Abstract
The reactions between [PdCl2(CH3CN)2] and dpk-h [dpk-h = di-2-pyridyl ketone benzoyl hydrazone (dpkbh) or di-2-pyridyl ketone 4-aminobenzoyl hydrazone (dpk-4-abh)] at room temperature in air produced [PdCl2(κ3-Npy,Nim,O-dpkbh)] (1) and PdCl2(κ3-Npy,Nim,O-dpk-4-abh)] (2). X-ray structural analysis on a single crystal of PdCl(κ3-N,N,O-dpk-4-abh-H)]·H2O·dmf (3) established its authenticity, points to keto-enol tautomerization due to solvent-compound interactions and revealed pseudo-coordination of the carbonyl group to the Pd ion. Solid-state infrared measurements confirmed the pseudo coordination of the carbonyl group of dpk-h as evident from the appearance of the ν(C=O) of coordinated dpk-h in close proximity to the ν(C=O) of uncoordinated dpk-h. 1H NMR measurements on protophilic solutions of 1 and 2 disclosed solvent dependence and keto-enol tautomerization while variable temperature studies established the predominance of the keto form. The electronic absorption spectra of 1 and 2 measured in protophilic solvents confirmed the coordination of the Pd ion to dpk-h as evident from the appearance of d-d and ligand based electronic transitions. The catalytic C–C cross-coupling reactions and electro-catalytic behavior of 1 and 2 toward a proton reduction were investigated and revealed good catalytic properties. Overall rate constants (kapp) for the electrocatalytic H2 evolution of (3.39 ± 0.3) × 103 and (4.04 ± 0.2) × 103 M−1 s−1 were estimated and overpotentials of 157 and 67 mV, and turnover numbers (TON) of 2.0 and 3.2 for 1 and 2, respectively, were determined.
Graphical Abstract
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Acknowledgement
The authors acknowledge Ms. Toni Johnson for NMR measurements.
Disclosure statement
No potential conflict of interest was reported by the authors.
Notes
1 The reaction rate constant, kapp (M–1 s–1), can be estimated from
(1)
where n is the number of electrons, ic is the plateau current (mA) at very fast scan rates, F is the Faraday’s constant (96,485 C mol–1), A is the area of the electrode surface (cm2), [cat] is the bulk concentration of the catalyst (M), D is the diffusion coefficient (cm2 s–1) and [H+] is the bulk concentration of acid (M).