Electronic Influences in Phosphinesulfonato Palladium(II

Article pubs.acs.org/Organometallics

Electronic Influences in Phosphinesulfonato Palladium(II) Polymerization Catalysts Philipp Wucher, Verena Goldbach, and Stefan Mecking* Chair of Chemical Materials Science, Department of Chemistry, University of Konstanz, Universitätsstrasse 10, 78457 Konstanz, Germany S Supporting Information *

ABSTRACT: To study the influence of electronics on catalytic polymerization properties independent from sterics, phosphinesulfonato Pd(II) complexes bearing remotely located substituents on the nonchelating P-bound aryls [κ2(P,O)-(4-R-2-anisyl)2PC6H4SO2O]Pd(Me)(dmso) (1a−edmso: 1a, R = CF3; 1b, R = Cl; 1c, R = H; 1d, R = CH3; 1e, R = OCH3) were prepared. The electron-poor complex 1admso (4-CF3) undergoes the fastest insertion of methyl acrylate (MA) and is the most active for ethylene polymerization. The polyethylene molecular weight increases by a factor of 2 for the more electron rich complex 1e-dmso (4-OCH3) (Mn = 17 × 103 vs 8 × 103 for 1a-dmso (4-CF3)). MA/ ethylene copolymerization experiments revealed that the MA incorporation ratio and copolymer molecular weights are largely independent of the electronic nature of the remote substituents. These trends were further confirmed by studies of two mixed Paryl/-alkyl complexes 1f-dmso ([κ2-(2,4,6-(OMe)3C6H2)(tBu)PC6H4SO2O]Pd(Me)(dmso)) and 1g-dmso ([κ2-(C6H5)(tBu) PC6H4SO2O]Pd(Me)(dmso)). In ethylene/MA copolymerization, 1f-dmso affords a significantly higher molecular weight polymer with reasonable MA incorporation (Mn = 12 × 103 and 7.7 mol % MA) and activities similar to those observed for complexes 1a−e-dmso.

■

ligands lead to higher molecular weights.12 In this context, it is noteworthy that such steric modifications usually go along with changes in the ligand acidity and that it is therefore difficult to separate steric effects from electronic influences of the ligand. Herein we report the synthesis of phosphinesulfonato Pd(II) complexes with remotely located electron-donating and -withdrawing groups in the para position of the nonchelating anisyl moiety and the effects of these electronic modifications on insertion and (co)polymerization behavior as well as their influence on the polymer microstructure.

INTRODUCTION Insertion polymerization of ethylene and propylene by earlytransition-metal catalysts is employed on a vast scale.1 Latetransition-metal catalysts have also been studied intensively for olefin polymerization and oligomerization, due to their different incorporation behavior, branch formation, and generally less oxophilic nature.2−6 The last feature is particularly advantageous with regard to the challenge of insertion polymerization of polar vinyl monomers. Thus, acrylates and ethylene can be copolymerized by cationic α-diimine Pd(II) complexes, yielding highly branched copolymers with acrylate units located at the end of branches.7 In contrast, neutral Pd(II) phosphinesulfonato catalysts afford linear ethylene−acrylate copolymers with the polar repeating units incorporated into the polymer backbone.8 In the past decade the scope of functional monomers amenable to insertion polymerization has been broadened extensively, even enabling the copolymerization of ethylene with acrylonitrile, vinyl acetate, or acrylic acid.9,10 In view of these unique catalytic properties, further substitution patterns of the phosphine aryl sulfonato motif have been reported. 11 So far, however, there is no comprehensive picture of how desirable properties such as high polymer molecular weights, high polymerization activities, and high comonomer incorporation correlate with the catalyst structure. For example, in some cases the PE molecular weights decrease with increased steric bulk,11b whereas other bulky © XXXX American Chemical Society

■

RESULTS AND DISCUSSION Ligand and Complex Synthesis. The phosphinesulfonato system with (P∧O) = {2-(2-anisyl)2PC6H4SO2O} (4c; Scheme 1), first described for ethylene−MA copolymerization by Drent et al. in their seminal work,8 remains the most well studied ligand motif. Corresponding catalysts have a high functional group tolerance as well as reasonable activity, combined with high comonomer incorporation ratios.8,9 For this reason, we sought to study purely electronic influences by modifications of the anisyl groups of this prototypical ligand motif. From structure analysis it is evident that the most suitable position for electronic modifications with a minimum steric impact is the 4position of the anisyl moieties.11c,13 Received: April 8, 2013

