Malaysian Journal of Analytical Sciences Vol 23 No 2 (2019): 247 - 254

EFFECT OF TEMPERATURE ON THE CATALYTIC ACTIVITY OF NEW SYMMETRICAL TETRADENTATE PALLADIUM(II) SCHIFF BASE COMPLEXES IN COPPER-FREE SONOGASHIRA REACTION

(Kesan Suhu Terhadap Aktiviti Pemangkinan Kompleks Baru Paladium(II) Tetradentat Bes Schiff Bersimetri dalam Tindak Balas Sonogashira Tanpa Kuprum)

Shahrul Nizam Ahmad¹*, Hadariah Bahron¹, Amalina Mohd Tajuddin²

¹Faculty of Applied Sciences,

Universiti Teknologi MARA, 40450 Shah Alam, Selangor, Malaysia

²Atta-ur-Rahman Institute for Natural Product Discovery,

Level 9, Building FF3, UiTM Selangor, Kampus Puncak Alam, Bandar Puncak Alam, Selangor, Malaysia

*Corresponding author: shahrulnizam85@gmail.com

Received: 29 August 2018; Accepted: 18 February 2019

Abstract

This paper reports the synthesis of two tetradentate Schiff bases namely 2,2'-(((2,2-dimethylpropane-1,3-diyl) bis(azanylylidene))bis(methanylylidene))bis(4-methoxylphenol), LM, and 2,2'-(((2,2-dimethylpropane-1,3-diyl)bis (azanylylidene))bis(methanylylidene))bis(4-nitrophenol), LN. The Schiff bases were reacted with palladium(II) acetate in 1:1 molar ratio yielding two palladium(II) complexes, PdLN and PdLM. The compounds were characterized through elemental analysis, infrared spectroscopy, ¹H and ¹³C Nuclear Magnetic Resonance (NMR), magnetic susceptibility, molar conductivity and melting point. Complexation was indicated to have occurred by the shifting of the characteristic n(C=N), n(C-O) and d(HC=N) peaks. This was supported by appearance of new peaks of n(M-N) and n(M-O) as well as disappearance of d(O-H) peak on the IR and ¹H NMR spectra of the palladium(II) complexes. The diamagnetic and non-electrolytic nature of the complexes suggested square planar d⁸ palladium(II) geometry and absence of counter ions, respectively. The catalytic activity of the palladium(II) complexes was investigated for copper-free Sonogashira reaction between iodobenzene and phenylacetylene in dimethylsulfoxide (DMSO) at 80 ^oC, 100 ^oC and 140 ^oC. The conversion of iodobenzene at 12 h reaction time was monitored by GC-FID. At 100 ^oC, the most active catalyst was PdLN, indicating that the electron withdrawing substituent –NO₂, has the ability to enhance catalytic properties of the complexes. At 140 ^oC, both palladium(II) complexes successfully converted 100% of iodobenzene.

Keywords: Schiff base, palladium(II) complexes, Sonogashira, temperature change

Abstrak

Kertas kajian ini melaporkan sintesis dua bes Schiff tetradentat iaitu 2,2'-(((2,2-dimetilpropana-1,3-diyl)bis(azanililidena))-bis(methanililidena))bis(4-metoksilfenol), LM dan 2,2'-(((2,2-dimetilpropana-1,3-diyl)bis(azanililidena))bis(methanili-lidena))bis(4-nitrofenol), LN. Bes Schiff tersebut telah ditindakbalaskan dengan palladium(II) asetat dengan nisbah mol 1:1, menghasilkan dua kompleks palladium(II), iaitu PdLN dan PdLM. Sebatian telah dicirikan melalui analisis unsur, spektroskopi inframerah (IM), Resonans Magnetik Nuklear (RMN) ¹H dan ¹³C, kerentanan magnetik, kekonduksian molar dan takat lebur. Pengkompleksan ditunjukkan telah berlaku dengan penganjakan puncak n(C=N), n(C-O) dan d(HC=N). Ia dikukuhkan lagi dengan munculnya puncak baru n(M-N) dan n(M-O) dan hilangnya puncak d(O-H) pada spektrum IM dan ¹H RMN kompleks paladium(II). Sifat diamagnetik dan bukan elektrolit komplek mencadangkan geometri satah segiempat sama d⁸ paladium(II) dan ketiadaan ion kaunter, masing-masing. Aktiviti pemangkinan komplek paladium(II) dikaji bagi tindakbalas Sonogashira tanpa kuprum antara iodobenzena dan fenilasetilena dalam dimetilsulfoksida (DMSO) pada 80 ^oC, 100 ^oC dan 140 ^oC. Peratusan penukaran iodobenzena pada jam ke-12 tindak balas dipantau dengan GC-FID. Pada 100 ^oC, pemangkin yang paling aktif adalah PdLN, menandakan bahawa kumpulan tertukar ganti penarik elektron, –NO₂, boleh meningkatkan sifat pemangkinan kompleks. Pada 140 ^oC, kedua-dua kompleks paladium(II) berjaya menukarkan 100% iodobenzena.

Kata kunci: Bes Schiff, kompleks paladium(II), Sonogashira, perubahan suhu

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