Cyclopentadienyl Ruthenium(II) Complexes with Bridging Alkynylphosphine Ligands: Synthesis and Electrochemical Studies

The reaction of [CpRuCl(PPh₃)₂] (Cp=cyclopentadienyl) and [CpRuCl(dppe)] (dppe=Ph₂PCH₂CH₂PPh₂) with bis‐ and tris‐phosphine ligands 1,4‐(Ph₂PC≡C)₂C₆H₄ ( 1 ) and 1,3,5‐(Ph₂PC≡C)₃C₆H₃ ( 2 ), prepared by Ni‐catalysed cross‐coupling reactions between terminal alkynes and diphenylchlorophosphine, has been investigated. Using metal‐directed self‐assembly methodologies, two linear bimetallic complexes, [{CpRuCl(PPh₃)}₂(μ‐dppab)] ( 3 ) and [{CpRu(dppe)}₂(μ‐dppab)](PF₆)₂ ( 4 ), and the mononuclear complex [CpRuCl(PPh₃)(η¹‐dppab)] ( 6 ), which contains a “dangling arm” ligand, were prepared (dppab=1,4‐bis[(diphenylphosphino)ethynyl]benzene). Moreover, by using the triphosphine 1,3,5‐tris[(diphenylphosphino)ethynyl]benzene (tppab), the trimetallic [{CpRuCl(PPh₃)}₃(μ₃‐tppab)] ( 5 ) species was synthesised, which is the first example of a chiral‐at‐ruthenium complex containing three different stereogenic centres. Besides these open‐chain complexes, the neutral cyclic species [{CpRuCl(μ‐dppab)}₂] ( 7 ) was also obtained under different experimental conditions. The coordination chemistry of such systems towards supramolecular assemblies was tested by reaction of the bimetallic precursor 3 with additional equivalents of ligand 2 . Two rigid macrocycles based on cis coordination of dppab to [CpRu(PPh₃)] were obtained, that is, the dinuclear complex [{CpRu(PPh₃)(μ‐dppab)}₂](PF₆)₂ ( 8 ) and the tetranuclear square [{CpRu(PPh₃)(μ‐dppab)}₄](PF₆)₄ ( 9 ). The solid‐state structures of 7 and 8 have been determined by X‐ray diffraction analysis and show a different arrangement of the two parallel dppab ligands. All compounds were characterised by various methods including ESIMS, electrochemistry and by X‐band ESR spectroscopy in the case of the electrogenerated paramagnetic species.     

Cobaltocenium Carboxylate Transition Metal Complexes: Synthesis,Structure, Reactivity,and Cytotoxicity

Cobaltocenium carboxylate is an unusual betaine that functions as a formally neutral carboxylate ligand with late transition metal centers comprising Co²⁺, Ni²⁺, Cu²⁺, Ag⁺, Zn²⁺, Cd²⁺, Hg²⁺, and Rh⁺. Structurally, a rich coordination chemistry is observed – from simple monomeric homoleptic complexes to heteroleptic dimeric, trimeric, and polymeric compounds, as shown by X‐ray diffraction of 11 compounds. Chemically, thermal decarboxylation was investigated aiming at the formation of cobaltocenium‐carbene transition metal complexes, in analogy to such chemistry of imidazolium carboxylate betaines. Cytotoxicity studies of cobaltocenium carboxylate transition metal complexes were performed to evaluate the medicinal bioorganometallic potential of these compounds. While cobaltocenium carboxylate was inactive, its complexes with Ag⁺, Cd²⁺, and Hg²⁺ triggered significant cytotoxic effects.     

Synthesis,Crystal Structure,and Characterization of a Novel Metallo‐Organically‐Templated Pentaborate with Mixed Ligands

A novel metallo‐organically templated pentaborate with layered framework, [Cd(TETA)(C₂H₃O₂)][B₅O₆(OH)₄] ( 1 ) (TETA = triethylenetramine), was synthesized under mild solvothermal conditions. The structure was determined by single‐crystal X‐ray diffraction and further characterized by FT‐IR spectroscopy, elemental analysis, thermogravimetric analysis, and photoluminescence spectroscopy. The structure consists of an isolated polyborate anion [B₅O₆(OH)₄]^– and the cadmium complex cation of [Cd(TETA)(C₂H₃O₂)]⁺, which contains both organic amine and organic acid ligands. The [B₅O₆(OH)₄]^– units are connected together by hydrogen bonds, and a 2D sheet‐like framework with rectangle‐like 12‐membered boron rings are formed. The [Cd(TETA)(C₂H₃O₂)]⁺ complex cations are located in the free space between the layers and connect the adjacent borate layers through hydrogen bonds to form a three‐dimensional supramolecular network. The luminescent properties of the compound were studied for the first time in the series of metallo‐organically‐templated pentaborates, and a blue luminescence occurs with an emission maximum at 468 nm upon excitation at 397 nm.     

