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New chiral ligands incorporating useful functionality: racemic palladium(II) dichloride complexes of bidentate ligands containing two non-coordinated ester groups and three chiral centres of known relative stereochemistry
www.elsevier.nl/locate/inoche Inorganic Chemistry Communications 2 (1999) 476–478
New chiral ligands incorporating useful functionality: racemic palladium(II) dichloride complexes of bidentate ligands containing two non-coordinated ester groups and three chiral centres of known relative stereochemistry Timothy S. Billson a, Jonathan D. Crane a,*, David Foster a, Caroline S.L. Russell a, Ekkehard Sinn a, Simon J. Teat b, Nigel A. Young a a
Department of Chemistry, The University of Hull, Cottingham Road, Kingston-upon-Hull, HU6 7RX, UK b CCLRC, Daresbury Laboratory, Daresbury, Warrington, Cheshire, WA4 4AD, UK Received 5 August 1999
Abstract The cycloaddition of a pyridyl-azomethine to dimethylfumarate produces an approximately equimolar mixture of diastereomeric, C1symmetric, N,N-bidentate ligands. The corresponding palladium(II) dichloride complexes are readily separated by fractional crystallisation and contain non-coordinated ester groups, one of which lies above the plane of the palladium centre. q1999 Elsevier Science S.A. All rights reserved. Keywords: Palladium; Bidentate ligands; Chiral ligands; Stereochemistry
1. Introduction
chiral environments around the palladium centre whilst retaining the same basic ligand–metal framework.
Over recent years the palladium-catalysed allylation of carbon nucleophiles has been intensively studied as a versatile method for the formation of carbon–carbon bonds [1]. Furthermore, a wide range of chiral, bidentate ligands have been shown to induce asymmetry in the product with high enantioselectivity [2]. Traditionally these ligands contain different donor atom types (P/N, P/O, S/O, etc.) in order to facilitate regioselective nucleophilic attack on a non-symmetrical p-allyl ligand, and enantioselectivity is achieved through the ligand chirality controlling the relative stability/ reactivity of the two diastereomeric p-allyl complexes. Recently several C2- and C1-symmetric, N,N-bidentate ligands have also been reported to achieve high enantioselectivity [3,4]. We herein report the synthesis of racemic palladium(II) complexes of the C1-symmetric, N,N-bidentate ligands (")-L1 and (")-L2 of known relative stereochemistry (Scheme 1). Moreover, these ligands have the potential for variation of the N-methyl group and derivatisation of the ester groups, allowing scope for the construction of varied * Corresponding author. Tel.: q44 1482 465 457; fax q44 1482 466 410; e-mail: [email protected]
