Mixed Allyl–Borohydride Lanthanide Complexes ... - ACS Publications

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Mixed Allyl−Borohydride Lanthanide Complexes: Synthesis of Ln(BH4)2(C3H5)(THF)3 (Ln = Nd, Sm), Characterization, and Reactivity toward Polymerization Sami Fadlallah, Michael̈ Terrier, Chloe Jones, Pascal Roussel, Fanny Bonnet,* and Marc Visseaux* Univ. Lille, CNRS, Centrale Lille, ENSCL, Univ. Artois, UMR 8181-UCCS-Unité de Catalyse et Chimie du Solide, F-59000 Lille, France S Supporting Information *

ABSTRACT: New mixed allyl−borohydrido lanthanide complexes Ln(BH4)2(C3H5)(THF)3 (Ln = Nd (1), Sm (2)) could be prepared in good yield by reacting Ln(BH4)3(THF)3 (Ln = Sm, Nd) with 1/2 equiv of Mg(C3H5)2(THF)x. X-ray structure analysis revealed monomeric structures with two terminal BH4 ligands, one π-allyl ligand, and three THF molecules. In an assessment of isoprene polymerization, 1 afforded trans-1,4-polyisoprene in good yield, as a single component or in combination with Mg cocatalyst. Both 1 and 2 were found to be extremely active toward ε-caprolactone polymerization.

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to cis-selective polymerization.8 On the other hand, the borohydride complexes of the rare earths are now considered to be very useful for polymerization:9 although they are inactive when used alone, we found that, in combination with alkyl reagents, they are efficient precatalysts toward nonpolar monomers such as ethylene,10 styrene,11 and conjugated dienes.12 They are also efficient toward polar monomers, affording hydroxy-telechelic poly(caprolactone) by ring-opening polymerization of ε-caprolactone, as demonstrated by Guillaume,13 while they are also able to initiate the polymerization of L- and rac-lactide.14 Herein, we report the synthesis of the first lanthanide complexes bearing both borohydride and allyl ligands, Ln(BH4)2(C3H5)(THF)3 (Ln = Nd (1), Sm (2)), as well as their X-ray structures. The ability of complexes 1 and 2 to polymerize isoprene and ε-caprolactone is also examined.

INTRODUCTION Lanthanide complexes bearing allyl ligands are of both fundamental and applied interest, notably due to their catalytic performance toward stereospecific diene polymerization.1 The first organolanthanide complexes containing the allyl moiety, (C5H5)2Ln(C3H5) (Ln = lanthanide), were reported by Tsutsui in 1975.2 Later in the 1980s, the anionic tetrakis(allyl) lanthanide complexes [Li(1,4-dioxane)n][Ln(allyl)4] were reported by Mazzei and Lugli.3 Significant work in the chemistry of allylic derivatives of the rare earths was then performed during the 1990s by the group of Taube, who especially reported the neutral homoleptic tris(allyl) complexes, obtained via allyllithium abstraction from their tetrakis(allyl) anionic congeners [Ln(allyl)3·x(dioxane)]n (Ln = La, x = 1.5; Ln = Nd, x = 1) and unsolvated Ln(allyl)3 after vacuum treatment.4 Meanwhile, important studies showed that allylic compounds could be considered as potent intermediates in the lanthanide-mediated polymerization of olefins.5 Since then, a panel of allylic derivatives of the rare earths were synthesized and thoroughly studied, especially in the field of polymerization catalysis.6 The homoleptic tri- and tetraanionic allyl complexes (Nd, La) disclosed by Taube were found to catalyze the transselective polymerization of butadiene,7 while combining the former complexes with aluminum cocatalysts resulted in a shift © XXXX American Chemical Society

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RESULTS AND DISCUSSION Taube had earlier reported the easy synthesis of the tris(allyl)Nd complex from NdI3 and the Grignard reagent (C3H5)MgI.6b Attempts at BH4/allyl exchange by reacting Ln(BH4)3(THF)3 with Grignard reagents as starting materials Received: October 16, 2015

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DOI: 10.1021/acs.organomet.5b00877 Organometallics XXXX, XXX, XXX−XXX

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Organometallics led to untractable mixtures. In turn, we could prepare complexes 1 and 2 in good yields via the straightforward reaction of Ln(BH4)3(THF)3 (Ln = Nd, Sm)15 with 1/2 equiv of Mg(C3H5)2(THF)x (x = 1.5, 3, depending on the crop of reagent used, for 1 and 2, respectively).16 The reaction was conducted in THF at room temperature (Scheme 1), showing Scheme 1. Synthesis of Mixed Allyl−Borohydride Complexes 1 and 2

