Catalytic C-C cross-coupling and hydrogen evolution by two Pd(II)-complexes of di-2-pyridyl ketone benzoyl hydrazones

• Published in: Journal of coordination chemistry Vol. 72; no. 13; pp. 2261 - 2278
• Main Authors: Bakir, Mohammed, Lawrence, Mark W., Nelson, Peter, Yamin, M. Bohari
• Format: Journal Article
• Language: English
• Published: Abingdon Taylor & Francis 03-07-2019; Taylor & Francis Ltd
• Subjects: Absorption spectra; C-C cross-coupling; Carbonyl groups; Carbonyls; Catalysis; Chemical reactions; Coordination; Cross coupling; Crystal structure; Dependence; di-2-pyridyl ketone benzoyl hydrazones; electrochemistry; Hydrazones; Hydrogen evolution; NMR; Nuclear magnetic resonance; Palladium; Rate constants; Single crystals; Solvents; spectroscopy; Structural analysis
• ISSN: 0095-8972; 1029-0389
• DOI: 10.1080/00958972.2019.1645329

The reactions between [PdCl
2
(CH
3
CN)
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 [PdCl
2
(κ
3
-N
py
,N
im
,O-dpkbh)] (1) and PdCl
2
(κ
3
-N
py
,N
im
,O-dpk-4-abh)] (2). X-ray structural analysis on a single crystal of PdCl(κ
3
-N,N,O-dpk-4-abh-H)]·H
2
O·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.
1
H 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 (k
app
) for the electrocatalytic H
2
evolution of (3.39 ± 0.3) × 10
3
and (4.04 ± 0.2) × 10
3
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.