Supplementary Materials: Homo‐polymerization of 1‐ Hexene Catalysed by O^n^n (salicylaldimine)iron(iii) Pre‐catalysts to Branched Poly(1‐hexene)

Figure S1. The 1 H NMR spectrum of poly(1‐hexene) synthesised using (salicylaldimine)iron(III) pre‐ catalyst 1 with EtAlCl2. Figure S2. 13 C{ 1 H} NMR spectrum of the poly(1‐hexene) obtained using (salicylaldimine)iron(III) pre‐ catalyst 1 (Table 1: entry 7).


Introduction
The polymerisation of α-olefins to low molecular weight, hyper-branched polymers with narrow molecular weight distribution is of considerable interest.These hyper-branched polymers have applications as lubricants and as starting materials for lubricant additives [1].The production of these low molecular weight hyper-branched polymers has been catalysed mainly by metallocenes [2][3][4][5][6][7].The metallocene catalysts provide access to new or improved materials but at a high cost.The metallocene catalysts are also quite sensitive to either moisture or air and in some instances even to both moisture and air.As such there is great interest in finding late transition metal catalysts that have lower cost and are stable to both moisture and air for the polymerisation of α-olefins [8][9][10][11][12][13][14][15][16].Such late transition metal catalysts should have other desirable properties such as being less oxophilic and hence tolerant toward functional groups [11,12,15,16].Furthermore the late transition metal catalysts should be able to undergo "chain-walking" reactions [9,10,[14][15][16][17][18] thereby producing a variety of novel branched olefin polymers.
We report on the polymerisation of 1-hexene with various (salicyladimine)iron(III) halide pre-catalysts. 1 H and 13 C{ 1 H} NMR spectroscopy of the poly(1-hexene) produced in this study show branched microstructures.Details of this study are provided in this report.

Syntheses of (Salicylaldimine)Iron(III) Complexes
The syntheses of the OˆNˆN-(salicylaldimine)iron(III) complexes 1-4 (Scheme 1) have been reported by us recently [44]; but complex 5 (Scheme 1) is new and was synthesised following a similar procedure in the literature [44].The reaction of iron(II) chloride with 2,4-di-tert-butyl-6-[(2-pyridin-2-yl-ethylimino)-methyl]-phenol (L3) formed the iron(III) complex [FeCl 2 (L3)].Similar to the syntheses of 1-4 [44], we envisage that the intermediate iron(II) complex {FeCl(L3)] was formed, which is then oxidized by HCl (a by-product from the reaction) to the iron(III) product [FeCl 2 (L3) (5).Micro analysis and high resolution mass spectral data were in agreement with the proposed structure of complex 5 in Scheme 1, which suggested that the coordination of L3 in 5 is through the phenoxy-O, the imine-N and the pyridine-N similar to the single crystal X-ray structures of complexes 1 and 2 [44].
We report on the polymerisation of 1-hexene with various (salicyladimine)iron(III) halide precatalysts. 1H and 13 C{ 1 H} NMR spectroscopy of the poly(1-hexene) produced in this study show branched microstructures.Details of this study are provided in this report.

Syntheses of (Salicylaldimine)Iron(III) Complexes
The syntheses of the O^N^N-(salicylaldimine)iron(III) complexes 1-4 (Scheme 1) have been reported by us recently [44]; but complex 5 (Scheme 1) is new and was synthesised following a similar procedure in the literature [44].The reaction of iron(II) chloride with 2,4-di-tert-butyl-6-[(2-pyridin-2-yl-ethylimino)-methyl]-phenol (L3) formed the iron(III) complex [FeCl2(L3)].Similar to the syntheses of 1-4 [44], we envisage that the intermediate iron(II) complex {FeCl(L3)] was formed, which is then oxidized by HCl (a by-product from the reaction) to the iron(III) product [FeCl2(L3) (5).Micro analysis and high resolution mass spectral data were in agreement with the proposed structure of complex 5 in Scheme 1, which suggested that the coordination of L3 in 5 is through the phenoxy-O, the imine-N and the pyridine-N similar to the single crystal X-ray structures of complexes 1 and 2 [44].

