Cyanide Ligands Research Articles

ChemInform Abstract: Transition-Metal-Promoted Cyclization Reactions of Nitrile Ligands in Complexes of Platinum(II): Synthesis of 2-Oxazoline Derivatives and X- Ray Structure of Cyclic cis-Cl2Pt(N=C(Ph)OCH2CH2)2.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

μ-1,2-Bis(diphenylphosphino)ethane-κ2P:P′]bis{[1,2-bis(diphenylphosphino)ethane-κ2P,P′]cyanidocopper(I)} methanol disolvate

The title centrosymmetric complex, [Cu2(CN)2(C26H24P2)3]·2CH3OH, consists of two five-membered [Cu(dppe)CN] rings [dppe is 1,2-bis­(diphenyl­phosphino)ethane] bridged by one μ2-dppe ligand, and two methanol solvent mol­ecules. The angles around the central metal atom indicate that each CuI atom is located in the center of a distorted tetra­hedron. The coordination sphere of each CuI atom is formed by three P atoms from two dppe ligands, and one C atom from the cyanide ligand. The crystal structure is stabilized by O—H⋯N hydrogen bonds, which are formed by the O—H donor group from methanol and the N-atom acceptor from a cyanide ligand.

Catena-poly[[[(2,2′-bipyridine-2κ2N,N′)-μ-cyanido-1:2κ2N:C-cyanido-2κC-tris(methanol-1κO)(nitrato-1κ2O,O′)iron(II)yttrium(III)]-di-μ-cyanido-1:2′κ2N:C;2:1′κ2C:N] methanol solvate hemihydrate

The title complex, {[FeIIYIII(CN)4(NO3)(C10H8N2)(CH3OH)3]·CH3OH·0.5H2O}n, is built up of ladder-like chains oriented along the c axis. Each ladder consists of two strands based on alternating FeII and YIII ions connected by cyanide bridges. Two such parallel chains are connected by additional cyanide anions (the ‘rungs’ of the ladder), which likewise connect FeII and YIII ions, such that each [Fe(bipy)(CN)4]2− (bipy is 2,2′-bipyridine) unit coordinates with three YIII ions and each YIII ion connects with three different [Fe(bipy)(CN)4]2− units. The FeII atom is six-coordinated in a distorted octa­hedral geometry and the YIII atom cation is eight-coordinated in a distorted dodeca­hedral environment. The uncoordinated methanol solvent mol­ecules are involved in hydrogen-bonding inter­actions with the one terminal cyanide group and a coordinated methanol mol­ecule from another [YIII(NO3)(CH3OH)3]2+ unit. Adjacent ladder-like chains are also held together by hydrogen bonds between the terminal cyanide ligands of the [Fe(CN)4(bipy)]2− units in one chain and the OH donors of CH3OH ligands from [YIII(NO3)(CH3OH)3] units in neighboring chains. The water molecule exhibits half-occupation.

Trans-K3[TcO2(CN)4

The structure of the title compound, tripotassium trans-tetra­cyanidodioxidotechnetate(V), is isotypic with its Re analogue. The [TcO2(CN)4]3− trans-tetra­cyanido­dioxido­technetate anion has a slightly distorted octa­hedral configuration. The Tc atom is located on a center of inversion and is bound to two O atoms in axial and to four cyanide ligands in equatorial positions. The Tc—O distance is consistent with a double-bond character. The two potassium cations, one located on a center of inversion and one in a general position, reside in octa­hedral or tetra­hedral environments, respectively. K⋯O and K⋯N inter­actions occur in the 2.7877 (19)–2.8598 (15) Å range.

Synthesis, Characterization, and Reactivity Studies of (Cyclohexenyl)nickel(II) Complexes

The synthesis and characterization of the complexes [(cyclohexenyl)Ni(NCMe)2][B(ArF)4] (1) and [(cyclohexenyl)Ni(mesitylene)][B(ArF)4] (2) are reported. Abstraction of the nitrile ligands in 1 with B(C6F5)3 yields a “ligand-free” [(cyclohexenyl)NiII]+ species which coordinates 1,3-dienes, including butadiene (BD), isoprene (IP), 1,3-cyclohexadiene (1,3-CHD), 1,4-cyclohexadiene (1,4-CHD), and 2,3-dimethyl-1,3-butadiene (DMBD) at low temperatures. Diene insertion is observed at temperatures above ca. −20 °C. An s-trans diene complex is formed upon coordination of DMBD. Hydrogen transfer is observed when complex 2 is exposed to 1-hexene or cyclopentadiene to generate new allyl nickel complexes and 1 equiv of cyclohexene. Polymerization of 1,3-CHD and DMBD with 2 is described, and a coupling product formed between DMBD and 2 is observed and characterized.

