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Synthesis, structure, and reactivity of yttrium complexes with chiral biaryldiamine-based N4-ligands
Inorganic Chemistry Communications 13 (2010) 445–448
Contents lists available at ScienceDirect
Inorganic Chemistry Communications journal homepage: www.elsevier.com/locate/inoche
Synthesis, structure, and reactivity of yttrium complexes with chiral biaryldiamine-based N4-ligands Guofu Zi a,*, Li Xiang a, Xue Liu a, Qiuwen Wang a, Haibin Song b a b
Department of Chemistry, Beijing Normal University, Beijing 100875, China State Key Laboratory of Elemento-Organic Chemistry, Nankai University, Tianjin 300071, China
a r t i c l e
i n f o
Article history: Received 17 November 2009 Accepted 14 January 2010 Available online 20 January 2010 Keywords: Chiral N4-ligands Yttrium complexes Synthesis Structure Reactivity
a b s t r a c t The chiral biaryl-based N4-ligands, (R)-5,50 ,6,60 ,7,70 ,8,80 -octahydro-2,20 -bis(pyrrol-2-ylmethyleneamino)1,10 -binaphthyl (1H2) and (S)-2,20 -bis(pyrrol-2-ylmethyleneamino)-6,60 -dimethyl-1,10 -biphenyl (2H2), can effectively stabilize the chiral rare earth metal chloride complexes such as 1-YCl(dme) (3) and 2YCl(dme) (4), which offers important intermediates for the preparation of chiral rare earth catalysts containing the M–C or M–X (X = heteroatom) bonds. For example, treatment of 3 with half equiv of 1Na2 in THF gives the binuclear complex 1-Y(thf)-1-Y(thf)-1 (5) in 70% yield. These complexes have been characterized by various spectroscopic techniques, elemental analyses, and X-ray diffraction analyses. The complex 5 is an active catalyst for the ring-opening polymerization of rac-lactide, affording isotactic-rich polylactides. Ó 2010 Elsevier B.V. All rights reserved.
Chiral rare earth metal complexes based on non-Cp ligands have received growing attention in the past decades [1–6], because the lability of rare earth metal element-ligand bonds and the flexibility of their coordination geometries make these elements highly suitable for use in catalysis. However, the rare earth metal complexes supported by non-Cp ligands usually encounter salt addition, dimerization or ligand redistribution, and these factors also make it difficult to generate well-defined chiral architectures that will lead to efficient enantioselective reactions [1]. Thus, chiral multidentate ligands have attracted considerable interest, which can provide proper sterics and electronics for the rare earth metal center to prevent the side-reactions mentioned above via varying the size and electron affinity of the substituents. Although many rare earth catalysts based on non-Cp ligands have been reported [1–6], the development of new chiral rare earth catalysts is a desirable and challenging goal. In recent years, we have developed a series of rare earth complexes based on chiral non-Cp multidentate ligands, and they have shown that they are useful catalysts for a range of transformations [7–12]. In our attempt to further explore the chiral non-Cp ligand system and their application in rare earth chemistry, we have recently extended our research work to chiral tetradentate N4-ligands, (R)-5,50 ,6,60 ,7,70 ,8,80 -octahydro-2,20 -bis (pyrrol-2-ylmethyleneamino)-1,10 -binaphthyl (1H2) and (S)-2,20 bis(pyrrol-2-ylmethyleneamino)-6,60 -dimethyl-1,10 -biphenyl (2H2) [13,14], and found they are useful to stabilize the rare earth metal chloride complexes, which are important intermediates for the * Corresponding author. Tel.: +86 10 5880 7843; fax: +86 10 5880 2075. E-mail address: [email protected] (G. Zi). 1387-7003/$ - see front matter Ó 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.inoche.2010.01.008
