A dinuclear [{(p-cym)Ru^IICl}₂(μ-bpytz˙⁻)]⁺ complex bridged by a radical anion: synthesis, spectroelectrochemical, EPR and theoretical investigation (bpytz = 3,6-bis(3,5-dimethylpyrazolyl)1,2,4,5-tetrazine; p-cym = p-cymene)

Abstract

The reaction of the chloro-bridged dimeric precursor [{(p-cym)Ru(II)Cl}(μ-Cl)]2 (p-cym = p-cymene) with the bridging ligand 3,6-bis(3,5-dimethylpyrazolyl)-1,2,4,5-tetrazine (bpytz) in ethanol results in the formation of the dinuclear complex [{(p-cym)Ru(II)Cl}2(μ-bpytz˙(-))](+), [1](+). The bridging tetrazine ligand is reduced to the anion radical (bpytz˙(-)) which connects the two Ru(II) centres. Compound [1](PF6) has been characterised by an array of spectroscopic and electrochemical techniques. The radical anion character has been confirmed by magnetic moment (corresponding to one electron paramagnetism) measurement, EPR spectroscopic investigation (tetrazine radical anion based EPR spectrum) as well as density functional theory based calculations. Complex [1](+) displays two successive one electron oxidation processes at 0.66 and 1.56 V versus Ag/AgCl which can be attributed to [{(p-cym)Ru(II)C}2(μ-bpytz˙(-))](+)/[{(p-cym)Ru(II)Cl}2(μ-bpytz)](2+) and [{(p-cym)Ru(II)Cl}2(μ-bpytz)](+)/[{(p-cym)Ru(III)Cl}2(μ-bpytz)](2+) processes (couples I and II), respectively. The reduction processes (couple III-couple V), which are irreversible, likely involve the successive reduction of the bridging ligand and the metal centres together with loss of the coordinated chloride ligands. UV-Vis-NIR spectroelectrochemical investigation reveals typical tetrazine radical anion containing bands for [1](+) and a strong absorption in the visible region for the oxidized form [1](2+), which can be assigned to a Ru(II) → π* (tetrazine) MLCT transition. The assignment of spectroscopic bands was confirmed by theoretical calculations.

Sustainable and selective transfer hydrogenation using waste shrimp shell‐based tetrazene‐Ru (II) para‐cymene catalyst with ethanol as a hydrogen source

“…The TGA curve of S‐Tz‐Ru‐P‐Cym exhibited that a weight loss of approximately 74% within the temperature range of 200–600°C arises due to the loss of shrimp support (Figure S27). The electron paramagnetic resonance (EPR) study of the diruthenium complex, [ Ru‐1 ], indicates a ligand‐based spin consistent with the findings reported in the literature 27 …”

“…Additionally, the presence of energetically low-lying vacant π* orbitals further contributes to the stability of the metal complex (S-Tz-Ru-P-Cym) in comparison with the complex [Ru( p-cym)Cl 2 ] 2 on shrimp shell without tetrazine (S-Ru-P-Cym). 27,28 However, in terms of selectivity, we did not find any anomalies between all four catalysts. The scope and generality of the hydrogenation reaction were thoroughly investigated using chalcones encompassing a wide range of substrates.…”

“…The synthesis of the homogeneous Ru (II) complexes of BDMPZ‐Tz [ Ru ‐ 1 ] and DMPZ‐Tz‐NH 2 [ Ru ‐ 2 ] involved reacting their respective ligands with [Ru( p ‐cym)Cl 2 ] 2 in methanol, under a temperature of 85°C for 6 h using reported procedure (Scheme 2). 27 A materials ( S‐Tz ) was obtained by carrying out a nucleophilic substitution reaction between the surface‐exposed amino groups of waste shrimp shells ( S ) and BDMPZ‐Tz in toluene, under a temperature of 100°C for a duration of 12 h, as depicted in Scheme 1b.…”

“…The electron paramagnetic resonance (EPR) study of the diruthenium complex, [Ru-1], indicates a ligand-based spin consistent with the findings reported in the literature. 27 In contrast, the monometallic ruthenium complex of DMPZ-Tz-NH 2 , [Ru-2], exhibits an EPR spectrum with a g-value of 2.19. The disparity in g-values between [Ru-1] and [Ru-2] can be attributed to differences in their electronic environments, anisotropy, spin-orbit coupling, and zero-field splitting, arising from their distinct structures.…”

A tunable lanthanide cubane platform incorporating air-stable radical ligands for enhanced magnetic communication

“…Here, we propose an avenue to reinvigorate the field of magnetic lanthanide cubane clusteraggregates, by incorporating air-stable radical ligands within their frameworks, thereby promoting non-negligible magnetic interactions. This work focuses on the non-innocent redox properties of 3,6-bis(3,5-dimethylpyrazol-1-yl)−1,2,4,5-tetrazine (BPyTz), whose coordination to first row transition metal ions has previously yielded anionic air-stable radicals (BPyTz •− ) 21,22 . The ability of this ligand to generate air-stable radicals is rather unique compared to other radical-bridged systems, such as those based on 2,2′-bipyrimidine 23 , N 2 24 , or tetrapyridophenazine 25 , all of which are highly unstable in air and require strong reducing agents during synthesis.…”