Bromido[1-(η6-4-tert-butyl­benz­yl)-3-(2,4,6-trimethyl­benz­yl)benzimidazol-2-yl­idene]chloridoruthenium(II)

Hakan Arslan; Don VanDerveer; İsmail Özdemir; Serpil Demir; Bekir Çetinkaya

doi:10.1107/S1600536808042256

. 2008 Dec 20;65(Pt 1):m97–m98. doi: 10.1107/S1600536808042256

Bromido[1-(η⁶-4-tert-butylbenzyl)-3-(2,4,6-trimethylbenzyl)benzimidazol-2-ylidene]chloridoruthenium(II)

Hakan Arslan ^a,^b,^*, Don VanDerveer ^c, İsmail Özdemir ^d, Serpil Demir ^d, Bekir Çetinkaya ^e

PMCID: PMC2967929 PMID: 21581560

Abstract

A new ruthenium complex, [RuBrCl(C₂₈H₃₂N₂)], has been synthesized and characterized by elemental analysis, ¹H NMR, ¹³C NMR, IR-spectroscopy and a single-crystal X-ray diffraction study. The Ru atom in this complex is best described as having a considerably distorted octahedral coordination environment with the arene occupying three coordination sites. Two further coordination sites are occupied by chloride and bromide ligands, while the sixth site is occupied by the carbene. The carbene portion of the ligand is a benzimidazole ring. This ring is connected to the C₆H₄C(CH₃)₃ arene by a CH₂ bridge. This leads to a system with very little apparent strain. The two halogen atoms are disordered between Br and Cl. Two partial Cl atoms share the same sites as two partial Br atoms so that the title compound effectively has one Cl and one Br atom. C—H⋯X (X = Cl, Br) hydrogen bonds help to stabilize the crystal structure.

Related literature

For synthesis, see: Yaşar et al. (2008 ▶); Çetinkaya et al. (2003 ▶). For general background, see: Herrmann (2002 ▶); Arduengo & Krafczyc (1998 ▶); Arduengo et al. (1991 ▶). For related compounds, see: Begley et al. (1991 ▶); Arslan et al. (2004b ▶, 2005a ▶,b ▶, 2007b ▶,c ▶). For related literature, see: Arslan et al. (2004a ▶, 2007a ▶); Herrmann et al. (1995 ▶); Navarro et al. (2006 ▶); Özdemir et al. (2001 ▶); Çetinkaya et al. (2001 ▶, 2002 ▶).

Experimental

Crystal data

[RuBrCl(C₂₈H₃₂N₂)]
M _r = 611.69
Monoclinic,
a = 7.6336 (15) Å
b = 27.725 (6) Å
c = 12.051 (2) Å
β = 98.80 (3)°
V = 2520.5 (9) Å³
Z = 4
Mo Kα radiation
μ = 2.29 mm⁻¹
T = 153 (2) K
0.26 × 0.12 × 0.02 mm

Data collection

Rigaku Mercury CCD diffractometer
Absorption correction: multi-scan (REQAB; Jacobson, 1998 ▶) T _min = 0.581, T _max = 0.955
17799 measured reflections
4449 independent reflections
3288 reflections with I > 2σ(I)
R _int = 0.089

Refinement

R[F ² > 2σ(F ²)] = 0.089
wR(F ²) = 0.255
S = 1.04
4449 reflections
306 parameters
H-atom parameters constrained
Δρ_max = 2.45 e Å⁻³
Δρ_min = −1.38 e Å⁻³

Data collection: CrystalClear (Rigaku/MSC, 2006 ▶); cell refinement: CrystalClear; data reduction: CrystalClear; program(s) used to solve structure: SHELXTL (Sheldrick, 2008 ▶); program(s) used to refine structure: SHELXTL; molecular graphics: SHELXTL; software used to prepare material for publication: SHELXTL.

Supplementary Material

Crystal structure: contains datablocks global, I. DOI: 10.1107/S1600536808042256/at2686sup1.cif

e-65-00m97-sup1.cif^{(31.9KB, cif)}

Structure factors: contains datablocks I. DOI: 10.1107/S1600536808042256/at2686Isup2.hkl

e-65-00m97-Isup2.hkl^{(218KB, 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
C14—H14⋯Cl2ⁱ	0.96	2.65	3.406 (11)	135
C16—H16C⋯Br1	0.96	2.92	3.563 (11)	125
C19—H19A⋯Br1	0.96	2.92	3.323 (11)	106

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Symmetry code: (i) Inline graphic .

Acknowledgments

We thank the Scientific and Technological Research Council of Turkey TÜBİTAK-CNRS [TBAG-U/181 (106 T716)] and İnönü University Research Fund (BAP. 2008/03 Güdümlü) for financial support.

supplementary crystallographic information

Comment

N-Heterocyclic carbenes have received great attention since the first synthesis of a carbene compound,1,3-di-l-adamantylimidazol-2-ylidene, by Arduengo et al., (1991). N-heterocyclic carbenes generally derived from imidazolium, tetrahydropyrimidin-1-ium and benzimidazolium salts, have attracted wide spread attention as ligands for main group elements and transition metals. The N-heterocyclic carbene metal complexes are remarkably stable toward heat, air, and moisture, and many organic reactions using these complexes as catalysts have been investigated. These include Suzuki-Miyura, Sonogashira, Stille and Heck reactions (Herrmann et al., 1995; Herrmann, 2002; Navarro et al., 2006; Arduengo & Krafczyc,1998).