Polymerisation of 1-hexene
The ability of all the (salicylaldimine)iron(III) complexes 1-5 to polymerise 1-hexene was investigated by activating the complexes with EtAlCl 2 at an optimum Al:Fe ratio of 400:1.The polymerisation reactions were performed in hexane at varying reaction temperatures from 30-60 ˝C.When GC analysis showed no evidence of 1-hexene oligomers, the reaction mixtures were worked up by evaporating the solvent to give viscous oily products.Catalysts activities ranged from 2.17 ˆ10 6 to 2.83 ˆ10 6 g polymer mol Fe ´1 h ´1 (Table 1: entries 1-5).GPC data for these products showed them to be low molecular weight poly(1-hexenes) that have M n values slightly higher than 1000 Da.The polydispersity indices of the poly(1-hexene) produced by all the catalysts are relatively narrow (1.19-1.24)(Table 1), indicative of the single-site nature of the (salicylaldimine)iron(III) catalysts.Changing the second N-donor in the ligand from imidazolyl (2.83 ˆ10 6 g polymer mol Fe ´1 h ´1, Table 1: entry 1) to pyridyl (2.31 ˆ10 6 g polymer mol Fe ´1 h ´1, Table 1: entry 5) resulted in a decrease in catalyst activity; an observation that can be attributed to the weaker σ-donor ability of the imidazolyl group in pre-catalyst 1 compared to the pyridyl group in pre-catalyst 5, which makes the iron centre in the (imidazloylsalicylaldimine)iron(III) catalyst (1) more electrophilic and hence more active than the (pyridylsalicylaldimine)iron(III) catalyst (5).Complex 4 is the least active most likely because of its low solubility.The activity of the chloro iron(III) pre-catalyst 1 (2.83 ˆ10 6 g polymer mol Fe ´1 h ´1) was found to be slightly higher than the bromo iron(III) catalyst 2 (2.35 ˆ10 6 g polymer mol Fe ´1 h ´1) and the iodo iron(III) catalyst 3 (2.25 ˆ10 6 g polymer mol Fe ´1 h ´1).This can be attributed to the chloride ion being a stronger conjugate base than the bromide and iodide ions, and hence is readily abstracted by the EtAlCl 2 co-catalyst.All three catalysts nevertheless produced poly(1-hexene) with identical properties (Table 1: entries 1-3).The effects of reaction temperature and monomer equivalents were investigated using 1/EtAlCl 2 .The effect of reaction temperature on the polymerisation activity of 1/EtAlCl 2 was conducted over 60 min at Al:Fe ratio of 400:1 (Table 1: entries 1 and 6-8).Activity increased with increasing reaction temperature from 2.83 ˆ10 6 to 2.88 ˆ10 6 and to 3.10 ˆ10 6 g polymer molFe ´1 h ´1 at 30, 40 and 50 ˝C respectively (Table 1: entries 1, 6 and 7).Catalyst activity, however, decreased to 2.42 ˆ10 6 g polymer mol Fe ´1 h ´1 at 60 ˝C (Table 1: entry 8).It is evident from these observations that at 60 ˝C the catalysts start to decompose and that optimum temperature for this catalyst is 50 ˝C; however, at 60 ˝C it appears chain transfer [19][20][21][22] or chain termination [8][9][10] is favoured over chain propagation.This leads to lower molecular weight polymers and some degree of branching of the poly(1-hexene) (Table 1: entries 1, 6-8).Significantly, the polydispersity indices remained narrow and did not change with the variations in temperature, indicating that the active sites for propagation in the catalysts are not affected by increase in reaction temperature.Marques et al. [32] have also reported this observation where narrow polydispersity indices are observed at temperatures ranging from ´11 to 25 ˝C.
Different monomer concentrations were also investigated by varying the monomer equivalents.Increase in both the productivity and activity were observed when the monomer equivalent was increased from 1500 to 2000 (Table 1: entries 1 and 9) with a corresponding increase in polymer molecular weight.However, catalyst activity decreased slightly when the monomer concentration was increased to 2500, an observation which is likely due to saturation of the system.The resultant polymer M n varies from 1045 Da to 1038 Da to 1084 Da as monomer equivalents increased from 1500 to 2000 and 2500 respectively (Table 1: entries 1, 9 and 10).

