- Email: [email protected]
Ligand chirality-controlled selective formation of mono- and dinuclear copper complexes
www.elsevier.com/locate/ica Inorganica Chimica Acta 331 (2002) 194– 198
Ligand chirality-controlled selective formation of mono- and dinuclear copper complexes Xiang-Ge Zhou a, Jie-Sheng Huang a, Zhong-Yuan Zhou b, Kung-Kai Cheung a, Chi-Ming Che a,* b
a Department of Chemistry, The Uni6ersity of Hong Kong, Pokfulam Road, Hong Kong, People’s Republic of China Department of Applied Biology and Chemical Technology, The Hong Kong Polytechnic Uni6ersity, Hung Hom, Kowloon, Hong Kong, People’s Republic of China
Received 13 July 2001; accepted 26 November 2001 Dedicated to Professor A.G. Sykes on the occasion of his 65th birthday
Abstract Reaction of copper(II) acetate with the (S)-enantiomer of a tridentate binaphthyl Schiff base ligand, 2-(3,5-dichloro-2-hydroxybenzylideneamino)-2%-hydroxy-1,1%-binaphthyl (H2L), in methanol afforded mononuclear copper(II) complex [CuII(HL)2] ((S,S)1) in 52% isolated yield. The same reaction gave dinuclear copper(II) complex [CuII 2 (L)2] ((R,S)-2) in 73% isolated yield when racemic-H2L was used instead of (S)-H2L. Both complexes (S,S)-1 and (R,S)-2 were characterized by elemental analysis, mass spectrometry, and X-ray crystallography. The present work highlights the functioning of ligand chirality as a ‘switch’ for selective formation of mono- and dinuclear metal complexes. © 2002 Elsevier Science B.V. All rights reserved. Keywords: Chirality; Copper complexes; Schiff base ligands; Crystal structures
1. Introduction The selective formation of mono- and dinuclear metal complexes is an important issue in synthetic chemistry, ranging from the synthesis of complexes with metal –ligand multiple bonds [1] to the synthesis of model compounds for the active sites of enzymes [2], and to the synthesis of homogenous catalysts in metalmediated catalysis [3]. A common strategy in the literature lies in the manipulation of steric hindrance of the ligands involved. For example, to selectively prepare a mononuclear complex by destabilizing its dinuclear counterparts, almost all efforts are directed to functionalize the ligands with sterically demanding substituents. Interestingly, recent work by Noyori and co-workers demonstrated that the stability of a dinuclear zinc complex is significantly affected by the chirality of the ligand in the complex [4]. Herein we report on the * Corresponding author. Tel.: + 852-2859 2154; fax: + 852-2857 1586. E-mail address: [email protected] (C.-M. Che).
syntheses and X-ray crystal structures of a mononuclear copper complex, [CuII(HL)2] ((S,S)-1), and a dinuclear copper complex, [CuII 2 (L)2] ((R,S)-2), which were isolated from reactions of copper(II) acetate with the (S)-enantiomer and the racemic sample, respectively, of the same tridentate binaphthyl Schiff base ligand 2-(3,5dichloro-2-hydroxybenzylideneamino)-2%-hydroxy-1,1%binaphthyl (H2L), providing a unique case where manipulation of ligand chirality results in the selective formation of a mono- or dinuclear metal complexes.
2. Experimental
2.1. General procedure Copper(II) acetate (98%) was purchased from Aldrich. All solvents were of AR grade and were used as received. The tridentate Schiff base ligand H2L was prepared by Carreira’s method [5]. FAB mass spectra were measured on a Finnigan MAT95 mass spectrome-
0020-1693/02/$ - see front matter © 2002 Elsevier Science B.V. All rights reserved. PII: S 0 0 2 0 - 1 6 9 3 ( 0 1 ) 0 0 8 0 6 - 4
X.-G. Zhou et al. / Inorganica Chimica Acta 331 (2002) 194–198
ter. ESR spectrum was recorded on a Bruker EMX100 ESR spectrometer. Elemental analyses were performed at the Institute of Chemistry, the Chinese Academy of Sciences.
2.2. Preparation of [Cu II(HL)2] ((S,S) -1) To a solution of (S)-H2L (57 mg, 0.12 mmol) in methanol (20 ml) copper(II) acetate (12 mg, 0.066 mmol) in the same solvent (10 ml) was added. The mixture was stirred at room temperature (r.t.) for 2 h, leading to the formation of a homogenous solution. After removal of the solvent, the residue was purified by recrystallization from dichloromethane/hexane. Yield: 52%. FAB MS; m/z: 978 (M+). ESR (298 K): g =2.053. Anal. Calc. for C54H32Cl4N2O4Cu: C, 66.30; H, 3.30; N, 2.86. Found: C, 66.09; H, 3.36; N, 2.62%.