preparation of chiral rare earth catalysts containing the M–C or M–X (X = heteroatom) bonds. We report herein on some observation concerning the ligands 1H2 and 2H2 use in rare earth chemistry. Deprotonation of the chiral ligands (R)-5,50 ,6,60 ,7,70 ,8,80 -octahydro-2,20 -bis(pyrrol-2-ylmethyleneamino)-1,10 -binaphthyl (1H2) and (S)-2,20 -bis(pyrrol-2-ylmethyleneamino)-6,60 -dimethyl-1,10 biphenyl (2H2) are achieved by reaction with an excess of NaH in DME or THF. The resulting disodium salt 1Na2 or 2Na2 thus formed is reacted with 1 equiv of YCl3 in a mixed solution of DME and toluene or a solution of THF, after recrystallization from a benzene or DME solution, to give the chiral yttrium chloride complexes 1-YCl(dme)0.5C7H80.5C6H6 (30.5C7H80.5C6H6) and 2-YCl(dme)0.375DME0.125THF (40.375DME0.125THF) in good yields, respectively (Schemes 1 and 2). The rare earth metal chloride complexes are important intermediates for the preparation of rare earth catalysts containing the Ln–C or Ln–X (X = heteroatom) bonds, i.e., the chlorine atom in these rare earth metal chloride complexes can be replaced by other groups via metathesis reactions. For example, treatment of 3 with half equiv of 1Na2 in THF gives, after recrystallization from a toluene solution, the binuclear complex 1-Y(thf)-1-Y(thf)-1C7H8 (5C7H8) in 70% yield, which can also be prepared in 54% yield by salt metathesis reaction between YCl3 with 1.5 equiv of 1Na2 (Scheme 1). These complexes are stable in dry nitrogen atmosphere, while they are very sensitive to moisture. They are soluble in organic solvents such as THF, DME, pyridine, toluene, and benzene, but only slightly soluble in n-hexane. They have been characterized by
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G. Zi et al. / Inorganic Chemistry Communications 13 (2010) 445–448
N 1) xs NaH H 2) YCl3 H DME N
N
N
N Y N
1H2
Cl N
3
C 7 H8 /THF
1) xs NaH 2) 0.67 YCl3
1Na2 THF/C 7 H8
N
N N
N thf
N dme
N
N
Y
Y
thf
N
N
N
N
N N
5 Scheme 1.
N
N
N H
1) xs NaH 2) YCl3
N
H N
DME
N
2H 2
Y
N dme Cl N
4 Scheme 2.
various spectroscopic techniques, elemental analyses, and X-ray diffraction analyses (Table 1). Their 1H and 13C NMR spectra indicate that they are symmetric on the NMR time scale, which is consistent with their C2-symmetric structures. The 1H NMR spectra of
3 and 4 support the ratio of DME and ligand 1 or 2 is 1:1, and the 1H NMR spectrum of 5 supports the ratio of THF, toluene and ligand 1 is 2:1:3. Their IR spectra exhibit a weak typical characteristic N@C absorption at about 1620 cm1, and the typical characteristic N–H absorption of the ligands 1H2 and 2H2 [13,14] in the region of 3200–3400 cm1 disappear. The single-crystal X-ray diffraction analyses show that there are two molecules 1-YCl(dme) and one toluene molecule and one benzene molecule for 3, and eight molecules 2-YCl(dme) and three DME molecules and one THF molecule for 4, in the lattice. In each molecule 1-YCl(dme) or 2-YCl(dme), the Y3+ is r-bound to four nitrogen atoms of the ligand 1 or 2 and two oxygen atoms from DME and one chlorine atom in a distorted-pentagonal-bipyramidal geometry (Figs. 1 and 2) with the average distance of Y–N (2.422(4) Å) for 3 and (2.410(5) Å) for 4, and the average distance
Table 1 Crystal data and experimental parameters for compounds 3, 4, and 5. Compound
30.5C7H80.5C6H6
40.375DME0.125THF
5C7H8
Formula Formula weight Crystal system Space group a (Å) b (Å) c (Å) a (deg) b (deg) c (deg) V (Å3) Z Dcalc (g/cm3) l (Mo/Ka)calc (mm1) Size (mm) F (000) 2h range (deg) No. of reflns, collected No. of unique reflns No. of obsd reflns Abscorr (Tmax, Tmin) R Rw wR2 (all data) gof
C81H90N8Cl2O4Y2 1488.34 Orthorhombic P212121 14.735(1) 15.047(1) 16.451(1) 90 90 90 3647.6(2) 4 1.355 1.712 0.32 0.22 0.20 1552 3.66–52.02 30177 7173 (Rint = 0.0864) 5534 0.73, 0.61 0.054 0.103 0.113 1.01
