Bis[μ-2-(2H-benzotriazol-2-yl)-4-methyl­phenolato]bis­[dimethyl­aluminium(III)]

Chen-Yu Li; Chia-Her Lin; Bao-Tsan Ko

doi:10.1107/S1600536809018492

. 2009 May 23;65(Pt 6):m670. doi: 10.1107/S1600536809018492

Bis[μ-2-(2H-benzotriazol-2-yl)-4-methylphenolato]bis[dimethylaluminium(III)]

Chen-Yu Li ^a, Chia-Her Lin ^a, Bao-Tsan Ko ^a,^*

PMCID: PMC2969717 PMID: 21583031

Abstract

The title complex, [Al₂(CH₃)₄(C₁₃H₁₀N₃O)₂], is dimeric, bridged through the O atoms of the phenolate anions. The asymmetric unit contains one half of the molecule and there is a crystallographic inversion centre in this molecule. Each Al atom is pentacoordinated by one N atom and two bridging O atoms of two N,O-bidentate benzotriazolylphenolate ligands and by two C atoms from two methyl groups, forming a distorted trigonal–bipyramidal environment.

Related literature

For background information, see: Liu et al. (2001 ▶); Wu et al. (2006 ▶). For related structures, see: Lewinski et al. (2003 ▶); Tsai et al. (2009 ▶).

Experimental

Crystal data

[Al₂(CH₃)₄(C₁₃H₁₀N₃O)₂]
M _r = 562.58
Triclinic,
a = 7.4220 (4) Å
b = 9.7120 (5) Å
c = 11.6331 (6) Å
α = 112.517 (2)°
β = 94.824 (3)°
γ = 109.574 (2)°
V = 707.79 (7) Å³
Z = 1
Mo Kα radiation
μ = 0.14 mm⁻¹
T = 296 K
0.48 × 0.25 × 0.25 mm

Data collection

Bruker APEXII CCD diffractometer
Absorption correction: multi-scan (SADABS; Bruker, 2008 ▶) T _min = 0.937, T _max = 0.966
11757 measured reflections
3405 independent reflections
2923 reflections with I > 2σ(I)
R _int = 0.017

Refinement

R[F ² > 2σ(F ²)] = 0.039
wR(F ²) = 0.122
S = 1.03
3405 reflections
182 parameters
H-atom parameters constrained
Δρ_max = 0.28 e Å⁻³
Δρ_min = −0.26 e Å⁻³

Data collection: APEX2 (Bruker, 2008 ▶); cell refinement: SAINT (Bruker, 2008 ▶); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008 ▶); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008 ▶); molecular graphics: SHELXTL (Sheldrick, 2008 ▶); software used to prepare material for publication: SHELXTL.

Supplementary Material

Crystal structure: contains datablocks I, global. DOI: 10.1107/S1600536809018492/rk2147sup1.cif

e-65-0m670-sup1.cif^{(16.2KB, cif)}

Structure factors: contains datablocks I. DOI: 10.1107/S1600536809018492/rk2147Isup2.hkl

e-65-0m670-Isup2.hkl^{(167KB, hkl)}

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

Acknowledgments

The authors gratefully acknowledge financial support from the National Science Council, Taiwan (grant No. NSC97-2113-M-033-005-MY2) and from the Project of the Specific Research Fields in Chung Yuan Christian University, Taiwan (grant No. CYCU-97-CR-CH).

supplementary crystallographic information

Comment

Due to the biodegradable, biocompatible, and permeable properties, aliphatic polyesters, such as poly(ε-caprolactone) - (PCL), poly(lactide) - (PLA) and their co-polymers have been widely used in the biomedical and pharmaceutical fields. Therefore, it has been of great interest to develop new catalytic/initiating systems for the preparation of PCL and PLA. Metal complex-catalyzed ring-opening polymerization (ROP) of lactones/lactides has been proven to be the most promising method to synthesize these polymers (Wu et al., 2006). Among them, a variety of main group metal complexes, such as magnesium, zinc, tin, lithium, and calcium as well as aluminum complexes have been reported to be efficient initiators/catalysts. In particular, Liu with co-workers, (2001) have reported the aluminum alkoxide complexes supported by the bulky bisphenol ligand and these complexes have been demonstrated as efficient initiators to catalyze ROP of caprolactones and lactides. Recently, our group is interested in the synthesis and preparation of various metal complexes derived from the benzotriazol-phenol ligands. For instance, we have successfully synthesized and structural characterized a Pd(II) complex with 4-methyl-2-(2H-benzotriazol-2-yl)-phenolate ligands (Tsai et al., 2009). We report herein the synthesis and crystal structure of N,O-bidentate benzotriazol-phenolate ligands incorporated Al^III complex (I), a potential catalyst for the ROP of cyclic esters in the presence of alcohols (Scheme 1).

The solid structure of title compound (I) reveals a dimeric Al^III complex (Fig. 1), doubly bridged through the O atoms of the phenolate anions. It was found that the asymmetric unit has one half of molecule and there exists a crystallographic inversion centre of symmetry in this molecule. The geometry around each Al atom is penta-coordinated with a distorted trigonal bipyramidal environment in which one N atom and two bridging O atoms come from N,O–bidentate benzotriazol-phenolate ligand and two C atoms are from two methyl groups. The sums of bond angles around Al center are 359.97 (7)°. The bond distances between the Al atom and O, N1, Oⁱ (symmetry code: (i) -x, -y, -z + 2), C14 and C15 are 1.8338 (11), 2.1061 (13), 2.0918 (11), 1.9767 (17), 1.9725 (17) Å, respectively. These bond distances are longer than those found in other Schiff base Al^III complexes with four-coordinated geometry (Lewinski et al., 2003). It is interesting to note that the six-member ring formed from the bidentate benzotriazol-phenolate ligand and Al atom is almost coplanar with the mean deviation of 0.006 (2) Å.

Experimental

The title compound I was synthesized by the following procedures (see Fig. 2): to a rapidly stirred solution of 4-methyl-2-(2H-benzotriazol-2-yl)phenol (0.22 g, 1.0 mmol) in toluene (20 ml) was slowly added AlMe₃ (0.5 ml, 1.0 mmol). The mixture was further stirred at room temperature for 2 h and then dried under vacuum. The residue was extracted with hot toluene (10 ml) and the saturated solution was cooled to 273 K, yielding yellow crystals. Yield: 0.24 g (86%). ¹H NMR (CDCl₃, p.p.m.): δ 7.04–8.14 (14H, m, ArH), 2.40 (6H, s, CH₃), -0.57 (12H, s, AlCH₃).