MIXED-LIGAND HETEROMETALLIC COMPLEXES OF Ge(IV)-M2+ (Mn, Fe, Co, Ni, Zn) WITH 1,3-DIAMINO-2-HYDROXYPROPANE N,N,N',N'-TETRAACETIC ACID

There have been developed a novel synthetic method that allowed to obtain raw of mixed-ligand heterometallic binuclear complexes of Ge(IV)-M2+ (Mn, Fe, Co, Ni, Zn) with 1,3-diamino‑2-hydroxypropane N, N, N’, N’-tetraacetic acid (H5hpdta). Compounds have been characterized by the set of methods: elemental analysis, thermogravimetry, IR‑spectroscopy, spectrum of diffuse reflection, magnetic suspensibility. According to the elemental analysis, the molar ratio Ge: M: H5hpdta: bipy= 1:1:1:1 in the obtained compounds 1‑5 corresponds to the formula [(H2O)(OH)Ge(m-hpdta)M(bipy)]·nН2О (M=Mn n=3 (1), Fe n=2 (2), Co n=4 (3), Ni n=4 (4), Zn n=3 (5). Complexes have yellow (1), red (2), orange (3), violet (4) and pink (5) colors and are stable on air. Compounds 1‑5 exist in the form of crystal hydrates, that contain certain amount of water molecules, that are eliminated into the gas phase while heating in the wide range of temperatures (t=80‑250 °C), which is accompanied with the low-temperature endothermic effect. This indicates the presence of a system of stable hydrogen bonds in their crystal structure. Analysis of the IR‑spectra 1‑5 revealed that form and coordination of ligands is similar. Deprotonation of all carboxylic groups in the ligands (H5hpdta) and their bonding to germanium and d-metal is confirmed with the absence in the IR‑spectra 1‑5 absorption bands characteristic for the free СООН H5hpdta (1716 сm‑1) and nas(СОО-) і ns(СОО-) bands. Disappearance of the ν(С-OН)-1210 сm‑1 and appearance of the ν(С-O)alk., νas(Ge-O-M), νs(Ge-O- M) absorption band indicates that OH‑group of H5hpdta is deprotonated and performs bridging function. 2,2`-bipyridine bidentatly coordinates to the d-metal, binds to the O, N‑atoms of hpdta5- ligand and reaches coordination number 6. The last ligand plays the bringing role between Ge-dmetal, shows itself as ditopic, octadentate in total. According to the magnetic moments of 3, 4 and their diffuse reflection spectra, polyhedrons of Co (II), Ni (II) are octahedrons, which are realized due to the bidentate coordination of bipyridine and four bonds with nitrogen and oxygen of hpdta5-. Structure of heterometallic binuclear complexes 1‑5 is similar. Ligand hpdta5- shows itself as octadentate ditopic, all carboxylate groups monodentatly coordinate to metals, oxygen atom of the deprotonated OH‑group performs the bridging function.