2. Experimental 2.1. Synthesis of the 50:50 mixture of cis,trans- and trans,trans-1-methyl-2-pyridin-2-yl-pyrrolidine-3,4dicarboxylic acid dimethyl ester [(")-L1] and [(")-L2] Dimethylfumarate (2.88 g, 20 mmol), N-methylglycine (3.56 g, 40 mmol) and pyridine-2-carboxaldehyde (2.14 g, 20 mmol) in xylene (120 cm3) were heated at reflux (2 h) under nitrogen. The pale yellow reaction mixture was filtered and the solvent removed under reduced pressure to yield a cloudy, orange oil. The crude product was dissolved in diethyl ether (10 cm3) and passed through a short silica gel column (70–230 mesh) with diethyl ether as eluant. The solvent was removed under reduced pressure to yield a pale yellow, clear oil; yield 4.8 g (86%). 1H NMR (400 MHz, CDCl3): d 8.59 (1H, d, Ha1 or Ha2), 8.56 (1H, d, Ha1 or Ha2), 7.68 (1H, dt, Hc1 or Hc2), 7.66 (1H, dt, Hc1 or Hc2), 7.43 (1H, d, Hd1 or Hd2), 7.36 (1H, d, Hd1 or Hd2), 7.20 (1H, ddd, Hb1 or Hb2), 7.17 (1H, ddd, Hb1 or Hb2), 3.95–3.40 (8H, m, He1–h1 and
1387-7003/99/$ - see front matter q All rights reserved. PII S 1 3 8 7 - 7 0 0 3 ( 9 9 ) 0 0 1 2 5 - 2
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12.0 Hz). 13C NMR (67.9 MHz, dmso): d 170.4, 169.5, 160.2, 149.1, 140.1, 125.0, 124.8, 79.2, 60.0, 52.5, 52.1, 49.8, 48.1, 44.3. 2: Anal. Calc. for C14H18Cl2N2O4Pd (MWs455.63): C, 36.91; H, 3.98; N, 6.15. Found: C, 37.05; H, 3.97; N, 6.13%. 1H NMR (400 MHz, dmso): d 8.85 (1H, dd, Ha), 8.16 (1H, dt, Hc), 7.74 (1H, d, Hd), 7.64 (1H, ddd, Hb), 4.43 (1H, d, He, Js10.0 Hz), 4.27 (1H, dd, Hh, Js11.5, 2.0 Hz), 4.26 (1H, dd, Hf, Js10.0, 7.0 Hz), 3.74 (3H, s, Hj or Hk), 3.67 (3H, s, Hj or Hk), 3.63 (1H, ddd, Hg, Js10.5, 7.0, 2.0 Hz), 2.82 (1H, dd, Hi, Js11.5, 10.5 Hz), 2.76 (3H, s, Hl). 13C NMR (67.9 MHz, dmso): d 171.7, 170.2, 161.2, 149.8, 140.4, 125.1, 124.7, 79.5, 61.4, 52.6, 52.2, 47.9, 43.5.
3. Results and discussion
Scheme 1. Synthesis of (")-L1 and (")-L2.
He2–h2), 3.76 (3H, s, Hj2, Hk1 or Hk2), 3.72 (3H, s, Hj2, Hk1 or Hk2), 3.63 (3H, s, Hj2, Hk1 or Hk2), 3.16 (3H, s, Hj1), 2.77 (1H, t, Hi1 or Hi2), 2.62 (1H, t, Hi1 or Hi2), 2.23 (3H, s, Hl1 or Hl2), 2.16 (3H, s, Hl1 or Hl2). The 1H NMR spectrum shows the product to be a 50:50 mixture of (")–L1 and (")–L2, and the only significant impurities were traces of xylenes. The product was used in the subsequent reaction without further purification. 2.2. Synthesis of (")-PdL1Cl2 (1) and (")-PdL2Cl2 (2) The above mixture of (")-L1 and (")-L2 (0.30 g, 1.05 mmol) and palladium dichloride (0.18 g, 1.00 mmol) in methanol (50 cm3) were heated at reflux (6 h). The yellow solution was filtered whilst hot and allowed to cool to room temperature. Pure (")-PdL1Cl2 (1) crystallised during cooling (20 min) as golden yellow plates, yield 0.17 g (74%). Upon standing at room temperature (24 h) pure (")-PdL2Cl2 (2) was obtained as orange crystals suitable for a single crystal X-ray structure determination, yield 0.15 g (65%). 1: Anal. Calc. for C14H18Cl2N2O4Pd (MWs455.63): C, 36.91; H, 3.98; N, 6.15%. Found: C, 36.91; H, 3.91; N, 6.00%. 1H NMR (400 MHz, dmso): d 8.76 (1H, dd, Ha), 8.15 (1H, dt, Hc), 7.74 (1H, d, Hd), 7.60 (1H, ddd, Hb), 4.70 (1H, d, He, Js11.0 Hz), 4.58 (1H, ddd, Hg, Js12.0, 8.5, 7.5 Hz), 4.19 (1H, dd, Hh, Js11.0, 7.5 Hz), 3.96 (1H, dd, Hf, Js11.0, 8.5 Hz), 3.68 (3H, s, Hk), 3.17 (3H, s, Hj), 2.82 (3H, s, Hl), 2.52 (1H, dd, Hi, Js11.0,