C60H69.5N8Cl2O5.75Y2 1243.46 Monoclinic P1211 14.462(1) 32.499(2) 14.467(1) 90 104.65(1) 90 6568.1(8) 4 1.257 1.890 0.20 0.16 0.14 2574 3.16–54.28 58879 28381 (Rint = 0.0542) 21162 0.78, 0.70 0.060 0.137 0.151 1.01
C105H108N12O2Y2 1747.85 Triclinic P1 11.084(3) 11.095(2) 19.865(5) 76.89(1) 85.72(1) 80.05(1) 2341.8(9) 1 1.239 1.289 0.16 0.10 0.10 916 3.74–52.00 23427 15129 (Rint = 0.0448) 10460 0.88, 0.82 0.058 0.141 0.148 0.93
G. Zi et al. / Inorganic Chemistry Communications 13 (2010) 445–448
Fig. 1. Molecular structure of 3 (thermal ellipsoids drawn at the 35% probability level).
Fig. 2. Molecular structure of 4 (thermal ellipsoids drawn at the 35% probability level).
of Y–O(DME) (2.457(3) Å) for 3 and (2.420(4) Å) for 4, and the distance of Y–Cl (2.577(2) Å) for 3 and (2.595(2) Å) for 4. These
447
structural data are close to those found in [(R)-C20H12(NCHC4H3 N)2]YCl(dme) [7]. The torsion angle between two aryl rings is (73.7(1)°) for 3 and (69.9(6)°) for 4, which are comparable to that (70.1(3)°) found in [(R)-C20H12(NCHC4H3N)2]YCl(dme) [7]. The single-crystal X-ray diffraction analysis shows that there are two molecules 1-Y(thf)-1-Y(thf)-1 and two toluene molecules of solvent in the lattice. Coordination of three ligands 1 around two Y3+ ions results in the formation of the binuclear complex 1Y(thf)-1-Y(thf)-1, in which the two Y3+ ions are linked by one ligand anion 1 (Fig. 3a). Fig. 3b shows that each Y3+ ion is r-bound to six nitrogen atoms from two ligand anions 1 and one oxygen atom from THF in a distorted-pentagonal-bipyramidal with the average distance of Y–N (2.438(6) Å) for Y(1) and Y–N (2.445(6) Å) for Y(2), and the distance of Y–O (2.339(4) Å) for Y(1) and (2.355(4) Å) for Y(2). These structural data are close to those found in 3 and 4 (Table 2). The torsion angles between two naphthyl rings are 69.7(2)°, 72.8(2)° and 79.9(2)°, which are comparable to that found in 3 (73.7(1)°). The polymerization data show that the complex 5 can initiate the ring-opening polymerization (ROP) of racemic-lactide under mild conditions (Table 3). It allows the complete conversion of 1000 equiv of lactide within 3 h at room temperature in toluene at [rac-LA] = 1.0 mol L1 (Table 3, entry 1). However, polymerizations with this yttrium initiator/catalyst proceed much more slowly in THF (Table 3, entry 2), presumably due to the competitive coordination between the monomer and this donor solvent [15]. This difference in activity between toluene and THF solvent is observed more clearly at a lower temperature (Table 3, entries 3 and 4) than at higher temperature (Table 3, entries 5 and 6). The resulting polylactides are all isotactic rich under the conditions examined. Molecular weights and polydispersities of the polymers produced ranged from 34.7 to 70.9 kg mol1 and 1.21 to 1.32, respectively. Our results show that the catalytic activities of 5 resembles that of [(S)-2MeO-C20H20-20 -(NCHC4H3N)]2YN(SiMe3)2}2 [12]. Under similar reaction conditions, no detectable polymerization activity is observed for complexes 3 and 4, even stirred at room temperature for one week. In conclusion, the chiral biaryl-based N4-ligands 1H2 and 2H2 can effectively stabilize the rare earth metal chloride complexes, which offers important intermediates for the preparation of chiral rare earth catalysts containing the M–C or M–X (X = heteroatom) bonds. For example, the chlorine atom in complex 3 can be replaced by sodium amide salt 1Na2 to give a binuclear complex 1Y(thf)-1-Y(thf)-1 (5). The complex 5 is an active catalyst for the ring-opening polymerization of rac-lactide, affording isotactic-rich polylactides.
