Isocyanide Ligands Research Articles

Monomeric Chini‐Type Triplatinum Clusters Featuring Dianionic and Radical‐Anionic π*‐Systems

AbstractOwing to their unique topologies and abilities to self‐assemble into a variety of extended and aggregated structures, the binary platinum carbonyl clusters [Pt3(CO)6]n2− (“Chini clusters”) continue to draw significant interest. Herein, we report the isolation and structural characterization of the trinuclear electron‐transfer series [Pt3(μ‐CO)3(CNArDipp2)3]n− (n=0, 1, 2), which represents a unique set of monomeric Pt3 clusters supported by π‐acidic ligands. Spectroscopic, computational, and synthetic investigations demonstrate that the highest‐occupied molecular orbitals of the mono‐ and dianionic clusters consist of a combined π*‐framework of the CO and CNArDipp2 ligands, with negligible Pt character. Accordingly, this study provides precedent for an ensemble of carbonyl and isocyanide ligands to function in a redox non‐innocent manner.

Synthesis and Simple Immobilization of Palladium(II) Acyclic Diaminocarbene Complexes on Polystyrene Support as Efficient Catalysts for Sonogashira and Suzuki–Miyaura Cross-Coupling

Immobilization of palladium(II) acyclic diaminocarbene (Pd(II)-ADC) complexes on a resin support surface has been easily performed by metal-mediated addition of amino groups of benzhydrylamine-polystyrene to the coordinated isocyanide ligand of cis-PdCl2(CNR)2 (R = t-Bu, Cy). The investigation of the benzhydrylamine reaction with palladium-coordinated isocyanides in solution has revealed that, depending on the reaction conditions, two carbene-type complexes can be obtained as a result of the addition to the CN triple bond, as well as a third complex which is formed via substitution of the isocyanide ligand by benzhydrylamine. Nucleophilic addition of an amino group to the isocyanide ligand has led to a cis-acyclic diaminocarbene complex or a cationic diaminocarbene complex with trans configuration and an intramolecular hydrogen-bonded chloride anion (the nature of this noncovalent interaction was analyzed by DFT calculations, including AIM analysis). The unsupported and resin-supported palladium catalysts...

Steric and Electronic Influence of Aryl Isocyanides on the Properties of Iridium(III) Cyclometalates.

Cyclometalated iridium complexes with efficient phosphorescence and good electrochemical stability are important candidates for optoelectronic devices. Isocyanide ligands are strong-field ligands: when attached to transition metals, they impart larger HOMO-LUMO energy gaps, engender higher oxidative stability at the metal center, and support rugged organometallic complexes. Aryl isocyanides offer more versatile steric and electronic control by selective substitution at the aryl ring periphery. Despite a few reports of alkyl isocyanide of cyclometalated iridium(III), detailed studies on analogous aryl isocyanide complexes are scant. We report the synthesis, photophysical properties, and electrochemical properties of 11 new luminescent cationic biscyclometalated bis(aryl isocyanide)iridium(III) complexes. Three different aryl isocyanides--2,6-dimethylphenyl isocyanide (CNAr(dmp)), 2,6-diisopropylphenyl isocyanide (CNAr(dipp)), and 2-naphthyl isocyanide (CNAr(nap))--were combined with four cyclometalating ligands with differential π-π* energies--2-phenylpyridine (ppy), 2,4-difluorophenylpyridine (F2ppy), 2-benzothienylpyridine (btp), and 2-phenylbenzothiazole (bt). Five of them were crystallographically characterized. All new complexes show wide redox windows, with reduction potentials falling in a narrow range of -2.02 to -2.37 V and oxidation potentials spanning a wider range of 0.97-1.48 V. Efficient structured emission spans from the blue region for [(F2ppy)2Ir(CNAr)2]PF6 to the orange region for [(btp)2Ir(CNAr)2]PF6, demonstrating that isocyanide ligands can support redox-stable luminescent complexes with a range of emission colors. Emission quantum yields were generally high, reaching a maximum of 0.37 for two complexes, whereas btp-ligated complexes had quantum yields below 1%. The structure of the CNAr ligand has a minimal effect on the photophysical properties, which are shown to arise from ligand-centered excited states with very little contribution from metal-to-ligand charge transfer in most cases.

Crystal structure of fac-tricarbon-yl(cyclo-hexyl isocyanide-κC)(quinoline-2-carboxyl-ato-κ(2) N,O)rhenium(I).