Figure 1. X-ray structure showing one of the two configurations of Nd(BH4)2(C3H5)(THF)3 (1). Hydrogen atoms are partially omitted for the aid of clarity. Selected bond lengths (Å) and angles (deg): Nd− C1 = 2.719(7), Nd−C2 = 2.740(6), Nd−C3 = 2.699(6), Nd−B1 = 2.726(7), Nd−B2 = 2.672(8), Nd−O1 = 2.524(5), Nd−O2 = 2.492(5), Nd−O3 = 2.553(4); B1−Nd−B2 = 171.6(2).

instantaneous color change upon mixing the reagents. The 1H NMR spectrum of the mixture of reagents prepared at the NMR scale showed their total consumption, revealing the immediacy of that reaction. No evidence of disproportionation affording Ln(allyl)3 was observed.4 In the case of neodymium complex 1, the filtration and evaporation of the THF afforded a green solid in 60% yield, whose molecular formula corresponded to Nd(BH4)2(C3H5)(THF)3 according to 1H NMR and elemental analysis. An additional step was in turn necessary to get 2 as a pure compound: extraction with toluene followed with redissolution in THF and removal of the volatiles afforded 83% of Sm(BH4)2(C3H5)(THF)3 as a violet solid. Although complexes 1 and 2 are paramagnetic, the 1H NMR spectra of both could be interpreted (see Figures S1 and S2 in the Supporting Information). The 1H NMR spectrum of 1 in C6D6 displays a broad BH4 signal at δ 92 ppm, three allyl signals at δ 22.6, 13.1, and 1.3 ppm with a typical 1/2/2 allyl pattern, and THF resonances at −2.4 and −5.8 ppm. Note that in THF-d8 the spectrum is very similar. Complex 2 behaves differently: in C6D6, the two BH4 groups display a broad singlet at −10.6 ppm, the allyl signals are at 16.2, 11.2, and 9.7 ppm (relative intensities 1/2/2), and the THF resonances appear at 1.6 and 0.2 ppm. In THF-d8 in turn, two signals assigned to the allyl group in a 4:1 ratio (11.4 and 8.9 ppm, respectively) are observed this time, revealing a dynamic syn−anti interconversion of the allyl group in this solvent.17 Such uncommon fluxionality of the lanthanide−allyl moiety has been noticed recently by Okuda.6g Green X-ray-quality crystals of compound 1 were obtained from a cold THF solution (−20 °C), whereas recrystallization from a mixture of THF and pentane at room temperature was necessary to afford violet crystals of 2. From structural analysis, complexes 1 and 2 were both found to be monomeric, in agreement with the formula Ln(BH4)2(C3H5)(THF)3 (Figure 1 and Figure S3 in the Supporting Information). 1 and 2 are isostructural, with little variations of angles and distances due to the lanthanide contraction from Nd to Sm. In both complexes, the 6-fold coordination sphere (formal coordination number 7 if allyl counts for 2) around the metal center is formed by the η3-allylic ligand, two tridentate BH4 ligands, and three THF molecules, showing a distorted-octahedral geometry. In comparison with Ln(BH4)3(THF)3 complexes, which are known to be monomeric and display one bidentate and two tridentate borohydride ligands,15 one bidentate BH4 in each structure reported herein is replaced by an allyl group. The tridentate borohydride groups are in positions trans to each other, showing a nearly linear setup (B1−Nd−B2 = 171.6° and B1−Sm−B2 = 171.8°), whereas in the cationic [Y(BH4)(Me)-

(THF)5][BPh4],18 another rare example of a mixed alkyl− borohydride rare-earth complex, the BH4 group is trans to the methyl. The Nd−B distances are 2.672 and 2.726 Å, and the Sm−B distances are 2.637 and 2.730 Å, which falls within the expected range for η3-coordinated BH4.19,9 The three carbons of the allyl group are not equidistant from the metal center: the central carbon atom is at 2.740 Å from Nd, while the other two are located at 2.699 and 2.719 Å (2.696, 2.685, and 2.663 Å, respectively, from the Sm center). However, this longest Nd− C(allyl) distance is in the range observed for the complexes Nd(C3H5)3(C4H8O2),4 (C5Me5)Nd(C3H5)2(C4H8O2),6b [Nd(C3H5)2Cl(THF)2]2,20 and [Mg(THF)6][Sm(C3H5)4]2(THF)221 (2.740, 2.722, 2.717, and 2.721 Å, respectively). In 1, the allyl group is not vertical with the Nd atom but it shows a degree of inclination (Scheme 2) close to Scheme 2. Schematic View Showing the Inclination of the Allyl Group in 1