ChemInform Abstract: Synthesis of Nitrile Ligands Bearing Tricarbonyl (η6-Arene)chromium Complexes and Conjugated Spacers.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Unraveling the biosynthesis of nature's fastest hydrogenase.

Take two cyanides and report to work! Cyanide is an essential ingredient of the [FeFe]-hydrogenases. Recent studies have revealed how nature makes these cyanide ligands coordinated to the diiron core of the active site (see structure). Rapidly unfolding research on the maturation process is revealing new dimensions of biosynthesis. The transformations discovered may lead to the development of useful organometallic reactions.

Synthesis of the 2Fe subcluster of the [FeFe]-hydrogenase H cluster on the HydF scaffold

The organometallic H cluster at the active site of [FeFe]-hydrogenase consists of a 2Fe subcluster coordinated by cyanide, carbon monoxide, and a nonprotein dithiolate bridged to a [4Fe-4S] cluster via a cysteinate ligand. Biosynthesis of this cluster requires three accessory proteins, two of which (HydE and HydG) are radical S-adenosylmethionine enzymes. The third, HydF, is a GTPase. We present here spectroscopic and kinetic studies of HydF that afford fundamental new insights into the mechanism of H-cluster assembly. Electron paramagnetic spectroscopy reveals that HydF binds both [4Fe-4S] and [2Fe-2S] clusters; however, when HydF is expressed in the presence of HydE and HydG (HydF(EG)), only the [4Fe-4S] cluster is observed by EPR. Insight into the fate of the [2Fe-2S] cluster harbored by HydF is provided by FTIR, which shows the presence of carbon monoxide and cyanide ligands in HydF(EG). The thorough kinetic characterization of the GTPase activity of HydF shows that activity can be gated by monovalent cations and further suggests that GTPase activity is associated with synthesis of the 2Fe subcluster precursor on HydF, rather than with transfer of the assembled precursor to hydrogenase. Interestingly, we show that whereas the GTPase activity is independent of the presence of the FeS clusters on HydF, GTP perturbs the EPR spectra of the clusters, suggesting communication between the GTP- and cluster-binding sites. Together, the results indicate that the 2Fe subcluster of the H cluster is synthesized on HydF from a [2Fe-2S] cluster framework in a process requiring HydE, HydG, and GTP.

Photochemical and photophysical properties of ruthenium(II) bis-bipyridine bis-nitrile complexes: Photolability

The electrochemical and photophysical properties of two bis-nitrilo ruthenium(II) complexes formulated as [Ru(bpy) 2(L) 2](PF 6) 2, where bpy is 2,2′-bipyridine and L is AN = CH 3CN and sn = NC–CH 2CH 2–CN, have been investigated. Electrochemical data are typical of Ru-bpy complexes with two reversible reduction peaks located near −1.3 and −1.6 V assigned to each bipyridine ligand and one Ru II/Ru III oxidation wave centered at approximately +1.5 V. The sn derivative is both IR and Raman active with its coordinated CN stretch appearing at 2277 cm −1 and 2273 cm −1, respectively. The UV/Vis absorption spectrum of the sn derivative is dominated by an intense ( ε max ∼ 58700 M −1 cm −1) absorption band at 287 nm assigned as a LC (π → π∗) transition. The peak observed at 418 nm ( ε ∼ 10 400 M −1 cm −1) is an MLCT band while the one at 244 nm ( ε ∼ 23 600 M −1 cm −1) is of LMLCT character. The AN derivative behaves similarly. Both complexes show low-temperature emission at around 537 nm with a lifetime near 10.0 μs. 1H and 13C assignments are consistent with the formulation of the complexes. The complexes undergo photosubstitution of solvent with quantum efficiencies near one. Calculated and experimental results support replacement of the nitrile ligands by solvent. Based on DFT calculations, the electron density of the HOMO lies on the metal center, the bipyridine ligands and the nitrile ligands and electron density of the LUMO resides primarily on the bipyridine ligands. The electronic spectra obtained from TDDFT calculations closely match the experimental ones.