2.3. Preparation of [Cu II 2 (L)2] ((R,S) -2) To a solution of racemic-H2L (57 mg, 0.12 mmol) in methanol (20 ml) copper(II) acetate (22 mg, 0.12 mmol) in the same solvent (10 ml) was added. After the mixture was stirred at r.t. for 2 h, a green precipitate was formed. The precipitate was collected by filtration, washed with a small amount of methanol and water, and dried. Yield: 73%. FAB MS; m/z: 1040 (M+). Anal. Calc. for C54H30Cl4N2O4Cu2: C, 62.38; H, 2.91; N, 2.69. Found: C, 62.31; H, 2.90; N, 2.46%.
2.4. X-ray structure determination Single crystals of (S,S)-1·2H2O (0.42 ×0.32 × 0.28 mm) and (R,S)-2·4CH2Cl2 (0.25 ×0.25 ×0.07 mm) were obtained from slow evaporation of the solutions of the complexes in dichloromethane/methanol exposed to the atmosphere at r.t. The data for (S,S)-1·2H2O were collected on a Siemens P4 diffractometer, and the structure was solved by direct methods and refined by full-matrix least-squares on F 2 (SHELXL). In the case of
195
(R,S)-2·4CH2Cl2, data collection was carried out on a MAR diffractometer with a 300-mm image plate detector; the structure was solved by direct methods and expanded by Fourier method and refined by full-matrix least-squares on F (TEXSAN). For both crystals, a graphite-monochromatized Mo Ka radiation (u= 0.71073 A, ) was used in the data collection. All non-hydrogen atoms were refined anisotropically, whereas hydrogen atoms were located at calculated positions and not refined.
3. Results and discussion
3.1. Syntheses and characterization Treatment of copper(II) acetate with 2 equiv. of (S)-H2L in methanol at room temperature for 2 h led to formation of a homogenous solution, workup of which gave the mononuclear complex (S,S)-1 as a crystalline solid in 52% yield (reaction (1) in Scheme 1). Interestingly, when copper(II) acetate was treated with 1 equiv. of racemic-H2L in methanol, the reaction resulted in the formation of the dinuclear species (R,S)-2 as a precipitate in 73% yield (reaction (2) in Scheme 1). This kind of dinuclear copper complex could not be isolated from the reaction of copper(II) acetate with 1 equiv. of (S)-H2L (which again afforded (S,S)-1 rather than (S,S)-2 as the sole isolable copper complex containing L). Satisfactory analytical results were obtained for both (S,S)-1 and (R,S)-2. Complex (S,S)-1 is paramagnetic, exhibiting an ESR spectrum similar to mononuclear copper(II) complexes of tetradentate Schiff bases [6]. On the contrary, complex (R,S)-2 is diamagnetic, like a previously reported dinuclear copper(II) complex with analogous Cu(m-OR)2Cu bridges [7]. For either (S,S)-1 or (R,S)-2, the FAB mass spectrum shows a prominent cluster peak assignable to the respective parent ion.
3.2. X-ray crystal structures
Scheme 1.
The crystal data and structure refinement for (S,S)1·2H2O and (R,S)-2·4CH2Cl2 are summarized in Table 1. Figs. 1 and 2 depict their ORTEP drawings with the atom-numbering schemes, respectively. Selected bond lengths and angles are given in Table 2. Complex (S,S)-1 shows no element of symmetry in the solid state; its copper atom adopts a distorted tetrahedral geometry, with the N1Cu1O1 and N2Cu1O2 planes constituting a dihedral angle of 30°. The oxygen atom of one of the water molecules in (S,S)-1·2H2O is hydrogen bonded to the O(3) and O(4) atoms of (S,S)-1, with the O···O distances of 2.84 and 2.89 A, , respectively. The absolute structure
X.-G. Zhou et al. / Inorganica Chimica Acta 331 (2002) 194–198
196
Table 1 Crystal data and structure refinement parameters for (S,S)-1 and (R,S)-2
Empirical formula Formula weight Temperature (K) Crystal system Space group Unit cell dimensions a (A, ) b (A, ) c (A, ) h (°) i (°) k (°) V (A, 3) Z Dcalc (g cm−3) F(000) v (Mo Ka) (cm−1) Number of collected reflections Number of unique reflections Number of parameters R indices
(S,S)-1·2H2O
(R,S)-2·4CH2Cl2
C54H36Cl4N2O6Cu 1014.19 294 tetragonal P43212
C58H38Cl12N2O4Cu2 1379.48 301 monoclinic P21/c
19.884(3) 19.884(3) 25.964(5) 90 90 90 10 266(3) 8 1.312 4152 6.83 10 023
10.953(2) 16.039(3) 16.785(3) 90 95.64(2) 90 2934.4(9) 2 1.561 1388 13.18 24 382
9073
5552
610 R1 = 0.0550, wR2 = 0.16 1.089 0.00
352 R= 0.072, wR=0.097 1.73
Goodness-of-fit Absolute structure parameter Largest difference peak 0.629 and −0.306 and hole (e A, −3)
0.86 and −0.91
Fig. 1. ORTEP drawing and the atom-numbering scheme for (S,S)1·2H2O. Hydrogen atoms and the solvent molecules are omitted for clarity.