that found for the complexes already described by Taube,7 with Nd−C1−H10 and Nd−C3−H13 angles of 78.1 and 76.9°, respectively, while the Nd−C1−H9, Nd−C3−H12, and Nd− C2−H11 angle are 116.2, 117.0, and 128.5°, respectively. The same kind of deviation was noticed for complex 2. Nd−O distances between the metal center and the THF molecules in 1 (2.492, 2.553, and 2.525 Å) are slightly shorter than those observed for Nd−O in the 1,4-dioxane complexes of Taube: 2.609 Å in Nd(C3H5)3.C4H8O2 and 2.583 Å in Nd(C5Me5)(C3H5)2·C4H8O2.4,6b In fact, complexes 1 and 2 are the borohydride parents of the chloride NdCl2(C3H5)(THF)2, but this latter complex, which was not structurally characterized, is thought to be strongly associated,19 similarly to the hexameric dimethylpentadienyl complex [Nd6(2,4(CH3)2C5H5)6Cl12(THF)2].22 This is more evidence that the borohydride group brings a steric/electronic compromise that allows different structural/chemical behavior vs the chloride group.9 B

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Organometallics Table 1. Polymerization of Isoprene (IP) Using 1a entry

cocatalyst (equiv/Nd)

time, h

yield, %

Mn/Đb (Mn(th))c

1 2 3 4 5

BEM (1) Mg(C3H5)2(diox)0.5 (1) AliBu3 (10) MAO (30)

3 2 2 1 1

53 58 27 100 97

29600/1.54 (35300) 16900/1.54 (40900) 5300/1.23 (18400) 20300/2.23 (67700) 41600/2.25 (68700)

trans (cis), %d 92.2 96.0 92.7 78.7 68.2

(6.4) (1.7) (1.0) (20.1) (28.6)

Conditions: Vtoluene = VIP = 1 mL, [IP]/[Nd] = 1000, T = 50 °C. bDetermined by SEC in THF at 40 °C with respect to polystyrene standards with the correction Mn = Mn(PS) × 0.5,23 Đ = Mw/Mn. cMn(th) = [IP]/[Ln] × 68.12 × conversion. dDetermined by 1H NMR spectroscopy in CDCl3.

a

Table 2. Polymerization of ε-Caprolactone Using 1 and 2a entry

catalyst

CL:Ln

time, min

yield, %b

Mn/Đc

6 7 8 9 10 11 12 13 14 15

1 1 1 1 1 1 2 2 2 Mg(C3H5)2(THF)1.5

100 250 500 1000 5000 10000 250 500 1000 100

0.08 0.1 0.2 0.25 0.4 0.8 0.3 0.7 0.8 0.01

72 83 90 98 97 95 84 86 98 77

5400/1.17 6800/1.35 10600/1.53 20000/1.59 75000/1.56 120000/1.53 6700/1.33 10900/1.50 16000/1.58 15200/2.53

Conditions: n(Ln) = 8.7 × 10−6 mol, solvent THF, VTHF = VCL, T = 25 °C. bDetermined by gravimetry. cSEC in THF at 40 °C against polystyrene standards with the correction Mn = Mn(PS) × 0.56,28 Đ = Mw/Mn.