A

dx.doi.org/10.1021/om400297x | Organometallics XXXX, XXX, XXX−XXX

Organometallics

Article

Scheme 1. Synthesis of Different Phosphonium Sulfonates

activation with silver salts.14 Hence, no labile ligand (L), which decreases activity by shifting the equilibrium [(P∧O)Pd(polymeryl)L] + ethylene ⇄ [(P∧O)Pd(polymeryl)ethylene] + L toward the dormant species, is present in the polymerization mixture.15 To underline the effects of varied electron density at phosphorus, further electron-rich P-alkyl-substituted phosphinesulfonato catalyst precursors with a weakly coordinated labile ligand (dmso) were prepared. Such complexes are known to promote polar olefin copolymerization as well.10b,16,17 The new P-aryl/-alkyl complex 1f-dmso (Figure 2) was prepared, as well as a dmso-substituted analogue of the known lutidine complex 1g-lut.17 The methoxy substituents of 1f-dmso represent a more electron-rich variation of complex 1g-dmso, analoguous to the electron-rich modification of the prototypical anisyl motif 1a−e-dmso. The required phosphonium sulfonates 5g,f were obtained by a stepwise procedure similar to the approach described above. The identity of the complexes was confirmed unambiguously by one- and two-dimensional NMR spectroscopy and elemental analysis (see the Supporting Information) as well as the crystal structures of [{1a-μLiCl}2], [{1d-μLiCl}2], 1e-dmso, and 1fdmso (Figure 3). All complexes crystallized in the monoclinic space group P21/c and exhibit a square-planar coordination sphere around the palladium center, with the palladium methyl group and the phosphorus atom located mutually cis to each other. The bond lengths around the palladium center are in the expected range for phosphinesulfonato Pd(II) complexes (Table 1).18 The complexes [{1a-μLiCl}2] and [{1d-μLiCl}2] are binuclear, with both Pd centers bridged via LiCl, similar to the reported structure of [{1c-μNaCl}2].19 One additional solvent molecule is coordinated to the Li atom. The labile ligand dmso is κ-S-coordinated to the Pd atom in both 1edmso and 1f-dmso. The factors determining this coordination mode remain unclear, since both κ-S and κ-O coordination of dmso to phosphinesulfonato complexes is observed and there is no obvious correlation between sterics and electronics in the environment of the Pd(II) center and the coordination mode.20−22 The 31P NMR shifts of the isolated Pd-dmso complexes 1a− e-dmso in CD2Cl2 correlate nicely with the Hammett constants of the different substituents, as an established measure for the electronic nature of aromatic substituents (Figure 4).23 The phosphorus resonances are shifted to high field for complexes bearing electron-donating groups. Insertion of Methyl Acrylate. The reaction with methyl acrylate is one of the most well studied reactions of such κ2(P∧O)-phosphinesulfonato Pd(II) complexes.11c,12,19,24 While it

Different 2-bromoanisole derivatives 2 were synthesized by nucleophilic aromatic substitution of the corresponding 1bromo-2-fluorobenzene compounds with sodium methoxide. From such anisole derivatives, the anionic ligands 4 were either synthesized in a one-pot synthesis as described by Goodall et al.11a or by a stepwise synthesis as shown in Scheme 1. The 4chloro-substituted ligand 4b was prepared via an in situ generated Grignard reagent. Protonation of the salts 4 afforded the zwitterionic phosphonium sulfonates H(P∧O) (5) with the acidic proton located at the phosphorus atom, as indicated by a characteristic coupling constant of about 1JP−H ≈ 600 Hz. This is also exemplified by the solid-state structure of the phosphonium sulfonate 5b (Figure 1). 5b crystallized in the

Figure 1. ORTEP plot of phosphonium sulfonate 5b. Ellipsoids are drawn at the 50% probability level. All hydrogen atoms, except H23 (P−H), are omitted for clarity.

monoclinic space group C2/c. The position of the hydrogen atom H23 (P−H) was found in the electron density map at a distance of 1.293 Å to the phosphorus atom. These phosphonium sulfonates could be reacted with [(tmeda)PdMe 2] to yield the binuclear tmeda-bridged complexes 1a−e-tmeda, from which the dmso complexes 1a−e-dmso are directly accessible (Scheme 2). A complementary approach is given by the reaction of the anionic ligands 4 with [(COD)PdMeCl] to the chloride-bridged binuclear palladate complexes [{1a−e-μMCl}2] (M = Na, Li), which are very active in polymerization and in insertion reactions upon B