Fig. 3a. Molecular structure of 5 (thermal ellipsoids drawn at the 35% probability level).
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G. Zi et al. / Inorganic Chemistry Communications 13 (2010) 445–448
Fig. 3b. Core structure of 5 (thermal ellipsoids drawn at the 35% probability level).
Appendix A. Supplementary material
Table 2 Selected bond distances (Å) and bond angles (deg) for compounds 3, 4, and 5. Compound
3
4
5
Y–N (av)
2.422(4)
2.410(5)
Y–O
2.479(3) 2.434(3) 2.577(2) 73.7(1)
2.421(4) 2.419(4) 2.595(2) 69.9(6)
Y(1): Y(2): Y(1): Y(2):
Y–Cl Torsion (aryl–aryl)
2.438(6) 2.445(6) 2.339(4) 2.355(4)
69.7(2) 72.8(2) 79.9(2)
References
Table 3 Polymerization of rac-lactide catalyzed by complex 5.a
O
O O
O O
+
O
complex
O
O
O rac-Lactide
O
O
O
O
O
O
On
m
Isotactic Polylactide b
CCDC 754817, 754818 and 754819 contain the supplementary crystallographic data for this paper. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif. Supplementary data associated with this article can be found, in the online version, at doi:10.1016/j.inoche.2010.01.008.
Entry
T (°C)
Solvent
Conv. (%)
Mn (kg/mol)
Mw/Mnb
Pmc (%)
1 2 3 4 5 6
20 20 10 10 40 40
Toluene THF Toluene THF Toluene THF
100 87 85 45 100 100
70.9 58.2 56.4 34.7 69.2 68.7
1.23 1.27 1.21 1.24 1.32 1.29
72 64 76 67 68 65
a Conditions: precat./LA (mol/mol) = 1/1000; polymerization time, 3 h; solvent, 5 mL; [LA] = 1.0 mol/L. b Measured by GPC (using polystyrene standards in THF). c Pm is the probability of meso linkages between monomer units and is determined from the methine region of the homonuclear decoupling 1H NMR spectrum in CDCl3 at 25 °C.
Acknowledgements This work was supported by the National Natural Science Foundation of China (20972018), and Beijing Municipal Commission of Education.
