Group 8 metallocenes as bulky functional groups in glucopyranosides

Carbohydrate Research 365 (2013) 26–31

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Group 8 metallocenes as bulky functional groups in glucopyranosides Dirk Schwidom, Mirjam Volkmann, Anne Wolter, Jürgen Heck ⇑ University of Hamburg, Institute for Inorganic and Applied Chemistry, Martin-Luther-King-Platz 6, D-20146 Hamburg, Germany

a r t i c l e

i n f o

Article history: Received 18 July 2012 Received in revised form 15 October 2012 Accepted 16 October 2012 Available online 2 November 2012 Keywords: Carbohydrates Ferrocene Ruthenocene Mononuclear complexes X-ray structure determination

a b s t r a c t The functionalization of methyl D-glucopyranosides at positions 4 and 6 with bulky moieties was carried out by using ferrocenyl and ruthenocenyl substituents. The synthesis succeeded by reaction of the methyl D-glucopyranosides with the corresponding metallocene monocarbaldehyde dimethyl acetal catalysed by iodine in acetonitrile. The resulting compounds methyl 4,6-O-(metallocenylmethylidene)-a-D-glucopyranoside (M = Fe (1) and M = Ru (3)) and methyl 4,6-O-(metallocenylmethylidene)-b-D-glucopyranoside (M = Fe (2) and M = Ru (4)) were characterized by 1H and 13C NMR spectroscopy, by crystal structure determination as well as elemental analysis. Ó 2012 Elsevier Ltd. All rights reserved.

1. Introduction The combinations of ferrocene and ruthenocene derivatives with biologically important ligands are of increasing interest especially concerning their medicinal applications.1,2 Only a few examples using monosaccharides in organometallic chemistry are reported.3–5 Ferrocenyl substituted glucose derivatives, which were applied as chiral ligands in Pd catalysed enantioselective allylic alkylation, are examples of the small number of publications.4,5b,c Of particular interest in metallocenes of group eight elements in combination with carbohydrates is their pharmaceutical activity.2a A structural study of 1,10 -dixylofuranose-ferrocene compounds was published by Romão and co-workers.6 Various ferrocene modified manno- and glucopyranosidato complexes were studied concerning the NMR spectroscopic, their electrochemical and calorimetric behaviours as well as their binding capacities to receptors.7 2. Results and discussion 2.1. Synthesis Our interest in glucopyranosides is enrooted in studying their suitability as ligands in precatalysts for polymerization-, stereoselective hydroamination- as well as allylation reactions.2b Traditionally, functional groups in 4,6-O-position like benzylidene- and naphthyl-20 -methylidene groups only displayed a weak influence on the stereochemistry in catalytic reactions. Hence, we are looking for sterically more demanding substituents in the pyranosidato ⇑ Corresponding author. Fax: +49 40 428386945. E-mail address: [email protected] (J. Heck). 0008-6215/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.carres.2012.10.015

ligands.8 Obviously, potential candidates are metallocenes, which are easily available and stable against oxygen and moisture. The steric demand of the metallocenyl substituents would even be enlarged because of the rotating ability through a C–C-single bond. Our studies provide the first examples of the preparation of methyl 4,6-O-(ferrocenylmethylidene)-a-D-glucopyranoside (1) and methyl 4,6-O-(ferrocenylmethylidene)-b-D-glucopyranoside (2) as well as the Ru derivatives. In order to bind a metallocenyl moiety covalently to the glucopyranoside unit the acetal function with 4,6-O-position was chosen, which may undergo transannular interaction in stereoselective transformations. Therefore, the related metallocene monocarbaldehyde dimethylacetal of iron and ruthenium was prepared with an excess of trimethylorthoformate and pyridinium-para-toluenesulfonate as catalyst starting from the corresponding metallocene monocarbaldehyde.9 After purification of the metallocene monocarbaldehyde dimethylacetal, several attempts were made to synthesize the metallocene modified glucopyranosides. Unsuccessful trials were made using HBF4 in DMF.10 In another reaction para-toluenesulfonic acid was employed as catalyst in acetonitrile, which results in traces of the desired product.11 Finally the application of iodine as catalyst12 revealed the ferrocene containing products 1 in 53% and 2 in 71% yield after column chromatography on silica and ethyl acetate/n-hexane (Scheme 1). The corresponding ruthenocene derivatives 3 and 4 were obtained in 57% and 41% yields. 2.2. Molecular structure Suitable crystals for X-ray structure analysis of 1 were obtained after dissolving the crude product in hot 0.1 M NaHCO3 solution,