Organometallics

Article

Scheme 2. Synthesis of Phosphinesulfonato Pd(II) Complexes

insertion of MA into the Pd−Me bond (kobs = 3.0 × 10−3 s−1), which is significantly faster than for 1c-dmso (kobs = 6.1 × 10−4 s−1) and even 1 order of magnitude faster than for complexes 1d-dmso (kobs = 3.8 × 10−4 s−1) and 1e-dmso (kobs = 2.1 × 10−4 s−1). The P-aryl/P-alkyl complex 1f-dmso (kobs = 3.1 × 10−4 s−1) shows approximately the same net rate constant for the first insertion as the electron-rich complexes 1d-dmso and 1e-dmso. These results reflect the general reactivity pattern for migratory insertion reactions into metal−carbon bonds: namely, a faster insertion for more electron deficient complexes due to a more effective activation of the olefin.25 Further reactions from the first insertion product 6, such as β-hydride elimination to methyl crotonate or further MA insertion to the double-insertion product 7, occur simultaneously. Overlapping resonances hamper a detailed kinetic analysis of these processes. However, the ratio of formation of methyl crotonate and the double-insertion product 7 can be compared to determine whether β-hydride elimination is influenced by electronics. The samples were analyzed after 15 h at 298 K. Under these conditions, all samples still contained some residual first insertion product 6 (Figure 5). Whereas the reactivity of this first insertion product for both β-hydride elimination and further insertion is highest for the electronpoor complexes 1a-dmso and 1b-dmso, there is no clear correlation between the tendency for β-hydride elimination and the electronic nature of the phosphinesulfonato ligand and complex. A second MA insertion is favored over β-hydride elimination for all complexes except the 4-chloro-substituted complex 1b-dmso. A consecutive insertion into product 7 results in two diastereomers, with characteristic 1H methyl resonances at around 0.9 ppm. The characteristic chemical shifts of the aromatic proton 12-H (ortho position of the P-substituted

Figure 2. Mixed P-aryl-/P-alkyl-substituted Pd(II) complexes 1gdmso and 1f-dmso.

is known that sterics can strongly influence the rate of insertion and the insertion mode and even reverse the regioselectivity,22 the (κ2-(P∧O)-(2-anisyl)2)phosphinesulfonato Pd(II) complex 1c-dmso is known to clearly favor the electronically preferred 2,1-insertion mode.22a,24c The first 2,1-insertion product 6 can undergo either β-hydride elimination to methyl crotonate or insert another MA molecule to form the double-insertion product 7 (Scheme 3). The reactions of an excess of MA (ca. 20 equiv) with complexes 1a−e-dmso ([Pd] = 7 mmol L−1) were monitored by NMR at 298 K. The first insertion of MA into the palladium−methyl bond to the 2,1-insertion product 6 was relatively fast at room temperature for all complexes 1a−edmso and was complete within about 1 h at room temperature (see the Supporting Information, Figure S5.1). Note that the observed rate constants are a combination of the preequilibrium 1a−e-dmso + MA ⇄ 1a−e-MA + dmso and the actual rate of insertion from 1a−e-MA. Due to overlapping resonances in some cases, either the decay of the Pd−Me signal or the decay of proton 6-H (ortho to the SO3 group) was analyzed. Under these pseudo-first-order conditions, the electron-poor complex 1a-dmso (4-CF3) undergoes the fastest C


Organometallics

Article

Figure 3. ORTEP plots of the Pd(II) complexes [{1a-μLiCl}2], 1e-dmso, and 1f-dmso. Ellipsoids are drawn at the 50% probability level. All hydrogen atoms and solvent molecules are omitted for clarity. Top right: structure of [{1a-μLiCl}2].

Table 1. Selected Bond Lengths (Å) of Complexes [{1aμLiCl}2], [{1d-μLiCl}2], 1e-dmso, and 1f-dmso bond

[{1a-μLiCl}2]

[{1d-μLiCl}2]

1e-dmso

1f-dmso

Pd−P Pd−O Pd−C Pd−Cl/S

2.215(8) 2.214(9) 2.029(2) 2.371(7)

2.224(3) 2.231(8) 2.019(3) 2.399(0)

2.267(1) 2.174(4) 2.039(3) 2.313(9)

2.268(4) 2.151(4) 2.025(7) 2.333(2)

Scheme 3. Reaction of Methyl Acrylate with Complexes 1a− e-dmso to 6, Followed by β-Hydride Elimination or Further MA Insertion (7)

Figure 4. 31P NMR chemical shifts of Pd(II)-dmso complexes 1a−edmso vs Hammett parameter (σp) of the remote substituents.