[1] H.C. Aspinall, Chem. Rev. 102 (2002) 1807–1850. [2] F.T. Edelmann, D.M.M. Freckmann, H. Schumann, Chem. Rev. 102 (2002) 1851–1896. [3] O. Dechy-Cabaret, B. Martin-Vaca, D. Bourissou, Chem. Rev. 104 (2004) 6147–6176. [4] J. Gromada, J.-F. Carpentier, A. Mortreux, Coord. Chem. Rev. 248 (2004) 397–410. [5] W.E. Piers, D.J.H. Emslie, Coord. Chem. Rev. 233–234 (2002) 131–155. [6] G. Zi, Dalton Trans. (2009) 9101–9109. [7] L. Xiang, Q. Wang, H. Song, G. Zi, Organometallics 26 (2007) 5323–5329. [8] Q. Wang, L. Xiang, H. Song, G. Zi, Inorg. Chem. 47 (2008) 4319–4328. [9] G. Zi, L. Xiang, H. Song, Organometallics 27 (2008) 1242–1246. [10] Q. Wang, L. Xiang, G. Zi, J. Organomet. Chem. 693 (2008) 68–76. [11] Q. Wang, L. Xiang, H. Song, G. Zi, J. Organomet. Chem. 694 (2009) 691–696. [12] G. Zi, Q. Wang, L. Xiang, H. Song, Dalton Trans. (2008) 5930–5944. [13] G. Zi, F. Zhang, X. Liu, L. Ai, H. Song, J. Organomet. Chem. (2009), doi:10.1016/ j.jorganchem.2009.12.008. [14] M. Kettunen, C. Vedder, F. Schaper, M. Leskelä, I. Mutikainen, H.-H. Brintzinger, Organometallics 23 (2004) 3800–3807. [15] A. Amgoune, C.M. Thomas, T. Roisnel, J.-F. Carpentier, Chem.-Eur. J. 12 (2006) 169–179.
Contents lists available at ScienceDirect
Inorganic Chemistry Communications journal homepage: www.elsevier.com/locate/inoche
Synthesis, structure, and reactivity of yttrium complexes with chiral biaryldiamine-based N4-ligands Guofu Zi a,*, Li Xiang a, Xue Liu a, Qiuwen Wang a, Haibin Song b a b
Department of Chemistry, Beijing Normal University, Beijing 100875, China State Key Laboratory of Elemento-Organic Chemistry, Nankai University, Tianjin 300071, China
a r t i c l e
i n f o
Article history: Received 17 November 2009 Accepted 14 January 2010 Available online 20 January 2010 Keywords: Chiral N4-ligands Yttrium complexes Synthesis Structure Reactivity
a b s t r a c t The chiral biaryl-based N4-ligands, (R)-5,50 ,6,60 ,7,70 ,8,80 -octahydro-2,20 -bis(pyrrol-2-ylmethyleneamino)1,10 -binaphthyl (1H2) and (S)-2,20 -bis(pyrrol-2-ylmethyleneamino)-6,60 -dimethyl-1,10 -biphenyl (2H2), can effectively stabilize the chiral rare earth metal chloride complexes such as 1-YCl(dme) (3) and 2YCl(dme) (4), which offers important intermediates for the preparation of chiral rare earth catalysts containing the M–C or M–X (X = heteroatom) bonds. For example, treatment of 3 with half equiv of 1Na2 in THF gives the binuclear complex 1-Y(thf)-1-Y(thf)-1 (5) in 70% yield. These complexes have been characterized by various spectroscopic techniques, elemental analyses, and X-ray diffraction analyses. The complex 5 is an active catalyst for the ring-opening polymerization of rac-lactide, affording isotactic-rich polylactides. Ó 2010 Elsevier B.V. All rights reserved.
