Dicarba-closo-dodecarborane-containing half-sandwich complexes of ruthenium, osmium, rhodium and iridium : biological relevance and synthetic strategies

This review describes how the incorporation of dicarba-closo-dodecarboranes into half-sandwich complexes of ruthenium, osmium, rhodium and iridium might lead to the development of a new class of compounds with applications in medicine. Such a combination not only has unexplored potential in traditional areas such as Boron Neutron Capture Therapy agents, but also as pharmacophores for the targeting of biologically important proteins and the development of targeted drugs. The synthetic pathways used for the syntheses of dicarba-closo-dodecarboranes-containing half-sandwich complexes of ruthenium, osmium, rhodium and iridium are also reviewed. Complexes with a wide variety of geometries and characteristics can be prepared. Examples of addition reactions on the metal centre, B–H activation, transmetalation reactions and/or direct formation of metal–metal bonds are discussed (103 references)

Structural studies on silver(I) complexes containing phenylcyanamido ligands and uranyl(VI) complexes with beta-ketophenolates : a dissertation presented in partial fulfilment for the degree of Master of Science in Chemistry at Massey University

This thesis is divided into two parts. In Section One studies on the interaction of phenylcyanamides with silver(I) are reported. Section Two describes the results of studies on the complexes formed from β-ketophenol ligands and the uranyl ion. Section One Chapter 1 is a brief overview of the use of phenylcyanamides in forming coordination complexes with transition metals. In Chapter 2 the preparation of a series of silver complexes of the general formula [Ag(Ph₃P)₃(pcyd)], where pcyd is a phenylcyanamido anion, is described. The crystal structures of [Ag(Ph₃P)₃(4-Brpcyd)] and [Ag(Ph₃P)₃(4-MeOpcyd)] have been determined, in which the silver atom occupies a distorted tetrahedral environment, and the latter complex has a very short terminal C-N bond within the 4-methoxyphenylcyanamido ligand. Chapter 3 provides a comparison of all those transition metal complexes of phenylcyanamides that have been structurally characterised. Section Two Chapter 4 is a brief overview of the use of β-diketonate ligands in forming dinuclear complexes, especially those in which the uranyl ion (UO₂²+) is present. In Chapter 5 the preparation of the mononuclear complexes [UO₂(HL¹)₂(MeOH)], (UO₂(HL²)₂(EtOH)], the heterobinuclear complexes [U0₂Mn(L¹)₂(EtOH)]·1.5H₂O, and [UO₂Mn(L²)₂(EtOH)]·2H₂₂O and the oxo-ligand adducts [UO₂(HL¹)₂(Ph₃AsO)]·2H₂O, [U0₂(HL²)₂(Ph₃PO)] and [UO₂(HL²)₂(Ph₃AsO)] (H₂L¹ = 1-(2-hydroxyphenyl)-3- butanedione and H₂L² = 1-(2-hydroxyphenyl)-3-phenyl-l,3-propanedione) is described. The complexes have been characterized by a variety of physicochemical techniques and the crystal structures of [UO₂(HL¹)₂(EtOH)] and [UO₂(HL²)₂(EtOH)]·EtOH determined. Both complexes contain seven coordinate uranium(VI) in a pentagonal bipyramidal geometry in which the two bidentate β-diketonato ligands and the ethanol ligand make up the equatorial pentagonal plane. For the complex [UO₂(HL¹)₂(EtOH)] the HL¹ ligands are in a trans arrangement with respect to one another, whereas for the [UO₂(HL²)₂(EtOH)]·EtOH complex the HL² ligands adopt a cis arrangement. However, in solution variable temperature ¹H NMR spectra indicate that the cis and trans isomers are in equilibrium for both complexes