parameter of (S,S)-1 (Table 1) is consistent with its chirality. Complex (R,S)-2 is centrosymmetric with two distorted tetrahedral copper centers and a planar Cu(1), O(2), Cu(1*), O(2*) unit. The N(1), O(1), Cu(1), N(1*), O(1*), Cu(1*) atoms are virtually co-planar, and the
plane composed of these six atoms makes an angle of 20° with the Cu(1), O(2), Cu(1*), O(2*) plane. The Cu(1)Cu(1*) distance is 3.022(1) A, . The CuN and CuO distances in (S,S)-1 and (R,S)-2 are normal. The
Fig. 2. ORTEP drawing and the atom-numbering scheme for (R,S)2·4CH2Cl2. Hydrogen atoms and the solvent molecules are omitted for clarity. Table 2 Selected bond lengths (A, ) and bond angles (°) for (S,S)-1 and (R,S)-2 (S,S)-1 Bond lengths Cu(1)O(1) Cu(1)N(1) C(27)O(1) C(1)O(3) C(20)N(1) C(28)N(2)
1.899(1) 1.986(2) 1.304(2) 1.332(2) 1.447(2) 1.470(2)
Cu(1)O(2) Cu(1)N(2) C(54)O(2) C(47)O(4) C(21)N(1) C(48)N(2)
1.892(1) 1.978(2) 1.304(2) 1.354(3) 1.289(2) 1.273(2)
Bond angles O(1)Cu(1)N(1) O(1)Cu(1)N(2) N(1)Cu(1)O(2) C(27)O(1)Cu(1) C(20)N(1)Cu(1) C(28)N(2)Cu(1)
92.89(6) 92.25(6) 90.91(6) 128.1(1) 120.9(1) 117.5(1)
O(1)Cu(1)O(2) N(1)Cu(1)N(2) N(2)Cu(1)O(2) C(54)O(2)Cu(1) C(21)N(1)Cu(1) C(48)N(2)Cu(1)
155.38(6) 161.36(6) 91.86(6) 129.4(1) 123.1(1) 125.6(1)
(R,S)-2 Bond lengths Cu(1)O(1) Cu(1)O(2) C(1)O(1) C(7)N(1)
1.877(4) 1.938(4) 1.324(7) 1.299(7)
Cu(1)O(2*) Cu(1)N(1) C(27)O(2) C(8)N(1)
1.944(4) 1.940(5) 1.354(7) 1.459(7)
Bond angles O(1)Cu(1)N(1) O(1)Cu(1)O(2) N(1)Cu(1)O(2*) Cu(1)O(2)Cu(1*) C(27)O(2)Cu(1) C(7)N(1)Cu(1)
94.4(2) 164.7(2) 164.3(2) 102.2(2) 119.5(3) 123.8(4)
O(1)Cu(1)O(2*) 93.7(2) N(1)Cu(1)O(2) 97.0(2) O(2)Cu(1)O(2*) 77.8(2) C(1)O(1)Cu(1) 126.5(4) C(27)O(2)Cu(1*) 125.6(3) C(8)N(1)Cu(1) 117.6(4)
X.-G. Zhou et al. / Inorganica Chimica Acta 331 (2002) 194–198
Fig. 3. Model structures for: (a) (R,S)-1 and (b) (R,R)-2 with the coordination geometry of copper ion(s) identical with that of (S,S)-1 and (R,S)-2, respectively. The distances (A, ) between non-bonded atoms shorter than the sums of their van der Waals radii (H 1.2, O 1.40, Cl 1.80 A, ) are indicated. The inset in (b) shows the NOCu(mO%)2CuNO moiety viewed along the O%O% axis. All CH bond distances are set to be 0.96 A, .
dihedral angles of the binaphthyl units in these complexes range from 72 to 84°.
