ethylene Polymerization Ethylene Polymerization by Co1Co5/MAO systems
In the first instance Co4, in combination with methylaluminoxane (MAO) as co-catalyst, was selected as the test catalyst system with a view to optimizing the polymerization parameters, such as reaction temperatures, Al/Co ratios and reaction times.The results obtained from the polymerization screen under ambient pressure using these set of variables are summarized in Table 2.  Firstly, the effect of reaction temperature on catalytic performance of Co4/MAO was probed by varying it between 20 °C and 60 °C (entries 15, Table 2).This indicated an optimal temperature of 40 °C with a catalytic activity of 1.66 × 10 6 g(PE)•mol -1 (Co)•h -1 (entry 3, Table 2) for polyethylene formation.The higher the temperature applied, the lower the molecular weight of the polymers obtained, which is consistent with the GPC curves shown in Figure 2.This observation may be due to the increased chain transfer taking place to alkylaluminium or an increased rate of chain termination occurring by β-H elimination at elevated temperature.1c,1d,20 Meanwhile the unimodal characteristics in the GPC curves (Figure 2) exhibited single-site active species operating in the polymerization process.In comparison with the results obtained at 40 °C, the lower temperature runs (entries 1 and 2, Table 2) resulted in a slight reduction in the activities while a dramatic drop occured at higher temperatures (entries 4 and 5, Table 2), the latter observation probably due to partial decomposition of the active species and lower concentration of ethylene in toluene at higher temperature. 21Nevertheless, the activities were still up to 5 times higher than those observed using the imino C-methyl counterparts, [2-(1-(arylimino)ethyl)-9arylimino-5,6,7,8-tetrahydrocyclohepta[b]pyridyl]cobalt dichloride (D, Scheme 1).
12 Secondly, the polymerizations using Co4 were investigated at different MAO concentrations (Al/Co = 1000 to 3500), which showed the catalytic activity peaked at 1.71 × 10 6 g(PE)•mol -1 (Co)•h -1 with a Al/Co ratio of 2000 and then experienced a slight drop-off at higher ratios (entries 3, 610, Table 2).With a low molar ratio of Al/Co (1000), polyethylenes with higher molecular weight (M w = 5482 g•mol -1 ) were formed while at a high ratio (3500) the M w decreased to 1843 g•mol -1 ; the latter likely due to the facile chain transfer at higher MAO concentrations.4b,4c With regard to the lifetime of the active species, the highest activity of 2.01 × 10 6 g(PE)•mol was observed over the first 15 minute period of the run (entry 11, Table 2).On prolonging the reaction time (entries 7, 1113, Table 2) the activities smoothly decreased, indicating there was no induction time in the catalytic reaction; similar observations were noted for their imino C-methyl counterparts (D, Scheme 1).
Furthermore, the molecular weights of the resultant polyethylenes gradually increased with the longer reaction times as borne out by changes in the GPC curves (Figure 3).2).