Stepwise [FeFe]-hydrogenase H-cluster assembly revealed in the structure of HydAΔEFG

Complex enzymes containing Fe–S clusters are ubiquitous in nature, where they are involved in a number of fundamental processes including carbon dioxide fixation, nitrogen fixation and hydrogen metabolism. Hydrogen metabolism is facilitated by the activity of three evolutionarily and structurally unrelated enzymes: the [NiFe]hydrogenases, [FeFe]-hydrogenases and [Fe]-hydrogenases (Hmd). The catalytic core of the [FeFe]-hydrogenase (HydA), termed the H-cluster, exists as a [4Fe–4S] subcluster linked by a cysteine thiolate to a modified 2Fe subcluster with unique non-protein ligands. The 2Fe subcluster and non-protein ligands are synthesized by the hydrogenase maturation enzymes HydE, HydF and HydG; however, the mechanism, synthesis and means of insertion of H-cluster components remain unclear. Here we show the structure of HydA (HydA expressed in a genetic background devoid of the active site H-cluster biosynthetic genes hydE, hydF and hydG) revealing the presence of a [4Fe–4S] cluster and an open pocket for the 2Fe subcluster. The structure indicates that H-cluster synthesis occurs in a stepwise manner, first with synthesis and insertion of the [4Fe–4S] subcluster by generalized host-cell machinery and then with synthesis and insertion of the 2Fe subcluster by specialized hydE-, hydFand hydG-encoded maturation machinery. Insertion of the 2Fe subcluster presumably occurs through a cationically charged channel that collapses following incorporation, as a result of conformational changes in two conserved loop regions. The structure, together with phylogenetic analysis, indicates that HydA emerged within bacteria most likely from a Nar1-like ancestor lacking the 2Fe subcluster, and that this was followed by acquisition in several unicellular eukaryotes. The biosynthesis and assembly of active-site metallo-cofactors requires multiple enzymes, scaffolds and carriers. For [FeFe]hydrogenases, the gene products HydE, HydF and HydG are required for the maturation of the active-site H-cluster (Fig. 1). These gene products function to couple radical S-adenosyl-L-methionine (SAM) chemistry and nucleotide binding and hydrolysis to ligand synthesis, cluster assembly and insertion, and, ultimately, [FeFe]-hydrogenase maturation. Although several plausible schemes have been proposed for the generation of the carbon monoxide, cyanide and dithiolate ligands at the Fe site, including radical SAM-mediated sulphur insertion coupled to the decomposition or condensation of amino acids, the precise mechanism by which the various enzymes, scaffolds and carriers coordinate H-cluster maturation is unknown. Owing to their high catalytic rates of hydrogen production, much interest surrounds [FeFe]-hydrogenases as alternative biological catalysts to those containing precious metals such as platinum in hydrogen-fuelcell technology. Advancements in understanding how the H-cluster is synthesized by HydE, HydF and HydG could contribute significantly to both the genetic engineering of hydrogen-producing microorganisms and the synthesis of biomimetic hydrogen-production catalysts. HydF has been shown to transfer a cluster precursor to HydA in the final stage of [FeFe]-hydrogenase maturation and may act as a scaffold on which an H-cluster precursor is assembled. Our most recent results indicate that the H-cluster maturation machinery (the activities of HydE, HydF and HydG) is directed at the synthesis of only the 2Fe unit of the 6Fe cluster, and that the [4Fe–4S] subcluster can be synthesized independently. To better understand the synthesis and insertion of the individual [4Fe–4S]-subcluster and 2Fesubcluster components of the H-cluster during [FeFe]-hydrogenase maturation, we determined the X-ray crystal structure of HydA. We determined the structure of HydA from Chlamydomonas reinhardtii, heterologously expressed in Escherichia coli, by molecular replacement, using the structure of the [FeFe]-hydrogenase from Clostridium pasteurianum (CpI) as a search model, and refined it to a resolution of 1.97 A (Fig. 2a). We focused the study on the [FeFe]-hydrogenase from C. reinhardtii because our complementary biochemical and spectroscopic analyses examining maturation were conducted using this enzyme. In addition, C. reinhardtii HydA is of biotechnological interest and no structural information about it yet exists. The overall structure of C. reinhardtii HydA (Fig. 2a) is similar to that observed for active-site domains of the previously characterized [FeFe]-hydrogenases from C. pasteurianum (Fig. 2c) and Desulfovibrio

