Synthesis and application of N,N,N',N'-Tetrakis(2-hydroxyethyl)ethylenediamine

N,N,N',N'-Tetrakis(2-hydroxyethyl)ethylenediamine, an amino alcohol compound, exists as a transparent colorless to amber viscous liquid under ambient conditions and demonstrates excellent water solubility along with miscibility in most organic solvents. With multiple reactive coordination sites in its molecular structure, N,N,N',N'-Tetrakis(2-hydroxyethyl)ethylenediamine exhibits remarkable capacity to form complexation reactions with various metal ions, thereby rendering it particularly valuable in the fields of organometallic complexes and metal catalysis.

Synthesis

Ethylenediamine (0.56 mL, 8.32 mmol) and water (50 mL) were added to a round-bottomed flask fitted with an dropping funnel and a cooling finger. Ethylene oxide (9.11 mL, 0.17 mol) and water (20 mL) were added to the reaction mixture dropwise. The reaction stirred for two hours with the temperature kept under 5 degC. The water and excess ethylene oxide were removed by rotary evaporator, yielding N,N,N',N'-Tetrakis(2-hydroxyethyl)ethylenediamine (1.43 g, 73 %).

Chelation of metal ions

A novel water-soluble palladium(II) complex derived from N,N,N',N'-Tetrakis(2-hydroxyethyl)ethylenediamine (edteH₄) was synthesized in high yield and thoroughly characterized by a combination of NMR spectroscopic methods, including ¹H, ¹³C, HMQC, and COSY. Serving as the key ligand in this study, N,N,N',N'-Tetrakis(2-hydroxyethyl)ethylenediamine was identified to coordinate in a κ² (N,N')-mode, a configuration that leaves its four pendant CH₂CH₂OH arms free and which was definitively confirmed by single-crystal X-ray diffraction analysis to yield a cis square-planar geometry around the palladium center. The catalytic efficacy of this newly synthesized palladium complex was then evaluated alongside a previously reported triethanolamine-based palladium complex for the Suzuki-Miyaura cross-coupling of various aryl bromides with phenylboronic acid in aqueous media. Notably, electronically activated substrates such as 4-bromoacetophenone and 4-bromobenzaldehyde participated in the cross-coupling with remarkable efficiency, achieving turnover numbers of up to 100,000 in the absence of any organic solvent. The study describes the synthesis and characterization of a chelate-stabilized palladium(II) complex, [PdCl₂(edteH₄)] (2), utilizing N,N,N',N'-Tetrakis(2-hydroxyethyl)ethylenediamine (edteH₄) (1) as the foundational ligand. The selection of N,N,N',N'-Tetrakis(2-hydroxyethyl)ethylenediamine (edteH₄) was based on its advantageous properties as a water-soluble and cost-effective ligand, which is chemically recognized as the reduced form of edtaH₄. Notably, the investigation was prompted by the surprising observation that this particular ligand had not been previously explored within the context of palladium(II) coordination chemistry. For the purpose of a comparative assessment of catalytic performance, complex 3 was also prepared according to a literature method. The catalytic efficacy of both water-soluble complexes, 2 and 3, was subsequently evaluated for facilitating the Suzuki-Miyaura cross-coupling reaction in an aqueous medium. [1]

Experimental Procedure

Figure1: N,N,N',N'-Tetrakis(2-hydroxyethyl)ethylenediamine chelates palladium ions

A solution of N,N,N',N'-Tetrakis(2-hydroxyethyl)ethylenediamine (edteH₄) in dichloromethane was added dropwise to a stirred solution of [PdCl₂(MeCN)₂] in the same solvent, initiating the formation of the target palladium complex. Acting as the coordinating ligand, N,N,N',N'-Tetrakis(2-hydroxyethyl)ethylenediamine reacted completely over a 12-hour period at room temperature, a process accompanied by the gradual formation of a yellow precipitate from the reaction mixture. Following the completion of the reaction, the mother liquor was removed by filtration, and the resulting crude solid was sequentially washed with diethyl ether and subsequently subjected to crystallization using a methanol/diethyl ether solvent system to afford the final product as a pure yellow solid in an isolated yield of 93%. [1]

Application

Sensor synthesis

Based on an evaluation of fifty-one different adsorption coating materials, N,N,N',N'-Tetrakis(2-hydroxyethyl)ethylenediamine was identified as a highly effective coating for a silver-plated piezoelectric crystal sensor, demonstrating a notably sensitive response to carbon dioxide. When applied as a film with a specific loading of 91 μg, the sensor incorporating N,N,N',N'-Tetrakis(2-hydroxyethyl)ethylenediamine exhibited a wide detection range, a low detection limit of 100 ppm (v/v), and offered significant advantages including reversibility, excellent reproducibility, and a rapid response time, while showing minimal interference from other dissolved gases in transformer oil such as carbon monoxide, hydrogen, methane, ethane, ethylene, and acetylene. Furthermore, the practical application of this sensor for determining CO₂ content in a simulated transformer oil gas mixture yielded results with satisfactory precision. [2]

Reference

[1] Süleyman Gülcemal, N,N,N0,N0-Tetrakis(2-hydroxyethyl)ethylenediamine palladium(II) complex as efficient catalyst for the Suzuki/Miyaura reaction in water, Tetrahedron 66 2010, 66, 5602e5606.

[2] Cao Z, Xu D. Study on a coated piezoelectric crystal carbon dioxide sensor[J]. Journal of Hunan University: Natural Sciences, 1996, 23(6): 1-6.