3.3. Functioning of ligand chirality as a ‘switch’ for selecti6e formation of mono- and dinuclear metal complexes The synthesis of (S,S)-1 and (R,S)-2 as shown in Scheme 1 demonstrates that the reactions of a metal compound with the same ligand in enantiopure and racemic forms generate mono- and dinuclear metal complexes, respectively, indicating that ligand chirality can function as a ‘switch’ for the selecti6e formation of mono- and dinuclear metal complexes. This is significantly different from a recent report by Kanemasa et al. [3] that reactions of a metal compound with enantiopure and racemic ligands afford mononuclear metal complexes of different compositions. The present work also contrasts with the recent work by Sadler and co-workers [8], who reported that reaction of Cp2TiCl2 with a commercial hexadentate amino acid ligand affords a mixture of mono- and dinuclear titanium complexes, with the mono- and dinuclear species (which contain the racemic and meso ligands, respectively) separated from each other by controlling the pH of the reaction mixture. To rationalize the selective formation of (S,S)-1 and (R,S)-2 from the reactions as shown in Scheme 1, we build models for the species (R,S)-1, (R,R)-2 and (S,S)2, which were not observed from these reactions, by using CS CHEM3D Pro 4.0 software package on the basis of the crystal structures of (S,S)-1 and (R,S)-2. The model structures of (R,S)-1 and (R,R)-2 are de-
197
picted in Fig. 3. Note that the structure of (S,S)-2 is identical with that of (R,R)-2 and is not shown here. Inspection of the model structure of (R,S)-1 reveals severe strains between the indicated hydrogen and chlorine or oxygen atoms (Fig. 3(a)). Regarding the model structures of (R,R)-2 (Fig. 3(b)) and (S,S)-2, their NOCu(m-O%)2CuNO moieties are substantially distorted compared with the same moiety in the stable complex (R,S)-2. As described above, the structure of (R,S)-2 features a planar Cu(m-O%)2Cu arrangement with essentially co-planar terminal NCuO planes; however, the two terminal NCuO planes in either (R,R)-2 or (S,S)-2 form a dihedral angle of 36° and cannot accommodate a co-planar geometry when a planar Cu(m-O%)2Cu arrangement is maintained (Fig. 3(b), inset). Such distortions of the NOCu(m-O%)2CuNO moieties in (R,R)-2 and (S,S)-2 may considerably destabilize the two species. Further, both (R,R)-2 and (S,S)-2 suffer from significant strains between the hydrogen and oxygen atoms as indicated, for example, in Fig. 3(b). In contrast, no strains as observed for (R,S)1, (R,R)-2 and (S,S)-2 exist in the structures of (S,S)-1 and (R,S)-2. These might be the reasons why the dinuclear species (S,S)-2 was not isolated from reaction (1) in Scheme 1 and why (R,S)-2 rather than (S,S)-2/ (R,R)-2/(R,S)-1 was isolated from reaction (2) in the same scheme.
4. Supplementary material Tables of final coordinates, bond lengths, bond angles, and anisotropic displacement parameters of (S,S)1·2H2O and (R,S)-2·4CH2Cl2 are available from the authors on request.
Acknowledgements This work was supported by The University of Hong Kong, the Hong Kong Research Grants Council [PolyU 1/97C], and the Hong Kong University Foundation.
References [1] W.A. Nugent, J.M. Mayer, Metal Ligand Multiple Bonds, Wiley, New York, 1988. [2] R.H. Holm, P. Kennepohl, E.I. Solomon, Chem. Rev. 96 (1996) 2239. [3] S. Kanemasa, Y. Oderaotoshi, S. Sakaguchi, H. Yamamoto, J. Tanaka, E. Wada, D.P. Curran, J. Am. Chem. Soc. 120 (1998) 3074. [4] M. Kitamura, M. Yamakawa, H. Oka, S. Suga, R. Noyori, Chem. Eur. J. 2 (1996) 1173.
198
X.-G. Zhou et al. / Inorganica Chimica Acta 331 (2002) 194–198
[5] E.M. Carreira, R.A. Singer, W. Lee, J. Am. Chem. Soc. 116 (1994) 8837. [6] M. Valko, R. Boca, R. Klement, J. Kozisek, M. Mazur, P. Pelikan, H. Morris, H. Elias, L. Muller, Polyhedron 16 (1997) 903.
[7] J.S. DeCourcy, T.N. Waters, N.F. Curtis, J. Chem. Soc., Chem. Commun. (1977) 572. [8] M. Guo, H. Sun, S. Bihari, J.A. Parkinson, R.O. Gould, S. Parsons, P.J. Sadler, Inorg. Chem. 39 (2000) 206.