In the title compound, [Re(C10H6NO2)(C7H11N)(CO)3], the Re(I) atom is coordinated by three carbonyl ligands in a facial arrangement and by the N, O and C atoms from a chelating quinaldate anion and a monodentate isocyanide ligand, respectively. The resultant C4NO coordination sphere is distorted octa-hedral. A lengthening of the axial Re-CO bond trans to the isocyanide ligand is indicative of the trans effect. Individual complexes are stacked into rods parallel to [001] through displaced π-π inter-actions. Weak C-H⋯O hydrogen-bonding inter-actions between the rods lead to the formation of layers parallel to (010). These layers are stacked along [010] by C-H⋯H-C van der Waals contacts.

Non-Precious-Metal Catalytic Systems Involving Iron or Cobalt Carboxylates and Alkyl Isocyanides for Hydrosilylation of Alkenes with Hydrosiloxanes.

A mixture of an iron or a cobalt carboxylate and an isocyanide ligand catalyzed the hydrosilylation of alkenes with hydrosiloxanes with high efficiency (TON >10(3)) and high selectivity. The Fe catalyst showed excellent activity for hydrosilylation of styrene derivatives, whereas the Co catalyst was widely effective in reaction of alkenes. Both of them catalyzed the reaction with allylic ethers. Chemical modification and cross-linking of silicones were achieved by choosing the right catalyst and reaction conditions.

Synthesis and cation-binding studies of gold(I) complexes bearing oligoether isocyanide ligands with ester and amide as linkers.

A series of dinuclear gold(I) isocyanide complexes of bis(alkynyl)calix[4]arene was designed and synthesized, and their photophysical and cation recognition properties were studied. Complex 1, [{calix[4]arene-(OCH2CONH-C6H4C≡C)2}{Au(CN-C6H4O(CH2CH2O)2CH3)}2], was found to show a high selectivity towards Al(3+) in CH2Cl2-MeCN (1 : 1 v/v). Upon addition of Al(3+), drastic changes in the electronic absorption, emission and (1)H NMR spectra were observed. These changes have been attributed to the formation of Au(I)Au(i) interactions induced by the high binding affinity of the amide site for the Al(3+) ion, instead of the high binding affinity expected of the oligoether site for alkali and alkaline earth metal ions. Further studies with the control complex, [{calix[4]arene-(OOC-C6H4C≡C)2}{Au(CN-C6H4O(CH2CH2O)2CH3)}2] (4), indicated that the amide carbonyl oxygen in the flexible pendants is crucial for the binding of Al(3+).

Synthesis and photophysical properties of isocyano Ruthenium(II) quinoline-8-thiolate complexes with visible-light and near-infrared emission

The reactions of [RuII(SQ)2(PPh3)2] (SQ = quinoline-8-thiolate) with different isocyanide ligands affords a series of emissive bis(quinoline-8-thiolate) ruthenium(II) complexes [RuII(SQ)2(PPh3)(CNR)] (1–6). Two isomeric forms, i.e. cis,trans (1a – 6a) and cis,cis (1b – 6b) have been separated in these reactions. With the variation on the π-accepting ability of the isocyanide ligands, the CN stretches, lowest energy absorptions and the photoluminescence can be systematically modified.

Nitrene Metathesis and Catalytic Nitrene Transfer Promoted by Niobium Bis(imido) Complexes.

We report a metathesis reaction in which a nitrene fragment from an isocyanide ligand is exchanged with a nitrene fragment of an imido ligand in a series of niobium bis(imido) complexes. One of these bis(imido) complexes also promotes nitrene transfer to catalytically generate asymmetric dialkylcarbodiimides from azides and isocyanides in a process involving the Nb(V)/Nb(III) redox couple.

Towards Cardiolite‐Inspired Carbon Monoxide Releasing Molecules – Reactivity of d4, d5 Rhenium and d6 Manganese Carb­onyl Complexes with Isocyanide Ligands