Synthesis and Structural Characterization of Neutral Hexacoordinate Silicon(IV) Complexes with SiO2N4 Skeletons

Surrounded by six : A series of novel neutral hexacoordinate silicon(IV ) complexes with SiO₂N₄ skeletons, containing two bidentate monoanionic O,N ligands and two monoanionic NCX (X = O, S) ligands, was synthesized. The formation of the title compounds involved some unexpected transformations of the bidentate O,N ligands.

     

Substituted Cyclooctatetraene Complexes of Yttrium and Erbium with Bis(phosphinimino)methanides — Synthesis and Structure

A one pot reaction of Li₂{1, 4‐(Me₃Si)₂C₈H₆}, LnCl₃, and K{CH(PPh₂NSiMe₃)₂} leads to the 1, 4‐bis(trimethylsilyl)cyclooctatetraene bis(phosphinimino)methanide complexes of yttrium and erbium, [{CH(PPh₂NSiMe₃)₂}Ln(η⁸‐{1, 4‐(Me₃Si)₂C₈H₆})] (Ln = Y, Er). Both complexes have been characterized by single crystal X‐ray diffraction. The solid state structures show that the two bulky ligands cause a steric crowding around the lanthanide atom. As a result of this steric crowding both ligands are asymmetrically attached to the lanthanide atom.     

Substituted Bisphosphanylamines as Ligands in Gold(I) Chemistry – Synthesis and Structures

Dimethyl 5‐aminoisophthalate, which is a building block of amino‐substituted tetralactam macrocycles, was used as ligand in gold(I) chemistry to form model complexes for macrocyclic gold compounds. Reaction of dimethyl 5‐aminoisophthalate with chlorodiphenylphosphine gave the diphosphine compound dimethyl 5‐[N,N‐bis(diphenylphosphanyl)amino]isophthalate (dmbpaip). This compound can further be reacted with [AuCl(tht)] (tht = tetrahydrothiophene) to give the dinuclear complex [Au₂Cl₂(dmbpaip)]. In contrast, treatment of dmbpaip with [Au(tht)₂]ClO₄ resulted in the ionic compound [Au₂(dmbpaip)₂](ClO₄)₂ in which the cation forms an eight‐membered Au₂P₄N₂ heterocycle. In both gold(I) compounds Au···Au interactions are observed. All new compounds were characterized by single‐crystal X‐ray diffraction.     

Dinuclear Five‐Coordinate Copper(II) Complexes with Chelating Diphosphonic Acid Ligands: Hydrothermal Synthesis,Structure, and Thermal Properties

The synthesis of two new diphosphonic acid ligands,[ethane‐1, 2‐diylbis(azanediyl)]bis[(4‐chlorophenyl)methylene]diphosphonic acid (L₁P), [ethane‐1, 2‐diylbis(azanediyl)]bis[(4‐bromophenyl)methylene]diphosphonic acid (L₂P), and their corresponding copper complexes, Cu₂(L₁P)₂ ( 1 ) and Cu₂(L₂P)₂ ( 2 ) are described herein. Complex 2 was structurally characterized with X‐ray single crystal diffraction. The structure of 2 consists of five‐coordinatecopper(II) ions with a distorted square pyramidal arrangement doubly bridged by OPO from phosphonate groups. The Cu–Cu distance is 4.7810(2) Å. The crystal packing is determined by interdinuclear hydrogen bonds, which lead to one‐dimensional chains. The results of thermogravimetric investigations (TG‐DTA), UV/Vis diffuse reflectance, infrared and (¹H and ¹³C) NMR spectroscopy, as well as elemental analyses of compounds 1 and 2 are also presented.     