Monday Oct 18 02:59 PM
The racemic ligands (")-L1 and (")-L2 were prepared as an equimolar mixture by the dipolar cycloaddition of dimethylfumarate and the azomethine II generated in situ from thermal decarboxylation of the heterocycle intermediate I, in turn formed by the condensation of N-methylglycine and pyridine-2-carboxaldehyde (Scheme 1) [5]. With dimethylfumarate the mutually trans arrangement of the ester groups is retained during the cycloaddition reaction and only products with mutually trans ester groups are formed. The separation of this ligand mixture was not attempted as reaction with palladium(II) chloride in methanol at reflux readily yielded the stable complexes (")-PdL1Cl2 (1) and (")PdL2Cl2 (2), which were separated by fractional crystallisation from the reaction mixture. The probable relative stereochemistries of 1 and 2 can be deduced by comparison of their 1H NMR spectra; molecular models show that because the methyl ester group in the 3position of 1 is cis to the pyridine ring (Hk1) it lies above the plane of the aromatic ring and is therefore characteristically shielded; an effect which is also apparent in the 1H NMR spectrum of the ligand mixture and allows the definitive assignment of this group. However, the relative stereochemistry of 2 was also confirmed by single crystal X-ray diffraction 1 (Fig. 1) [6,7]. The d8 palladium(II) centre adopts the 1 Crystal data: 2: C14H18Cl2N2O4Pd, Mrs455.60, monoclinic, space group ˚ , bs99.460(5)8, P21/c, as7.5816(13), bs15.472(3), cs14.084(3) A ˚ 3, Zs4, Dcs1.857 g cmy3, ms1.487 mmy1, Us1629.6(5) A F(000)s912. Crystal dimensions 0.06=0.06=0.01 mm. Data for 2 were ˚ , on a Bruker collected at 150(2) K employing a wavelength of 0.6890 A AXS SMART CCD area detector diffractometer with a silicon (111) crystal monochromator and a palladium coated focusing mirror on the single crystal diffraction station (no. 9.8) at Daresbury Laboratory Synchrotron Radiation Source. Coverage of a hemisphere of reciprocal space was achieved by 0.28 increments in v, with umins1.918 and umaxs29.338 (index ranges y10FhF10, y21FkF15, y19FlF17). Corrections were applied to account for incident beam decay. A solution was provided via direct methods and refined by full-matrix least-squares on F2. 11179 reflections were measured, producing 4440 unique data with Rints0.0339, and 3563 unique data [I)2s(I)]. 211 parameters refined to R1s0.0383 and wR2s0.0789 [I)2s(I)] with Ss1.000 and residual electron density extremes of 1.445 ˚ y3. See also Supplementary material. and y1.474 e A
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Fig. 1. ORTEP view of the molecular structure of (")-PdL2Cl2 (2), with ˚ ) and angles thermal ellipsiods shown at 50% [13]. Selected bond lengths (A (8): Pd(1)–N(1), 2.017(2); Pd(1)–N(2), 2.071(2); Pd(1)–Cl(1), 2.2892(8); Pd(1)–Cl(2), 2.3034(8); N(1)–Pd(1)–N(2), 80.82(9); N(1)–Pd(1)–Cl(1), 94.00(7); N(2)–Pd(1)–Cl(2), 94.49(7); Cl(1)– Pd(1)–Cl(2), 90.69(3).