Chiral rare earth metal complexes based on non-Cp ligands have received growing attention in the past decades [1–6], because the lability of rare earth metal element-ligand bonds and the flexibility of their coordination geometries make these elements highly suitable for use in catalysis. However, the rare earth metal complexes supported by non-Cp ligands usually encounter salt addition, dimerization or ligand redistribution, and these factors also make it difficult to generate well-defined chiral architectures that will lead to efficient enantioselective reactions [1]. Thus, chiral multidentate ligands have attracted considerable interest, which can provide proper sterics and electronics for the rare earth metal center to prevent the side-reactions mentioned above via varying the size and electron affinity of the substituents. Although many rare earth catalysts based on non-Cp ligands have been reported [1–6], the development of new chiral rare earth catalysts is a desirable and challenging goal. In recent years, we have developed a series of rare earth complexes based on chiral non-Cp multidentate ligands, and they have shown that they are useful catalysts for a range of transformations [7–12]. In our attempt to further explore the chiral non-Cp ligand system and their application in rare earth chemistry, we have recently extended our research work to chiral tetradentate N4-ligands, (R)-5,50 ,6,60 ,7,70 ,8,80 -octahydro-2,20 -bis (pyrrol-2-ylmethyleneamino)-1,10 -binaphthyl (1H2) and (S)-2,20 bis(pyrrol-2-ylmethyleneamino)-6,60 -dimethyl-1,10 -biphenyl (2H2) [13,14], and found they are useful to stabilize the rare earth metal chloride complexes, which are important intermediates for the * Corresponding author. Tel.: +86 10 5880 7843; fax: +86 10 5880 2075. E-mail address: [email protected] (G. Zi). 1387-7003/$ - see front matter Ó 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.inoche.2010.01.008
preparation of chiral rare earth catalysts containing the M–C or M–X (X = heteroatom) bonds. We report herein on some observation concerning the ligands 1H2 and 2H2 use in rare earth chemistry. Deprotonation of the chiral ligands (R)-5,50 ,6,60 ,7,70 ,8,80 -octahydro-2,20 -bis(pyrrol-2-ylmethyleneamino)-1,10 -binaphthyl (1H2) and (S)-2,20 -bis(pyrrol-2-ylmethyleneamino)-6,60 -dimethyl-1,10 biphenyl (2H2) are achieved by reaction with an excess of NaH in DME or THF. The resulting disodium salt 1Na2 or 2Na2 thus formed is reacted with 1 equiv of YCl3 in a mixed solution of DME and toluene or a solution of THF, after recrystallization from a benzene or DME solution, to give the chiral yttrium chloride complexes 1-YCl(dme)0.5C7H80.5C6H6 (30.5C7H80.5C6H6) and 2-YCl(dme)0.375DME0.125THF (40.375DME0.125THF) in good yields, respectively (Schemes 1 and 2). The rare earth metal chloride complexes are important intermediates for the preparation of rare earth catalysts containing the Ln–C or Ln–X (X = heteroatom) bonds, i.e., the chlorine atom in these rare earth metal chloride complexes can be replaced by other groups via metathesis reactions. For example, treatment of 3 with half equiv of 1Na2 in THF gives, after recrystallization from a toluene solution, the binuclear complex 1-Y(thf)-1-Y(thf)-1C7H8 (5C7H8) in 70% yield, which can also be prepared in 54% yield by salt metathesis reaction between YCl3 with 1.5 equiv of 1Na2 (Scheme 1). These complexes are stable in dry nitrogen atmosphere, while they are very sensitive to moisture. They are soluble in organic solvents such as THF, DME, pyridine, toluene, and benzene, but only slightly soluble in n-hexane. They have been characterized by
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G. Zi et al. / Inorganic Chemistry Communications 13 (2010) 445–448