a

the stereoselectivity of the reaction. The addition of 1 equiv of Mg(nBu)(Et) (BEM) to 1 (run 2) gives results quite equivalent to those observed with the previously reported Nd(BH4)3(THF)3/BEM catalytic system.12 In comparison to run 1, both the activity and stereoselectivity are higher, showing the beneficial role of the magnesium partner in such a process. The efficiency (Mn(th)/Mn) in run 2 is about 2.5, indicating that more than two polymer chains are growing this time, i.e. at least one chain initiated by the Ln−alkyl bond formed by alkylation of Ln−(BH4) with BEM and one initiated by the genuine Ln− allyl group. Moreover, the SEC curve in run 2 is monomodal (see Figure S4 in the Supporting Information), which clearly shows that Nd/Mg reversible transfer is occurring during the polymerization.25 When Mg(C3H5)2(C4H8O2)0.5 is combined with 1 as a cocatalyst (run 3), the activity decreases (yield 27% in 2 h) but the selectivity remains the same (92.7%) as that observed with 1 alone (92.2%). With triisobutylaluminum (AliBu3) or methylaluminoxane (MAO) as cocatalyst, higher activities were obtained (runs 4 and 5), affording total conversion in only 1 h, but the reactions were less stereoselective, with more cis proportion, as expected from the previous results of Taube.26 This change in selectivity is typical of a syn−anti conversion of the metal−allyl active species, as already observed when an Al cocatalyst was added to a trans-selective (allyl)lanthanide single-component catalyst.7a The ability of complexes 1 and 2 to perform the ring-opening polymerization (ROP) of ε-caprolactone (CL) was also examined. In these complexes, both [Ln]−(BH4)13 and [Ln]−(C3H5)6d could a priori initiate the polymerization. Results performed with various [CL]/[initiator] ratios are reported in Table 2. Upon addition of the monomer to the initiator in THF solution at room temperature, a very rapid increase of the viscosity was observed, affording 100% conversion in all cases in less than 1 min. This corresponds to an activity up to 7 × 107 g of polymer (mol of Nd)−1 h−1 with complex 1 (monomer to catalyst ratio 10000, run 11),

The reactivity of lanthanide allyl complexes 1 and 2 was logically assessed toward isoprene (IP) polymerization. The neodymium-based complex 1 was found to be active on its own or in combination with various alkylating agents, whereas its samarium analogue 2 showed no reactivity at all, in line with the well-known “neodymium effect”.1 Selected results are gathered in Table 1. Complex 1 was found to be active as a single-component catalyst, yielding 53% polyisoprene in 3 h (run 1). Such reactivity could be expected due to the presence in the complex of an Nd−allyl bond, which is known to be the active species in such a process (vide infra). The Mn value of the isolated polyisoprene determined by SEC (29600 g mol−1), in close agreement with the expected molecular weight (36000 g mol−1), and the rather narrow dispersity (Đ = 1.53), agree well with the expected growth of one polymer chain per metal center. Interestingly as well, the polymer displayed a stereoregular structure with 92.2% of trans units, as already observed with tris- and tetrakis(allyl) lanthanide initiators.7 As a comparison, the activity of 1 was somewhat lower than that previously observed for the dual-component Nd(BH4)3(THF)3/Mg(C3H5)2 catalytic system (80% yield in 3 h at 50 °C), as well as the trans stereoselectivity (95.4%), with comparable macromolecular data (Mn = 35100 g mol−1; Đ = 1.34).12b The rather inferior activity of 1 can be explained by the absence of magnesium in the catalyst used, which can play two roles during the process. First, Mg may coordinate the THF molecules (because of the more oxophilic nature of magnesium, as observed in lanthanide/magnesium bimetallic complexes21,24), which can compete with the monomer toward the coordination to the lanthanide center, and have a detrimental effect in terms of activity, without affecting other properties such as selectivity.12b Second, the small difference in reactivity observed indicates that the magnesium compound not only acts as an alkylating agent but also probably remains in the lanthanide coordination sphere in the form of a likely bimetallic active species,12a,24b influencing both the activity and C

DOI: 10.1021/acs.organomet.5b00877 Organometallics XXXX, XXX, XXX−XXX

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Organometallics

coordination−insertion mechanism with initiation by the borohydride moieties was established, thanks to end-group NMR studies. Further studies aiming at extending this new family of mixed borohydrido−allyl complexes to other rare-earth metals as well as the screening of their activity toward polar and nonpolar monomers are in progress and will be reported in due course in a forthcoming paper.

which to our knowledge is the best ever reported for such a reaction. For comparison, the activity reaches 3 × 106 g of polymer (mol of La)−1 h−1 with tris(allyl)lanthanide derivatives6d and ca. 3 × 105 g of polymer (mol of Sm)−1 h−1 with the tris(borohydrides) of the rare earths.13b A kind of synergy of ligands can be advanced here to account for the outstanding catalytic activity of mixed allyl(borohydride) complexes 1 and 2. The average molecular weights (Mn) of the obtained PCL (polycaprolactone) range from 5400 to 120000 g mol−1 as the ratio [CL]/[Nd] increases from 100 (run 6) to 10000 (run 11), along with relatively narrow dispersities (Đ = 1.17−1.59). Interestingly, careful examination of the 1H NMR spectrum of the isolated polymers showed a dihydroxytelechelic HO− PCL−OH structure. Accordingly, it can be proposed that the ROP process was initiated through the Ln−(BH4) bond13 rather than by insertion into the allyl group (Scheme 3).