rical p-allyl ligands bound at the palladium. Secondly, the methyl ester group in the 4-position of 2 lies above the plane of the palladium centre and, although inspection of molecular models indicates that this group is available for axial coor˚ dination to the metal, the Pd(1)∆O(4) distance of 3.75 A confirms the absence of any such interaction in the solid state. However, the location of this group (and derivatives thereof) may be useful for influencing the reactivity of the palladium centre. Thirdly, inspection of molecular models of 1 indicates that the 3-ester group lies above the plane of the palladium centre, but in a different position and orientation compared with the 4-ester group of 2. The study of the reactivity of 1 and 2, and the synthesis and investigation of the corresponding cationic p-allyl derivatives of these complexes is in progress, as is their resolution through the derivatisation of the ester groups with enantiopure chiral alcohols and amines. 4. Supplementary material
expected square-planar geometry with cis chloride ligands, ˚ is and the Pd–N(pyridine) bond distance of 2.017(2) A significantly shorter than the Pd–N(pyrrolidine) distance of ˚ . The difference in bond lengths (D(Pd–N)) of 2.071(2) A ˚ is due in part to the nature of the donor atoms, but 0.054 A its magnitude is probably also a consequence of the steric hindrance of the N-methylpyrrolidine ligand 2 [12]. The 1H NMR spectrum of 2 is consistent with the solid state structure being broadly retained in solution; the small coupling constant between the vicinal protons Hg2 and Hh2 (3Js2.0 Hz) correlates well with the crystallographically determined dihedral angle of 1038. The crystal structure of 2 reveals the potential of these chiral ligands for use in palladium catalysed reactions, and in particular nucleophilic allylation. Firstly, replacing the Nmethyl group of the pyrrolidine ligand with larger substituents may be expected to increase the difference in Pd–N bond distances and thus influence the regioselectivity of addition to cationic p-allyl derivatives of the palladium centre; it is also noteworthy that this group partially blocks the lower face of the metal ion and larger substituents would be appropriately positioned to influence the orientation of non-symmet2 Of the few structurally characterised PdLX2 complexes with C1-symmetric N(aromatic heterocycle), N(aliphatic)-bidentate ligands (L) the Pd–N bond distances are usually similar, but in the absence of steric hindrance the Pd–N(aliphatic) distance is always the longer [8–10]. For one complex ˚ has with a sterically hindered N(aliphatic) donor a D(Pd–N) of 0.062 A been reported [11].
Monday Oct 18 02:59 PM
Supplementary data for 2 are available from the CCDC, 12 Union Road, Cambridge, CB2 1EZ, UK, quoting the deposition number: CCDC 133085. References [1] B.M. Trost, L. Van Vranken, Chem. Rev. 96 (1996) 395. [2] P. von Matt, G.C. Lloyd-Jones, A.B.E. Minidis, A. Pfaltz, L. Macko, ¨ M. Neuburger, M. Zehnder, H. Ruegger, P.S. Pregosin, Helv. Chim. Acta 78 (1995) 265. [3] K. Nordstrom, E. Macedo, C. Moberg, J. Org. Chem. 62 (1997) 1604. ˜ ¨ [4] E. Pena-Cabrera, P.O. Norrby, M. Sjogren, A. Vitagliano, V. De ˚ Felice, J. Oslob, S. Ishii, D. O’Neill, B. Akermark, P. Helquist, J. Am. Chem. Soc. 118 (1996) 4299. [5] O. Tsuge, S. Kanemasa, M. Ohe, S. Takenaka, Bull. Chem. Soc. Jpn. 60 (1987) 4079. [6] R.J. Cernik, W. Clegg, C.R.A. Catlow, G. Bushnell-Wye, J.V. Flaherty, G.N. Greaves, I.D. Burrows, D.J. Taylor, S.J. Teat, M. Hamichi, J. Synchrotron Rad. 4 (1997) 279. [7] W. Clegg, M.R.J. Elsegood, S.J. Teat, C. Redshaw, V.C. Gibson, J. Chem. Soc., Dalton Trans. (1998) 3037. [8] T. Rau, M. Shoukry, R. van Eldik, Inorg. Chem. 36 (1997) 1454. [9] G. Pneumatikakis, C. Chassapis, A. Rontoyianni, J. Inorg. Biochem. 49 (1993) 83. [10] A. Caubet, V. Moreno, E. Molins, C. Miravitilles, J. Inorg. Biochem. 48 (1992) 135. [11] U. Florke, T. Seshadri, H.J. Haupt, Z. Kristallogr. 194 (1991) 137. [12] D.A. Fletcher, R.F. McMeeking, D. Parkin, The United Kingdom Chemical Database Service, J. Chem. Inf. Comput. Sci. 36 (1996) 746. [13] L.J. Farrugia, ORTEP-3 for Windows, J. Appl. Crystallogr. 30 (1997) 565.