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O

Table 1 Crystallographic and data collection parameters for 1, 2 and 3

M

CH(OCH3 )3 PPTS

MeOH T = 90°C O

M

HO HO HO

O I2 MeCN

OH O

M

O

O HO

O

O

HO HO HO

O

M

O

O HO

OH O

1 M = Fe, 53% 3 M = Ru, 57%

O

OH

O

O

OH

2 M = Fe, 71% 4 M = Ru, 41%

Compound

1

2

3

Empirical formula

C18H22O6Fe H2O 408.22 monoclinic P21 619.91(18) 733.4(2) 1933.4(6) 96.694(3) 0.8729(4) 2 1.553 100(2) 0.903 428 2.12–27.49 7933

C18H22O6Fe

C18H22O6Ru

390.21 monoclinic P21 635.4(10) 1061.05(2) 1260.0(3) 99.948(10) 0.86971(3) 2 1.549 100(2) 0.934 408 2.53–32.50 22110

435.43 orthorhombic P22121 581.0(2) 2527.4(9) 3546.6(13) – 5.208(3) 12 1.666 100(2) 0.935 2664 1.9–25.0 45096

3489(0.032)

5989(0.0348)

9140(0.2381)

3489/4/244 1.065 0.0369, 0.0893 0.0418, 0.0920 0.635 and 0.538

5989/1/229 1.056 0.0325, 0.0721 0.0360, 0.0741 0.607 and 0.317

9140/84/697 1.008 0.0769/ 0.1280 0.1599/ 0.1602 0.926 and 1.147

M Crystal system Space group a [pm] b [pm] c [pm] b [°] V [nm3] Z Dcalcd [g cm3] T [K] l(Mo-Ka) [mm1] F(0 0 0) h-Range [°] Number of reflections collected Number of independent reflections (Rint) Data/restraints/parameters Goodness-of-fit on F2 R1, wR2 [I > 2r(I)] R1, wR2 (all data) Largest difference in peak and hole [e Å3]

Scheme 1. Synthesis route for 1, 2, 3 and 4.

filtration and cooling the filtrate to 5 °C. Compound 1 crystallized in space group P21, with two molecules in the unit cell. Crystals of 2 were obtained in suitable quality for X-ray structure analysis by recrystallization from hot toluene. Compound 2 crystallized in the space group P21, with two molecules in the unit cell. Single crystals of 3 could be obtained in the same way like 2 in thin needles with only moderate scattering properties. Compound 3 crystallized in the space group P22121, with twelve molecules in the unit cell. The structural data of 1, 2 and 3 are listed in Table 1. The crystal structures of 1, 2 and 3 differ in a significant way (Figs. 1–3). Compound 1 displays hydrogen bridges between molecules packed in parallel aligned columns, which are interconnected by one crystallized water molecule and the oxygen atom in position 3 and the hydroxyl function in position 2 of the neighbouring column. The overall packing of the modified monosaccharide 1 resembles a herring-bone fashion. In the crystals of 2 the ferrocenyl modified glucopyranoside units are packed in columns as well, but the ferrocenyl substituents of the next column are arranged almost perpendicular to the former. As a result the sandwich substituents and the b-glucopyranosides each form a layer, which is stabilized by intermolecular hydrogen bridging bonds. Hydroxyl functions at positions 2 and 3 are interconnecting the single columns. Compound 3 crystallized in an even more complex way. The ruthenocenyl modified a-glucopyranoside molecules are also packed in columns. However, three columns are ordered together in the ‘a-way’, that hydroxyl functions in positions 2 and 3 are pointing towards each other and are kept together by intermolecular hydrogen bonds. As a consequence three columns form a triple helix. Selected interatomic distances and bond angles of 1, 2 and 3 are listed in Table 2 (see also Figs. 4 and 5). Notably, the dihedral angles of O2–C2–C3–O3 in solid state are quite flexible. In 1 the dihedral angle amounts to 74.1°, whereas in 2 it is 68.3°, which is close to the corresponding angle of 66.3° calculated for the benzylidene protected a-D-glucopyranoside.10 Concerning the dihedral angle of the glucopyranosidato ligand in the recently published zirconate complex, the dihedral angle O2–C2–C3–O3 ranges from 51.9° to 64.2° and for 3 from 58.9° to 64.9°.13