Characterization of Poly(1-hexene) Using 1 H NMR Spectroscopy
The microstructure of the poly(1-hexene) obtained using pre-catalyst 1 with EtAlCl 2 as co-catalyst (Table 1: entry 1) was studied using 1 H NMR spectroscopy (Figure S1).The 1 H NMR spectra for all the poly(1-hexene) produced under different conditions were similar to the spectrum in Figure S1.The peak at 0.83 ppm in Figure S1 is assigned to the methyl branches similar to observations made by Subramanyam et al. for polypropylene [45].The signal at 0.88 ppm (triplet) (Figure S1) is due to terminal methyl groups of butyl or longer chain branches.The signals at 0.75 and 0.76 ppm in Figure S1 are part of the methyl branches of the polymer similar to what has reported for polypropylene moieties in the literature [45].The spectrum (Figure S1) also shows a peak at 1.25 ppm characteristic of long chain methylene groups, (CH 2 ) n .This signal can arise from branches as well as from the polymer backbone.Thus the integration of the methyl and methylene peaks determined the degree of branching calculated to be between 220 and 300.We observed no terminal olefinic end groups in the NMR spectra of the polymers.This suggests that termination and/or chain transfer reactions in the polymerization takes place via transmetalation with organoaluminum species and not by β -H elimination.

Characterization of Poly(1-hexene) Using 13 C{ 1 H} NMR Spectroscopy
A typical 13 C{ 1 H} NMR spectrum of the poly(1-hexene) is shown in Figure 1 and Figures S2-S4 show other 13 C{ 1 H} NMR spectra that were used to determine the branched nature of poly(1-hexenes) obtained.
Almost all the peaks in Figure 1 have been assigned according to reported nomenclature [49,50], and tabulated in Table 2.The peaks that were not assigned have been marked with asterisk.In Table 2, the first column represents the numbering of peaks in Figure 1; the second column the chemical shifts, the third column resonance integral values relative to the integral value of peak 1 and the last column the carbon branch assignments.The signal at 14.13 ppm (peak 1, Figure 1) is assigned to the methyl carbon of butyl ( 1 B 4 ) or longer chain branches ( 1 B n ).The signal at 19.76 ppm (peak 3) is assigned exclusively to the methyl branches and is similar to branching in polypropylene [45].The observed multiplicity of peaks can be explained in terms of tacticity effects.Generally, the branches with methyl peaks appear in the region 14.00-17.00ppm.It is possible that these correspond to the methyl proton signals observed in the region 0.75-0.83ppm.Similar peaks have been observed in the poly(1-hexene) synthesised by Subramanyam et al. [45].Peaks 6 (26.44-27.59ppm, 2 B 2 and β B 2 ), 17 (33.77ppm, αB 2 ) and 21 (39.62 ppm, brB 2 ) are designated to ethyl branches, while the propyl branches are observed at 14.58 ppm ( 1 B 3 ).Other resonances associated with propyl branches are peaks 3 ( 2 B 3 ), 18 (αB 3 ) and 20 (brB 3 ).Signals typical of butyl branches are also observed at 14.13 ppm (peak 1, 1 B 4 ),  Polyethylene type of structural units, -(CH 2 -CH 2 )n-, are also observed with the appearance of the peak at 30.09 ppm (peak 11, γB 1 ).γ indicates how far the methyl group is from a branch point and this gives rise to the polyethylene type of units.A similar peak at 30.01 ppm is present in the spectra of poly(1-hexene) and EP co-polymer reported by Subramanyam et al. [45].
It is evident from the above 13 C{ 1 H} NMR data for poly(1-hexenes) obtained with pre-catalyst 1 that the polymers have micro-structures that consist of methyl, ethyl, propyl, butyl and longer branches on a polyethylene backbone.The polymers are generally atactic in structure, evident from the chemical shifts and intensities of peaks 1, 4, 9, 10, 14, 15 and 21.