Ligand chirality-controlled selective formation of mono- and dinuclear copper complexes Xiang-Ge Zhou a, Jie-Sheng Huang a, Zhong-Yuan Zhou b, Kung-Kai Cheung a, Chi-Ming Che a,* b
a Department of Chemistry, The Uni6ersity of Hong Kong, Pokfulam Road, Hong Kong, People’s Republic of China Department of Applied Biology and Chemical Technology, The Hong Kong Polytechnic Uni6ersity, Hung Hom, Kowloon, Hong Kong, People’s Republic of China
Received 13 July 2001; accepted 26 November 2001 Dedicated to Professor A.G. Sykes on the occasion of his 65th birthday
Abstract Reaction of copper(II) acetate with the (S)-enantiomer of a tridentate binaphthyl Schiff base ligand, 2-(3,5-dichloro-2-hydroxybenzylideneamino)-2%-hydroxy-1,1%-binaphthyl (H2L), in methanol afforded mononuclear copper(II) complex [CuII(HL)2] ((S,S)1) in 52% isolated yield. The same reaction gave dinuclear copper(II) complex [CuII 2 (L)2] ((R,S)-2) in 73% isolated yield when racemic-H2L was used instead of (S)-H2L. Both complexes (S,S)-1 and (R,S)-2 were characterized by elemental analysis, mass spectrometry, and X-ray crystallography. The present work highlights the functioning of ligand chirality as a ‘switch’ for selective formation of mono- and dinuclear metal complexes. © 2002 Elsevier Science B.V. All rights reserved. Keywords: Chirality; Copper complexes; Schiff base ligands; Crystal structures
1. Introduction The selective formation of mono- and dinuclear metal complexes is an important issue in synthetic chemistry, ranging from the synthesis of complexes with metal –ligand multiple bonds [1] to the synthesis of model compounds for the active sites of enzymes [2], and to the synthesis of homogenous catalysts in metalmediated catalysis [3]. A common strategy in the literature lies in the manipulation of steric hindrance of the ligands involved. For example, to selectively prepare a mononuclear complex by destabilizing its dinuclear counterparts, almost all efforts are directed to functionalize the ligands with sterically demanding substituents. Interestingly, recent work by Noyori and co-workers demonstrated that the stability of a dinuclear zinc complex is significantly affected by the chirality of the ligand in the complex [4]. Herein we report on the * Corresponding author. Tel.: + 852-2859 2154; fax: + 852-2857 1586. E-mail address: [email protected] (C.-M. Che).
syntheses and X-ray crystal structures of a mononuclear copper complex, [CuII(HL)2] ((S,S)-1), and a dinuclear copper complex, [CuII 2 (L)2] ((R,S)-2), which were isolated from reactions of copper(II) acetate with the (S)-enantiomer and the racemic sample, respectively, of the same tridentate binaphthyl Schiff base ligand 2-(3,5dichloro-2-hydroxybenzylideneamino)-2%-hydroxy-1,1%binaphthyl (H2L), providing a unique case where manipulation of ligand chirality results in the selective formation of a mono- or dinuclear metal complexes.
2. Experimental
2.1. General procedure Copper(II) acetate (98%) was purchased from Aldrich. All solvents were of AR grade and were used as received. The tridentate Schiff base ligand H2L was prepared by Carreira’s method [5]. FAB mass spectra were measured on a Finnigan MAT95 mass spectrome-
0020-1693/02/$ - see front matter © 2002 Elsevier Science B.V. All rights reserved. PII: S 0 0 2 0 - 1 6 9 3 ( 0 1 ) 0 0 8 0 6 - 4
X.-G. Zhou et al. / Inorganica Chimica Acta 331 (2002) 194–198
ter. ESR spectrum was recorded on a Bruker EMX100 ESR spectrometer. Elemental analyses were performed at the Institute of Chemistry, the Chinese Academy of Sciences.
2.2. Preparation of [Cu II(HL)2] ((S,S) -1) To a solution of (S)-H2L (57 mg, 0.12 mmol) in methanol (20 ml) copper(II) acetate (12 mg, 0.066 mmol) in the same solvent (10 ml) was added. The mixture was stirred at room temperature (r.t.) for 2 h, leading to the formation of a homogenous solution. After removal of the solvent, the residue was purified by recrystallization from dichloromethane/hexane. Yield: 52%. FAB MS; m/z: 978 (M+). ESR (298 K): g =2.053. Anal. Calc. for C54H32Cl4N2O4Cu: C, 66.30; H, 3.30; N, 2.86. Found: C, 66.09; H, 3.36; N, 2.62%.