Figure 5. 1H NMR spectra (400 MHz, CD2Cl2) of the reaction of 1a− e-dmso with excess methyl acrylate (ca. 20 equiv, [Pd] = 7 mmol L−1) after 15 h at 298 K.

anisyl moiety) and the γ-proton of complexes 7a,e were assigned by comparison to reported data.11c A ratio of the two diastereomers of about 2:1 was found, independent of the electronic modification (see the Supporting Information, Figure S5.25). Polymerization Results. All Pd(II) complexes prepared are precatalysts for ethylene polymerization at 80 °C (Table 2). As expected from general reactivity patterns of late-transitionmetal complexes,4a,11b,25b,26,27 the highest activity of 18.4 × 104 (mol of ethylene) (mol of Pd)−1 h−1 (Table 2, entry 2-1) was

observed with the electron-deficient complex 1a-dmso. The more electron rich complexes 1d-dmso and 1e-dmso exhibit a maximum activity of about 12.0 × 104 (mol of ethylene) (mol of Pd)−1 h−1 in a 15 min polymerization experiment (Table 2, entry 2-10). Polymerization experiments with variable reaction times as well as mass flow plots (see the Supporting Information, Figure S6.1−S6.8) also reveal a higher stability for more electron rich complexes. This may result from the D


Organometallics

Article

Table 2. Polymerization of Ethylene with Phosphinesulfonato Pd(II) Complexes 1a−g-dmsoa entry

cat. precursor

time (min)

yield (g)

productivity ((g of polymer)/(mmol of Pd))

TON (104 (mol of E) (mol Pd)−1)

av TOF (104 (mol of E) (mol of Pd)−1 h−1)

Mn(NMR)b × 103

Mn(GPC)c × 103

Mw/ Mnc

2-1 2-2 2-3 2-4 2-5 2-6 2-7 2-8 2-9 2-10 2-11 2-12 2-13 2-14 2-15 2-16 2-17 2-18 2-18

1a-dmso 1a-dmso 1a-dmso 1b-dmso 1b-dmso 1b-dmso 1c-dmso 1c-dmso 1c-dmso 1d-dmso 1d-dmso 1d-dmso 1e-dmso 1e-dmso 1e-dmso 1f-dmso 1f-dmsod 1f-dmsoe 1g-dmso

15 30 60 15 30 60 15 30 60 15 30 60 15 30 60 60 30 30 60

4.50 7.03 9.20 2.13 2.77 3.27 4.09 7.05 10.13 2.95 4.60 8.70 2.32 4.69 7.43 1.80 3.92 1.81 1.19

1288 2016 2632 616 784 924 1176 2016 2884 840 1316 2492 672 1344 2128 504 1120 504 336

4.6 7.2 9.4 2.2 2.8 3.3 4.2 7.2 10.3 3.0 4.7 8.9 2.4 4.8 7.6 1.8 4.0 1.8 1.2

18.4 14.3 9.4 8.8 5.6 3.3 16.7 14.4 10.3 12.0 9.4 8.9 9.5 9.6 7.6 1.8 8.0 3.6 1.2

10.1 10.1 11.2 13.4 14.1 14.6 13.8 14.2 13.5 17.1 17.4 17.5 20.0 19.0 19.6 >100 >100 >100 41.2

7.9 8.1 8.3 13.7 13.2 14.5 9.9 9.8 10.5 14.2 14.1 13.8 14.1 18.4 16.4 122 77.1 n.d. 15.8

1.9 2.0 1.9 2.3 2.4 2.3 2.2 2.2 2.1 2.3 2.4 2.5 2.5 2.1 2.4 2.2 1.5 n.d. 2.6

Reaction conditions: 3.5 μmol of Pd, 100 mL of toluene, 10 bar of ethylene, 80 °C reaction temperature, 250 mL stainless steel reactor. Determined by 1H NMR spectroscopy at 130 °C in C2D2Cl4. cDetermined by GPC at 160 °C in 1,2,4-trichlorobenzene vs linear PE. d97 °C reaction temperature. e40 bar ethylene pressure. a b