StyleTag -- Journal: INOCHE (Inorganic Chemistry Communications)
Article: 263
New chiral ligands incorporating useful functionality: racemic palladium(II) dichloride complexes of bidentate ligands containing two non-coordinated ester groups and three chiral centres of known relative stereochemistry Timothy S. Billson a, Jonathan D. Crane a,*, David Foster a, Caroline S.L. Russell a, Ekkehard Sinn a, Simon J. Teat b, Nigel A. Young a a
Department of Chemistry, The University of Hull, Cottingham Road, Kingston-upon-Hull, HU6 7RX, UK b CCLRC, Daresbury Laboratory, Daresbury, Warrington, Cheshire, WA4 4AD, UK Received 5 August 1999
Abstract The cycloaddition of a pyridyl-azomethine to dimethylfumarate produces an approximately equimolar mixture of diastereomeric, C1symmetric, N,N-bidentate ligands. The corresponding palladium(II) dichloride complexes are readily separated by fractional crystallisation and contain non-coordinated ester groups, one of which lies above the plane of the palladium centre. q1999 Elsevier Science S.A. All rights reserved. Keywords: Palladium; Bidentate ligands; Chiral ligands; Stereochemistry
1. Introduction
chiral environments around the palladium centre whilst retaining the same basic ligand–metal framework.
Over recent years the palladium-catalysed allylation of carbon nucleophiles has been intensively studied as a versatile method for the formation of carbon–carbon bonds [1]. Furthermore, a wide range of chiral, bidentate ligands have been shown to induce asymmetry in the product with high enantioselectivity [2]. Traditionally these ligands contain different donor atom types (P/N, P/O, S/O, etc.) in order to facilitate regioselective nucleophilic attack on a non-symmetrical p-allyl ligand, and enantioselectivity is achieved through the ligand chirality controlling the relative stability/ reactivity of the two diastereomeric p-allyl complexes. Recently several C2- and C1-symmetric, N,N-bidentate ligands have also been reported to achieve high enantioselectivity [3,4]. We herein report the synthesis of racemic palladium(II) complexes of the C1-symmetric, N,N-bidentate ligands (")-L1 and (")-L2 of known relative stereochemistry (Scheme 1). Moreover, these ligands have the potential for variation of the N-methyl group and derivatisation of the ester groups, allowing scope for the construction of varied * Corresponding author. Tel.: q44 1482 465 457; fax q44 1482 466 410; e-mail: [email protected]
2. Experimental 2.1. Synthesis of the 50:50 mixture of cis,trans- and trans,trans-1-methyl-2-pyridin-2-yl-pyrrolidine-3,4dicarboxylic acid dimethyl ester [(")-L1] and [(")-L2] Dimethylfumarate (2.88 g, 20 mmol), N-methylglycine (3.56 g, 40 mmol) and pyridine-2-carboxaldehyde (2.14 g, 20 mmol) in xylene (120 cm3) were heated at reflux (2 h) under nitrogen. The pale yellow reaction mixture was filtered and the solvent removed under reduced pressure to yield a cloudy, orange oil. The crude product was dissolved in diethyl ether (10 cm3) and passed through a short silica gel column (70–230 mesh) with diethyl ether as eluant. The solvent was removed under reduced pressure to yield a pale yellow, clear oil; yield 4.8 g (86%). 1H NMR (400 MHz, CDCl3): d 8.59 (1H, d, Ha1 or Ha2), 8.56 (1H, d, Ha1 or Ha2), 7.68 (1H, dt, Hc1 or Hc2), 7.66 (1H, dt, Hc1 or Hc2), 7.43 (1H, d, Hd1 or Hd2), 7.36 (1H, d, Hd1 or Hd2), 7.20 (1H, ddd, Hb1 or Hb2), 7.17 (1H, ddd, Hb1 or Hb2), 3.95–3.40 (8H, m, He1–h1 and