Previous work from our research groups in this area has focused on the elaboration of olefins as electron-rich heterocyclic carbene precursors to allow the formation of chelating carbenes. We have also looked at the rapidly developing chemistry of η⁶-arene ruthenium(II) complexes containing substituted imidazolidin-2-ylidenes (Özdemir et al., 2001; Çetinkaya et al., 2001, 2002, 2003), and on synthesis, characterization, crystal structure, and using palladium, platinum and ruthenium N-heterocyclic carbene complexes as catalysts (Yaşar et al., 2008; Arslan et al., 2007a, 2007b, 2007c, 2004a, 2004b, 2005a, 2005b).

In the present study, we have synthesized and characterized a new ruthenium complex, (1-(4-tert-butylbenzyl)-3-(2,4,6-trimethylbenzyl)-benzimidazol-2-ylidene)ruthenium(II) bromide chloride, (I). The molecular structure of the title compound, (I), is depicted in Fig. 1.

The carbene portion of the ligand is a benzimidazole ring. This ring is connected to the C₆H₄C(CH₃)₃ arene by a CH₂ bridge. This leads to a system with very little apparent strain. The ruthenium atom in the title compound is best described as having an octahedral coordination environment, with the arene occupying three coordination sites. Two further coordination sites are occupied by Cl and Br ligands, while the sixth site is occupied by the carbene carbon of benzimidazole ring. The ruthenium atom is situated 1.658 (5) Å from the ring centroid of the arene atom. While there are substantial differences in the C—C and C—Ru distances for the arene ring, there is no evidence of the alternating C—C bonds observed in some ruthenium-arene complexes (Begley et al., 1991). The arene ring is essentially planar, the mean deviation from the plane being 0.013 (12) Å. In addition, the trimethylbenzyl and benzimidazole rings are almost planar with the maximum deviations of 0.009 (12) Å for atom C25 and, 0.003 (11) Å for atom C2. The benzimidazole moiety is planar and it forms dihedral angles of 87.16 (6)° and 85.31 (7)°, respectively, with the mean planes through the arene and trimethylbenzyl rings.

The two halogen atoms are disordered between Br and Cl. Two chlorine atoms share the same site as two bromine atoms so that the title compound effectively has one Cl and one Br atom. The occupancies of the Cl1 and Cl2 atoms are 0.399 (11) and 0.630 (11), respectively, and those of the Br1 and Br2 atoms are 0.601 (11) and 0.370 (11), respectively.

The structure of the title compound is assembled by intermolecular C—H···Cl hydrogen bonds, to form a two-dimensional framework (Fig. 2, 3 and Table 1) (Macrae et al., 2006). The intermolecular contacts, C—H···Br, are also listed in Table 1.

Experimental

All reactions for the preparation of (I) and (II) were carried out under Ar in flame-dried glass-ware using standard Schlenk-type flasks. The solvents used were purified by distillation over the drying agents indicated and were transferred under Ar: CH₂Cl₂ (P₄O₁₀), hexane, toluene (Na). RuClBr[η¹-CN{CH₂(η⁶-C₆H₄CMe₃-4)}C₆H₄N(CH₂C₆H₂Me₃-2,4,6)]: A suspension of 1-(4-terbutylbenzyl)-3-(2,4,6-trimethylbenzyl)benzimidazolium bromide (1.00 g, 2.10 mmol), Cs₂CO₃ (0.7 g, 2.14 mmol), [RuCl₂(p-cymene)]₂ (0.5 g, 0.82 mmol) and molecular sieves was heated under reflux in degassed dry toluene (20 ml) for 12 h. The reaction mixture was then filtered while hot, and the volume was reduced to about 10 ml before addition of n-hexane (10 ml). The precipitate formed was crystallized from CH₂Cl₂/hexane (5:10 ml) to give the crystal product (Fig. 3). Yield 1.00 g (82%). M.p.: 339–340 ^oC. FT—IR (KBr pellet, cm^-1): ν_CN 1432 cm^-1. Anal. Found: C, 54.91; H, 5.29; N: 4.54. Calc. for C₂₈H₃₂N₂RuClBr: C, 54.86; H, 5.26; N, 4.57. ¹H NMR (δ, 399.9 MHz, CDCl₃): 1.25, 1.31 and 1.37 [s, 9H, CH₂C₆H₄C(CH₃)₃-p]; 2.17 [m, 9H, CH₂C₆H₂(CH₃)₃-2,4,6]; 5.07 and 5.67 [m, 4H, CH₂C₆H₂(CH₃)₃-2,4,6 and CH₂C₆H₄C(CH₃)₃-p]; 6.79–7.60 [m, 10H, NC6H4 N, CH₂C₆H₂(CH₃)₃-2,4,6 and CH₂C₆H₄C(CH₃)₃-p]. ¹³C {H} NMR (δ, 100.5 MHz, CDCl₃): 20.4 and 21.5 [CH₂C₆H₂(CH₃)₃-2,4,6]; 31.3 [CH₂C₆H₄C(CH₃)₃-p]; 34.7 [CH₂C₆H₄C(CH₃)₃-p]; 45.0 [CH₂C₆H₂(CH₃)₃-2,4,6]; 53.2 [CH₂C₆H₄C(CH₃)₃-p]; 89.1, 90.1, 91.1, 93.0, 93.7, 98.9, 100.9, 109.7, 113.0, 113.8, 123.3, 125.3, 127.9, 129.0, 131.5, 133.4, 137.9 and 150.1 [CH₂C₆H₂(CH₃)₃-2,4,6;NC₆H₄N and CH₂C₆H₄C(CH₃)₃-p]; 184.1 [C_carbene].