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Using the optimum conditions (viz., 40 °C, Al/Co = 2000 within 30 min) established for Co4/MAO, the other derivatives, Co1, Co2, Co3 and Co5, were also investigated as ethylene polymerization catalysts (entries 1417, Table 2).In all cases, high activities were observed with Co1/MAO the most active giving 1.73 × 10 6 g(PE)•mol Table 2).By inspection of the data recorded for all five precatalysts under the same conditions (entries 7, 1417, Table 2), it is apparentthat the activity of polymerization is susceptible to the nature of the ortho substituents on the Naryl group as reported elsewhere. 4,6The less bulky methyl substituted complex Co1 was more active than the bulkier ethyl-and isopropyl-substituted complexes (Co2 and Co3).This is because the steric hindrance of the ortho substituents affects the rate of the ethylene monomer insertion as the ethylene monomer is more hindered in its approach to the metal center.When comparing Co1 vs. Co4 and Co2 vs. Co5, respectively, the additional electron-donating methyl group in the N-aryl para position shows only modest effects on the activity with its presence, if anything, resulting in lowering of the activity. 22s a further point, the steric bulk imparted by the ortho substituents of N-aryl group in Co1-Co5 exhibited a significant effect on the properties of the polyethylenes.As has been observed in a number of previous reports, 6,12,13 the presence of bulky groups in these cobalt catalysts leads to polymers with higher molecular weight.For example, the polymer obtained using 2,6-diisopropyl substituted complex Co3 possesses the highest molecular weight (M w = 151.9Kg•mol ; entry 15, Table 2) and the dimethyl substituted Co1 (M w = 2.3 Kg•mol -1 ; entry 14, Table 2). 4While the steric properties of the N-aryl group in these cobalt catalysts undoubtedly affect the molecular weights of these polyethylenes, it seems likely that the presence of the imino C-phenyl group is also infuential. 12,13 3).This journal is © The Royal Society of Chemistry 20xx Please do not adjust margins Please do not adjust margins ethylene pressure (viz., 10 atm) and the optimal conditions were again established using Co4 as the test precatalyst (Table 3).With the Al/Co ratio fixed at 1500, 60 °C was now identified as the temperature leading to the highest catalytic activity (entry 3, Table 3).The molar Al/Co ratio was then varied from 1000 to 3000 at 60 °C (entries 3, 7-10, Table 3), and the best activity of 8.65 × 10 6 g(PE)•mol determined with a Al/Co ratio of 2500 (entry 9, Table 3).Notably, this good thermal-stability for Co4/MAO coupled with good catalytic performance is superior to that reported for both [2-(1-(arylimino)ethyl)-9-arylimino-5,6,7,8-tetra hydrocyclohepta[b]pyridyl]cobalt dichloride (D) 12 and [α,α'bis(arylimino)-2,3:5,6-bis(pentamethylene)pyridyl]cobalt chlorides (E) 13 .
The GPC curves obtained for polyethylenes produced using Co4/MAO at different Al/Co ratios (Figure 4) indicate only gradual changes of molecular weight and similar molecular weight distributions.With regard to catalyst lifetime, the highest activity for Co4 was observed over a 10 minute period with an activity of 14.18 × 10 6 g(PE)•mol Table 3).Even on extending the run time to 60 minutes, this system still maintained a good activity of 6.56 × 10 6 g(PE)•mol -1 (Co)•h -1 (entry 13, Table 3).For purposes of comparison, cobalt analogs D 12 and E, 13 showed inferior (Co)•h -1 , entry 16, Table 3) was again more active than Co2 and Co3 and complexes with bulkier substituents give higher molecular weights (113.2Kg•mol -1 , entry 18, Table 3).However, the molecular weights of the polyethylenes obtained at 10 atm possessed less obvious variations compared with the PEs obtained under ambient ethylene pressure.As shown in Figure 5, the M w for Co1 and Co4 were quite similar as is also the case for Co2 and Co5, while Co3 displayed a clear tendency to shift to highmolecular-weight fraction.Interestingly, the catalysts with para-methyl groups (Co5 and Co4) performed with better activity than those without which was opposite to that observed at 1 atm ethylene pressure.This might be due to the para-methyl group being able to stablize the active species at higher temperature.6i In general, the combination of high activity and good thermal stability of these cobalt systems exceeds that reported for previously documented cobalt catalysts, 4,12 including [2-(1-(arylimino)ethyl)-9arylimino-5,6,7,8-tetrahydrocyclohepta[b]pyridyl]cobalt dichloride (D), 12 [α,α'-bis(arylimino)-2,3:5,6-bis(pentamethylene)pyridyl]cobalt chlorides (E) 13 and other fused-ring cobalt systems.6c,6f Significantly, Co4/MAO even showed good activity at industrially significant temperatures of 80 °C (1.85 × 10 6 g(PE)•mol , entry 5, Table 