AbstractCarbon monoxide releasing molecules (CORMs) are investigated widely in synthetic and medicinal chemistry owing to the potential therapeutic applications of the CO gas. Organometallic carbonyl complexes are best suited to play the role of CO carriers as they allow the exogenous release of CO under controlled conditions, and the toxicity of the gas can be overcome. With the long‐term goal of developing CORMs with similar properties to those of the sesta‐methoxyisobutylisonitrile (sesta‐mibi) 99mTc complex (Cardiolite), we have studied the reactivity of isocyanide ligands towards 16‐ and 17‐electron cis‐[Re(CO)2Br4]–/2– species and the [Mn(CO)5Br] complex. Six different isocyanide ancillary ligands (CNR), including mibi, were selected for this study. Their reactions with cis‐dicarbonyl ReIII and ReII complexes were accompanied by two‐ and one‐electron reduction of the metal center and resulted in the formation of stable cis‐mer‐[Re(CO)2(CNR)3Br] species, whereas the same reactions with [Mn(CO)5Br] gave fac‐[Mn(CO)3(CNR)2Br] compounds. All of the complexes were fully characterized, and single‐crystal X‐ray diffraction structure determinations were performed for selected species. In addition, unique monocarbonyl complexes were obtained from the reactions of cis‐[Re(CO)2Br4]– (1) with tert‐butyl isocyanide and cis‐[Re(CO)2Br4]2– (2) with mibi. The species, a heptacoordinate ReIII and a hexacoordinate ReII complex, respectively, were also characterized structurally. The CO‐releasing profiles, the cytotoxic effects against 3T3 fibroblast cells, and the antibacterial properties of the compounds were also investigated.

Synthesis and evaluation of a novel 99mTcN(PNP)-complex with metronidazole isocyanide ligand as a marker for tumor hypoxia

The [99mTcN(PNP)]2+ core offers a unique route for the preparation of asymmetric 99mTc-complexes. Though bidentate chelators such as dithiocarbamates are most commonly used ligands in this approach, present study explores the possibility of using a monodentate ligand, a isocyanide derivative of metronidazole (MetroNC), for preparing a 99mTcN(PNP) complex for detecting tumor hypoxia. MetroNC could be prepared in good yield and subsequently radiolabeled with [99mTcN(PNP)]2+ precursor complex prepared from [99mTcN]2+ core and N-(2-methoxyethyl)-2-(diphenylphosphino)-N-(2-(diphenylphosphino)ethyl)ethanamine (PNP2) ligand. Preliminary biodistribution studies showed tumor uptake pattern similar to previous studies wherein, about 75 % of the tumor activity observed at 60 min post injection (p.i.) was still found to remain in tumor at 180 min p.i.

Kinetic Destabilization of Metal-Metal Single Bonds: Isolation of a Pentacoordinate Manganese(0) Monoradical.

The 17e(-) monoradical [Mn(CO)5 ] is widely recognized as an unstable organometallic transient and is known to dimerize rapidly with the formation of a MnMn single bond. As a result of this instability, isolable analogues of [Mn(CO)5 ] have remained elusive. Herein, we show that two sterically encumbering isocyanide ligands can destabilize the MnMn bond leading to the formation of the isolable, manganese(0) monoradical [Mn(CO)3 (CNAr(Dipp2) )2 ] (Ar(Dipp2) =2,6-(2,6-(iPr)2 C6 H3 )2 C6 H3 ). The persistence of [Mn(CO)3 (CNAr(Dipp2) )2 ] has allowed for new insights into nitrosoarene spin-trapping studies of [Mn(CO)5 ].

Kinetic Destabilization of Metal–Metal Single Bonds: Isolation of a Pentacoordinate Manganese(0) Monoradical

AbstractThe 17e− monoradical [Mn(CO)5] is widely recognized as an unstable organometallic transient and is known to dimerize rapidly with the formation of a MnMn single bond. As a result of this instability, isolable analogues of [Mn(CO)5] have remained elusive. Herein, we show that two sterically encumbering isocyanide ligands can destabilize the MnMn bond leading to the formation of the isolable, manganese(0) monoradical [Mn(CO)3(CNArDipp2)2] (ArDipp2=2,6‐(2,6‐(iPr)2C6H3)2C6H3). The persistence of [Mn(CO)3(CNArDipp2)2] has allowed for new insights into nitrosoarene spin‐trapping studies of [Mn(CO)5].

1,3-Dipolar cycloaddition of nitrones to transition metal-bound isocyanides: DFT and HSAB principle theoretical model together with analysis of vibrational spectra

The hard and soft acids and bases (HSAB) principle together with the density functional theory (DFT) calculations were used to analyze the driving forces of the hypothetical 1,3-dipolar cycloaddition (CA) of the nitrone CH2N(Me)O to the uncomplexed CNMe and to isocyanide ligands in various transition metal complexes. The calculated activation (ΔGs≠) and reaction (ΔGs) energies depend from the electronic chemical potential (μ), the global electrophilicity (ω) and nucleophilicity (N) indexes of the dipolarophiles, the static charge transfer “nucleophile → electrophile” (ΔN0), and the maximum amount of electronic charge that the electrophile system may accept (ΔNmax). Thus, the HSAB principle may be successfully apply for the study of reactivity of such compounds. The ΔGs≠ and ΔGs and the calculated stretching vibration frequencies ν(CN) of isocyanides well correlated with each other, i.e. higher values of ν(CN) correspond to lower values of ΔGs≠ and ΔGs. The application of the reactivity descriptors discussed in this work is a possible alternative and a complement addition to the estimates based on the classical frontier molecular orbital (FMO) theory.