Trans-bis(alkynyl) ruthenium complexes: synthesis, structure and reactivity

This Thesis describes the synthesis and characterisation of a series of trans-bis(alkynyl) ruthenium complexes, trans-[Ru(C≡CR)2(L)4], to better understand how the variation of the metal ancillary ligands (L) affect electronic structure and spectroscopic properties, chemical reactivity, and behaviour in metal|molecule|metal junctions. Reactions of cis-[RuCl2(dppm)2] with terminal alkyne HC≡CC6H4-4-R, in the presence of TlBF4 and base, gives into trans-bis(alkynyl) complexes, trans-[Ru(C≡CC6H4-4-R)2(dppm)2], for electron withdrawing R groups or cationic η3-butenynyl complexes, E-­[Ru(η3-{HC(C6H4-4-R)=CC≡C(C6H4-4-R)})(dppm)2]+ for electron donating R groups. Reactions of cis-[RuCl2(dppm)2] with di-terminal alkynes HC≡CC6H4-2,5-X2-4-C≡CH, in the presence of TlBF4 and [NnBu4]Cl, gives trans-[RuCl(C≡CC6H2-2,5-X2-4-CCl=CH2)(dppm)2], inferring a quinoidal cumulene intermediate. Multi-metallic trans-bis(alkynyl) {Ru(dppe)2} complexes, varying in binding groups and bridging ligands, have been prepared. Reversible oxidation processes, whilst corresponding to the number of integrated metal centres, exhibit a high degree of alkynyl character in all cases. The vibrational and electronic spectra of both neutral and oxidised complexes are complicated by the presence of numerous spectroscopically distinct rotamer conformations and redox isomers. For example in the case of mono-oxidised complexes, a principal low-energy (π-π*) NIR band is exhibited along with multiple higher energy (MLCT-type) NIR bands, which can be assigned by comparison with smaller model systems. Finally, trans-bis(alkynyl) {Ru{P(OEt)3}4} complexes have been synthesised. As a result of the increased (pseudo D4h) molecular symmetry and consequent fewer distinct rotamer conformations, a lesser number of NIR bands are exhibited for trans­[Ru(C≡CR)2{P(OEt)3}4]+ than bis-chelating dppm and dppe derivatives. Between trans-[Ru(C≡CR)2(PPʹ)] (PPʹ = (dppe)2, {P(OEt)3}4) complexes, the {Ru(dppe)2} derivatives give rise to conductance histograms with additional features. These features are attributed to contacts formed at or across the dppe-phenyl rings, leading to suggestions that phosphite complexes might be novel ‘insulated’ molecular wires

Bonding and electronic properties of linear diethynyl oligothienoacene-bridged diruthenium complexes and their oxidized forms

A series of five diruthenium diethynyl complexes based on α,β-fused oligothienoacenes in the core of the bridging ligands [{Ru­(dppe)­Cp*}₂(μ-CC–L–CC)] [dppe = 1,2-bis­(diphenylphosphino)­ethane, Cp* = η⁵-C₅Me₅; L = thieno­[3,2-<i>b</i>]­thiophene (<b>4</b>), thieno­[2,3-<i>b</i>]­thiophene (<b>5</b>), 3,4-dimethylthieno­[2,3-<i>b</i>]­thiophene (<b>6</b>), dithieno­[3,2-<i>b</i>:2′,3′-<i>d</i>]­thiophene (<b>7</b>), and thieno­[3,2-<i>b</i>]­thieno­[2′,3′:4,5]­thieno­[2,3-<i>d</i>]­thiophene (<b>8</b>)] have been synthesized and fully characterized electrochemically and spectroscopically. Elongation of the redox noninnocent oligothienoacene bridge core causes a smaller potential difference between the initial two anodic steps, not seen for free dialkyl oligothienoacenes, and increased positive charge delocalization over the conjugated bridge backbone. The highest occupied molecular orbital of the parent complexes resides predominantly on the oligothienoacene core, with strong participation of the ethynyl linkers and slightly smaller contribution from the metallic termini. This bonding character makes the initial one-electron oxidation symmetrical, as revealed by combined voltammetric and spectroscopic (IR, UV–vis–near-IR, and electron paramagnetic resonance) methods as well as density functional theory (DFT) and time-dependent DFT calculations of truncated and selected nontruncated models of the studied series. The remarkable gradual appearance of two CC stretching absorptions in the IR spectra of the monocationic diethynyl complexes is ascribed to increasing vibronic coupling of the IR-forbidden ν_s(CC) mode of the oxidized −[CC–core–CC]⁺– bridge with a low-lying π–π*­(intrabridge)/metal-to-ligand charge-transfer electronic transition in the near-to-mid-IR spectral region

Multistep oxidation of diethynyl oligophenylamine-bridged diruthenium and diiron complexes

Homodinuclear nonlinear complexes [{M(dppe)Cp*}2{μ-(-C≡C)2X}] (X = triphenylamine (TPA), M = Ru (1a) and Fe (1b); X = N,N,N',N',-tetraphenylphenylene-1,4-diamine (TPPD), M = Ru (2a)) were prepared and characterized by 1H, 13C and 31P NMR and single crystal X-ray diffraction (1a, 2a). Attempts to prepare the diiron analogue of 2a were not successful. Experimental data obtained from cyclic voltammetry (CV), square wave voltammetry (SWV), UV-vis-NIR spectroelectrochemistry and very informative IR spectroelectrochemistry in the C≡C-stretching region, combined with density functional theory calculations, afford to make an emphasizing assessment of the close association between the metal‒ethynyl termini and the oligophenylamine bridge core as well as their respective involvement in sequential one-electron oxidations of these complexes. The anodic behavior of the homobimetallic complexes depends strongly both on the metal center and the length of the oligophenylamine bridge core. The poorly separated first two oxidations of diiron complex 1b are localized on the electronically nearly independent Fe termini. In contrast, diruthenium complex 1a exhibits a significantly delocalized character and a marked electronic communication between the ruthenium centers through the diethynyl-TPA bridge. The ruthenium-ethynyl halves in 2a, separated by the doubly extended and more flexible TPPD bridge core, show a lower degree of electronic coupling, resulting in close-lying first two anodic waves and the NIR electronic absorption of [2a]+ with an indistinctive IVCT character. Finally, the third anodic waves in the voltammetric responses of the homobimetallic complexes are associated with the concurrent exclusive oxidation of the TPA or TPPD bridge cores

