Racemic tricarbon­yl[7-meth­oxy-2-(η6-phen­yl)chromane]­chromium(0)

Mukut Gohain; Theunis J Muller; Barend C B Bezuidenhoudt

doi:10.1107/S1600536811008683

. 2011 Mar 12;67(Pt 4):m438–m439. doi: 10.1107/S1600536811008683

Racemic tricarbonyl[7-methoxy-2-(η⁶-phenyl)chromane]chromium(0)

Mukut Gohain ^a, Theunis J Muller ^a,^*, Barend C B Bezuidenhoudt ^a

PMCID: PMC3099749 PMID: 21753961

Abstract

In the title compound, [Cr(C₁₆H₁₆O₂)(CO)₃], the Cr⁰ atom of the Cr(CO)₃ unit is coordinated to the phenyl ring of the flavan ligand in an η⁶ mode, with a normal arene-to-metal distance. The Cr(CO)₃ unit exhibits a three-legged piano-stool conformation, while the dihydropyran ring displays a distorted envelope configuration. The phenyl ring is twisted away from the fused ring system by 25.5 (2)°. The methoxy group is almost coplanar with the phenyl ring [C_Me—O—C_ar—C_ar torsion angle = 8.46 (2)°]. The crystal packing is stabilized by intermolecular C—H⋯O interactions.

Related literature

For similar structures, see: van Tonder et al. (2010a ▶,b ▶) and for other related structures, see: van Tonder et al. (2009a ▶,b ▶). For the synthesis of the title compound, see: Müller et al. (1999 ▶) and for the sythesis of 7-methoxyflavan-4-one, see: Sato et al. (2006 ▶). For standard bond lengths, see: Allen et al. (1987 ▶). For the importance of flavonoids in biological investigations, see: Rice-Evans & Packer (2003 ▶). For the use of tricarbonyl(arene)chromium complexes in regioselective organic synthesis, see: Muschalek et al. (2007 ▶).

Experimental

Crystal data

[Cr(C₁₆H₁₆O₂)(CO)₃]
M _r = 376.32
Monoclinic,
a = 9.7703 (5) Å
b = 19.1820 (9) Å
c = 8.8049 (4) Å
β = 97.494 (2)°
V = 1636.07 (14) Å³
Z = 4
Mo Kα radiation
μ = 0.73 mm⁻¹
T = 100 K
0.34 × 0.23 × 0.08 mm

Data collection

Bruker X8 APEXII 4K KappaCCD diffractometer
Absorption correction: multi-scan (SADABS; Bruker, 2008 ▶) T _min = 0.818, T _max = 0.942
29057 measured reflections
4069 independent reflections
3526 reflections with I > 2σ(I)
R _int = 0.033

Refinement

R[F ² > 2σ(F ²)] = 0.034
wR(F ²) = 0.090
S = 1.00
4069 reflections
222 parameters
H-atom parameters constrained
Δρ_max = 0.73 e Å⁻³
Δρ_min = −0.52 e Å⁻³

Data collection: APEX2 (Bruker, 2008 ▶); cell refinement: SAINT-Plus (Bruker, 2008 ▶); data reduction: SAINT-Plus; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008 ▶); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008 ▶); molecular graphics: DIAMOND (Brandenberg & Putz, 2005 ▶); software used to prepare material for publication: WinGX (Farrugia, 1999 ▶).

Supplementary Material

Crystal structure: contains datablocks global, I. DOI: 10.1107/S1600536811008683/hp2002sup1.cif

e-67-0m438-sup1.cif^{(19.1KB, cif)}

Structure factors: contains datablocks I. DOI: 10.1107/S1600536811008683/hp2002Isup2.hkl

e-67-0m438-Isup2.hkl^{(195.4KB, hkl)}

Additional supplementary materials: crystallographic information; 3D view; checkCIF report

Table 1. Hydrogen-bond geometry (Å, °).

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
C4′—H4′⋯O2ⁱ	0.93	2.54	3.459 (2)	169
C2′—H2′⋯O4ⁱⁱ	0.93	2.46	3.153 (2)	132
C1—H1C⋯O4ⁱⁱⁱ	0.96	2.57	3.314 (2)	134

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Symmetry codes: (i) Inline graphic ; (ii) ; (iii) .

Acknowledgments

The University of the Free State and Sasol Ltd are gratefully acknowledged for financial support and Johannes van Tonder for the NMR data and help with the synthesis of the title compound. Special thanks are due to Prof Andreas Roodt.

supplementary crystallographic information

Comment

The title compound, [Cr(CO)₃(C₁₆H₁₆O₂)] forms part of a series of chromium(0) complexes of the type [Cr(flav)(CO)₃] (flav = flavan, flavone or isoflavone ligand) (van Tonder et al., 2009a,b and 2010a,b). Our interest in this type of chromium(0) complexes is partly due to regioselective organic syntesis (Muschalek et al., 2007) and to the general biological activity of flavanoids (Rice-Evans & Packer, 2003).