Rhenium-isocyanide complexes

No abstract available

C–N Coupling of Isocyanide Ligands Promoted by Acetylide Addition to Diiron Aminocarbyne Complexes

The bis-isocyanide aminocarbyne diiron complexes [Fe2{μ-CN(Me)(R)}(μ-CO)(CNR′)2(Cp)2][SO3CF3] (R = R′ = Xyl, 1a; R = Me, R′ = Xyl, 1b; R = Xyl, R′ = tBu, 1c; Xyl = 2,6-C6H3Me2) and the analogous thiocarbyne complex [Fe2{μ-CS(Me)}(μ-CO)(CNXyl)2(Cp)2][SO3CF3], 2, were prepared in high yields from [Fe2{μ-C(E)}(μ-CO)(CO)2(Cp)2][SO3CF3] [E = N(Me)(R) or SMe, respectively], by reaction with Me3NO in the presence of the appropriate isocyanide. The addition of LiC≡CR′′ to 1a–b promoted intramolecular C–N coupling between the two isocyanide moieties, resulting in the formation of [Fe2(μ-CO){μ-CN(Me)(R)}{μ-C(NXyl)N(Xyl)C(C≡CR′′)}(Cp)2] (R = Xyl, R″ = Ph, 3a; R = Xyl, R″ = Tol, 3b; R = Me, R″ = Ph, 3c; Tol = 4-C6H5Me), in ca. 60% yields. The reaction of 1a with LiC≡CSiMe3 proceeded with coupling between two dinuclear units, to give the tetranuclear complex C2[Fe2(μ-CO)(Cp)2{μ-CN(Me)(Xyl)}{μ-C(NXyl)N(Xyl)C}]2, 4, in 65% yield. The reaction of 2 with LiC≡CTol resulted in the formation of a mixture of nonidentified products. The new complexes were purified by alumina chromatography and fully characterized by analytical techniques, IR and NMR spectroscopy. The molecular structures of 3b and 4 were ascertained by X-ray diffraction studies.

Tailoring precursors for deposition: synthesis, structure, and thermal studies of cyclopentadienylcopper(i) isocyanide complexes.

We report here the synthesis and characterization of a family of copper(I) metal precursors based around cyclopentadienyl and isocyanide ligands. The molecular structures of several cyclopentadienylcopper(I) isocyanide complexes have been unambiguously determined by single-crystal X-ray diffraction analysis. Thermogravimetric analysis of the complexes highlighted the isopropyl isocyanide complex [(η(5)-C5H5)Cu(CN(i)Pr)] (2a) and the tert-butyl isocyanide complex [(η(5)-C5H5)Cu(CN(t)Bu)] (2b) as possible copper metal chemical vapor deposition (CVD) precursors. Further modification of the precursors with variation of the substituents on the cyclopentadienyl ligand system (varying between H, Me, Et, and (i)Pr) has allowed the affect that these changes would have on features such as stability, volatility, and decomposition to be investigated. As part of this study, the vapor pressures of the complexes 2b, [(η(5)-MeC5H4)Cu(CN(t)Bu)] (3b), [(η(5)-EtC5H4)Cu(CN(t)Bu)] (4b), and [(η(5)-(i)PrC5H4)Cu(CN(t)Bu)] (5b) over a 40-65 °C temperature range have been determined. Low-pressure chemical vapor deposition (LP-CVD) was employed using precursors 2a and 2b to synthesize thin films of metallic copper on silicon, gold, and platinum substrates under a H2 atmosphere. Analysis of the thin films deposited onto both silicon and gold substrates at substrate temperatures of 180 and 300 °C by scanning electron microscopy and atomic force microscopy reveals temperature-dependent growth features: Films grown at 300 °C are continuous and pinhole-free, whereas films grown at 180 °C consist of highly crystalline nanoparticles. In contrast, deposition onto platinum substrates at 180 °C shows a high degree of surface coverage with the formation of high-density, continuous, and pinhole-free thin films. Powder X-ray diffraction and X-ray photoelectron spectroscopy (XPS) both show the films to be high-purity metallic copper.