obtained are highly linear, as revealed by high-temperature 13C NMR spectra, with degrees of branching between one and two methyl branches per 1000 carbon atoms. This tendency to produce higher molecular weight polyethylene was further confirmed by studies of 1f-dmso and 1gdmso, with an electron-donating alkyl substituent at the phosphorus. Complex 1g-dmso with the known17 tBu-/Phsubstituted phosphinesulfonato motif produced polyethylene with a weight of about 41.2 × 103. In comparison, the polymer produced by the more electron rich (and more bulky substituted) complex 1f-dmso shows no quantifiable end groups in the 1H NMR spectra, which corresponds to a molecular weight of at least 100 × 103 (Mn(GPC) = 122 × 103) while the activities are similar (about 104 (mol of ethylene) (mol of Pd)−1 h−1, as also observed for all other complexes 1a− e-dmso and 1g-dmso). Note that the activities are not limited by mass transfer with the mechanically stirred pressure reactor employed (cf. the Supporting Information) Copolymerization of Ethylene and Methyl Acrylate. Complexes 1a−e-dmso are also active in copolymerization of ethylene and methyl acrylate (Table 3). While the stoichiometric MA insertion experiments (vide supra) indicate a faster MA insertion into electron-poor complexes, in the copolymerization experiments, the MA incorporation ratio is independent of the electronic nature of the phosphinesulfonato ligand within experimental error (ca. 12 mol % of MA for [MA] = 0.6 M and p(ethylene) = 5 bar; this corresponds to a relative reactivity ratio for insertion into the growing polymeryl chain of ca. 20 in favor of ethylene).29 As expected, MA incorporation increases with increasing MA concentration in the reaction mixture. Molecular weights decrease with increasing MA incorporation, since β-hydride elimination is more pronounced after the incorporation of an MA repeat unit, as seen by end group analysis. The ratio of MA vs ethylene derived end groups increases with higher MA content in the copolymer but does not correlate with the electronic nature of the catalyst. In

different tendencies for reductive elimination from the intermediately formed Pd hydride complexes, which is an entry into the most relevant decomposition pathway, as revealed recently.28 The origin of the relatively low activity of complex 1b-dmso remains unclear, but it parallels the results of the stoichiometric MA insertion experiments (vide supra). A more pronounced trend is found for the molecular weights of the polyethylenes produced. The influence of electronics, represented by the Hammett parameter (σp),23 correlates with the molecular weight of the polyethylenes obtained (Figure 6).

Figure 6. Average molecular weight of polyethylenes vs Hammett parameter (σp).

That is, the average molecular weight of the samples, as determined by high-temperature 1H NMR spectroscopy, increases moderately with more electron donating ability of the ligands, resulting in a factor of 2 for the 4-OMe substituted complex 1e-dmso (20.0 × 103) compared to the 4-CF3 substituted complex 1a-dmso (10.1 × 103). The electronic modifications of the ligand have no obvious effect on the branching structure of the polymers. All polymers E


Organometallics

Article

Table 3. Copolymerization of Ethylene and Methyl Acrylatea entry

cat. precursor

MA (M)

yield (g)

productivity((g of polymer)/(mmol of Pd))

TON ethyleneb

TON MAb

incorp MA (mol %)c

end groups MA:E

Mnc × 103

3-1 3-2 3-3 3-4 3-5 3-6 3-7 3-8 3-9 3-10 3-11 3-12 3-13 3-14 3-15 3-16 3-17 3-18 3-19

1a-dmso 1a-dmso 1a-dmso 1b-dmso 1b-dmso 1b-dmso 1c-dmso 1c-dmso 1c-dmso 1d-dmso 1d-dmso 1d-dmso 1e-dmso 1e-dmso 1e-dmso 1f-dmso 1f-dmso 1g-dmso 1g-dmso

0.2 0.6 1.2 0.2 0.6 1.2 0.2 0.6 1.2 0.2 0.6 1.2 0.2 0.6 1.2 0.6 1.2 0.6 1.2

3.42 0.90 0.77 0.54 0.22 0.10 2.08 0.68 0.28 2.73 0.82 0.28 2.07 0.60 0.32 0.45 0.19 0.53 0.33

171 45 38 27 11 5 104 34 14 136 41 14 103 30 16 22 10 26 16

5600 1200 830 860 290 110 3300 900 290 4430 1070 290 3320 790 360 670 240 820 460

160 130 180 40 30 20 130 100 70 150 130 70 120 90 40 40 30 20 30

3.7 12.2 20.1 5.1 12.5 19.9 5.0 12.3 20.8 4.1 12.8 21.0 4.5 12.6 19.4 7.7 14.5 6.1 10.5