3).The origin of the enhanced performance characteristics is uncertain but it may be that the imino C-phenyl in these systems is preventing deprotonation in a way that could potentially occur for imino C-methyl counterpart D and hence stabilizing the catalyst at higher temperature.8a In addition, the difference of Co-N imino bond lengths between D and Co3 (vide supra) might also affect the catalytic performances of these pre-catalysts.In all cases, the molecular weight distributions of the polyethylenes generally remained narrow and unimodal (PDIs = 1.9  2.4), and similar to those of their analogs E. 13 The melting points of all the polymers were in the range 126.8 -133.7 °C, consistent with highly linear materials.3) Figure 6.The 1 H-NMR spectrum of the polyethylene produced by Co4/MAO (entry 9,Table 3).3).To understand the microstructure of the polyethylenes obtained, a representative sample prepared using Co4/MAO at 60 °C was examined using 1 H NMR spectroscopy at 100 °C in deuterated 1,1,2,2-tetrachloroethane (C 2 D 2 Cl 4 ).The 1 H NMR spectrum (Figure 6) reveals a downfield multiplet at 5.90 ppm and an apparent triplet at 5.05 ppm, consistent with the polymer being mainly an α-olefin; no evidence for internal olefins could be detected.To corroborate this, the 13 C NMR spectrum (Figure 7) revealed two single peaks existing between 140-110 ppm in agreement with the presence of a vinyl-group on the polyethylene.Furthermore, both the 1 H NMR and 13 C NMR spectra showed that the PE samples were strictly linear. 14,23As a general comment, these highly linear, low molecular vinyl-polyethylenes are likely to be of high demand as new comonomers for long-chain branched polymers and coating materials.Hence, a coordination-insertion mechanism allows chain propagation and β-hydrogen elimination facilitates chain termination to afford these vinyl-terminated linear polyethylenes (Scheme 3).We are currently interested in integrating the observed catalyst stability into a high temperature industrial process for generating polyethylenes of this type.

Ethylene Polymerization by Co1Co5/MMAO Systems.
As a separate study we also examined the effect of using modified methylaluminoxane (MMAO) as the co-catalyst to activate Co1 -Co5.As before, the precatalyst Co4 was employed to allow optimization of the reaction parameters; the results obtained at ambient ethylene pressure are tabulated in Table 4.With the Al/Co ratio fixed at 1500, the catalyst's activity was recorded in the 10 -50 °C range and was found to peak at 1.39 × 10 6 g(PE)•mol -1

(Co)•h
-1 at 30 °C (entries 15, Table 4).Notably, these values are five times higher than the activities of [α,α'-bis(arylimino)-2,3:5,6bis(pentamethylene)pyridyl]cobalt chlorides (E) under comparable conditions. 13he molecular weights of the resultant polyethylenes obtained using Co4/MMAO decreased with an increase in the reaction temperature, consistent with the trend seen in the GPC curves (Figure 8) and attributable to facile chain transfer to alkylaluminium at higher temperature.When employing different molar ratios of Al/Co from 1000 to 3500, similar activities were observed (entries 3, 610, Table 4), with the activity showing a maximum of 1.51 × 10 6 g(PE)•mol at a Al/Co ratio of 2500 (entry 8, Table 4).Using these optimized conditions, the other cobalt precatalysts, Co1, Co2, Co3 and Co5, were investigated for their polymerization behavior (entries 1114, Table 4).In general, all the complexes showed the same order of activities as observed     4) In comparison with the results obtained using MAO at 1 atm ethylene pressure, all the cobalt complexes revealed slightly lower activities while the polymers showed similar molecular weight distributions but higher molecular weights (up to 219.8 Kg•mol -1 , entry 13, Table 4).These variations are likely to stem from subtle differences in precatalyst activation between MMAO or MAO as well as counterion effects in the polymerization process.The T m values of all the polymers generated were found to exceed 126.0 °C, indicative of high linearity for the polyethylene.It is noteworthy that linear PEs (wax) are in high demand as lubricants and colorants for plastics.As with the results obtained with MAO, higher molecular weight polyethylenes were obtained with the cobalt precatalysts bearing bulkier substituents: Co3 (220 Kg•mol -1 ; entry 13, Table 4)＞Co2 (22 Kg•mol -1 ; entry 12, Table 4)＞Co1 (5.1 Kg•mol -1 ; entry 11, Table 4) and Co5 (22 Kg•mol -1 ; entry 14, Table 4)＞Co4 (4.8 Kg•mol -1 ; entry 11, Table 4).In comparison with the polyethylenes obtained by [α,α'-bis(arylimino)-2,3:5,6-bis(pentamethylene)pyridyl] cobalt chlorides (E), 13 the PDI values of polyethylenes herein are slightly broader (2.12.8)but still display unimodal feature consistent with semi-single site active species.