2.3. NMR characterization The order of proton signals in 1H NMR spectra (see Fig. 6 and Section 3) is comparable between 1 and 3 as well as 2 and 4. In general, the signals of glucopyranose protons are shifted slightly to lower frequencies for the Ru-compounds 3 and 4 than observed for the Fe-homologues 1 and 2, whereas a reverse behaviour is observed for the Cp-protons. The same order of the shifts of the Cp signals is found for the free metallocenes. This behaviour is in disagreement with the stronger group electronegativity of ruthenocene with respect to ferrocene,14 and may be rationalized by the different magnetic anisotropy of the sandwich complex entities.15 2.4. Conclusions Four glucopyranosides were successfully synthesized with organometallic sandwich complexes which are linked through an acetal in positions 4 and 6, when the reactions were carried out with catalytic amounts of iodine. All compounds were characterized by NMR spectroscopy and elemental analysis. Three compounds were characterized by crystal structure analysis. The application of these metallocenyl substituted glucopyranosides in complexation reactions is subject of current studies. 3. Experimental 3.1. General methods 1

H and 13C NMR spectra were recorded with a Bruker AVANCE 400 instrument at room temperature. Elemental analysis was carried out with a Vario EL III instrument at Zentrale Elementanalytik, Fachbereich Chemie, Universität Hamburg. 3.1.1. General procedure 1-Metallocenyl monocarbaldehyde (1.19 mmol), pyridinium para-toluene-sulfonate (65 mg, 0.276 mmol) and trimethylorthoformiate (10.1 mL, 9.71 g, 91.5 mmol) were dissolved in methanol

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Figure 1. ORTEP-diagram of the crystal packing of a-MeFcmGlcH2 (1). Thermal ellipsoids with 50% probability level. The hydrogen atoms of H2O and at O2 and O3 are shown to evince the stabilization of crystal packing by bridging H-atoms.

Figure 2. ORTEP-diagram of the crystal packing of b-MeFcmGlcH2 (2). Thermal ellipsoids with 50% probability level (hydrogen atoms are omitted for clarity).

(30 mL). After stirring under reflux for 17 h dichloromethane (50 mL) was added to the reaction. The resulting mixture was washed two times with saturated NaHCO3-solution (50 mL). The aqueous layer was extracted with dichloromethane (2  50 mL). The combined organic layers were washed with H2O (3  50 mL) and dried over Na2SO4. After evaporation of the solvent, the oily residue was degassed and dissolved in dry acetonitrile (10 mL). This solution was added to methyl D-glucopyranoside (231 mg, 1.19 mmol) and iodine (30 mg, 0.118 mmol) and stirred for 20 h at room temperature. The reaction was finished by removing the solvent in vacuo. The residue was purified by column chromatography (SiO2, ethylacetate/n-hexane 4:1).

3.2. Methyl 4,6-O-(ferrocenylmethylidene)-a-D-glucopyranoside (1) Compound 1 was obtained as beige-orange-residue (241 mg, 1 0.618 mmol, 53%): mp 66 °C; ½a25 D 90 (c 0.13, CHCl3); H NMR (400 MHz, CDCl3, 23 °C, TMS): d = 5.39 (s, 1H, 7-H), 4.78 (d, 1H, J1,2 3.92 Hz, 1-H), 4.35–4.33 (m, 2H, 10-H), 4.25–4.22 (m, 1H, 6Heq), 4.18 (s, 5H, 12-H), 4.15–4.14 (m, 2H, 11-H), 3.88 (dd, 1H, J3,4;3,2 9.24 Hz, 3-H), 3.74–3.60 (m, 3H, 5-H, 6-Hax, 2-H), 3.45 (s, 3H, 8-H), 3.40 (dd, 1H, J4,5 9.18 Hz, J3,4 9.24 Hz, 4-H) ppm; 13C NMR (100 MHz, CDCl3, 23 °C, TMS): d = 101.06 (C-7), 99.88 (C-1), 84.65 (C-9), 80.89 (C-4), 73.01 (C-2), 72.04 (C-3), 69.25 (C-12),