1.6 3.7 8.0 1.8 4.4 42.3 1.4 3.5 5.4 1.0 4.4 5.9 1.4 2.1 5.5 9.6 25.8 3.9 56.8

2.0 2.0 1.5 4.1 2.6 1.0 3.1 2.9 1.5 5.4 2.7 3.9 4.5 3.9 1.5 12.3 5.8 8.7 5.9

Reaction conditions: 20 μmol of Pd, 50 mL total volume (toluene + MA), 5 bar of ethylene, 200 mg of BHT, 93 °C reaction temperature, 30 min reaction time, 250 mL stainless steel reactor. bIn units of (mol of monomer consumed) (mol of Pd)−1. cDetermined by 1H NMR spectroscopy at 130 °C in C2D2Cl4. a

weight copolymers at reasonable MA incorporation ratios and activities similar to those of the symmetrically substituted complexes 1a−e-dmso. Also, they offer additional possibilities for further electronic and steric modifications. As this study revealed, the electronic effect of the P-aryl substituents alone is limited, and combined fine tuning of electronics and especially sterics is necessary to improve the properties of the phosphinesulfonato system.

contrast to ethylene polymerization, the molecular weights of the copolymers do not correlate that well with the Hammett parameter of the substituent. This may be due to a larger number of competing reaction pathways, such as chain growth by insertion of either olefin or β-hydride elimination after an acrylate or ethylene repeat unit, respectively, which are all influenced to some extent by the electronic nature of the ligand. Additional polymerization experiments with the binuclear complexes [{1-μMCl}2] after in situ chloride abstraction by AgBF 4 showed the same trends (see the Supporting Information, Table S7.1). The mixed P-aryl/P-alkyl complexes 1f-dmso and 1g-dmso exhibit similar activities while incorporating less MA than the symmetrically substituted P-diaryl complexes under identical conditions (compare e.g. entries 3-16/3-18 and 3-8; estimated reactivity ratios are 32 and 43 in favor of ethylene vs MA for 1f,g, respectively).29 Both complexes, however, produce copolymers with significantly higher molecular weights. Interestingly, the three methoxy groups of complex 1f-dmso not only promote an increase in molecular weight but also the MA incorporation is about 50% higher in comparison to the PtBu-/PPh-substituted complex 1g-dmso.

■

ASSOCIATED CONTENT

S Supporting Information *

Text, figures, tables, and CIF files giving supplemental polymerization data, crystallographic data, general experimental procedures, details of the syntheses, additional NMR spectra, and crystal structures. This material is available free of charge via the Internet at http://pubs.acs.org.

■

AUTHOR INFORMATION

Corresponding Author

*S.M.: e-mail, [email protected]; fax, +49 7531 88-5152; tel, +49 7531 88-5151.

■

Notes

The authors declare no competing financial interest.

■

SUMMARY AND CONCLUSION This study of partially novel phosphinesulfonato Pd(II) complexes with remotely located electron-withdrawing or -donating substituents shows that electron-rich complexes produce polyethylene with higher molecular weight at the expense of activity. More electron rich complexes appear to be more stable over time under the polymerization conditions. Stoichiometric insertion experiments with methyl acrylate again indicate a faster olefin insertion into more electron-deficient complexes. Copolymerization experiments show no clear correlation of the acrylate incorporation ratio with the electronic nature of the ligand. The two mixed P-alkyl-/Paryl-substituted complexes 1f,g-dmso produce higher molecular

ACKNOWLEDGMENTS Financial support by the DFG (Me1388/10-1) is gratefully acknowledged. We thank Lars Bolk for GPC, Anke Friemel and Ulrich Haunz for support with NMR measurements, and Hannes Leicht for the synthesis of complex 1g-dmso.

■

REFERENCES

(1) Mülhaupt, R. Macromol. Chem. Phys. 2003, 204, 289−327. (2) (a) Ittel, S. D.; Johnson, L. K.; Brookhart, M. Chem. Rev. 2000, 100, 1169−1203. (b) Gibson, V. C.; Spitzmesser, S. K. Chem. Rev. 2003, 103, 283−315. (c) Mecking, S. Coord. Chem. Rev. 2000, 203, 325−351. (d) Mecking, S. Angew. Chem., Int. Ed. 2001, 40, 534−540.