New Bis‐o‐Benzoquinoid Ligands with Ethylene Bridge and Their Metal Complexes

The treatment of di‐o‐quinone 4,4′‐(ethane‐1,2‐diyl)‐bis(3,6‐di‐tert‐butyl‐o‐benzoquinone) (Q–CH₂–CH₂–Q, 1 ) leads to its rearrangement to form di‐p‐quinomethide 4,4′‐(ethane‐1,2‐diylidene)bis(2‐hydroxy‐3,6‐di‐tert‐butyl‐cyclohexa‐2,5‐dienone) ( 2 ). The subsequent oxidation of 2 by an alkaline solution of K₃[Fe(CN)₆] yielded the new di‐o‐quinone 4,4′‐(ethene‐1,2‐diyl)bis(3,6‐di‐tert‐butyl‐o‐benzoquinone) (Q–CH=CH–Q, 3 ), which contains an ethylene bridge. The formation of mono‐ and poly‐reduced derivatives of 2 and 3 with potassium, thallium was studied by EPR technique. The dinuclear thallium derivative of 3 , Tl(SQ–CH=CH–SQ)Tl, was found to exist in the diamagnetic quinomethide form. The most stable derivatives of 2 and 3 are triphenyltin(IV) bis‐p‐quinomethide‐phenolate ( 4 ) and triphenylantimony(V) bis‐catecholate ( 5 ), which have been synthesized and isolated. The molecular structures of 2 , 3 , and 5 were characterized by single‐crystal X‐ray diffraction.     

Synthesis,Structures, and Photophysics of Polynuclear Silver(I) Thiolate and Silver(I) Thiocarboxylate Complexes with Dppm Ligands

Trinuclear silver(I) thiolate and silver(I) thiocarboxylate complexes [Ag₃(μ‐dppm)₃(μ_n‐SR)₂](ClO₄) [n = 2, R = C₆H₄Cl‐4 ( 1 ) and C{O}Ph ( 2 ); n = 3, R = tBu ( 3 )], pentanuclear silver(I) thiolate complex [Ag₅(μ‐dppm)₄(μ₃‐SC₆H₄NO₂‐4)₄](PF₆) ( 4 ), and hexanuclear silver(I) thiolate complexes [Ag₆(μ‐dppm)₄(μ₃‐SR)₄]Y₂ [Y = ClO₄, R =C₆H₄CH₃‐4 ( 5 ) and C₁₀H₇ (2‐naphthyl) ( 7 ); Y = PF₆, R = C₆H₄OCH₃‐4( 6 )], were synthesized [dppm = bis(diphenylphosphanyl)methane] and their crystal structures as well as photophysical properties were studied. In the solid state at 77 K, trinuclear silver(I) thiolate and silver(I) thiocarboxylate complexes 1 and 2 exhibit luminescence at 470–523 nm, tentatively attributed to originate from the ³IL (intraligand) of thiolate or thiocarboxylate ligands, whereas hexanuclaer silver(I) thiolate complexes 5 and 7 produce dual emission, in which high‐energy emission is tentatively attributed to come from the ³IL of thiolate ligands and low‐energy emission is tentatively assigned to come from the admixture of metal ··· metal bond‐to‐ligand charge‐transfer (MMLCT) and metal‐centered (MC) excited states.     

Pseudohalogeno Complexes of Sterically Hindered Tripyrrinatopalladium (TrpyPd) Fragments

Eight new pseudohalogeno complexes of sterically hindered TrpyPd fragments 4 – 11 have been prepared by salt metathesis in one step from known trifluoroacetates TrpyPdOAc^F 1 – 3 , using sodium salts of N₃, NCO, NCS, NCSe, dicyanamide (dca) and tricyanomethanide (tcm) anions. Despite the propensity of the co‐ligands to bind to two or more metal centres in a bridging coordination mode all new complexes have been shown by NMR spectroscopy to be essentially monomeric in solution. X‐ray diffraction studies performed on TrpyPdNCS( 6 ), TrpyPddca( 8 ), TrpyPddca( 9 ), and TrpyPdtcm( 10 ) revealed the presence of two different conformers in the solid state, one with a helically distorted Trpy backbone for 6 and 10 , and one with an almost planar tripyrrole but a tetrahedral distortion of the Pd^II coordination, a so‐called pseudoplanar form, for 8 and 9 . Interestingly the helical forms are also detected by unusual wavenumbers for the ν_CN stretching bands in their IR spectra. The reason for the occurrence of two different conformers in the solid state appears to be the crystal packing which depends mainly on the shape of the anionic co‐ligand and on the presense of alkyl groups on the TrpyPd fragment.     