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Figure 3. ORTEP-diagram of the crystal packing of a-MeRcmGlcH2 (3). Thermal ellipsoids with 50% probability level (hydrogen atoms omitted for clarity).

Table 2 Selected interatomic distances [Å] and bond angles [°] of 1, 2 and 3

a

Distance

1

2

3a

Angle

1

2

3a

O6–C7 O6–C6 O3–C3 O4–C7 O4–C4 O2–C2 O1–C1 O1–C8 C7–CMc

1.426(4) 1.432(3) 1.427(4) 1.421(3) 1.415(3) 1.416(4) 1.402(4) 1.432(4) 1.499(4)

1.424(2) 1.431(2) 1.425(2) 1.426(2) 1.434(2) 1.401(2) 1.383(2) 1.442(2) 1.492(2)

1.418(9) 1.456(8) 1.442(8) 1.440(8) 1.440(8) 1.416(8) 1.391(9) 1.453(9) 1.496(10)

C7–O6–C6 C7–O4–C4 O2–C2–C3 O2–C2–C1 C1–O1–C8 O3–C3–C4 O3–C3–C2 O4–C7–CMc O6–C7–CMc O2–C2–C3–O3

110.4(2) 110.4(2) 111.5(3) 107.1(3) 112.0(2) 109.1(3) 108.5(2) 109.1(2) 109.1(2) 74.1

110.98(11) 108.98(11) 107.62(12) 110.56(12) 112.97(12) 108.44(12) 110.49(12) 110.29(12) 108.00(11) 68.3

110.2(6) 107.9(6) 111.7(6) 111.9(6) 110.9(7) 108.4(7) 110.8(6) 107.6(6) 111.7(7) 58.9–64.9

For compound 3 three independent molecules are found in the unit cell. Therefore, the mean values are given in Table 2.

68.99 (C-6), 68.48, 68.42 (C-11), 67.18, 66.76 (C-10), 62.56 (C-5), 55.73 (C-8) ppm; C18H22FeO6 (390.21): Calcd C 55.40, H 5.68. Found C 55.09, H 5.84. 3.3. Methyl 4,6-O-(ferrocenylmethylidene)-b-D-glucopyranoside (2) Compound 2 was obtained as beige-orange-residue (332 mg, 1 0.851 mmol, 71%): mp 146 °C (dec); ½a25 D 35 (c 0.08, CHCl3); H NMR (400 MHz, CDCl3, 23 °C, TMS): d = 5.39 (s, 1H, 7-H),

4.36–4.34 (m, 2H, 10-H), 4.31–4.27 (m, 2H, 1-H, 6-Heq), 4.18 (s, 5H, 12-H), 4.18–4.15 (m, 2H, 11-H), 3.76 (dd, 1H, J3,4 8.84 Hz, J3,2 8.64 Hz, 3-H), 3.71 (dd, 1H, J6ax,5 10.0 Hz, J6ax,6eq 10.3 Hz, 6-Hax), 3.58 (s, 3H, 8-H), 3.50–3.43 (m, 2H, 2-H, 4-H), 3.37 (ddd, 1H, J5,6ax 10.0 Hz; J5,4 9.14 Hz, J5,6eq 4.84 Hz, 5-H) ppm; 13C NMR (100 MHz, CDCl3, 23 °C, TMS): d = 104.33 (C-1), 101.12 (C-7), 84.51 (C-9), 80.61 (C-4), 74.70 (C-2), 73.43 (C-3), 69.19 (12), 68.76 (C-6), 68.41, 68.35 (C-11), 67.10, 66.73 (C-10), 66.63 (C-5), 57.72 (C-8) ppm; C18H22FeO6 (390.21): Calcd C 55.40, H 5.68. Found C 55.33, H 5.86.