In order to investigate the effect of elevated pressure on catalytic performance and polymer properties, Co1 -Co5 were also screened at 10 atm. of ethylene in the presence of MMAO; the results are collected in Table 5.For Co4, the most optimal conditions were established at 70 °C with an Al/Co ratio of 1500 leading to an activity of 3.43 × 10 6 g(PE)•mol -

(Co)•h
-1 (entry 3, Table 5).Under these conditions, Co1, Co2, Co3 and Co5, were also explored (entries 1013, Table 5).All catalytic systems showed much better thermal stability and higher catalytic activities toward ethylene polymerization when compared with Please do not adjust margins Please do not adjust margins pyridylcobalt chlorides (E) 13 .Once again this can be attributed to the presence of the imino C-phenyl group that prevents deprotonation at higher temperature.8a In addition, the higher the ethylene pressure, the better the activities of polymerizations observed.With regard to the properties of the polyethylenes (entries 3, 1013, Table 5), the GPC curves revealed a broad range of molecular weights spanning from thousands (Co1, 5.7 Kg•mol -1 , entry 10, Table 5) to tens of thousands (Co3, 77.0 Kg•mol -1 , entry 12, Table 5) with unimodal distributions (Figure 9).Moreover, the catalysts containing para-methyl groups were more active than those without, paralleling the trend seen using a MAO at 10 atm.which is also in line with thermal stability improvements imparted by para electron-donating substituents.6i The melting points of all resultant polymers were higher than 126.0 °C, suggesting highly linear polyethylenes.Though there was no direct evidence for enhancing the thermal stability of cobalt complexes by phenyl modification, the results of these new catalytic systems have convincingly demonstrated that cobalt complexes with preferable thermal stability can be obtained.

Conclusions
A series of [2-(1-aryliminobenzylidene)-9-arylimino-5,6,7,8tetrahydrocyclohepta[b]pyridyl]cobalt chlorides (F, Scheme 1: Co1 -Co5) have been successfully synthesized and characterized.On activation with methylaluminoxane (MAO) or modified methylaluminoxane (MMAO), Co1 -Co5 all gave high activities toward ethylene polymerization with relatively narrow molecular distributions and unimodal features for the polymers.On comparison with previously reported [2-(1arylimino)ethyl-9-arylimino-5,6,7,8-tetrahydro cycloheptapyridyl]cobalt dichloride (D, Scheme 1) and [α,α'bis(arylimino)-2,3:5,6-bis(pentamethylene)pyridyl]cobalt chlorides (E, Scheme 1), Co1 -Co5 all showed enhanced thermal stability and longer catalytic lifetimes.When the polymerization run is increased to a more industrially relevant temperature of 80 °C, Co4/MAO system still displays good activity (1.85 × 10 6 g(PE)•mol ).It is likely that this improved temperature stability can be attributed to the presence of the imino C-phenyl substituent present in all the cobalt complexes.In addition, the steric bulk of the ortho position on the N-aryl moiety plays an essential role in controlling the molecular weights of the polyethylenes.The molecular weight of the polymer obtained using Co3 (up to 219.8 Kg•mol -1 ) is over ten times higher than M w using Co1 and more than three times higher than M w using Co2.
Significantly, these new thermally stable cobalt complexes show considerable promise for producing vinyl-polyethylenes under industrially relevant conditions.Multiple applications are envisaged including as super-long chain α-olefins in copolymerization with ethylene or as a block for blockpolymers through Click-reaction strategies and further functionalizations. 24Subsequent investigations of these frameworks will focus on other core metals and further derivatives of the ligands.