Hybrid P,E Ligands: Synthesis, Coordination Chemistry and Catalysis

<p>This thesis provides an account of research into a family of novel hybrid P,E ligands containing an o-xylene backbone. A methodology for the synthesis of these ligands has been developed, and their coordination behaviour with platinum(II) and platinum(0) precursors has been explored, with particular focus on a phosphinethioether (P,S) ligand of this type. The coordination modes of this P,S ligand with palladium precursors have also been investigated, and the utility of the ligand in a palladium and copper co-catalysed Sonogashira carbon-carbon bond-forming reaction has been evaluated. A range of hybrid P,E ligands of the type o-C₆H₄(CH₂PBut₂)(CH₂E) (E = PR₂, SR, S(O)But, NR₂, SiPh₂H) have been synthesised in two or three steps from the novel substrate, o-C₆H₄(CH₂PBut₂(BH₃)}(CH₂Cl). The initial step involved treatment of the substrate with the appropriate nucleophilic reagent, or preparation of a Grignard reagent from o-C₆H₄{CH₂PBut₂(BH₃)}(CH₂Cl) and reaction with the appropriate electrophile. In most cases, this versatile strategy produced air-stable crystalline ligand precursors. Phosphine deprotection was achieved via one of three methods, dependent upon the properties of the second functional group. The reactivity of three of these ligands — o-C₆H₄{CH₂PBut₂)(CH₂SBut) (14a), o-C₆H₄{CH₂PBut₂){CH₂S(O)But} (16) and o-C₆H₄(CH₂PBut₂)(CH₂NMe₂) (18a) — with Pt(II) and Pt(0) precursor complexes has been investigated. Chelated [PtCl₂(P,E)] complexes were synthesised with P,S ligand 14a and P,N ligand 18a, but attempts to produce the equivalent species with P,S=O ligand 16 were unsuccessful. The X-ray crystal structure of [PtCl₂(P,S)] complex 21 displayed an unexpectedly small ligand bite angle of 86.1°. A series of platinum(II) hydride complexes of the types [PtHL(P,S)₂] and [PtHL(P,S)₂]CH(SO₂CF₃)₂ (L = Cl¯, H¯, NCMe, −CH₂SBut , CO, pta) have been synthesised, where ligand 14a binds in a monodentate fashion through the phosphorus donor atom. This work has demonstrated the hemilability of ligand 14a, via the facile and reversible conversion between [PtH(κ¹P-14a)(κ²P,S-14a)]CH(SO₂CF₃)₂ (26) and [PtH(NCMe)(κ¹P-14a)₂]CH(SO₂CF₃)₂ (28). The X-ray crystal structure of [PtH₂(P,S)₂] complex 25 was used to calculate a cone angle of 180° for the phosphine moiety in ligand 14a. Reaction of P,S ligand 14a and P,S=O ligand 16 with [Pt(alkene)₃] complexes (alkene = ethene, norbornene) gave the chelated [Pt(alkene)(P,E)] complexes 32–35; however, under similar conditions a [Pt(norbornene)(P,N)] complex did not form. A large ligand bite angle of 106.6° was observed in the X-ray crystal structure of [Pt(norbornene)(P,S)] complex 34. Reaction of two equivalents of each of the P,E ligands with [Pt(norbornene)₃] gave the corresponding 14-electron linear complexes [Pt(P,E)₂] (36–38) with the ligands coordinated through the phosphorus donor atoms only. The reactivity of [Pt(norbornene)(P,S)] complex 34 and [Pt(P,S)₂] complex 36 has been investigated, resulting in the complexes [PtH{CH(SO₂CF₃)₂}(P,S)] (39), [Pt(norbornyl)(P,S)] (40), [Pt(ethyne)(P,S)] (41) and [Pt(O₂)(P,S)₂] (42). The reactivity of P,S ligand 14a was investigated with Pd(II) and Pd(0) precursors, resulting in the identification of five coordination modes of this ligand. Monodentate binding was observed in [Pd(P,S)₂] complex 44, and chelation in the [Pd(alkene)(P,S)] complexes 47 (alkene = norbornene) and 48 (alkene = dba). Reaction of ligand 14a with [PdCl₂(NCBut)₂] at raised temperature resulted in S−C bond cleavage and the formation of palladium dimer 43 with bidentate coordination of the ligand through phosphine and bridging thiolate moieties. Reaction of ligand 14a with [Pd(OAc)₂] resulted in C−H activation of the aryl backbone and formation of [Pd(μ-OAc)(P,C)]₂ dimer 46. In the presence of excess [Pd(OAc)₂], palladium hexamer 45 was formed, with a combination of P,C palladacycle and monodentate thioether binding resulting in bridging P,C,S coordination of ligand 14a. The Sonogashira cross-coupling of 4-bromoanisole and phenylethyne was performed with 3 mol% of a pre-catalyst mixture containing P,S ligand 14a, [Pd(OAc)₂] and CuI, resulting in quantitative conversion to 4-(phenylethynyl)anisole in four hours. Two enyne by-products were also identified from the reaction. Variations to the pre-catalyst mixture and catalyst loading indicated there was a significant ligand dependence on the yield and selectivity of the reactions. Mercury drop tests and dynamic light scattering experiments confirmed the presence of palladium nanoparticles in the reaction solution; however, the active catalytic species in these reactions has not been identified.</p>