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Figure 4. ORTEP-diagrams of the molecular structures of a-MeFcmGlcH2 (1) and b-MeFcmGlcH2 (2). Thermal ellipsoids with 50% probability level (hydrogen atoms omitted for clarity).

4.29 (d, 1H, J1,2 7.72 Hz, 1-H), 4.22 (dd, 1H, J6eq,6ax 10.08 Hz, J6eq,5 4.74 Hz, 6-Heq), 3.73 (dd, 1H, J3,4;3,2 8.96 Hz, 3-H), 3.62 (dd, 1H, J6ax,5 10.08 Hz, J6ax,6eq 10.08 Hz, 6-Hax), 3.56 (s, 3H, 8-H), 3.44 (dd, 1H, J2,1 7.72 Hz, J2,3 8.96 Hz, 2-H), 3.39 (dd, 1H, J4,3 8.96 Hz, J4,5 9.24 Hz, 4-H), 3.32 (ddd, 1H, J5,6ax 10.08 Hz; J5,4 9.24 Hz, J5,6eq 4.84 Hz, 5-H) ppm; 13C NMR (100 MHz, CDCl3, 23 °C, TMS): d = 104.33 (C-1), 101.12 (C-7), 84.51 (C-9), 80.61 (C-4), 74.70 (C2), 73.43 (C-3), 69.19 (12), 68.76 (C-6), 68.41, 68.35 (C-11), 67.10, 66.73 (C-10), 66.63 (C-5), 57.72 (C-8) ppm; C18H22RuO6 (435.43): Calcd C 49.65, H 5.09. Found C 49.57, H 5.41. 3.6. Crystal structure determination of 1, 2 and 3 Figure 5. ORTEP-diagram of the molecular structure of a-MeRcmGlcH2 (3). Thermal ellipsoids with 50% probability level (hydrogen atoms omitted for clarity).

11

10

M

9 12

O 7

O

6 5 O 4

HO

3

1 2

OH

O 8

Figure 6. Structure of the molecule, with numbering of carbon atoms. (M = Fe, Ru).

3.4. Methyl 4,6-O-(ruthenocenylmethylidene)-a-Dglucopyranoside (3) Compound 3 was obtained as beige residue (193 mg, 1 0.443 mmol, 57%): mp 143 °C (dec); ½a25 D 99 (c 0.08, CHCl3); H NMR (400 MHz, CDCl3, 23 °C, TMS): d = 5.22 (s, 1H, 7-H), 4.76–4.75 (m, 3H, 1-H, 10-H), 4.56 (s, 5H, 12-H), 4.53–4.52 (m, 2H, 11-H), 4.16 (dd, 1H, J6eq,6ax 4.56 Hz, J6eq,5 9.92 Hz, 6-Heq), 3.88 (dd, 1H, J3,4;3,2 9.28 Hz, 3-H), 3.67 (ddd, 1H, J5,6ax 10.12 Hz; J5,4 9.32 Hz, J5,6eq 4.56 Hz, 5-H), 3.60–3.55 (m, 2H, 6-Hax, 2-H), 3.43 (s, 3H, 8-H), 3.33 (dd, 1H, J4,5 9.32 Hz, J3,4 9.28 Hz, 4-H) ppm; 13C NMR (100 MHz, CDCl3, 23 °C, TMS): d = 101.06 (C-7), 99.88 (C-1), 84.65 (C-9), 80.89 (C-4), 73.01 (C-2), 72.04 (C-3), 69.25 (12), 68.99 (C-6), 68.48, 68.42 (C-11), 67.18, 66.76 (C-10), 62.56 (C-5), 55.73 (C-8) ppm; C18H22RuO6 (435.43): Calcd C 49.65, H 5.09. Found C 49.63, H 5.31. 3.5. Methyl 4,6-O-(ruthenocenylmethylidene)-b-Dglucopyranoside (4) Compound 4 was obtained as beige residue (138 mg, 1 0.317 mmol, 41%): mp 125 °C (dec); ½a25 D 4 (c 0.08, CHCl3); H NMR (400 MHz, CDCl3, 23 °C, TMS): d = 5.23 (s, 1H, 7-H), 4.76– 4.75 (m, 2H, 10-H), 4.56 (s, 5H, 12-H), 4.53–4.52 (m, 2H, 11-H),