1387-7003/99/$ - see front matter q All rights reserved. PII S 1 3 8 7 - 7 0 0 3 ( 9 9 ) 0 0 1 2 5 - 2
Monday Oct 18 02:58 PM
StyleTag -- Journal: INOCHE (Inorganic Chemistry Communications)
Article: 263
T.S. Billson et al. / Inorganic Chemistry Communications 2 (1999) 476–478
477
12.0 Hz). 13C NMR (67.9 MHz, dmso): d 170.4, 169.5, 160.2, 149.1, 140.1, 125.0, 124.8, 79.2, 60.0, 52.5, 52.1, 49.8, 48.1, 44.3. 2: Anal. Calc. for C14H18Cl2N2O4Pd (MWs455.63): C, 36.91; H, 3.98; N, 6.15. Found: C, 37.05; H, 3.97; N, 6.13%. 1H NMR (400 MHz, dmso): d 8.85 (1H, dd, Ha), 8.16 (1H, dt, Hc), 7.74 (1H, d, Hd), 7.64 (1H, ddd, Hb), 4.43 (1H, d, He, Js10.0 Hz), 4.27 (1H, dd, Hh, Js11.5, 2.0 Hz), 4.26 (1H, dd, Hf, Js10.0, 7.0 Hz), 3.74 (3H, s, Hj or Hk), 3.67 (3H, s, Hj or Hk), 3.63 (1H, ddd, Hg, Js10.5, 7.0, 2.0 Hz), 2.82 (1H, dd, Hi, Js11.5, 10.5 Hz), 2.76 (3H, s, Hl). 13C NMR (67.9 MHz, dmso): d 171.7, 170.2, 161.2, 149.8, 140.4, 125.1, 124.7, 79.5, 61.4, 52.6, 52.2, 47.9, 43.5.
3. Results and discussion
Scheme 1. Synthesis of (")-L1 and (")-L2.
He2–h2), 3.76 (3H, s, Hj2, Hk1 or Hk2), 3.72 (3H, s, Hj2, Hk1 or Hk2), 3.63 (3H, s, Hj2, Hk1 or Hk2), 3.16 (3H, s, Hj1), 2.77 (1H, t, Hi1 or Hi2), 2.62 (1H, t, Hi1 or Hi2), 2.23 (3H, s, Hl1 or Hl2), 2.16 (3H, s, Hl1 or Hl2). The 1H NMR spectrum shows the product to be a 50:50 mixture of (")–L1 and (")–L2, and the only significant impurities were traces of xylenes. The product was used in the subsequent reaction without further purification. 2.2. Synthesis of (")-PdL1Cl2 (1) and (")-PdL2Cl2 (2) The above mixture of (")-L1 and (")-L2 (0.30 g, 1.05 mmol) and palladium dichloride (0.18 g, 1.00 mmol) in methanol (50 cm3) were heated at reflux (6 h). The yellow solution was filtered whilst hot and allowed to cool to room temperature. Pure (")-PdL1Cl2 (1) crystallised during cooling (20 min) as golden yellow plates, yield 0.17 g (74%). Upon standing at room temperature (24 h) pure (")-PdL2Cl2 (2) was obtained as orange crystals suitable for a single crystal X-ray structure determination, yield 0.15 g (65%). 1: Anal. Calc. for C14H18Cl2N2O4Pd (MWs455.63): C, 36.91; H, 3.98; N, 6.15%. Found: C, 36.91; H, 3.91; N, 6.00%. 1H NMR (400 MHz, dmso): d 8.76 (1H, dd, Ha), 8.15 (1H, dt, Hc), 7.74 (1H, d, Hd), 7.60 (1H, ddd, Hb), 4.70 (1H, d, He, Js11.0 Hz), 4.58 (1H, ddd, Hg, Js12.0, 8.5, 7.5 Hz), 4.19 (1H, dd, Hh, Js11.0, 7.5 Hz), 3.96 (1H, dd, Hf, Js11.0, 8.5 Hz), 3.68 (3H, s, Hk), 3.17 (3H, s, Hj), 2.82 (3H, s, Hl), 2.52 (1H, dd, Hi, Js11.0,
Monday Oct 18 02:59 PM