Hybrid P,E Ligands: Synthesis, Coordination Chemistry and Catalysis

<p>This thesis provides an account of research into a family of novel hybrid P,E ligands containing an o-xylene backbone. A methodology for the synthesis of these ligands has been developed, and their coordination behaviour with platinum(II) and platinum(0) precursors has been explored, with particular focus on a phosphinethioether (P,S) ligand of this type. The coordination modes of this P,S ligand with palladium precursors have also been investigated, and the utility of the ligand in a palladium and copper co-catalysed Sonogashira carbon-carbon bond-forming reaction has been evaluated. A range of hybrid P,E ligands of the type o-C₆H₄(CH₂PBut₂)(CH₂E) (E = PR₂, SR, S(O)But, NR₂, SiPh₂H) have been synthesised in two or three steps from the novel substrate, o-C₆H₄(CH₂PBut₂(BH₃)}(CH₂Cl). The initial step involved treatment of the substrate with the appropriate nucleophilic reagent, or preparation of a Grignard reagent from o-C₆H₄{CH₂PBut₂(BH₃)}(CH₂Cl) and reaction with the appropriate electrophile. In most cases, this versatile strategy produced air-stable crystalline ligand precursors. Phosphine deprotection was achieved via one of three methods, dependent upon the properties of the second functional group. The reactivity of three of these ligands — o-C₆H₄{CH₂PBut₂)(CH₂SBut) (14a), o-C₆H₄{CH₂PBut₂){CH₂S(O)But} (16) and o-C₆H₄(CH₂PBut₂)(CH₂NMe₂) (18a) — with Pt(II) and Pt(0) precursor complexes has been investigated. Chelated [PtCl₂(P,E)] complexes were synthesised with P,S ligand 14a and P,N ligand 18a, but attempts to produce the equivalent species with P,S=O ligand 16 were unsuccessful. The X-ray crystal structure of [PtCl₂(P,S)] complex 21 displayed an unexpectedly small ligand bite angle of 86.1°. A series of platinum(II) hydride complexes of the types [PtHL(P,S)₂] and [PtHL(P,S)₂]CH(SO₂CF₃)₂ (L = Cl¯, H¯, NCMe, −CH₂SBut , CO, pta) have been synthesised, where ligand 14a binds in a monodentate fashion through the phosphorus donor atom. This work has demonstrated the hemilability of ligand 14a, via the facile and reversible conversion between [PtH(κ¹P-14a)(κ²P,S-14a)]CH(SO₂CF₃)₂ (26) and [PtH(NCMe)(κ¹P-14a)₂]CH(SO₂CF₃)₂ (28). The X-ray crystal structure of [PtH₂(P,S)₂] complex 25 was used to calculate a cone angle of 180° for the phosphine moiety in ligand 14a. Reaction of P,S ligand 14a and P,S=O ligand 16 with [Pt(alkene)₃] complexes (alkene = ethene, norbornene) gave the chelated [Pt(alkene)(P,E)] complexes 32–35; however, under similar conditions a [Pt(norbornene)(P,N)] complex did not form. A large ligand bite angle of 106.6° was observed in the X-ray crystal structure of [Pt(norbornene)(P,S)] complex 34. Reaction of two equivalents of each of the P,E ligands with [Pt(norbornene)₃] gave the corresponding 14-electron linear complexes [Pt(P,E)₂] (36–38) with the ligands coordinated through the phosphorus donor atoms only. The reactivity of [Pt(norbornene)(P,S)] complex 34 and [Pt(P,S)₂] complex 36 has been investigated, resulting in the complexes [PtH{CH(SO₂CF₃)₂}(P,S)] (39), [Pt(norbornyl)(P,S)] (40), [Pt(ethyne)(P,S)] (41) and [Pt(O₂)(P,S)₂] (42). The reactivity of P,S ligand 14a was investigated with Pd(II) and Pd(0) precursors, resulting in the identification of five coordination modes of this ligand. Monodentate binding was observed in [Pd(P,S)₂] complex 44, and chelation in the [Pd(alkene)(P,S)] complexes 47 (alkene = norbornene) and 48 (alkene = dba). Reaction of ligand 14a with [PdCl₂(NCBut)₂] at raised temperature resulted in S−C bond cleavage and the formation of palladium dimer 43 with bidentate coordination of the ligand through phosphine and bridging thiolate moieties. Reaction of ligand 14a with [Pd(OAc)₂] resulted in C−H activation of the aryl backbone and formation of [Pd(μ-OAc)(P,C)]₂ dimer 46. In the presence of excess [Pd(OAc)₂], palladium hexamer 45 was formed, with a combination of P,C palladacycle and monodentate thioether binding resulting in bridging P,C,S coordination of ligand 14a. The Sonogashira cross-coupling of 4-bromoanisole and phenylethyne was performed with 3 mol% of a pre-catalyst mixture containing P,S ligand 14a, [Pd(OAc)₂] and CuI, resulting in quantitative conversion to 4-(phenylethynyl)anisole in four hours. Two enyne by-products were also identified from the reaction. Variations to the pre-catalyst mixture and catalyst loading indicated there was a significant ligand dependence on the yield and selectivity of the reactions. Mercury drop tests and dynamic light scattering experiments confirmed the presence of palladium nanoparticles in the reaction solution; however, the active catalytic species in these reactions has not been identified.</p>