Rationalisation of Formation of the Different Branches in the Poly(1-hexene) Microstructure
The formation of the different types of branches in our poly(1-hexene) are explained by the regiochemistry of monomer insertion; and these are typical of chain growth where 2,1-insertion of the 1-hexene monomer into the iron-polymer bond during the polymerisation process is quite high.This is the result of the ability of the metal centre to migrate along the growing polymer chain through β-hydride elimination and reinsertion steps.Schemes 1-4 which are based on reports in literature [13,31,45,51,52], are used to rationalise how the various branching occur.The percentage of each type of branch with respect to the total branching was also calculated according to literature procedure [45].The main branches were determined to be methyl (17%), butyl (30%) and longer chains (43%) while ethyl (3%) and propyl (7%) branches were present but in small percentages compared to the total branching.

Butyl Branches
These arise from successive 1,2-insertion of 1-hexene into the iron-carbon bond A (Scheme 2) to form D.

Rationalisation of Formation of the Different Branches in the Poly(1-hexene) Microstructure
The formation of the different types of branches in our poly(1-hexene) are explained by the regiochemistry of monomer insertion; and these are typical of chain growth where 2,1-insertion of the 1-hexene monomer into the iron-polymer bond during the polymerisation process is quite high.This is the result of the ability of the metal centre to migrate along the growing polymer chain through β-hydride elimination and reinsertion steps.Schemes 1-5, which are based on reports in literature [13,31,45,51,52], are used to rationalise how the various branching occur.The percentage of each type of branch with respect to the total branching was also calculated according to literature procedure [45].The main branches were determined to be methyl (17%), butyl (30%) and longer chains (43%) while ethyl (3%) and propyl (7%) branches were present but in small percentages compared to the total branching.

Butyl Branches
These arise from successive 1,2-insertion of 1-hexene into the iron-carbon bond A (Scheme 2) to form D. Scheme 2. Formation of butyl branches in 1-hexene polymerization.

Methyl Branches
For methyl branches to be formed there is 1,2-insertion of 1-hexene to form C (Scheme 3) followed by migration of the iron metal centre by a series of β-hydride elimination till the terminal carbon (2,6-enchainment) forming E. Scheme 3. Formation of methyl branches in 1-hexene polymerization.Scheme 2. Formation of butyl branches in 1-hexene polymerization.

Methyl Branches
For methyl branches to be formed there is 1,2-insertion of 1-hexene to form C (Scheme 3) followed by migration of the iron metal centre by a series of β-hydride elimination till the terminal carbon (2,6-enchainment) forming E.

Rationalisation of Formation of the Different Branches in the Poly(1-hexene) Microstructure
The formation of the different types of branches in our poly(1-hexene) are explained by the regiochemistry of monomer insertion; and these are typical of chain growth where 2,1-insertion of the 1-hexene monomer into the iron-polymer bond during the polymerisation process is quite high.This is the result of the ability of the metal centre to migrate along the growing polymer chain through β-hydride elimination and reinsertion steps.Schemes 1-5, which are based on reports in literature [13,31,45,51,52], are used to rationalise how the various branching occur.The percentage of each type of branch with respect to the total branching was also calculated according to literature procedure [45].The main branches were determined to be methyl (17%), butyl (30%) and longer chains (43%) while ethyl (3%) and propyl (7%) branches were present but in small percentages compared to the total branching.

Butyl Branches
These arise from successive 1,2-insertion of 1-hexene into the iron-carbon bond A (Scheme 2) to form D. Scheme 2. Formation of butyl branches in 1-hexene polymerization.

Methyl Branches
For methyl branches to be formed there is 1,2-insertion of 1-hexene to form C (Scheme 3) followed by migration of the iron metal centre by a series of β-hydride elimination till the terminal carbon (2,6-enchainment) forming E. Scheme 3. Formation of methyl branches in 1-hexene polymerization.Scheme 3. Formation of methyl branches in 1-hexene polymerization.

Long Chain Branches
The dominant branches in the polymers are long chains longer than butyl.These long chain branches results from an initial 2,1-insertion of 1-hexene into the active catalyst depicted by (E) in Scheme 4 to form (L). The 2,1-insertion therefore results in the butyl branch near the Fe centre, but subsequent "chain walking" to the primary carbon gives rise to the resultant long chains in the polymer depicted in (M) (Scheme 4).