Comparative measure of the electronic influence of highly substituted aryl isocyanides.

To assess the relative electronic influence of highly substituted aryl isocyanides on transition metal centers, a series of C4v-symmetric Cr(CNR)(CO)5 complexes featuring various alkyl, aryl, and m-terphenyl substituents have been prepared. A correlation between carbonyl-ligand (13)C{(1)H} NMR chemical shift (δCO) and calculated Cotton-Kraihanzel (C-K) force constant (kCO) is presented for these complexes to determine the relative changes in isocyanide σ-donor/π-acid ratio as a function of substituent identity and pattern. For nonfluorinated aryl isocyanides possessing alkyl or aryl substitution, minimal variation in effective σ-donor/π-acid ratio is observed over the series. In addition, aryl isocyanides featuring strongly electron-releasing substituents display an electronic influence that nearly matches that of nonfluorinated alkyl isocyanides. Lower σ-donor/π-acid ratios are displayed by polyfluorinated aryl isocyanide ligands. However, the degree of this attenuation relative to nonfluorinated aryl isocyanides is not substantial and significantly higher σ-donor/π-acid ratios than CO are observed in all cases. Substituent patterns for polyfluorinated aryl isocyanides are identified that give rise to low relative σ-donor/π-acid ratios but offer synthetic convenience for coordination chemistry applications. In order to expand the range of available substitution patterns for comparison, the syntheses of the new m-terphenyl isocyanides CNAr(Tripp2), CNp-MeAr(Mes2), CNp-MeAr(DArF2), and CNp-FAr(DArF2) are also reported (Ar(Tripp2) = 2,6-(2,4,6-(i-Pr)3C6H2)2C6H3); p-MeAr(Mes2) = 2,6-(2,4,6-Me3C6H2)2-4-Me-C6H2); p-MeAr(DArF2) = 2,6-(3,5-(CF3)2C6H3)2-4-Me-C6H2); p-FAr(DArF2) = 2,6-(3,5-(CF3)2C6H3)2-4-F-C6H2).

From an Electron‐Rich Bis(boraketenimine) to an Electron‐Poor Diborene

The reaction of the bisboracumulene (CAAC)2 B2 (CAAC=1-(2,6-diisopropylphenyl)-3,3,5,5-tetramethylpyrrolidin-2-ylidene) with excess tert-butylisocyanide resulted in complexation of the isocyanide at boron. Though this compound might be formally drawn with a lone pair on boron, these electrons are highly delocalized throughout a conjugated π-network consisting of the π-acidic CAAC and isocyanide ligands. Heating this compound to 110 °C liberated the organic periphery of both isocyanide ligands, yielding the first example of a dicyanodiborene. Cyclic voltammetry conducted on this diborene indicated the presence of reduction waves, making this compound unique among diborenes, which are otherwise highly reducing.

Carbon monoxide-isocyanide coupling promoted by acetylide addition to a diiron complex.

C-N bond formation involving carbon monoxide and isocyanide ligands is promoted by addition of a series of lithium acetylides to a diiron μ-aminocarbyne complex, i.e. [Fe2{μ-CN(Me)(Xyl)}(μ-CO)(CO)(CNXyl)(Cp)2][SO3CF3] (Xyl = 2,6-C6H3Me2). The reaction proceeds in three steps, i.e. (a) acetylide addition to the CO ligand, (b) acetylide migration to the isocyanide ligand, and (c) C-N coupling. The X-ray molecular structures of 1a and 1b comprise the first example of a κ(C,C')-N-carbonyl-aminocarbene ligand.

Light-driven hydrogen production from aqueous protons using molybdenum catalysts.

Homogeneous light-driven systems employing molecular molybdenum catalysts for hydrogen production are described. The specific Mo complexes studied are six-coordinate bis(benzenedithiolate) derivatives having two additional isocyanide or phosphine ligands to complete the coordination sphere. Each of the complexes possesses a trigonal prismatic coordination geometry. The complexes were investigated as proton reduction catalysts in the presence of [Ru(bpy)3](2+), ascorbic acid, and visible light. Over 500 TON are obtained over 24 h. Electrocatalysis occurs between the Mo(IV)/Mo(III) and Mo(III)/Mo(II) redox couples, around 1.0 V vs SCE. Mechanistic studies by (1)H NMR spectroscopy show that upon two-electron reduction the Mo(CNR)2(bdt)2 complex dissociates the isocyanide ligands, followed by addition of acid to result in the formation of molecular hydrogen and the Mo(bdt)2 complex.