Strong bidentate coordination for surface passivation and ligand-shell engineering of lead halide perovskite nanocrystals in the strongly quantum confined regime

The surface of lead halide perovskite nanocrystals (PNCs) is unique compared to conventional metal chalcogenide or pnictogenide semiconductor nanoparticles for its ionic character and the dynamic ligand layer, which makes them unstable in stock solutions and hinders the development of surface engineering strategies. This work employs a chelating strategy to form stable coordination on the PNC surface. Through screening a series of heterocyclic aromatic carboxylates, we found the best ligand, picolinate (PIC), with exceptional passivation effect to the surface traps of CsPbBr3 PNCs in the strongly quantum confined regime, resulting in > 0.8 photoluminescence quantum yields. The exciton lifetime in the passivated PNC approaches the radiative decay limit in various solvents. From an NMR titration experiment, the binding affinity of PIC is estimated to be at least 15 to 30 folds stronger than the original ligand from synthesis. The NMR and FTIR spectroscopic data and first-principles calculations elucidate the bidentate nature of the PIC coordination at the surface Pb site and the coadsorption of the ammonium-PIC ion pair. In apolar solvents, such as cyclohexane, the binding of PIC is stoichiometric to the available surface sites, suggesting the structure as a potent candidate for anchoring functional molecular structures to the PNC surface. In polar solvents, the strong affinity of PIC on the PNC surface provides protection for carrying out the precipitation-redissolution purification procedure that removes synthetic residual from the as-synthetic PNC samples. By modifying the purification procedure, we also develop a cation exchange procedure to replace the original oleylammonium cation with desired structures that consist of an ammonium anchoring group. Our results provide a direction for constructing strong interactions to protect the vulnerable surface of PNCs and pave the road for developing surface engineering strategies to functionalize these nanoparticles.

: Strong bidentate coordination for surface passivation and ligand-shell engineering of lead halide perovskite nanocrystals in the strongly quantum confined regime

The surface of lead halide perovskite nanocrystals (PNCs) is unique compared to conventional metal chalcogenide or pnictogenide semiconductor nanoparticles for its ionic character and the dynamic ligand layer, which makes them unstable in stock solutions and hinders the development of surface engineering strategies. This work employs a chelating strategy to form stable coordination on the PNC surface. Through screening a series of heterocyclic aromatic carboxylates, we found the best ligand, picolinate (PIC), with exceptional passivation effect to the surface traps of CsPbBr3 PNCs in the strongly quantum confined regime, resulting in > 0.8 photoluminescence quantum yields. The exciton lifetime in the passivated PNC approaches the radiative decay limit in various solvents. From an NMR titration experiment, the binding affinity of PIC is estimated to be at least 15 to 30 folds stronger than the original ligand from synthesis. The NMR and FTIR spectroscopic data and first-principles calculations elucidate the bidentate nature of the PIC coordination at the surface Pb site and the coadsorption of the ammonium-PIC ion pair. In apolar solvents, such as cyclohexane, the binding of PIC is stoichiometric to the available surface sites, suggesting the structure as a potent candidate for anchoring functional molecular structures to the PNC surface. In polar solvents, the strong affinity of PIC on the PNC surface provides protection for carrying out the precipitation-redissolution purification procedure that removes synthetic residual from the as-synthetic PNC samples. By modifying the purification procedure, we also develop a cation exchange procedure to replace the original oleylammonium cation with desired structures that consist of an ammonium anchoring group. Our results provide a direction for constructing strong interactions to protect the vulnerable surface of PNCs and pave the road for developing surface engineering strategies to functionalize these nanoparticles.