Group VIII transition metal complexes for nonlinear optical switching

Metal alkynyl complexes have been shown to be potentially useful third-order nonlinear optical switches, with large two-photon absorption cross-sections and strong changes in photon absorption properties on oxidation. By forming multinuclear complexes, switches with more then two states can be made. Chapter 1 presents an introduction to nonlinear optics and reviews some inorganic materials which have had their nonlinear optical properties measured. Chapter 2 details new synthetic routes into binuclear complexes incorporating an osmtum chloro-alkynyl metal centre. Structural, electrochemical and spectroelectrochemical studies on selected examples have been carried out. Chapter 3 details new facile synthetic routes into osmtum ammine-alkynyl and osmium bis-alkyny1 complexes. Synthesis of osmium and ruthenium binuclear and trinuclear complexes with both diethyny1 and triethyny1 bridges between the metal atoms has been explored. Structural, electrochemical, spectroelectrochemical and theoretical studies have been carried out on selected complexes. Chapter 4 reports the synthesis of a number of branched multinuclear complexes incorporating both osmium and ruthenium metal atoms. Electrochemical and spectroelectrochemical studies have been carried out on selected examples. The Z-scan technique has been used to investigate the third-order nonlinear optical properties of a number of linear and branched bimetallic complexes, showing large effects but some photo-induced instability. Chapter 5 details the formation of a number of new mononuclear and unsymmetrical binuclear iron alkynyl complexes. The electrochemical and spectroelectrochemical behaviour of the complexes exhibiting a reversible redox process has been explored. - provided by Candidate

Polynuclear carbon-rich organometallic complexes: clarification of the role of the bridging ligand in the redox properties.

International audienceIn this Perspective, we highlight the non-innocent behaviour of the bridging ligand in organometallic polynuclear metallic complexes displaying metal-carbon σ bonds between the metallic units and a strongly coupled conjugated carbon-rich bridging ligand. With the help of representative experimental and theoretical studies on polymetallic systems, but also on monometallic complexes, we point out that the level of implication of the carbon rich ligand in the redox processes is very sensitive to the nature of (i) the metal(s), (ii) the ancillary ligands and (iii) the carbon-rich ligand itself, and that this participation is frequently found to be major. Consequently, the general denomination M((n + 1)) that is usually used for oxidized species gives the picture that only the metal density is affected, which is misleading. Moreover, for polymetallic species, these elements make the mixed valence denomination and the use of standard methodologies to rationalize intramolecular electron transfer, such as the Hush model inaccurate. Indeed, these theoretical treatments of mixed-valent complexes have at their core the assumption of metal-based redox state changes. Quantum mechanical calculations, coupled with spectroscopic methods, such as EPR spectroscopy, turn out to be a valuable suite of tools to both identify and better describe those systems with appreciable ligand redox non-innocent character. Finally, some examples and perspectives of applications for this carbon-rich type of complexes that take advantage of their peculiar electronic structure are presented

Synthesis, structure and electrochemistry of organometallic compounds bearing C(_n)N ligands

In this thesis, the synthesis of the organic cyanoacetylenes NCC≡CC(_6)H(_5) and NCC≡CC(_6)H(_4)-4-NMc(_2) and the metal cyanoacetylides Ru(C≡CC≡N)(PPh(_3))(_2)Cp, Ru(C≡CC≡N)(dppe)Cp* and Fe(C≡CC≡N)(dppe)Cp is presented and their coordination chemistry is explored. The structure and electrochemical behaviour of these novel cyano-carbon complexes is investigated and spectro-electrochemical methods are used to investigate the electronic structure of the cyanoacetylide compounds. In addition, in order to gain a greater understanding of the metal/ligand bonding interaction in these systems, the synthesis, structure and electrochemical behaviour of a series of metal nitriles [Ru(N≡CC(_6)H(_4)X)(PPh(_3))(_2)Cp][PF(_6)] (X = NO(_2), NMe(_2), CN) and [M(N≡CC(_6)H(_4)X)L(_2)Cp'][PF(_6)] (M = Ru, L = PPh(_3), Cp' = Cp; M = Ru, L2 = dppe, Cp' = Cp*; M = Fe, L(_2) = dppe, Cp' = Cp) were investigated, as were the complexes [{Ru(PPh(-3))(_2)Cp}(_2){μ-M(CN)(_4)}] (M = Ni, Pd, Pt) and [{Ru(dppe)Cp*}(_2){ μ - M(CN)(_4)}] (M = Ni, Pd , Pt), which feature a group 10 tetracyanometallate as a bridging moiety