Long Chain Branches
The dominant branches in the polymers are long chains longer than butyl.These long chain branches results from an initial 2,1-insertion of 1-hexene into the active catalyst depicted by (E) in Scheme 4 to form (L). The 2,1-insertion therefore results in the butyl branch near the Fe centre, but subsequent "chain walking" to the primary carbon gives rise to the resultant long chains in the polymer depicted in (M) (Scheme 4).Scheme 4. Formation of long chain branches in 1-hexene polymerization.

Effect of Reaction Conditions on the Poly(1-hexene) Microstructure
The microstructure of the poly(1-hexene) obtained is likely to be affected by reaction conditions particularly reaction temperature and monomer concentration.As such the microstructure of polymers produced at a different reaction temperature and monomer concentrations were monitored by 13 C{ 1 H} NMR spectroscopy.The effect of temperature on the microstructure of the poly(1-hexene) was investigated at 50 °C for 1 h with 2000 monomer equivalent.The percentage of butyl branches remained the same at 30% whereas the percentage of longer chain branches decreased from 43% to 39% at 30 and 50 °C respectively.Methyl branches on the other hand showed a significant increase from 17% (30 °C) to 20% (50 °C) which implies that the rate of 2,6-enchainment and chain walking process is increased at elevated reaction temperature.Such observation has also been reported by Azoulay et al. [13].Ethyl (5%) and propyl (6%) branches were still observed but did not follow any clear trend.
Varying the monomer concentration by varying the monomer equivalent from 1500 to 2000 and to 2500 at 30 °C for 1 h did not present any clear trend either.Long chain branches were the dominant branches observed (69% (1500) to 43% (2000) to 50% (2500)).However, the amount of butyl branches increased as the monomer equivalent increased from 1500 (29%) to 2000 (30%) and to 2500 (31%).This is expected as increase in monomer concentration favours 1,2-insertion [31].

General Materials and Instrumentations
All procedures were performed under dry Argon using standard Schlenk techniques.All solvents were of analytical grade, were dried and distilled under nitrogen prior to use.The compounds FeCl2, 1-hexene and ethylaluminium dichloride (EtAlCl2, 1.0 M in hexane) were purchased from Sigma-Aldrich (Johannesburg, South Africa) and used as received.The ligand, 2,4di-tert-butyl-6-[(2-pyridin-2-yl-ethylimino)-methyl]-phenol (L3), [53] and the iron(III) pre-catalysts 1-5 [53], were prepared according to literature procedures.Infrared (IR) spectra were recorded on a Bruker Tensor 27 equipped with a diamond ATR.Elemental analyses were performed on a Vario Elementar III microcube CHNS analyser at Rhodes University (South Africa).Mass spectra were Scheme 4. Formation of long chain branches in 1-hexene polymerization.

Effect of Reaction Conditions on the Poly(1-hexene) Microstructure
The microstructure of the poly(1-hexene) obtained is likely to be affected by reaction conditions particularly reaction temperature and monomer concentration.As such the microstructure of polymers produced at a different reaction temperature and monomer concentrations were monitored by 13 C{ 1 H} NMR spectroscopy.The effect of temperature on the microstructure of the poly(1-hexene) was investigated at 50 ˝C for 1 h with 2000 monomer equivalent.The percentage of butyl branches remained the same at 30% whereas the percentage of longer chain branches decreased from 43% to 39% at 30 and 50 ˝C respectively.Methyl branches on the other hand showed a significant increase from 17% (30 ˝C) to 20% (50 ˝C) which implies that the rate of 2,6-enchainment and chain walking process is increased at elevated reaction temperature.Such observation has also been reported by Azoulay et al. [13].Ethyl (5%) and propyl (6%) branches were still observed but did not follow any clear trend.
Varying the monomer concentration by varying the monomer equivalent from 1500 to 2000 and to 2500 at 30 ˝C for 1 h did not present any clear trend either.Long chain branches were the dominant branches observed (69% (1500) to 43% (2000) to 50% (2500)).However, the amount of butyl branches increased as the monomer equivalent increased from 1500 (29%) to 2000 (30%) and to 2500 (31%).This is expected as increase in monomer concentration favours 1,2-insertion [31].