Self‐Assembly and Structure of Cobalt(II) Complexes Using Diaminodiamide Ligands

The self‐assembly of Co(II) with two diaminodiamide ligands, 4,7‐diazadecanediamide and 4,8‐diazaundecanediamide, gave two different crystals, [(C₈H₁₈N₄O₂)Co(OH)₂Co(C₈H₁₈N₄O₂)]Cl₂ ( 1 ) [Co(C₉H₂₀N₄O₂)(Cl)(H₂O)]·Cl·2H₂O ( 2 ). Structures of 1 and 2 were characterized by single‐crystal X‐ray diffraction analysis. Structural data for 1 shows a novel type of binuclear complex with distorted octahederal coordination geometry around the Co atoms through the hydroxo bridges. By using inter‐connector N‐H···N hydrogen bonding interactions as building forces, each cationic moiety [(C₈H₁₈N₄O₂)Co(OH)₂Co(C₈H₁₈N₄O₂)]²⁺ is linked to neighboring ones, producing a charged hydrogen‐bonded 1D chain‐like structure. The chains are further connected into a 2D layer in a (4,4)‐topology via N‐H···Cl_free hydrogen‐bonding interactions. Structural data for 2 indicate that the cobalt atom adopts a six‐coordinated N₂O₄ environment, giving a distorted octahedral geometry, where two N‐ and two O‐donor sets of ligand located at equatorial positions and one water and one chloride occupied at axial positions. Through NH···Cl‐Co and OH···Cl‐Co contacts, each cationic moiety [Co(C₉H₂₀N₄O₂)(Cl)(H₂O)]⁺ in 2 is linked to neighboring ones, producing a charged hydrogen‐bonded 1D chainlike structure. Thus, the crystal‐engineering approach has proved successful in the solid‐state packing due to steric strain effect of the diaminodiamide ligand.     

Chiral Ditopic Cyclophosphazane (CycloP) Ligands: Synthesis,Coordination Chemistry,and Application in Asymmetric Catalysis

A series of dichlorocyclophosphazanes [{ClP(μ‐NR)}₂] containing chiral and achiral R groups was obtained from simple commercially available amines and PCl₃. Their condensation reactions with axially chiral biaryl diols yielded ansa‐bridged chiral cyclophosphazane (CycloP) ligands. This highly modular methodology allows extensive elaboration of the ligand set, in which the chirality can be introduced at the diol bridge and/or the amido R group. This provides the possibility to observe match and mismatch effects in catalysis. A series of twenty CycloP ligands was synthesized and characterized by multinuclear NMR spectroscopy, HRMS, elemental analysis, and in selected cases, single‐crystal X‐ray diffraction. These studies show that all of the ditopic CycloP ligands are C₂ symmetric, rendering their metal coordination sites symmetry equivalent. Two well‐established enantioselective reactions were explored by using late‐transition metal CycloP complexes as catalysts; the gold‐catalyzed hydroamination of γ‐allenyl sulfonamides and the asymmetric nickel‐catalyzed three‐component coupling of a diene and an aldehyde. The steric demands of the CycloP ligands have a subtle influence on the reactivity and selectivity observed in both reactions. Good enantiomeric ratios (e.r.) as high as 89:11 in the gold‐catalyzed reaction and 92:8 in the nickel‐catalyzed bis‐homoallylation reaction were observed.     

Syntheses and Structural Characterization of Four New Silver(I) Complexes with the N,N′(O)‐bidentate Bridging Ligands

Four new bridged silver(I) complexes, namely [Ag₂(μ₂‐teda)(μ₂‐fbc)₂] ( 1 ), [Ag₂(μ₂‐1,6‐dah)₂](bpdc) · 4H₂O ( 2 ), [Ag₂(μ₂‐2‐ap)(2‐ap)(bnb)] · 0.34H₂O ( 3 ), [Ag₂(μ₂‐pyc)₂(2‐apy)₂] · 0.5H₂O ( 4 ), have been synthesized and characterized by elemental analysis and crystallographic methods [fbc = 4‐fluorobenzoate, teda = triethylenediamine ( 1 ); bpdc = biphenyl‐4,4′‐dicarboxylate, 1,6‐dah = 1,6‐diaminohexane ( 2 ); bnb = 3,5‐binitrobenzoate, 2‐ap = 2‐aminopyrimidine ( 3 ); pyc = 3‐pyridinecarboxylate acid, 2‐apy = 2‐aminopyridine ( 4 )]. Complex 1 contains a 1D linear chain paralleling to the c‐axis, whereas in complex 2 silver(I) atoms were bridged by the 1,6‐dah ligand into a zigzag chain, further giving a 1D ribbon by weak Ag ··· Ag interactions. Complex 3 consists of a dinuclear silver(I) [Ag₂(μ₂‐2‐ap)(2‐ap)(bnb)] moiety and a lattice water molecule, forming a 3D network via a number of hydrogen‐bonding interactions such as N–H ··· O, N–H ··· N and C–H ··· O hydrogen bond and other weak interactions such Ag ··· Ag, Ag ··· N, N ··· O as well as O ··· O interaction. Similar to 3 , the asymmetric unit of 4 consists of one dinuclear silver(I) [Ag₂(μ₂‐pyc)₂(2‐apy)₂] moiety and half lattice water molecule, further generating a tetranuclear silver(I) {[Ag₂(μ₂‐pyc)₂(2‐apy)₂]₂ · H₂O} moiety. These moieties construct a 3D supramolecular network structure of 4 through N–H ··· O, O–H ··· O and C–H ··· O hydrogen bonds as well as other weak interactions such as Ag ··· O and N ··· O interactions.     