F


Organometallics

Article

(3) Johnson, L. K.; Killian, C. M.; Brookhart, M. J. Am. Chem. Soc. 1995, 117, 6414−6415. (4) (a) Wang, C.; Friedrich, S.; Younkin, T. R.; Li, R. T.; Grubbs, R. H.; Bansleben, D. A.; Day, M. W. Organometallics 1998, 17, 3149− 3151. (b) Hicks, F. A.; Brookhart, M. Organometallics 2001, 20, 3217− 3219. (c) Zhang, L.; Brookhart, M.; White, P. S. Organometallics 2006, 25, 1868−1874. (5) Keim, W. Angew. Chem., Int. Ed. 1990, 29, 235−244. (6) (a) Small, B. L.; Brookhart, M.; Bennett, A. M. A. J. Am. Chem. Soc. 1998, 120, 4049−4050. (b) Britovsek, G. J. P.; Gibson, V. C.; Kimberley, B. S.; Maddox, P. J.; McTavish, S. J.; Solan, G. A.; White, A. J. P.; Williams, D. J. Chem. Commun. 1998, 849−850. (c) Small, B. L.; Brookhart, M. J. Am. Chem. Soc. 1998, 120, 7143−7144. (d) Mecking, S. Macromol. Rapid Commun. 1999, 20, 139−143. (e) Mecking, S. (Basell Polyolefine GmbH) Eur. Pat. Appl. 963 385 B1, 2004. (f) Mihan, S.; Karer, R. Schmitz, H., Lilge D. (Basell Polyolefine GmbH), U.S. Pat. 8 003 740 B2, 2011. (7) Johnson, L. K.; Mecking, S.; Brookhart, M. J. Am. Chem. Soc. 1996, 118, 267−268. (8) Drent, E.; van Dijk, R.; van Ginkel, R.; van Oort, B.; Pugh, R. I. Chem. Commun. 2002, 744−745. (9) (a) Nakamura, A.; Ito, S.; Nozaki, K. Chem. Rev. 2009, 109, 5215−5244. (b) Chen, E. Y.-X. Chem. Rev. 2009, 109, 5157−5214. (c) Berkefeld, A.; Mecking, S. Angew Chem. Int. Ed. 2008, 47, 2538− 2542. (d) Nakamura, A.; Anselment, T. M. J.; Claverie, J.; Goodall, B.; Jordan, R. F.; Mecking, S.; Rieger, B.; Sen, A.; van Leeuwen, P. W. N. M.; Nozaki, K. Acc. Chem. Res. 2013, 46, 1438−1449. (10) (a) Kochi, T.; Noda, S.; Yoshimura, K.; Nozaki, K. J. Am. Chem. Soc. 2007, 129, 8948−8949. (b) Ito, S.; Munakata, K.; Nakamura, A.; Nozaki, K. J. Am. Chem. Soc. 2009, 131, 14606−14607. (c) Rünzi, T.; Fröhlich, D.; Mecking, S. J. Am. Chem. Soc. 2010, 132, 17690−17691. (11) (a) Allen, N. T.; Goodall, B. L.; McIntosh, L. H., III Eur. Pat. Appl. EP1760086A2, 2007. (b) Piche, L.; Daigle, J.-C.; Poli, R.; Claverie, J. P. Eur. J. Inorg. Chem. 2010, 4595−4601. (c) Neuwald, B.; Caporaso, L.; Cavallo, L.; Mecking, S. J. Am. Chem. Soc. 2013, 135, 1026−1036. (12) Skupov, K. M.; Marella, P. R.; Simard, M.; Yap, G. P. A.; Allen, N.; Conner, D.; Goodall, B. L.; Claverie, J. P. Macromol. Rapid Commun. 2007, 28, 2033−2038. (13) Newsham, D. K.; Borkar, S.; Sen, A.; Conner, D. M.; Goodall, B. L. Organometallics 2007, 26, 3636−3638. (14) Neuwald, B.; Ö lscher, F.; Göttker-Schnetmann, I.; Mecking, S. Organometallics 2012, 31, 3128−3137. (15) Friedberger, T.; Wucher, P.; Mecking, S. J. Am. Chem. Soc. 2012, 134, 1010−1018. (16) Ito, S.; Kanazawa, M.; Munakata, K.; Kuroda, J.; Okumura, Y.; Nozaki, K. J. Am. Chem. Soc. 2011, 133, 1232−1235. (17) Piche, L.; Daigle, J.-C.; Rehse, G.; Claverie, J. P. Chem. Eur. J. 2012, 18, 3277−3285. (18) For further X-ray structures of phosphinesulfonato complexes, see ref 11c and references cited therein. (19) Rünzi, T.; Guironnet, D.; Göttker-Schnetmann, I.; Mecking, S. J. Am. Chem. Soc. 2010, 132, 16623−16630. (20) κ-S-dmso: electron poor and bulky [κ2-(P,O)-P[o-(2′-6′(OMe)2C6H3)-C6H4]2(o-SO2O-C6H4)PdMe]-dmso.21a κ-O-dmso: less bulky, electron rich Pd complexes,21b neutral phosphinesulfonato Ni(II) complex,21a and bulky diazaphospholidine sulfonato Pd(II) complexes.22 DFT calculations gave an energy difference of only 4 kJ mol−1 between the two coordination modes for complex 1c-dmso.28 (21) (a) Guironnet, D.; Roesle, P.; Rünzi, T.; Göttker-Schnetmann, I.; Mecking, S. J. Am. Chem. Soc. 2009, 131, 422−423. (b) Leicht, H.; Göttker-Schnetmann, I.; Mecking, S. Angew. Chem., Int. Ed. 2013, 52, 3963−3966. (22) (a) Wucher, P.; Caporaso, L.; Roesle, P.; Ragone, F.; Cavallo, L.; Mecking, S.; Göttker-Schnetmann, I. Proc. Natl. Acad. Sci. U.S.A. 2011, 108, 8955−8959. (b) Wucher, P.; Roesle, P.; Falivene, L.; Cavallo, L.; Caporaso, L.; Göttker-Schnetmann, I.; Mecking, S. Organometallics 2012, 31, 8505−8515. (23) Hansch, C.; Leo, A.; Taft, R. W. Chem. Rev. 1991, 91, 165−195.