Synthesis, characterization, in-vitro anti-inflammatory and antimicrobial screening of metal(II) mixed diclofenac and acetaminophen complexes

Mixed ligand complexes derived from diclofenac potassium salt (Kdc) and acetaminophen (ace) has been synthesized and proposed to have a general formula [MB] where M = Co2+, Ni2+, Cu2+ and Zn2+and B = (ace)(dc)(H2O)2 except for Mn2+ complex which exists as [Mn(ace)(dc)OH2]. The complexes were characterized by solubility, melting point, conductivity, elemental analyses, UV-Vis, FT-IR spectroscopy, X-ray powder diffraction (XRPD) study and magnetic susceptibility measurement. Electronic absorption spectra data are characteristic of octahedral structures for [MB]. The IR spectra revealed a bidentate coordination mode. In acetaminophen, the nitrogen and carbonyl-O atoms of the amide group were involved while the carboxylate oxygen atoms of potassium diclofenac were used; typical of a carboxylic acid derivative. The compounds were screened for in-vitro anti-inflammatory activity by inhibition of albumin denaturation assay and antimicrobial activity against bacteria strains: Bacillus subtilis, Bacillus anthrax, Escherichia coli, Salmonella typhi and a fungus Aspergillus niger. Some of the tested compounds showed moderate anti-inflammatory activity when compared to the standard drug diclofenac potassium salt. The in-vitro antimicrobial screening revealed an increased activity of the complexes against the bacteria isolates compared to the free ligands. KEY WORDS: Metal(II) ion, NSAIDs, Anti-inflammatory activity, Diclofenac potassium salt, XRPD, Antimicrobial activity Bull. Chem. Soc. Ethiop. 2021, 35(1), 77-86. DOI: https://dx.doi.org/10.4314/bcse.v35i1.6

Chemical, spectroscopic characterization, molecular modeling and antibacterial activity assays of a silver (I) complex with succinic acid

A silver(I) complex with succinic acid in the form of succinate is presented. Chemical characterization confirms the molecular composition Ag2C4H4O4 for the complex. Infrared spectra suggest a bidentate coordination of both carboxylate groups of succinates to the two Ag(I) ions. Density functional theory (DFT) studies were used in the structures of succinic acid and Ag(I) succinate complex with coordination formula [Ag2(C4H4O4)] in order to optimize them to their minimum energy. The studies confirmed that each carboxylate group of the succinate anion is coordinated to one silver atom by the two oxygen in a bidentate mode and the bond lengths O···Ag theoretically determined range from 2.325 to 2.338 Å. The complex [Ag2(C4H4O4)] showed in vitro antibacterial activity against the bacterial strains of Staphylococcus aureus, Bacillus cereus, Escherichia coli and Pseudomonas aeruginosa complex. Anti-Mycobacterium tuberculosis analyses were also performed and the [Ag2(C4H4O4)] complex was shown to be active over M. tuberculosis H37Rv strain with MIC90 of 23.94 μg mL-1 while succinic acid itself showed a value higher than 25.00 μg mL-1.

Rollover Cyclometalation as a Valuable Tool for Regioselective C–H Bond Activation and Functionalization

Rollover cyclometalation constitutes a particular case of cyclometallation reaction. This reaction occurs when a chelated heterocyclic ligand loses its bidentate coordination mode and undergoes an internal rotation, after which a remote C–H bond is regioselectively activated, affording an uncommon cyclometalated complex, called “rollover cyclometalated complex”. The key of the process is the internal rotation of the ligand, which occurs before the C−H bond activation and releases from coordination a donor atom. The new “rollover” ligand has peculiar properties, being a ligand with multiple personalities, no more a spectator in the reactivity of the complex. The main reason of this peculiarity is the presence of an uncoordinated donor atom (the one initially involved in the chelation), able to promote a series of reactions not available for classic cyclometalated complexes. The rollover reaction is highly regioselective, because the activated C–H bond is usually in a symmetric position with respect to the donor atom which detaches from the metal stating the rollover process. Due to this novel behavior, a series of potential applications have appeared in the literature, in fields such as catalysis, organic synthesis, and advanced materials.