2.3. Preparation of [Cu II 2 (L)2] ((R,S) -2) To a solution of racemic-H2L (57 mg, 0.12 mmol) in methanol (20 ml) copper(II) acetate (22 mg, 0.12 mmol) in the same solvent (10 ml) was added. After the mixture was stirred at r.t. for 2 h, a green precipitate was formed. The precipitate was collected by filtration, washed with a small amount of methanol and water, and dried. Yield: 73%. FAB MS; m/z: 1040 (M+). Anal. Calc. for C54H30Cl4N2O4Cu2: C, 62.38; H, 2.91; N, 2.69. Found: C, 62.31; H, 2.90; N, 2.46%.
2.4. X-ray structure determination Single crystals of (S,S)-1·2H2O (0.42 ×0.32 × 0.28 mm) and (R,S)-2·4CH2Cl2 (0.25 ×0.25 ×0.07 mm) were obtained from slow evaporation of the solutions of the complexes in dichloromethane/methanol exposed to the atmosphere at r.t. The data for (S,S)-1·2H2O were collected on a Siemens P4 diffractometer, and the structure was solved by direct methods and refined by full-matrix least-squares on F 2 (SHELXL). In the case of
195
(R,S)-2·4CH2Cl2, data collection was carried out on a MAR diffractometer with a 300-mm image plate detector; the structure was solved by direct methods and expanded by Fourier method and refined by full-matrix least-squares on F (TEXSAN). For both crystals, a graphite-monochromatized Mo Ka radiation (u= 0.71073 A, ) was used in the data collection. All non-hydrogen atoms were refined anisotropically, whereas hydrogen atoms were located at calculated positions and not refined.
3. Results and discussion
3.1. Syntheses and characterization Treatment of copper(II) acetate with 2 equiv. of (S)-H2L in methanol at room temperature for 2 h led to formation of a homogenous solution, workup of which gave the mononuclear complex (S,S)-1 as a crystalline solid in 52% yield (reaction (1) in Scheme 1). Interestingly, when copper(II) acetate was treated with 1 equiv. of racemic-H2L in methanol, the reaction resulted in the formation of the dinuclear species (R,S)-2 as a precipitate in 73% yield (reaction (2) in Scheme 1). This kind of dinuclear copper complex could not be isolated from the reaction of copper(II) acetate with 1 equiv. of (S)-H2L (which again afforded (S,S)-1 rather than (S,S)-2 as the sole isolable copper complex containing L). Satisfactory analytical results were obtained for both (S,S)-1 and (R,S)-2. Complex (S,S)-1 is paramagnetic, exhibiting an ESR spectrum similar to mononuclear copper(II) complexes of tetradentate Schiff bases [6]. On the contrary, complex (R,S)-2 is diamagnetic, like a previously reported dinuclear copper(II) complex with analogous Cu(m-OR)2Cu bridges [7]. For either (S,S)-1 or (R,S)-2, the FAB mass spectrum shows a prominent cluster peak assignable to the respective parent ion.
3.2. X-ray crystal structures
Scheme 1.
The crystal data and structure refinement for (S,S)1·2H2O and (R,S)-2·4CH2Cl2 are summarized in Table 1. Figs. 1 and 2 depict their ORTEP drawings with the atom-numbering schemes, respectively. Selected bond lengths and angles are given in Table 2. Complex (S,S)-1 shows no element of symmetry in the solid state; its copper atom adopts a distorted tetrahedral geometry, with the N1Cu1O1 and N2Cu1O2 planes constituting a dihedral angle of 30°. The oxygen atom of one of the water molecules in (S,S)-1·2H2O is hydrogen bonded to the O(3) and O(4) atoms of (S,S)-1, with the O···O distances of 2.84 and 2.89 A, , respectively. The absolute structure
X.-G. Zhou et al. / Inorganica Chimica Acta 331 (2002) 194–198
196
Table 1 Crystal data and structure refinement parameters for (S,S)-1 and (R,S)-2
Empirical formula Formula weight Temperature (K) Crystal system Space group Unit cell dimensions a (A, ) b (A, ) c (A, ) h (°) i (°) k (°) V (A, 3) Z Dcalc (g cm−3) F(000) v (Mo Ka) (cm−1) Number of collected reflections Number of unique reflections Number of parameters R indices
(S,S)-1·2H2O
(R,S)-2·4CH2Cl2
C54H36Cl4N2O6Cu 1014.19 294 tetragonal P43212
C58H38Cl12N2O4Cu2 1379.48 301 monoclinic P21/c
19.884(3) 19.884(3) 25.964(5) 90 90 90 10 266(3) 8 1.312 4152 6.83 10 023
10.953(2) 16.039(3) 16.785(3) 90 95.64(2) 90 2934.4(9) 2 1.561 1388 13.18 24 382
9073
5552
610 R1 = 0.0550, wR2 = 0.16 1.089 0.00
352 R= 0.072, wR=0.097 1.73
Goodness-of-fit Absolute structure parameter Largest difference peak 0.629 and −0.306 and hole (e A, −3)
0.86 and −0.91
Fig. 1. ORTEP drawing and the atom-numbering scheme for (S,S)1·2H2O. Hydrogen atoms and the solvent molecules are omitted for clarity.
