Photoinduced Dimerization Reaction Coupled with Oxygenation of a Platinum(II)–Hydrazone Complex

Abstract

Photoreactivities of Ni(II)- and Pt(II)-hydrazone complexes, [NiCl(L)] (Ni1) and [PtCl(L)] (Pt1), respectively [HL = 2-(diphenylphosphino)benzaldehyde-2-pyridylhydrazone], were investigated in detail via UV-vis absorption, (1)H nuclear magnetic resonance (NMR) spectroscopy, and electrospray ionization time-of-flight (ESI-TOF) mass spectrometry; the two photoproducts obtained from the photoreaction of Pt1 were also successfully identified via X-ray analysis. The absorption bands of the Ni1 and Pt1 complexes were very similar, centered around 530 nm, and were assigned as an intraligand charge transfer transition of the hydrazone moiety. The absorption spectrum of Pt1 in a CH3CN solution changed drastically upon photoirradiation (λ = 530 nm), whereas no change was observed for Ni1. (1)H NMR and ESI-TOF mass spectra under various conditions suggested that the photoexcited Pt1* reacts with dissolved dioxygen to form a reactive intermediate, and the ensuing dark reactions afforded two different products without any decomposition. In contrast to the simple photo-oxidation of HL to form a phosphine oxide HL(P═O), the X-ray crystallographic analyses of the photoproducts clearly indicate the formation of a mononuclear Pt complex with the oxygenated hydrazone ligand (Pt1O) and a dinuclear Pt complex with the oxygenated and dimerized hydrazone ligand (Pt2). The photosensitized reaction in the presence of an (1)O2-generating photosensitizer, methylene blue (MB), also produced Pt1O and Pt2, indicating that the reaction between (1)O2 and ground-state Pt1 is the important step. In a highly viscous dimethyl sulfoxide solution, Pt1 was slowly, but quantitatively, converted to the mononuclear form, Pt1O, without the formation of the dinuclear product, Pt2, upon photoirradiation (and in the reaction photosensitized by MB), suggesting that this photoreaction of Pt1 involves at least one diffusion-controlled reaction. On the other hand, the same complexes Pt1O and Pt2 were also produced in the degassed solution, probably because of the reaction of the photoexcited Pt1* with the biradical character and H2O.

New Tridentate Hydrazone Metal Complexes Derived from 2-Hydroxy-4-Methoxyacetophenone and some Acid Hydrazides: Synthesis, Characterization and Antibacterial Activity Evaluation

“…They can act as bidentate, tridentate or tetradentate ligands depending on the nature of substituents attached to the hydrazone unit. Metal complexes of aroylhydrazone ligands have an attractive area of research because of their versatile coordination chemistry and a capability to generate varied molecular architecture and geometry (Banerjee et al, 2008;Kobayashi et al, 2014;Cindrić et al, 2017;Kendur et al, 2018).…”

Ligand-Modulated Nuclearity and Geometry in Nickel(II) Hydrazone Complexes: From Mononuclear Complexes to Acetato- and/or Phenoxido-Bridged Clusters

“…The protonation state of these ligands in metal complexes plays an important role as it offers fine-tuning of properties [24][25][26]. The ability of aroylhydrazones to act as neutral or as anionic ligands (in singly deprotonated HL − or doubly-deprotonated forms L 2-; Scheme S1) allows them to form a diverse range of metal complexes [27][28][29][30][31][32][33][34][35]. Some examples of structurally characterised nickel(II) complexes with hydrazone ligands include [Ni{dap(A) 2 }] 2 (dap(AH) 2 = 2,6-diacetylpyridine bis(anthraniloyl hydrazone) [36], [Ni(H 3 bsc) 2 ](ClO 4 ) 2 (H 3 bsc = 1,5-bis(salicylidene)carbohydrazide) [37], [Ni(L)(PPh 3 )] (L = hydroxylbenzylidenebenzenecarbohydrazone) [38], [Ni(L)] 2 (L = ferrocenyl hydrazone ligands [39], and [NiL 2 phen]•CH 3 CN (HL = 2-acetonaphthone salicylhydrazone, phen = 1,10-phenanthroline) [40].…”