Gallium(III) Tetraphenylporphyrinates Containing Hydrosulfide and Thiolate Ligands: Structural Models for Sulfur-Bound Iron(III) Hemes

Sol-Gel Dipping Devices for H2S Visualization

In this contribution we report the synthesis and full characterization, via a combination of different spectroscopies (e.g., ¹H NMR, UV-vis, fluorescence, MALDI), of a new family of fluorescent zinc complexes with extended π-conjugated systems, with the final aim of setting up higher performance H₂S sensing devices. Immobilization of the systems into a polymeric matrix for use in a solid-state portable device was also explored. The results provided proof-of-principle that the title complexes could be successfully implemented in a fast, simple and cost-effective H₂S sensing device.

The Ruthenium Nitrosyl Moiety in Clusters: Trinuclear Linear μ-Hydroxido Magnesium(II)-Diruthenium(II), μ3-Oxido Trinuclear Diiron(III)-Ruthenium(II), and Tetranuclear μ4-Oxido Trigallium(III)-Ruthenium(II) Complexes

The ruthenium nitrosyl moiety, {RuNO}6, is important as a potential releasing agent of nitric oxide and is of inherent interest in coordination chemistry. Typically, {RuNO}6 is found in mononuclear complexes. Herein we describe the synthesis and characterization of several multimetal cluster complexes that contain this unit. Specifically, the heterotrinuclear μ3-oxido clusters [Fe2RuCl4(μ3-O)(μ-OMe)(μ-pz)2(NO)(Hpz)2] (6) and [Fe2RuCl3(μ3-O)(μ-OMe)(μ-pz)3(MeOH)(NO)(Hpz)][Fe2RuCl3(μ3-O)(μ-OMe)(μ-pz)3(DMF)(NO)(Hpz)] (7·MeOH·2H2O) and the heterotetranuclear μ4-oxido complex [Ga3RuCl3(μ4-O)(μ-OMe)3(μ-pz)4(NO)] (8) were prepared from trans-[Ru(OH)(NO)(Hpz)4]Cl2 (5), which itself was prepared via acidic hydrolysis of the linear heterotrinuclear complex {[Ru(μ-OH)(μ-pz)2(pz)(NO)(Hpz)]2Mg} (4). Complex 4 was synthesized from the mononuclear Ru complexes (H2pz)[trans-RuCl4(Hpz)2] (1), trans-[RuCl2(Hpz)4]Cl (2), and trans-[RuCl2(Hpz)4] (3). The new compounds 4-8 were all characterized by elemental analysis, ESI mass spectrometry, IR, UV-vis, and 1H NMR spectroscopy, and single-crystal X-ray diffraction, with complexes 6 and 7 being characterized also by temperature-dependent magnetic susceptibility measurements and Mössbauer spectroscopy. Magnetometry indicated a strong antiferromagnetic interaction between paramagnetic centers in 6 and 7. The ability of 4 and 6-8 to form linkage isomers and release NO upon irradiation in the solid state was investigated by IR spectroscopy. A theoretical investigation of the electronic structure of 6 by DFT and ab initio CASSCF/NEVPT2 calculations indicated a redox-noninnocent behavior of the NO ancillary ligand in 6, which was also manifested in TD-DFT calculations of its electronic absorption spectrum. The electronic structure of 6 was also studied by an X-ray charge density analysis.

Hemeproteins as Targets for Sulfide Species

Significance: Sulfides are endogenous and ubiquitous signaling species that share the hemeproteins as biochemical targets with O₂, nitric oxide, and carbon monoxide. The description of the binding mechanisms is mandatory to anticipate the biochemical relevance of the interaction. Recent Advances: The binding of sulfide to ferric hemeproteins has been described in more than 40 systems, including native proteins, mutants, and model systems. Mechanisms of sulfide binding to ferric hemeproteins have been examined by a combination of kinetic and computational experiments. The distal control of the association process, dissected into the migration of the ligand to the active site and the binding event, reveals that neutral hydrogen sulfide (H₂S) reaches the active site and is the predominant binding ligand, while the HS^- is excluded by the protein matrix. Experiments with model compounds, devoid of a protein scaffold, reveal that both H₂S and HS^- can bind the ferric heme if accessing the site. A critical role of the proximal ligand in the prevention of the metal-centered reduction has been experimentally assessed. For metmyoglobin and methemoglobin, the coordination of sulfide leads to noncanonical functions: sulfide storage and its oxidative detoxification have been evidenced under physiological and excess sulfide concentrations, respectively. Critical Issues: The bound species is suggested to predominate in the monoprotonated form, although spectroscopic evidence is pending. Future Directions: A description of the role of hemeproteins as biochemical targets for inorganic sulfide requires understanding the reactivity of bound sulfide, for example: the metal-centered reduction, the reaction with excess sulfide, oxidants, or other gasotransmitters, among other biomolecules.