The racemic ligands (")-L1 and (")-L2 were prepared as an equimolar mixture by the dipolar cycloaddition of dimethylfumarate and the azomethine II generated in situ from thermal decarboxylation of the heterocycle intermediate I, in turn formed by the condensation of N-methylglycine and pyridine-2-carboxaldehyde (Scheme 1) [5]. With dimethylfumarate the mutually trans arrangement of the ester groups is retained during the cycloaddition reaction and only products with mutually trans ester groups are formed. The separation of this ligand mixture was not attempted as reaction with palladium(II) chloride in methanol at reflux readily yielded the stable complexes (")-PdL1Cl2 (1) and (")PdL2Cl2 (2), which were separated by fractional crystallisation from the reaction mixture. The probable relative stereochemistries of 1 and 2 can be deduced by comparison of their 1H NMR spectra; molecular models show that because the methyl ester group in the 3position of 1 is cis to the pyridine ring (Hk1) it lies above the plane of the aromatic ring and is therefore characteristically shielded; an effect which is also apparent in the 1H NMR spectrum of the ligand mixture and allows the definitive assignment of this group. However, the relative stereochemistry of 2 was also confirmed by single crystal X-ray diffraction 1 (Fig. 1) [6,7]. The d8 palladium(II) centre adopts the 1 Crystal data: 2: C14H18Cl2N2O4Pd, Mrs455.60, monoclinic, space group ˚ , bs99.460(5)8, P21/c, as7.5816(13), bs15.472(3), cs14.084(3) A ˚ 3, Zs4, Dcs1.857 g cmy3, ms1.487 mmy1, Us1629.6(5) A F(000)s912. Crystal dimensions 0.06=0.06=0.01 mm. Data for 2 were ˚ , on a Bruker collected at 150(2) K employing a wavelength of 0.6890 A AXS SMART CCD area detector diffractometer with a silicon (111) crystal monochromator and a palladium coated focusing mirror on the single crystal diffraction station (no. 9.8) at Daresbury Laboratory Synchrotron Radiation Source. Coverage of a hemisphere of reciprocal space was achieved by 0.28 increments in v, with umins1.918 and umaxs29.338 (index ranges y10FhF10, y21FkF15, y19FlF17). Corrections were applied to account for incident beam decay. A solution was provided via direct methods and refined by full-matrix least-squares on F2. 11179 reflections were measured, producing 4440 unique data with Rints0.0339, and 3563 unique data [I)2s(I)]. 211 parameters refined to R1s0.0383 and wR2s0.0789 [I)2s(I)] with Ss1.000 and residual electron density extremes of 1.445 ˚ y3. See also Supplementary material. and y1.474 e A
StyleTag -- Journal: INOCHE (Inorganic Chemistry Communications)
Article: 263
478
T.S. Billson et al. / Inorganic Chemistry Communications 2 (1999) 476–478
Fig. 1. ORTEP view of the molecular structure of (")-PdL2Cl2 (2), with ˚ ) and angles thermal ellipsiods shown at 50% [13]. Selected bond lengths (A (8): Pd(1)–N(1), 2.017(2); Pd(1)–N(2), 2.071(2); Pd(1)–Cl(1), 2.2892(8); Pd(1)–Cl(2), 2.3034(8); N(1)–Pd(1)–N(2), 80.82(9); N(1)–Pd(1)–Cl(1), 94.00(7); N(2)–Pd(1)–Cl(2), 94.49(7); Cl(1)– Pd(1)–Cl(2), 90.69(3).