parameter of (S,S)-1 (Table 1) is consistent with its chirality. Complex (R,S)-2 is centrosymmetric with two distorted tetrahedral copper centers and a planar Cu(1), O(2), Cu(1*), O(2*) unit. The N(1), O(1), Cu(1), N(1*), O(1*), Cu(1*) atoms are virtually co-planar, and the
plane composed of these six atoms makes an angle of 20° with the Cu(1), O(2), Cu(1*), O(2*) plane. The Cu(1)Cu(1*) distance is 3.022(1) A, . The CuN and CuO distances in (S,S)-1 and (R,S)-2 are normal. The
Fig. 2. ORTEP drawing and the atom-numbering scheme for (R,S)2·4CH2Cl2. Hydrogen atoms and the solvent molecules are omitted for clarity. Table 2 Selected bond lengths (A, ) and bond angles (°) for (S,S)-1 and (R,S)-2 (S,S)-1 Bond lengths Cu(1)O(1) Cu(1)N(1) C(27)O(1) C(1)O(3) C(20)N(1) C(28)N(2)
1.899(1) 1.986(2) 1.304(2) 1.332(2) 1.447(2) 1.470(2)
Cu(1)O(2) Cu(1)N(2) C(54)O(2) C(47)O(4) C(21)N(1) C(48)N(2)
1.892(1) 1.978(2) 1.304(2) 1.354(3) 1.289(2) 1.273(2)
Bond angles O(1)Cu(1)N(1) O(1)Cu(1)N(2) N(1)Cu(1)O(2) C(27)O(1)Cu(1) C(20)N(1)Cu(1) C(28)N(2)Cu(1)
92.89(6) 92.25(6) 90.91(6) 128.1(1) 120.9(1) 117.5(1)
O(1)Cu(1)O(2) N(1)Cu(1)N(2) N(2)Cu(1)O(2) C(54)O(2)Cu(1) C(21)N(1)Cu(1) C(48)N(2)Cu(1)
155.38(6) 161.36(6) 91.86(6) 129.4(1) 123.1(1) 125.6(1)
(R,S)-2 Bond lengths Cu(1)O(1) Cu(1)O(2) C(1)O(1) C(7)N(1)
1.877(4) 1.938(4) 1.324(7) 1.299(7)
Cu(1)O(2*) Cu(1)N(1) C(27)O(2) C(8)N(1)
1.944(4) 1.940(5) 1.354(7) 1.459(7)
Bond angles O(1)Cu(1)N(1) O(1)Cu(1)O(2) N(1)Cu(1)O(2*) Cu(1)O(2)Cu(1*) C(27)O(2)Cu(1) C(7)N(1)Cu(1)
94.4(2) 164.7(2) 164.3(2) 102.2(2) 119.5(3) 123.8(4)
O(1)Cu(1)O(2*) 93.7(2) N(1)Cu(1)O(2) 97.0(2) O(2)Cu(1)O(2*) 77.8(2) C(1)O(1)Cu(1) 126.5(4) C(27)O(2)Cu(1*) 125.6(3) C(8)N(1)Cu(1) 117.6(4)
X.-G. Zhou et al. / Inorganica Chimica Acta 331 (2002) 194–198
Fig. 3. Model structures for: (a) (R,S)-1 and (b) (R,R)-2 with the coordination geometry of copper ion(s) identical with that of (S,S)-1 and (R,S)-2, respectively. The distances (A, ) between non-bonded atoms shorter than the sums of their van der Waals radii (H 1.2, O 1.40, Cl 1.80 A, ) are indicated. The inset in (b) shows the NOCu(mO%)2CuNO moiety viewed along the O%O% axis. All CH bond distances are set to be 0.96 A, .
dihedral angles of the binaphthyl units in these complexes range from 72 to 84°.
