Racemic tricarbonyl[(4a,5,6,7,8,8a-η)-2-phenyl-3,4-dihydro-2H-1-benzopyran]chromium(0)

Johannes H van Tonder; Barend C B Bezuidenhoudt; J Marthinus Janse van Rensburg

doi:10.1107/S1600536810031028

. 2010 Aug 11;66(Pt 9):m1086. doi: 10.1107/S1600536810031028

Racemic tricarbonyl[(4a,5,6,7,8,8a-η)-2-phenyl-3,4-dihydro-2H-1-benzopyran]chromium(0)

Johannes H van Tonder ^a, Barend C B Bezuidenhoudt ^a,^*, J Marthinus Janse van Rensburg ^b

PMCID: PMC3007955 PMID: 21588503

Abstract

The title compound, [Cr(C₁₅H₁₄O)(CO)₃], displays a distorted envelope configuration of the dihydropyrane ring. The dihedral angle between the phenyl and phenylene rings is 50.63 (4)°. The Cr⁰ atom is coordinated by three CO groups and the phenylene ring of the flavan ligand in an η⁶ mode, with a common arene-to-metal distance

Related literature

For general background to chromium(0) complexes of the type [Cr(flav)(CO)₃] (flav = flavan, flavone or isoflavone ligand), see: Muschalek et al. (2007 ▶). For related structures, see: van Tonder et al. (2009a ▶,b ▶). For the synthesis, see: Müller et al. (1999 ▶).

Experimental

Crystal data

[Cr(C₁₅H₁₄O)(CO)₃]
M _r = 346.29
Monoclinic,
a = 12.0275 (2) Å
b = 13.1454 (2) Å
c = 10.4473 (2) Å
β = 111.717 (1)°
V = 1534.55 (5) Å³
Z = 4
Mo Kα radiation
μ = 0.76 mm⁻¹
T = 173 K
0.46 × 0.34 × 0.11 mm

Data collection

Bruker APEXII CCD diffractometer
Absorption correction: multi-scan (SADABS; Bruker, 2001 ▶) T _min = 0.766, T _max = 0.938
20468 measured reflections
5342 independent reflections
3728 reflections with I > 2σ(I)
R _int = 0.050

Refinement

R[F ² > 2σ(F ²)] = 0.038
wR(F ²) = 0.097
S = 0.95
5342 reflections
208 parameters
H-atom parameters constrained
Δρ_max = 0.67 e Å⁻³
Δρ_min = −0.32 e Å⁻³

Data collection: APEX2 (Bruker, 2007 ▶); cell refinement: SAINT-Plus (Bruker, 2007 ▶); data reduction: SAINT-Plus; program(s) used to solve structure: SIR97 (Altomare et al., 1999 ▶); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008 ▶); molecular graphics: DIAMOND (Brandenburg & Putz, 1999 ▶); software used to prepare material for publication: WinGX (Farrugia, 1999 ▶).

Supplementary Material

Crystal structure: contains datablocks global, I. DOI: 10.1107/S1600536810031028/hy2329sup1.cif

e-66-m1086-sup1.cif^{(18.2KB, cif)}

Structure factors: contains datablocks I. DOI: 10.1107/S1600536810031028/hy2329Isup2.hkl

e-66-m1086-Isup2.hkl^{(256.3KB, hkl)}

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

Table 1. Selected bond lengths (Å).

C5—Cr	2.1936 (18)
C6—Cr	2.2163 (19)
C7—Cr	2.2087 (19)
C8—Cr	2.2251 (17)
C9—Cr	2.2773 (17)
C10—Cr	2.2532 (17)
C11—Cr	1.8353 (19)
C12—Cr	1.8298 (19)
C13—Cr	1.8399 (17)

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Acknowledgments

Financial assistance from the University of the Free State and SASOL to JHvT is gratefully acknowledged. Opinions, findings, conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of SASOL. We would like to express our gratitude to the School of Chemistry at the University of the Witwatersrand for the use of diffractometer.

supplementary crystallographic information

Comment

The title compound 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). Our interest in this type of chromium(0) complexes is partly due to their importance in organic synthesis, as noted earlier (Muschalek et al., 2007).

As illustrated in Fig. 1, the Cr(CO)₃ group coordinates to the phenylene ring of the flavanoid backbone (Table 1). The distance between the Cr⁰ atom and the centroid of the A-η⁶-coordinated arene ring is 1.731 (1) Å (r.m.s of fitted atoms C5– C10 = 0.0186Å). Molecular distortion is displayed by the twisted flavan backbone. Atoms C4 and O5 is essentially in the plane of the coordinated arene ring (r.m.s of atoms C4–C10 and O5 = 0.0202Å), while atoms C2 and C3 are respectively displaced by -0.244 (2) and 0.478 (2) Å from the plane formed by atoms C4–C10 and O5. This distortion is a result of the expected envelope configuration in the dihydropyran ring. In turn the phenyl ring is twisted away from the plane of atoms C4–C10 and O5, with a dihedral angle of 50.88 (4)°. The crystal packing displays an intermolecular C—H···π soft contact [H···centroid distance = 2.92 Å] between the phenyl ring of one molecule and the arene ring of a neighbouring molecule (Fig. 2). The crystal packing is also stabilized by a C—H···O soft contact between atoms H8 and O5, with a distance of 2.57 Å and a C8—H8···O5 angle of 140°.

Experimental

Flavan was synthezised via H₂SO₄ catalyzed hydrogenation (5 bar) over 10% Pd/C from flavan-4-one [flavan-4-one (2.00 g, 8.9 mmol), 10 % Pd/C (0.10 g), 3 M H₂SO₄ (1 ml), EtOH (50 ml)]. Purification by means of flash column-chromatography yielded flavan (0.94 g, 49.9%) as a colourless oil. R_f 0.77 (H:A, 8:2).

Preparation of the title compound was based on a method described by Müller et al. (1999). A solution of flavan (0.51 g, 2.4 mmol) and Cr(CO)₆ (0.53 g, 2.4 mmol) in Bu₂O:THF (9:1, 10 ml per 100 mg) was degassed with argon, using standard Schlenk techniques, and refluxed (48 h) under an oxygen free atmosphere. The reaction mixture was cooled to room temperature and the solvent evaporated in vacuo. Purification through flash column-chromatography yielded tricarbonyl(A-η⁶flavan)chromium(0) (0.08 g, 9.2%) as a yellow solid. Recrystallization from diethyl ether yielded yellow cuboidal crystals. R_f 0.23 (hexane:acetone, 8:2); Mp 170.4°C.