X-ray diffraction measurements were performed on a Bruker SMART CCD diffractometer with Mo-Ka radiation. Crystal parameters and result of the structure refinement are given in Table 1. Programmes used: SAINT 6.02,16 SADABS,17 SHELXTL-NT V 5.118 and SHELXL-97.19 For graphical representation of the structures 1, 2 and 3 the programme ORTEP was used implemented in programme system WinGX.20 Crystallographic data for the structure have been deposited with the Cambridge Crystallographic Data Centre, CCDC 871710 (1) and CCDC 871711 (2) and CCDC 898398 (3). Copies of the data can be obtained free of charge on application to The Director, CCDC, 12 Union Road, Cambridge CB2 1EZ, UK (Fax: +44 (1223)336 033; e-mail for inquiry: fi[email protected]; e-mail for deposition: [email protected]). References 1. (a) Freiesleben, D.; Hauck, T.; Sünkel, K.; Beck, W. Z. Anorg. Allg. Chem. 2007, 633, 1100–1106; (b) Patra, M.; Gasser, G.; Wenzel, M.; Merz, K.; Bandow, J.; Metzler-Nolte, N. Organometallics 2010, 29, 4312–4319; (c) Patra, M.; MetzlerNolte, N. Chem. Commun. 2011, 11444–11446; (d) Förster, C.; Kovacˇevic´, M.; Barišic´, L.; Rapic´, V.; Heinze, K. Organometallics 2012, 31, 3683–3694. 2. (a) Allscher, T.; Klüfers, P.; Mayer, P. Glycoscience 2008, 4, 1077–1139; (b) Tschersich, S.; Böge, M.; Schwidom, D.; Heck, J. Rev. Inorg. Chem. 2011, 31, 27– 55. 3. (a) Metzler-Nolte, N.; Salmain, M. The Bioorganometallic Chemistry of Ferrocene. In Ferrocenes; Šteˇpnicˇka, P., Ed., 1st ed.; John Wiley & Sons: Chichester, 2008; pp 586–592; (b) Casas-Solvas, J. M.; Vargas-Berenguel, A.; Capitán-Vallvey, L. F.; Santoyo-González, F. Org. Lett. 2004, 6, 3687–3690; (c) Ferreira, C. L.; Ewart, C. B.; Barta, C. A.; Little, S.; Yardley, V.; Martins, C.; Polishchuk, E.; Smith, P. J.; Merkel, M.; Adam, M. J.; Orvig, C. Inorg. Chem. 2006, 45, 8414–8422. 4. Albinati, A.; Pregosin, P. S.; Wick, K. Organometallics 1996, 15, 2419–2421. 5. (a) Shirakami, S.; Itoh, S. T. Tetrahedron: Asymmetry 2000, 11, 2823–2833; (b) Nazarov, A. A.; Hartinger, C. G.; Arion, V. B.; Giester, G.; Keppler, B. K. Tetrahedron 2002, 58, 8489–8492; (c) Hartinger, C. G.; Nazarov, A. A.; Arion, V. B.; Giester, G.; Jaupec, M.; Galanski, M.; Keppler, B. K. New J. Chem. 2002, 26, 671–673. 6. Fernandes, A. C.; Romão, C. C.; Royo, B. J. Organomet. Chem. 2003, 682, 14–19. 7. Casas-Solvas, J. M.; Ortiz-Salmerón, E.; Giménez-Martínez, J. J.; García-Fuentes, L.; Capitán-Vallvey, L. F.; Santoyo-González, F.; Vargas-Berenguel, A. Chem. Eur. J. 2009, 15, 710–725. 8. (a) Küntzer, D.; Jessen, L.; Heck, J. Chem. Commun. 2005, 5653–5655; (b) Kitaev, P.; Zeysing, D.; Heck, J. Monosaccharide Ligands in Organotitanium and

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