A Novel Ligand Containing Oxygen Atoms in the Terminal Furan Rings and Its Palladium Compound

말단 퓨란 고리에 산소 원자를 함유한 리간드와 그것의 팔라듐 화합물

EXPERIMENTAL SECTION

All chemicals were purchased and purified. All solvents were distilled and stored over molecular sieves. IR spectra were recorded with a Nicolet 320 FTIR spectrophotometer. Elemental analyses were performed with EA1110 (CE instrument, Italy) at the Korea Basic Science Institute. [PdCl2(NCPh)2] was prepared by the literature method.14

Preparation of 1,2-bis(furan-2-ylmethylene)hydrazine (L). To an ethanol solution (30 mL) containing hydrazine (35 wt% solution in H2O) (0.916 mL, 10 mmol) and 2-furaldehyde (1.660 g, 20 mmol) was added a dichloromethane solution (30 mL) containing formic acid (0.2 mL), and the solution was stirred for 4 h. The resulting brown slurry was filtered, washed with hexane (25 mL×2), and dried under vacuum to give a yellow solid of L1. 96% yield. mp: 134–136℃. IR (KBr, cm–1): 1613, 1414, 728. Anal. Calcd for C10H8N2O2 (Mr = 188.18): C, 63.83; H, 4.29; N, 14.89. Found: C, 63.81; H, 4.29; N, 14.88.

Preparation of [PdL2Cl2] (1). At room temperature, a benzene solution (3mL) containing PdCl2(NCPh)2 (0.054 g, 0.14 mmol) was layered onto the top of a dichloromethane solution (3 mL) containing L (0.029 g, 0.15 mmol) in a test tube. After 3 days, the resulting solution was filtered, washed with diethyl ether (25 mL × 2), and then air-dried to give brown needle crystals of 1. 58% yield. mp: 176–178 ℃ (decom). IR (KBr, cm–1): 3098, 1522, 1388, 725. Anal. Calcd for C20H16Cl2N4O4Pd (Mr = 553.67): C, 43.39; H, 4.29; N, 10.12. Found: C, 43.44; H, 3.80; N, 9.98.

Table 1.aR1=Σ||Fo| - |F||/Σ|Fo|, bwR2=Σ[w(Fo2 - Fc2)2]/Σ[w(Fo2)2]1/2

X-ray Structure Determination. All X-ray data were collected with a Siemens P4 diffractometer equipped with a Mo X-ray tube. Intensity data for compound 1 were empirically corrected for absorption with y-scan data. All structures were solved by direct methods. All non-hydrogen atoms were refined anisotropically. Whereas hydrogen atoms in ligand L were located and refined isotropically, those in compound 1 were generated in idealized positions and refined in a riding model. All calculations were carried out with the SHELXTL programs.15 Details on crystal data, intensity collection, and refinement details are given in Table 1. Selected bond lengths and angles are given in Table 2.

Crystallographic data for the structural analysis have been deposited at the Cambridge Crystallographic Data Center: 619283 (L) and 619284 (1). Copies of this information may be obtained free of charge from: The director, CCDC, 12 Union Road, Cambridge, CB2 1EZ, UK (Fax: +44-1223-336-033; email: deposit@ccdc.cam.ac.uk or www: http://www.ccdc.cam.ac.uk).

 

RESULTS AND DISCUSSION

Preparation of a ligand. A novel potential linking ligands (L) containing oxygen donor atoms in two terminal heteroaromatic (furan) rings has been prepared in 96% isolation yield by the simple and straightforward Schiff-base condensation. Hydrazine reacted with 2-furaldehyde to give 1,2-bis(furan-2-ylmethylene)hydrazine (L) at room temperature under slightly acidic conditions (pH = 5–6) (eq 1).

This ligand was characterized by elemental analysis, IR spectroscopy, and X-ray diffraction. The IR spectrum of ligand L displays an absorption bands at 1613 cm-1 assignable to the C=N bond, consistent with the fact that C=N stretching frequencies of Schiff bases appear in the range 1680-1603 cm-1.16-18 The structure of ligand L is shown in Fig. 1. The central N-N bond length is 1.409(3) Å. The O···O distance between two terminal furan rings is 6.988 Å, and the whole molecule is conjugated.

Table 2.Symmetry transformations used to generate equivalent atoms: #1 = -x + 1, -y + 1, -z + 1; #2 = -x, -y, -z

Fig. 1.ORTEP drawing of of L with 50% probability thermal ellipsoids. Unlabeled atoms are related to labeled ones by the crystallographic inversion.

Molecular palladium compound. We tried to prepare palladium coordination polymers by employing ligand L. For this purpose, PdCl2(NCPh)2 was selected, because it possesses labile benzonitrile (NCPh) ligands. Inconsistent with our expectation, however, ligand L produced a molecular Pd compound from the reactions with PdCl2(NCPh)2, in which the Pd metal is bound to the nitrogen atoms in the Schiff-base imine groups, not to the oxygen atoms in the terminal heteroaromatic rings to give a polymeric species (eq 2).

Fig. 2.ORTEP drawing of compound 1. Unlabeled atoms are related to labeled ones by the crystallographic inversion.

The molecular structure of compound 1 is presented in Fig. 2, which clearly shows that the Pd metal is bonded to the nitrogen atom in the Schiffbase imine groups, not to the oxygen atoms in the terminal furan rings. The coordination sphere of the Pd metal can be described as square planar. The Pd–N bond lengths (2.036(4) Å for 1 and 2.040(3) Å for 2) indicate a single Pd–N bond.

In summary, we prepared a novel potential linking ligand, 1,2-bis(furan-2-ylmethylene)hydrazine (L) that contains oxygen atoms in the terminal furan rings. Ligand L reacted with [PdCl2(NCPh)2] to produce a molecular Pd compound, [PdL2Cl2] (1), in which the Pd metal is bound to the nitrogen atoms in the Schiff-base imine groups, not oxygen atoms to give polymers.