The title compound crystalized in the monoclinic space group P2(1)/c, with Z = 4. For the title compound the molecular structure displays the Cr(CO)₃ moiety complexed to the flavone C-ring, exhibiting the known three-legged piano-stool conformation. All bond distances and angles are within range (Allen et al., 1987). The distance between the Cr⁰ atom and the centroid of the A-η⁶-coordinated phenyl ring is 1.7119 (3) Å. The plane through C1'-C6' (r.m.s =0.0038 fitted atoms C1'-C6') of the phenyl ring is at an angle of 42.762 (43) ° to the plane formed between C4—C10 and O1 (r.m.s = 0.00824 fitted atoms C4, C5, C6, C7, C8, C9, C10 and O1). The dihydropyran ring displays a distored envelope configuration by displacement of atoms C2 and C3 from the fused ring system plane, with distances of 0.105 (2) 0.618 (2) Å respectively. The methoxy group at the C7 position is nearley coplanar to the plane created by the fused ring system. The methoxy forme a dihedral angle of -8.464 (23) ° between C1—O2—C7—C6. The molecules form chains through intermolecular C4—H4···O2ⁱ, C2—H2···O4ⁱⁱ and C1—H1C···O4ⁱⁱⁱ hydrogen interactions (Table 1).

Experimental

7-methoxyflavan-4-one was synthesized as described by Sato et al. (2006). 7-Methoxyflavan-4-one (1.00 g; 3.9 mmol), 10% Pd/C (0.10 g), 3 M H₂SO₄ (aq) (1 ml), ethanol (30 ml). Purification by means of flash column-chromatography yielded 7-methoxyflavan (0.67 g; 70.6%) as a colourless oil as described by Sato et al. (2006) R_f 0.65 (hexane:DCM:ethyl acetate; 50:50:1); ¹H NMR (600 MHz, CDCl₃) δ 7.44–7.41 (m, H-2' and H-6', 2H), 7.40–7.37 (m, H-3' and H-5', 2H), 7.34–7.31 (m, H-4', 1H), 6.99–6.97 (m, H-5, 1H), 6.50–6.47 (m, H-6 and H-8, 2H), 5.05 (dd, J = 10.19, 2.37 Hz, H-2 1H), 3.77 (s,-OCH₃, 3H), 2.92 (ddd, J = 16.08, 10.92, 6.02 Hz, H-4(a) 1H), 2.74 (ddd, J = 16.08, 5.12, 3.40 Hz, H-4(e) 1H), 2.22–2.18 (m, H-3 1H), 2.11–2.04 (m, H-3 1H); ¹³C NMR (151 MHz, CDCl₃) δ p.p.m. 24.47 (C-4), 30.19 (C-3), 55.38 (–OCH₃), 77.98 (C-2),101.71 (C-6/8), 107.54 (C-6/8), 114.01, 126.11, 127.93, 128.61, 130.05, 141.79, 155.91, 159.23.

Preparation of the title compound was based on a method described by Müller et al. (1999). A solution of 7-methoxyflavan (0.27 g, 1.1 mmol) and Cr(CO)₆ (0.25 g, 1.1 mmol, 1 eq) in butylether:THF (9:1; 25 ml) was degassed with argon, using standard Schlenk techniques, and refluxed (70 hr) under an oxygen free atmosphere. The reaction mixture was cooled to room temperature and evaporated in vacuo. Purification through flash column-chromotography yielded the title compound (0.10 g; 24%) as a yellow solid. Recrystallization from hexane:dichloromethane (6:1) yielded yellow plate like crystals suitable for X-ray analysis.

R_f 0.30 (hexane:ethyl acetate; 3:5); Mp 145–147 °C IR ν(CO) = 1952, 1894 and 1844 cm^-1;¹H NMR (600 MHz, CDCl₃) δ 6.96 (d, J = 8.3 Hz, 1H), 6.49 (dd, J = 8.3, 2.5 Hz, 1H), 6.48 (d, J = 2.5 Hz, 1H), 5.56 (d, J = 6.2 Hz, 1H), 5.43–5.41 (m, 1H), 5.37–5.32 (m, 3H), 4.67 (dd, J = 10.4, 2.3 Hz, 1H), 3.77 (s, 3H), 2.94–2.87 (m, 1H), 2.76 (m, 1H), 2.25 (m, 1H), 1.99 (m, 1H). ¹³C NMR (151 MHz, CDCl₃) δ p.p.m. 232.53, 159.27, 155.02, 129.85, 113.31, 111.38, 108.09, 101.51, 92.22, 91.62, 91.49, 91.22, 90.68, 75.37, 55.37, 29.89, 24.11.