3.3. Functioning of ligand chirality as a ‘switch’ for selecti6e formation of mono- and dinuclear metal complexes The synthesis of (S,S)-1 and (R,S)-2 as shown in Scheme 1 demonstrates that the reactions of a metal compound with the same ligand in enantiopure and racemic forms generate mono- and dinuclear metal complexes, respectively, indicating that ligand chirality can function as a ‘switch’ for the selecti6e formation of mono- and dinuclear metal complexes. This is significantly different from a recent report by Kanemasa et al. [3] that reactions of a metal compound with enantiopure and racemic ligands afford mononuclear metal complexes of different compositions. The present work also contrasts with the recent work by Sadler and co-workers [8], who reported that reaction of Cp2TiCl2 with a commercial hexadentate amino acid ligand affords a mixture of mono- and dinuclear titanium complexes, with the mono- and dinuclear species (which contain the racemic and meso ligands, respectively) separated from each other by controlling the pH of the reaction mixture. To rationalize the selective formation of (S,S)-1 and (R,S)-2 from the reactions as shown in Scheme 1, we build models for the species (R,S)-1, (R,R)-2 and (S,S)2, which were not observed from these reactions, by using CS CHEM3D Pro 4.0 software package on the basis of the crystal structures of (S,S)-1 and (R,S)-2. The model structures of (R,S)-1 and (R,R)-2 are de-
197
picted in Fig. 3. Note that the structure of (S,S)-2 is identical with that of (R,R)-2 and is not shown here. Inspection of the model structure of (R,S)-1 reveals severe strains between the indicated hydrogen and chlorine or oxygen atoms (Fig. 3(a)). Regarding the model structures of (R,R)-2 (Fig. 3(b)) and (S,S)-2, their NOCu(m-O%)2CuNO moieties are substantially distorted compared with the same moiety in the stable complex (R,S)-2. As described above, the structure of (R,S)-2 features a planar Cu(m-O%)2Cu arrangement with essentially co-planar terminal NCuO planes; however, the two terminal NCuO planes in either (R,R)-2 or (S,S)-2 form a dihedral angle of 36° and cannot accommodate a co-planar geometry when a planar Cu(m-O%)2Cu arrangement is maintained (Fig. 3(b), inset). Such distortions of the NOCu(m-O%)2CuNO moieties in (R,R)-2 and (S,S)-2 may considerably destabilize the two species. Further, both (R,R)-2 and (S,S)-2 suffer from significant strains between the hydrogen and oxygen atoms as indicated, for example, in Fig. 3(b). In contrast, no strains as observed for (R,S)1, (R,R)-2 and (S,S)-2 exist in the structures of (S,S)-1 and (R,S)-2. These might be the reasons why the dinuclear species (S,S)-2 was not isolated from reaction (1) in Scheme 1 and why (R,S)-2 rather than (S,S)-2/ (R,R)-2/(R,S)-1 was isolated from reaction (2) in the same scheme.
4. Supplementary material Tables of final coordinates, bond lengths, bond angles, and anisotropic displacement parameters of (S,S)1·2H2O and (R,S)-2·4CH2Cl2 are available from the authors on request.
Acknowledgements This work was supported by The University of Hong Kong, the Hong Kong Research Grants Council [PolyU 1/97C], and the Hong Kong University Foundation.
References [1] W.A. Nugent, J.M. Mayer, Metal Ligand Multiple Bonds, Wiley, New York, 1988. [2] R.H. Holm, P. Kennepohl, E.I. Solomon, Chem. Rev. 96 (1996) 2239. [3] S. Kanemasa, Y. Oderaotoshi, S. Sakaguchi, H. Yamamoto, J. Tanaka, E. Wada, D.P. Curran, J. Am. Chem. Soc. 120 (1998) 3074. [4] M. Kitamura, M. Yamakawa, H. Oka, S. Suga, R. Noyori, Chem. Eur. J. 2 (1996) 1173.
198
X.-G. Zhou et al. / Inorganica Chimica Acta 331 (2002) 194–198
[5] E.M. Carreira, R.A. Singer, W. Lee, J. Am. Chem. Soc. 116 (1994) 8837. [6] M. Valko, R. Boca, R. Klement, J. Kozisek, M. Mazur, P. Pelikan, H. Morris, H. Elias, L. Muller, Polyhedron 16 (1997) 903.
[7] J.S. DeCourcy, T.N. Waters, N.F. Curtis, J. Chem. Soc., Chem. Commun. (1977) 572. [8] M. Guo, H. Sun, S. Bihari, J.A. Parkinson, R.O. Gould, S. Parsons, P.J. Sadler, Inorg. Chem. 39 (2000) 206.