Experimental Section
General Considerations.All manipulations of air-and/or moisture-sensitive operations were processed in a nitrogen atmosphere using standard Schlenk techniques.Toluene was refluxed over sodium and distilled under nitrogen prior to use.Methylaluminoxane (1.46 M solution in toluene) and modified methylaluminoxane (MMAO, 1.93 M in n-heptane) were purchased from Akzo Nobel Corp. High-purity ethylene was purchased from Beijing Yanshan Petrochemical Co. and used as received.Other reagents were purchased from Aldrich, Acros, or local suppliers.NMR spectra were recorded on Bruker DMX 400 MHz instrument at ambient temperature using TMS as an internal standard.IR spectra were recorded on a Perkin-Elmer System 2000 FT-IR spectrometer.Elemental analysis was carried out using a Flash EA 1112 microanalyzer.Molecular weights and molecular weight distributions (MWD) of the polyethylenes were determined by a PL-GPC220 instrument at 150 °C, with 1,2,4trichlorobenzene as the solvent.DSC traces and melting points of the polyethylenes were obtained from the second scanning run on Perkin-Elmer TA Q2000 differential scanning calorimetry (DSC) analyzer under a nitrogen atmosphere.In the procedure, about 3.0 mg of sample was heated to 160 °C at a rate of 20 °C/min and kept for 2 min at 160 °C and then cooled at a rate of 20 °C/min to −40 °C.NMR spectra of the polyethylene was recorded on a Bruker DMX 300 MHz instrument at 100 °C in deuterated 1,1,2,2-tetrachloroethane with TMS as an internal standard.
Procedure for Ethylene Polymerization.Ethylene polymerization was carried out in a 250 mL stainless steel autoclave equipped with an ethylene pressure control system, a mechanical stirrer and a temperature controller.The autoclave was evacuated and back-filled with ethylene three times.Once the reactor had reached the desired temperature, toluene and a toluene solution of the catalytic precursor and co-catalyst (total volume was 100 mL) were injected into the autoclave under an ethylene atmosphere.The ethylene pressure was then increased to the desired pressure and maintained with a constant feed of ethylene.On completion Please do not adjust margins Please do not adjust margins of the run, the reactor was cooled with an ice-water bath and the excess ethylene vented.The resultant mixture was poured into HCl/ethanol solution, and the polymer collected and washed several times with ethanol and dried under reduced pressure.  .All hydrogen atoms were placed in calculated positions.Structure solution and refinement were performed by using the SHELXL-97 package. 25The free solvents from the structure Co3 were removed through the SQUEEZE option of the crystallographic program PLATON. 26etails of the X-ray structure determinations and refinements are provided in Table 6.This journal is © The Royal Society of Chemistry 20xx Please do not adjust margins Please do not adjust margins

Figure 1 .
Figure 1.Molecular structure of compound Co3 with thermal ellipsoids at 30% probability.Hydrogen atoms have been omitted for clarity.

1 (E 13 .
lifetimes with the activity of D being 4.70 × 10 6 g(PE)•mol -Co)•h -1 and E with 2.13 × 10 6 g(PE)•mol -1 (Co)•h -1 under comparable conditions.Based on the optimised reactions conditions determined for Co4, complexes Co1, Co2, Co3 and Co5, were also studied (entries 1619, Table3).On inspection of the data it is clear that high ethylene pressure significantly improves the catalytic activities and the thermal stability of the catalysts.A similar trend in catalytic activities was seen for analogs D12 and The dimethyl substituted complex Co1 (8.15 × 10 6 g(PE)•mol -1
and hole (e Å -3 ) 0.389 and -0.330 X-ray Crystallographic Studies.Single crystals of complex Co3 suitable for X-ray diffraction analysis were obtained by slow diffusion of diethyl ether into the mixture of methanol and dichloromethane at room temperature.Data collection for Co3 was carried out on Rigaku MM007-HF Saturn 724 + CCD diffractometer with confocal mirror monochromated Mo Kα radiation (λ = 0.71073 Å).Cell parameters were obtained by global refinement of the positions of all collected reflections.Intensities were corrected for Lorentz and polarization effects and empirical absorption.The structures were solved by direct methods and refined by full-matrix least squares on F 2

Table 6 .
Crystal data and Structure Refinement for Co3.