N 1) xs NaH H 2) YCl3 H DME N
N
N
N Y N
1H2
Cl N
3
C 7 H8 /THF
1) xs NaH 2) 0.67 YCl3
1Na2 THF/C 7 H8
N
N N
N thf
N dme
N
N
Y
Y
thf
N
N
N
N
N N
5 Scheme 1.
N
N
N H
1) xs NaH 2) YCl3
N
H N
DME
N
2H 2
Y
N dme Cl N
4 Scheme 2.
various spectroscopic techniques, elemental analyses, and X-ray diffraction analyses (Table 1). Their 1H and 13C NMR spectra indicate that they are symmetric on the NMR time scale, which is consistent with their C2-symmetric structures. The 1H NMR spectra of
3 and 4 support the ratio of DME and ligand 1 or 2 is 1:1, and the 1H NMR spectrum of 5 supports the ratio of THF, toluene and ligand 1 is 2:1:3. Their IR spectra exhibit a weak typical characteristic N@C absorption at about 1620 cm1, and the typical characteristic N–H absorption of the ligands 1H2 and 2H2 [13,14] in the region of 3200–3400 cm1 disappear. The single-crystal X-ray diffraction analyses show that there are two molecules 1-YCl(dme) and one toluene molecule and one benzene molecule for 3, and eight molecules 2-YCl(dme) and three DME molecules and one THF molecule for 4, in the lattice. In each molecule 1-YCl(dme) or 2-YCl(dme), the Y3+ is r-bound to four nitrogen atoms of the ligand 1 or 2 and two oxygen atoms from DME and one chlorine atom in a distorted-pentagonal-bipyramidal geometry (Figs. 1 and 2) with the average distance of Y–N (2.422(4) Å) for 3 and (2.410(5) Å) for 4, and the average distance
Table 1 Crystal data and experimental parameters for compounds 3, 4, and 5. Compound
30.5C7H80.5C6H6
40.375DME0.125THF
5C7H8
Formula Formula weight Crystal system Space group a (Å) b (Å) c (Å) a (deg) b (deg) c (deg) V (Å3) Z Dcalc (g/cm3) l (Mo/Ka)calc (mm1) Size (mm) F (000) 2h range (deg) No. of reflns, collected No. of unique reflns No. of obsd reflns Abscorr (Tmax, Tmin) R Rw wR2 (all data) gof
C81H90N8Cl2O4Y2 1488.34 Orthorhombic P212121 14.735(1) 15.047(1) 16.451(1) 90 90 90 3647.6(2) 4 1.355 1.712 0.32 0.22 0.20 1552 3.66–52.02 30177 7173 (Rint = 0.0864) 5534 0.73, 0.61 0.054 0.103 0.113 1.01
C60H69.5N8Cl2O5.75Y2 1243.46 Monoclinic P1211 14.462(1) 32.499(2) 14.467(1) 90 104.65(1) 90 6568.1(8) 4 1.257 1.890 0.20 0.16 0.14 2574 3.16–54.28 58879 28381 (Rint = 0.0542) 21162 0.78, 0.70 0.060 0.137 0.151 1.01
C105H108N12O2Y2 1747.85 Triclinic P1 11.084(3) 11.095(2) 19.865(5) 76.89(1) 85.72(1) 80.05(1) 2341.8(9) 1 1.239 1.289 0.16 0.10 0.10 916 3.74–52.00 23427 15129 (Rint = 0.0448) 10460 0.88, 0.82 0.058 0.141 0.148 0.93
G. Zi et al. / Inorganic Chemistry Communications 13 (2010) 445–448
Fig. 1. Molecular structure of 3 (thermal ellipsoids drawn at the 35% probability level).
Fig. 2. Molecular structure of 4 (thermal ellipsoids drawn at the 35% probability level).
of Y–O(DME) (2.457(3) Å) for 3 and (2.420(4) Å) for 4, and the distance of Y–Cl (2.577(2) Å) for 3 and (2.595(2) Å) for 4. These
447
structural data are close to those found in [(R)-C20H12(NCHC4H3 N)2]YCl(dme) [7]. The torsion angle between two aryl rings is (73.7(1)°) for 3 and (69.9(6)°) for 4, which are comparable to that (70.1(3)°) found in [(R)-C20H12(NCHC4H3N)2]YCl(dme) [7]. The single-crystal X-ray diffraction analysis shows that there are two molecules 1-Y(thf)-1-Y(thf)-1 and two toluene molecules of solvent in the lattice. Coordination of three ligands 1 around two Y3+ ions results in the formation of the binuclear complex 1Y(thf)-1-Y(thf)-1, in which the two Y3+ ions are linked by one ligand anion 1 (Fig. 3a). Fig. 3b shows that each Y3+ ion is r-bound to six nitrogen atoms from two ligand anions 1 and one oxygen atom from THF in a distorted-pentagonal-bipyramidal with the average distance of Y–N (2.438(6) Å) for Y(1) and Y–N (2.445(6) Å) for Y(2), and the distance of Y–O (2.339(4) Å) for Y(1) and (2.355(4) Å) for Y(2). These