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EXPERIMENTAL SECTION

General Methods. All operations were performed under an inert atmosphere using Schlenk techniques, or in a dry solvent-free glovebox (Jacomex O2 3.0σ(I), Rint = 0.028), total number of collected reflections 63707, converged to a final R1 = 3.21% (wR2 = 4.02%). Except for H atoms pertaining to BH4 groups, all hydrogen atoms were placed in calculated positions. Others were located in difference Fourier maps and refined with isotropic thermal parameters. CCDC 1421983. Polymerizations. Typical Isoprene Polymerization Experiment (Run 4, Table 1, Given as an Example). In a glovebox, 4.3 mg of 1 (0.01 mmol) was dissolved in 1 mL of dry and degassed toluene. A 10 equiv amount of Al(iBu)3 (d = 0.786, 25 μL, 10 μmol) was added with a micro syringe. A 1 mL portion of isoprene (10 mmol) was then added. The solution turned green within a few minutes, and the reaction was carried out at 50 °C for 1 h. At the end of the reaction the medium was completely solid. The reaction was quenched by addition of some methanol drops and a small amount of THF. Polymers were precipitated in methanol, filtered, and dried under vacuum. The yield reached 100%, the average molecular weight of the obtained polymer was Mn = 20300 g mol−1, and the dispersity was 2.23. 1H and 13C NMR analyses in CDCl3 showed that the polyisoprene obtained was 78.7% trans-1,4 regular. Typical ε-Caprolactone Polymerization Experiment (Run 9, Table 2, Given as an Example). In a glovebox, 5.2 mg of 1 (8.7 μmol) was dissolved in 1 mL of dry and degassed THF. A 1 mL portion of εcaprolactone (8.7 mmol) was then added. The solution turned green within a few seconds, and the reaction was carried out at room temperature for 15 s. At the end of the reaction the medium was completely solid. The polymer was dissolved in THF, poured into a large amount of methanol (400 mL), filtered, and dried under vacuum. The yield reached 98%, the average molecular weight of the obtained polymer was Mn = 20000 g mol−1, and the dispersity was 1.59. 1H NMR analysis of the isolated polycaprolactone in CDCl3 showed the dihydroxytelechelic structure HO−PCL−OH.

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The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The authors thank Aurélie Malfait for SEC analysis. Chevreul institute (FR 2638), Ministère de l’Enseignement Supérieur et de la Recherche (Ph.D. grants to S.F., M.T., and C.J.), Région Nord-Pas de Calais, and FEDER are acknowledged for supporting and funding this work.