Structure and Reactivity of a Unique Y‐Shaped Tricoordinate Bis(silyl)platinum(II)–NHC Complex

Y not? A unique, three‐coordinate Y‐shaped bis(silyl)platinum(II) complex was isolated and characterized (see structure; C light gray, N blue, Si pink, Pt dark gray). DFT studies on a model system shed light on the nature of this unusual coordination mode for platinum(II).

     

Oxamido‐bridged N4 Macrocyclic Complexes CuII/MII/CuII (M = Mn,Co): Synthesis,Crystal Structures and Magnetic Properties

Two new oxamido‐bridged N₄ macrocyclic complexes [(CuL)₂Mn(C₂H₅OH)₂](ClO₄)₂ · 2C₂H₅OH ( 1 ) and [(CuL)₂Co‐(C₂H₅OH)₂](ClO₄)₂ · 2C₂H₅OH ( 2 ) (H₂L = 2,3‐dioxo‐5,6:14,15‐di‐benzo‐7,13‐diphenyl‐1,4,8,12‐tetraazacyclo‐pentadeca‐7,13‐diene) have been synthesized and structurally characterized by X‐ray crystallographic investigations. In the two complexes, all copper(II) ions adopt a slightly distorted square‐planar configuration and the central manganese(II) and cobalt(II) ions are set in a distorted octahedral coordination sphere, connected to the other CuL fragments through exo‐cis oxamido bridges. The analyses of the magnetic properties were carried out by means of the theoretical expression of the magnetic susceptibility deduced from the spin Hamiltonian ? = –2J?₁?₂, leading to J = –14.58 cm^–1 for complex 1 and J = –26.95 cm^–1 for complex 2 , respectively.     

Synthesis and Crystal Structure of Novel Coordination Polymers with Nitrilotripropionic Acid

A novel three‐dimensional (3D) lanthanide‐organic framework [Pr₃(NTP)₃(H₂O)₆] · 10H₂O ( 1 ), (H₃NTP = 3,3′,3′‐nitrilotripropionic acid) was synthesized and characterized by elemental analyses, IR spectroscopy, and X‐ray diffraction analyses. The results show that complex 1 is connected through NTP ligands to form a 3D network with microchannels. The coordination mode of the NTP ligand was found for the first time. In order to investigate the temperature effects on controlling the dimensionality of the complexes, another two complexes, namely, [Nd(NTP)(H₂O)₂] · H₂O · HBr ( 2 ) and [Pr(H₂O)][⁺NH₃(CH₂CH₂COO^–)][OOCCOO]_1.5 ( 3 ) were synthesized and characterized. Notably, in complex 3 , the NTP ligand lost its two arms because of the high temperature. Furthermore, the thermogravimetric analyses of the three complexes are discussed in detail.     

Synthesis and Analysis of the Structure,Diffusion and Cytotoxicity of Heterocyclic Platinum(IV) Complexes

We have developed six dihydroxidoplatinum(IV) compounds with cytotoxic potential. Each derived from active platinum(II) species, these complexes consist of a heterocyclic ligand (H_L) and ancillary ligand (A_L) in the form [Pt(H_L)(A_L)(OH)₂]²⁺, where H_L is a methyl‐functionalised variant of 1,10‐phenanthroline and A_L is the S,S or R,R isomer of 1,2‐diaminocyclohexane. NMR characterisation and X‐ray diffraction studies clearly confirmed the coordination geometry of the octahedral platinum(IV) complexes. The self‐stacking of these complexes was determined using pulsed gradient stimulated echo nuclear magnetic resonance. The self‐association behaviour of square planar platinum(II) complexes is largely dependent on concentration, whereas platinum(IV) complexes do not aggregate under the same conditions, possibly due to the presence of axial ligands. The cytotoxicity of the most active complex, exhibited in several cell lines, has been retained in the platinum(IV) form.