structural data are close to those found in 3 and 4 (Table 2). The torsion angles between two naphthyl rings are 69.7(2)°, 72.8(2)° and 79.9(2)°, which are comparable to that found in 3 (73.7(1)°). The polymerization data show that the complex 5 can initiate the ring-opening polymerization (ROP) of racemic-lactide under mild conditions (Table 3). It allows the complete conversion of 1000 equiv of lactide within 3 h at room temperature in toluene at [rac-LA] = 1.0 mol L1 (Table 3, entry 1). However, polymerizations with this yttrium initiator/catalyst proceed much more slowly in THF (Table 3, entry 2), presumably due to the competitive coordination between the monomer and this donor solvent [15]. This difference in activity between toluene and THF solvent is observed more clearly at a lower temperature (Table 3, entries 3 and 4) than at higher temperature (Table 3, entries 5 and 6). The resulting polylactides are all isotactic rich under the conditions examined. Molecular weights and polydispersities of the polymers produced ranged from 34.7 to 70.9 kg mol1 and 1.21 to 1.32, respectively. Our results show that the catalytic activities of 5 resembles that of [(S)-2MeO-C20H20-20 -(NCHC4H3N)]2YN(SiMe3)2}2 [12]. Under similar reaction conditions, no detectable polymerization activity is observed for complexes 3 and 4, even stirred at room temperature for one week. In conclusion, the chiral biaryl-based N4-ligands 1H2 and 2H2 can effectively stabilize the rare earth metal chloride complexes, which offers important intermediates for the preparation of chiral rare earth catalysts containing the M–C or M–X (X = heteroatom) bonds. For example, the chlorine atom in complex 3 can be replaced by sodium amide salt 1Na2 to give a binuclear complex 1Y(thf)-1-Y(thf)-1 (5). The complex 5 is an active catalyst for the ring-opening polymerization of rac-lactide, affording isotactic-rich polylactides.
Fig. 3a. Molecular structure of 5 (thermal ellipsoids drawn at the 35% probability level).
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G. Zi et al. / Inorganic Chemistry Communications 13 (2010) 445–448
Fig. 3b. Core structure of 5 (thermal ellipsoids drawn at the 35% probability level).
Appendix A. Supplementary material
Table 2 Selected bond distances (Å) and bond angles (deg) for compounds 3, 4, and 5. Compound
3
4
5
Y–N (av)
2.422(4)
2.410(5)
Y–O
2.479(3) 2.434(3) 2.577(2) 73.7(1)
2.421(4) 2.419(4) 2.595(2) 69.9(6)
Y(1): Y(2): Y(1): Y(2):
Y–Cl Torsion (aryl–aryl)
2.438(6) 2.445(6) 2.339(4) 2.355(4)
69.7(2) 72.8(2) 79.9(2)
References
Table 3 Polymerization of rac-lactide catalyzed by complex 5.a
O
O O
O O
+
O
complex
O
O
O rac-Lactide
O
O
O
O
O
O
On
m
Isotactic Polylactide b
CCDC 754817, 754818 and 754819 contain the supplementary crystallographic data for this paper. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif. Supplementary data associated with this article can be found, in the online version, at doi:10.1016/j.inoche.2010.01.008.
Entry
T (°C)
Solvent
Conv. (%)
Mn (kg/mol)
Mw/Mnb
Pmc (%)
1 2 3 4 5 6
20 20 10 10 40 40
Toluene THF Toluene THF Toluene THF
100 87 85 45 100 100
70.9 58.2 56.4 34.7 69.2 68.7
1.23 1.27 1.21 1.24 1.32 1.29
72 64 76 67 68 65
a Conditions: precat./LA (mol/mol) = 1/1000; polymerization time, 3 h; solvent, 5 mL; [LA] = 1.0 mol/L. b Measured by GPC (using polystyrene standards in THF). c Pm is the probability of meso linkages between monomer units and is determined from the methine region of the homonuclear decoupling 1H NMR spectrum in CDCl3 at 25 °C.
Acknowledgements This work was supported by the National Natural Science Foundation of China (20972018), and Beijing Municipal Commission of Education.
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