(24) (a) Nakamura, A.; Munakata, K.; Kochi, T.; Nozaki, K. J. Am. Chem. Soc. 2008, 130, 8128−8129. (b) Skupov, K. M.; Hobbs, J.; Marella, P.; Conner, D.; Golisz, S.; Goodall, B. L.; Claverie, J. P. Macromolecules 2009, 42, 6953−6963. (c) Guironnet, D.; Caporaso, L.; Neuwald, B.; Göttker-Schnetmann, I.; Cavallo, L.; Mecking, S. J. Am. Chem. Soc. 2010, 132, 4418−4426. (d) Nakamura, A.; Munakata, K.; Ito, S.; Kochi, T.; Chung, L. W.; Morokuma, K.; Nozaki, K. J. Am. Chem. Soc. 2011, 133, 6761−6779. (25) (a) Malinoski, J. M.; Brookhart, M. Organometallics 2003, 22, 5324−5335. (b) Chan, M. S. W.; Deng, L.; Ziegler, T. Organometallics 2000, 19, 2741−2750. (c) Hanley, P. S.; Hartwig, J. F. J. Am. Chem. Soc. 2011, 133, 15661−15673. (26) (a) Bastero, A.; Göttker-Schnetmann, I.; Röhr, C.; Mecking, S. Adv. Synth. Catal. 2007, 349, 2307−2316. (b) Yu, S.-M.; Berkefeld, A.; Göttker-Schnetmann, I.; Müller, G.; Mecking, S. Macromolecules 2007, 40, 421−428. (c) Zuideveld, M. A.; Wehrmann, P.; Röhr, C.; Mecking, S. Angew. Chem., Int. Ed. 2004, 43, 869−873. (d) Soula, R.; Broyer, J. P.; Llauro, M. F.; Tomov, A.; Spitz, R.; Claverie, J.; Drujon, X.; Malinge, J.; Saudemont, T. Macromolecules 2001, 34, 2438−2442. (e) Popeney, C. S.; Levins, C. M.; Guan, Z. Organometallics 2011, 30, 2432−2452. (27) Guan et al. showed that activity in ethylene polymerization with acyclic cationic Pd(II) diimine complexes decreases with electronwithdrawing groups introduced at a remote position of the diimine: Popeney, C.; Guan, Z. Organometallics 2005, 24, 1145−1155. (28) Rünzi, T.; Tritschler, U.; Roesle, P.; Göttker-Schnetmann, I.; Möller, H. M.; Caporaso, L.; Poater, A.; Cavallo, L.; Mecking, S. Organometallics 2012, 31, 8388−8406. (29) This estimation assumes an ethylene solubility at 80 °C and 5 atm of 0.23 mol L−1; cf.: Plöcker, U.; Knapp, H.; Prausnitz, J. Ind. Eng. Chem. Process Dev. 1978, 17, 324−332.

G


Electronic Influences in Phosphinesulfonato Palladium(II

Recommend Documents