rical p-allyl ligands bound at the palladium. Secondly, the methyl ester group in the 4-position of 2 lies above the plane of the palladium centre and, although inspection of molecular models indicates that this group is available for axial coor˚ dination to the metal, the Pd(1)∆O(4) distance of 3.75 A confirms the absence of any such interaction in the solid state. However, the location of this group (and derivatives thereof) may be useful for influencing the reactivity of the palladium centre. Thirdly, inspection of molecular models of 1 indicates that the 3-ester group lies above the plane of the palladium centre, but in a different position and orientation compared with the 4-ester group of 2. The study of the reactivity of 1 and 2, and the synthesis and investigation of the corresponding cationic p-allyl derivatives of these complexes is in progress, as is their resolution through the derivatisation of the ester groups with enantiopure chiral alcohols and amines. 4. Supplementary material
expected square-planar geometry with cis chloride ligands, ˚ is and the Pd–N(pyridine) bond distance of 2.017(2) A significantly shorter than the Pd–N(pyrrolidine) distance of ˚ . The difference in bond lengths (D(Pd–N)) of 2.071(2) A ˚ is due in part to the nature of the donor atoms, but 0.054 A its magnitude is probably also a consequence of the steric hindrance of the N-methylpyrrolidine ligand 2 [12]. The 1H NMR spectrum of 2 is consistent with the solid state structure being broadly retained in solution; the small coupling constant between the vicinal protons Hg2 and Hh2 (3Js2.0 Hz) correlates well with the crystallographically determined dihedral angle of 1038. The crystal structure of 2 reveals the potential of these chiral ligands for use in palladium catalysed reactions, and in particular nucleophilic allylation. Firstly, replacing the Nmethyl group of the pyrrolidine ligand with larger substituents may be expected to increase the difference in Pd–N bond distances and thus influence the regioselectivity of addition to cationic p-allyl derivatives of the palladium centre; it is also noteworthy that this group partially blocks the lower face of the metal ion and larger substituents would be appropriately positioned to influence the orientation of non-symmet2 Of the few structurally characterised PdLX2 complexes with C1-symmetric N(aromatic heterocycle), N(aliphatic)-bidentate ligands (L) the Pd–N bond distances are usually similar, but in the absence of steric hindrance the Pd–N(aliphatic) distance is always the longer [8–10]. For one complex ˚ has with a sterically hindered N(aliphatic) donor a D(Pd–N) of 0.062 A been reported [11].
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Supplementary data for 2 are available from the CCDC, 12 Union Road, Cambridge, CB2 1EZ, UK, quoting the deposition number: CCDC 133085. References [1] B.M. Trost, L. Van Vranken, Chem. Rev. 96 (1996) 395. [2] P. von Matt, G.C. Lloyd-Jones, A.B.E. Minidis, A. Pfaltz, L. Macko, ¨ M. Neuburger, M. Zehnder, H. Ruegger, P.S. Pregosin, Helv. Chim. Acta 78 (1995) 265. [3] K. Nordstrom, E. Macedo, C. Moberg, J. Org. Chem. 62 (1997) 1604. ˜ ¨ [4] E. Pena-Cabrera, P.O. Norrby, M. Sjogren, A. Vitagliano, V. De ˚ Felice, J. Oslob, S. Ishii, D. O’Neill, B. Akermark, P. Helquist, J. Am. Chem. Soc. 118 (1996) 4299. [5] O. Tsuge, S. Kanemasa, M. Ohe, S. Takenaka, Bull. Chem. Soc. Jpn. 60 (1987) 4079. [6] R.J. Cernik, W. Clegg, C.R.A. Catlow, G. Bushnell-Wye, J.V. Flaherty, G.N. Greaves, I.D. Burrows, D.J. Taylor, S.J. Teat, M. Hamichi, J. Synchrotron Rad. 4 (1997) 279. [7] W. Clegg, M.R.J. Elsegood, S.J. Teat, C. Redshaw, V.C. Gibson, J. Chem. Soc., Dalton Trans. (1998) 3037. [8] T. Rau, M. Shoukry, R. van Eldik, Inorg. Chem. 36 (1997) 1454. [9] G. Pneumatikakis, C. Chassapis, A. Rontoyianni, J. Inorg. Biochem. 49 (1993) 83. [10] A. Caubet, V. Moreno, E. Molins, C. Miravitilles, J. Inorg. Biochem. 48 (1992) 135. [11] U. Florke, T. Seshadri, H.J. Haupt, Z. Kristallogr. 194 (1991) 137. [12] D.A. Fletcher, R.F. McMeeking, D. Parkin, The United Kingdom Chemical Database Service, J. Chem. Inf. Comput. Sci. 36 (1996) 746. [13] L.J. Farrugia, ORTEP-3 for Windows, J. Appl. Crystallogr. 30 (1997) 565.
StyleTag -- Journal: INOCHE (Inorganic Chemistry Communications)
Article: 263