Hydrosulfide complexes of the transition elements: diverse roles in bioinorganic, cluster, coordination, and organometallic chemistry

Molecules containing transition metal hydrosulfide linkages are diverse, spanning a variety of elements, coordination environments, and redox states, and carrying out multiple roles across several fields of chemistry.

Iridium porphyrin complexes with μ-nitrido, hydroxo, hydrosulfido and alkynyl ligands

Iridium porphyrin complexes containing μ-nitrido, hydroxo, hydrosulfido, and alkynyl ligands have been synthesized and structurally characterized, and their oxidation has been studied. The alkyl-IrIII porphyrin complex [Ir(tpp)R] (tpp2- = 5,10,15,20-tetraphenylporphyrin dianion; R = C8H13; 1) was synthesized by reaction of [Ir(cod)Cl]2 (cod = 1,5-cyclooctadiene) with H2tpp in refluxing monoethylene glycol. Treatment of 1 with PPh3 and [(LOEt)Ru(N)Cl2] (LOEt- = [(η5-C5H5)Co{P(O)(OEt)2}3]-) gave [Ir(tpp)(R)(PPh3)] (2) and the μ-nitrido complex [R(tpp)Ir(μ-N)RuCl2(LOEt)] (3), respectively. The cyclic voltammogram of 3 exhibited a reversible oxidation couple at 0.44 V versus Fc+/0 (Fc = ferrocene). The oxidation of 3 with [(4-BrC6H4)3N](SbCl6) resulted in Ir-C bond homolysis and formation of the chloride complex [Cl(tpp)Ir(μ-N)RuCl2(LOEt)] (4). The short Ir-N(nitrido) bond distances in 3 [1.944(3) Å] and 4 [1.831(4) Å] are indicative of multiple bond character and thus these two μ-nitrido complexes can be described by the two resonance forms: IrIII-N[triple bond, length as m-dash]RuVI and IrV[double bond, length as m-dash]N[double bond, length as m-dash]RuIV. Similarly, the oxidation of 2 with [(4-BrC6H4)3N](SbCl6) yielded [Ir(tpp)Cl(PPh3)] (5). Chloride abstraction of 5 with TlPF6 in tetrahydrofuran (thf) afforded [Ir(tpp)(PPh3)(thf)](PF6) (6) that reacted with CsOH·H2O and Li2S to give the hydroxo [Ir(tpp)(OH)(PPh3)] (7) and hydrosulfido [Ir(tpp)(PPh3)(SH)] (8) complexes, respectively. Treatment of 6 with phenylacetylene in the presence of CuI and Et3N yielded the bimetallic complex [Ir(tpp)(PPh3)(μ-η1:η2-C[triple bond, length as m-dash]CPh)(CuI)] (9), whereas the transmetallation of 6 with LiC[triple bond, length as m-dash]CPh afforded the mononuclear alkynyl complex [Ir(tpp)(PPh3)(C[triple bond, length as m-dash]CPh)] (10). The electrochemistry of the Ir porphyrin complexes has been studied using cyclic voltammetry. On the basis of the measured redox potentials of [Ir(tpp)(PPh3)X], the ability of X- to stabilize the IrIV state is ranked in the order: R- > PhC[triple bond, length as m-dash]C- > Cl- ∼ OH-. Oxidation of 8 and 9 with [(4-BrC6H4)3N](SbCl6) led to isolation of 5 and [Ir(tpp)(PPh3)(H2O)]+, respectively. The crystal structures of complexes 3, 4, and 7-10 have been determined.

Spectroscopic investigation of the reaction of metallo-protoporphyrins with hydrogen sulfide

Hydrogen sulfide (H₂S) is the most recently discovered gasotransmitter molecule joining nitric oxide and carbon monoxide. In addition to being biologically important gases, these gasotransmitters also provide distinct modes of reactivity with biomimetic metal complexes. The majority of previous investigations on the reactivity of H₂S with bioinorganic models have focused on Fe-based porphyrin systems, whereas investigations with other metals remains underinvestigated. To address this gap, we report here an examination of the reactions of H₂S, HS^-, and S₈ with Mg^II, Cu^II, Co^II, Zn^II, Cr^II, Sn^IV, and Mn^II/III protoporphyrins.

Gallium(III) and Indium(III) Complexes with meso-Monophosphorylated Porphyrins: Synthesis and Structure. A First Example of Dimers Formed by the Self-Assembly of meso-Porphyrinylphosphonic Acid Monoester

The synthesis and structural characterization, both in solution by means of ¹H and ³¹P NMR and UV-vis spectroscopies and in the solid state by X-ray diffraction on single crystal, of a series of gallium(III) and indium(III) meso-mono(diethoxyphosphoryl)porphyrins bearing different peripheral substituents as well as the corresponding monoesters and phosphonic acids are reported. This work describes the first example of the X-ray structure of a self-assembled dimer formed via strong binding between the oxygen atom of the phosphonate substituent and the gallium(III) cations of adjacent porphyrin molecules [Ga-O = 1.9708(13) Å].