General Materials and Instrumentations
All procedures were performed under dry Argon using standard Schlenk techniques.All solvents were of analytical grade, were dried and distilled under nitrogen prior to use.The compounds FeCl 2 , 1-hexene and ethylaluminium dichloride (EtAlCl 2 , 1.0 M in hexane) were purchased from Sigma-Aldrich (Johannesburg, South Africa) and used as received.The ligand, 2,4-di-tert-butyl-6-[(2-pyridin-2-yl-ethylimino)-methyl]-phenol (L3), [53] and the iron(III) pre-catalysts 1-5 [53], were prepared according to literature procedures.Infrared (IR) spectra were recorded on a Bruker Tensor 27 equipped with a diamond ATR.Elemental analyses were performed on a Vario Elementar III microcube CHNS analyser at Rhodes University (South Africa).Mass spectra were recorded on a Waters API Quattro Micro spectrophotometer.The resulting polymers were characterized using GPC, 1 H and 13 C{ 1 H} NMR spectroscopy.Gel permeation chromatography (GPC) was measured on a SEC instrument which consists of a Waters 1515 isocratic HPLC pump, a Waters 717plus auto-sampler, Waters 600E system controller (run by Breeze Version 3.30 SPA) and a Waters in-line Degasser AF.A Waters 2414 differential refractometer was used at 30 ˝C in series with a Waters 2487 dual wavelength absorbance UV/Vis detector operating at variable wavelengths.Tetrahydrofuran (THF, HPLC grade, stabilized with 0.125% BHT) was used as eluent at flow rates of 1 mL¨min ´1.The column oven was kept at 30 ˝C and the injection volume was 100 µL.Two PLgel (Polymer Laboratories) 5 µm Mixed-C (300 ˆ7.5 mm) columns and a pre-column (PLgel 5 µm Guard, 50 ˆ7.5 mm) were used.Calibration was done using narrow polystyrene standards ranging from 580 to 2 ˆ10 6 g mol ´1.All molecular weights were reported as polystyrene equivalents.Samples for SEC were dissolved in BHT stabilized THF (2 mg mL ´1).Sample solutions were filtered via syringe through 0.45 µm syringe filters before subjected to analysis.The NMR spectra were recorded on a Bruker 400 MHz instrument ( 1 H at 400 MHz and 13 C{ 1 H} at 100 MHz) at room temperature.Chemical shifts are reported in δ (ppm) and referenced to the residual proton and (7.24 and 77.0 ppm for CDCl 3 ).The total number of branches per 1000 carbon atoms was calculated from the integration of the methyl and methylene signals in the 1 H NMR spectrum.

General Procedure for the Polymerization of 1-Hexene
In a typical experiment, a carousel parallel reactor equipped with a magnetic stirrer was loaded with the pre-catalyst (11 µmol), higher olefin and solvent.The solution was stirred at the desired temperature for 2 min after which EtAlCl 2 , the activator, was added.After the set reaction time period the reaction was quenched by adding 2 M HCl and some sampled for GC analysis.The organic phase was then separated from the aqueous phase and washed three times with water.The organic phase was dried over anhydrous MgSO 4 and the solvent evaporated to obtain the viscous oily product.The oily product was dried until a constant weight was obtained.

Conclusions
A new set of iron(III) pre-catalysts produce active catalysts for the polymerisation of 1-hexene with ethylaluminium dichloride (EtAlCl 2 ), resulting in branched poly(1-hexenes) with low molecular weights.The narrow polydispersity indices regardless of reaction condition demonstrate that these are excellent single-site late transition metal catalysts.The 13 C{ 1 H} NMR data confirm the branching in the polymers to be mainly methyl, butyl and longer chains higher than butyl; the dominant longer chain branches indicate that 2,1-insertion of monomer is favoured in the polymerisation reactions.

Table 2 .
Chemical shifts and assignments for the numbered peaks in Figure1.