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The Synthesis, Characterization and Reactivity of a Series of Ruthenium N-triphosPh Complexes
Published on: April 10, 2015
Cationic heteroleptic Ni(II) complexes of dithiocarbamate and phosphine ligands: synthesis, characterization and
Sarvesh Kumar Pal1, Anjali Mishra1, Gaurav Kumar Mishra2
1Department of Chemistry, Institute of Science, Banaras Hindu University, Varanasi-221005, India. kamlesh.kumar@bhu.ac.in.
Abstract:
Three cationic heteroleptic Ni(II) dithiocarbamate complexes ([Ni(L)(L')n]PF6, n = 1 or 2) were synthesized and characterized to explore the relationship between diphosphine chelate ring size and their electrocatalytic activity for hydrogen production. These complexes (1-3) feature a common dithiocarbamate ligand (L) and varied diphosphine ligands (L'): dppm (1), dppe (2), and dppp (3). Single-crystal X-ray analysis showed a distorted square pyramidal geometry for 1 and square planar geometries for 2 and 3 around the NiP2S2 core. Electrochemical studies revealed a small variation in redox potentials (ΔE1/2 ≈ 60 mV), suggesting a weak electronic effect of ligands from dppm (1) to dppp (3). However, a significant difference in catalytic half-wave potentials (ΔEcat/2 ≈ 200 mV in 4 mM CH3COOH) indicates a strong influence of the P-Ni-P bite angles. The catalytic activity of the complexes is significantly influenced by the chelate ring size and their P-Ni-P bite angles, which follow the trend 92.07(4)° (3) > 86.84(6)° (2) > 75.24(3)° (1). The enhanced electrocatalytic performance of 3 with a low overpotential (∼600 mV), a high turnover frequency (∼706 s-1), and faradaic efficiency (88%) is attributed to the conformational flexibility of the six-membered chelate ring in 3 due to the dppp ligand. Both experimental data and DFT calculations support an ECEC mechanism for the HER catalysed by heteroleptic Ni(II) complexes with the formation of Ni(III)-H intermediate species.
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