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(1) (a) Takeuchi, D. Stereoselective Polymerization of Conjugated Dienes. in Encyclopedia of Polymer Science and Technology; Wiley: New York, 2013; pp 1−25. (b) Zhang, Z. C.; Cui, D. M.; Wang, B. L.; Liu, B.; Yang, Y. Struct. Bonding (Berlin, Ger.) 2010, 137, 49−108. (c) Friebe, L.; Nuyken, O.; Obrecht, W. Adv. Polym. Sci. 2006, 204, 1− 154. (d) Fischbach, A.; Anwander, R. Adv. Polym. Sci. 2006, 204, 155− 281. (e) Monakov, Y. B.; Mullagaliev, I. R. Russ. Chem. Bull. 2004, 53, 1−9. (f) Taube, R. In Metalorganic Catalysts for Synthesis and Polymerization; Kaminsky, W., Ed.; Springer: Berlin, 1999; pp 531− 548. (g) Porri, L.; Ricci, G.; Giarrusso, A.; Shubin, N.; Lu, Z. Recent Developments in Lanthanide Catalysts for 1,3-Diene Polymerization. In Olefin Polymerization; Arjunan, P., McGrath, J. E., Hanlon, T. L., Eds.; American Chemical Society: Washington, DC, 1999; ACS Symposium Series 749, pp 15−30. 10.1021/bk-2000-0749.ch002. (2) Tsutsui, M.; Ely, N. J. Am. Chem. Soc. 1975, 97, 3551−3553. (3) (a) Mazzei, A. Makromol. Chem. 1981, 4, 61−72. (b) Brunelli, M.; Poggio, S.; Pedretti, U.; Lugli, G. Inorg. Chim. Acta 1987, 131, 281−285. (4) Taube, R.; Windisch, H.; Maiwald, S.; Hemling, H.; Schumann, H. J. Organomet. Chem. 1996, 513, 49−61. (5) Evans, W. J.; DeCoster, D. M.; Greaves, J. Organometallics 1996, 15, 3210−3221. (6) Selected references: (a) Baudry-Barbier, D.; Andre, N.; Dormond, A.; Pardes, C.; Richard, P.; Visseaux, M.; Zhu, C. J. Eur. J. Inorg. Chem. 1998, 1998, 1721−1727. (b) Taube, R.; Maiwald, S.; Sieler, J. J. Organomet. Chem. 2001, 621, 327−336. (c) Kirillov, E.; Lehmann, C. W.; Razavi, A.; Carpentier, J. F. J. Am. Chem. Soc. 2004, 126, 12240−12241. (d) Sanchez-Barba, L. F.; Hughes, D. L.; Humphrey, S. M.; Bochmann, M. Organometallics 2005, 24, 3792− 3799. (e) Jian, Z.; Cui, D.; Hou, Z.; Li, X. Chem. Commun. 2010, 46, 3022−3024. (f) Carpentier, J. F.; Guillaume, S. M.; Kirillov, E.; Sarazin, Y. C. R. Chim. 2010, 13, 608−625. (g) Cui, P.; Spaniol, T. P.; Okuda, J. Organometallics 2013, 32, 1176−1182. (7) (a) Taube, R.; Windisch, H.; Weissenborn, H.; Hemling, H.; Schumann, H. J. Organomet. Chem. 1997, 548, 229−236. (b) Maiwald, S.; Weissenborn, H.; Sommer, C.; Muller, G.; Taube, R. J. Organomet. Chem. 2001, 640, 1−9. (8) (a) Maiwald, S.; Sommer, C.; Muller, G.; Taube, R. Macromol. Chem. Phys. 2001, 202, 1446−1456. (b) Maiwald, S.; Sommer, C.; Muller, G.; Taube, R. Macromol. Chem. Phys. 2002, 203, 1029−1039. (9) Visseaux, M.; Bonnet, F. Coord. Chem. Rev. 2011, 255, 374−420. (10) Visseaux, M.; Chenal, T.; Roussel, P.; Mortreux, A. J. Organomet. Chem. 2006, 691, 86−92. (11) (a) Barbier-Baudry, D.; Blacque, O.; Hafid, A.; Nyassi, A.; Sitzmann, H.; Visseaux, M. Eur. J. Inorg. Chem. 2000, 2000, 2333− 2336. (b) Zinck, P.; Visseaux, M.; Mortreux, A. Z. Anorg. Allg. Chem. 2006, 632, 1943−1944. (12) (a) Bonnet, F.; Visseaux, M.; Pereira, A.; Barbier-Baudry, D. Macromolecules 2005, 38, 3162−3169. (b) Terrier, M.; Visseaux, M.; Chenal, T.; Mortreux, A. J. Polym. Sci., Part A: Polym. Chem. 2007, 45, 2400−2409. (c) Visseaux, M.; Mainil, M.; Terrier, M.; Mortreux, A.; Roussel, P.; Mathivet, T.; Destarac, M. Dalton Trans. 2008, 4558− 4561. (d) Bonnet, F.; Violante, C.; Roussel, P.; Mortreux, A.; Visseaux, M. Chem. Commun. 2009, 3380−3382. (e) Loughmari, S.; Hafid, A.; Bouazza, A.; El Bouadili, A.; Zinck, P.; Visseaux, M. J. Polym. Sci., Part A: Polym. Chem. 2012, 50, 2898−2905. (f) Ventura, A.; Chenal, T.;

ASSOCIATED CONTENT

* Supporting Information S

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.organomet.5b00877. Experimental details, characterization data, and X-ray structure of compound 2 (PDF) Crystallographic data for compound 1 (CIF) Crystallographic data for compound 2 (CIF)

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REFERENCES

AUTHOR INFORMATION

Corresponding Authors

*E-mail for F.B.: [email protected]. *E-mail for M.V.: [email protected]. E

DOI: 10.1021/acs.organomet.5b00877 Organometallics XXXX, XXX, XXX−XXX

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DOI: 10.1021/acs.organomet.5b00877 Organometallics XXXX, XXX, XXX−XXX