π-Back-Donation Effect of the Cyanide Ligands on the Electron Correlation and Charge Transfer in Prussian Blue RbMn[Fe(CN)6

The temperature-induced charge transfer between the Mn and Fe sites in RbMn[Fe(CN)(6)] was analyzed by density functional theory calculations. Our analysis indicates that the extent of electron correlation (equivalently, the pairing energy or the on-site repulsion) is much greater for the Mn(n+) ion than for the Fe(n+) ion (n = 2, 3). This surprising and counterintuitive finding is a consequence of the pi-back-donation effect of the CN ligands.

Functionally Relevant Interplay between the Fe4S4 Cluster and CN− Ligands in the Active Site of [FeFe]-Hydrogenases

[FeFe]-hydrogenases are highly efficient H(2)-evolving metalloenzymes that include cyanides and carbonyls in the active site. The latter is an Fe(6)S(6) cluster (the so-called H-cluster) that can be subdivided into a binuclear portion carrying the CO and CN(-) groups and a tetranuclear subcluster. The fundamental role of cyanide ligands in increasing the basicity of the H-cluster has been highlighted previously. Here a more subtle but crucial role played by the two CN(-) ligands in the active site of [FeFe]-hydrogenases is disclosed. In fact, QM/MM calculations on all-atom models of the enzyme from Desulfovibrio desulfuricans show that the cyanide groups fine-tune the electronic and redox properties of the active site, affecting both the protonation regiochemistry and electron transfer between the two subclusters of the H-cluster. Despite the crucial role of cyanides in the protein active site, the currently available bioinspired electrocatalysts generally lack CN(-) groups in order to avoid competition between the latter and the catalytic metal centers for proton binding. In this respect, we show that a targeted inclusion of phosphine ligands in hexanuclear biomimetic clusters may restore the electronic and redox features of the wild-type H-cluster.

ReCl4(CN)2]2−: A High Magnetic Anisotropy Building Unit Giving Rise to the Single-Chain Magnets (DMF)4MReCl4(CN)2 (M = Mn, Fe, Co, Ni)

An S = 3/2, high-anisotropy building unit, trans-[ReCl(4)(CN)(2)](2-), representing the first paramagnetic complex with a mixture of just cyanide and halide ligands, has been synthesized through the reaction of (Bu(4)N)CN with ReCl(4)(THF)(2). This species is characterized in detail and employed in directing the formation of a series of one-dimensional coordination solids of formula (DMF)(4)MReCl(4)(CN)(2) (M = Mn (2), Fe (3), Co (4), Ni (5)). Variable-temperature dc magnetic susceptibility measurements demonstrate the presence of intrachain antiferromagnetic (2) and ferromagnetic (3-5) exchange coupling within these solids. In addition, probing the ac magnetic susceptibility as a function of both temperature and frequency reveals that all of the chain compounds exhibit slow relaxation of the magnetization. The relaxation time is shown to be thermally activated, with energy barriers to relaxation of Delta(tau) = 31, 56, 17, and 20 cm(-1) for 2-5, respectively. Notably, the field-dependent magnetization of the iron congener exhibits a significant hysteresis effect at low temperature, with a coercive field of H(C) = 1.0 T, thus demonstrating magnetlike behavior in this one-dimensional system. Finally, the magnetization dynamics of all solids occur within the finite-size regime, where the magnetic domain growth is limited due to physical defects along the chains within the crystals.

FeFe]‐Hydrogenase Cyanide Ligands Derived From S‐Adenosylmethionine‐Dependent Cleavage of Tyrosine

What's your poison? Hydrogenases catalyze the reversible formation of dihydrogen from two electrons and two protons. The maturation of the [FeFe]-hydrogenase active-site cofactor (H cluster) requires three gene products, HydE, HydF, and HydG. Cyanide has been characterized as one of the products of tyrosine cleavage by the S-adenosylmethionine-dependent enzyme HydG, clarifying its role in H-cluster biosynthesis. DOA=deoxyadenosine.

FeFe]‐Hydrogenase Cyanide Ligands Derived From S‐Adenosylmethionine‐Dependent Cleavage of Tyrosine

Ungewöhnliches Terrain für einen klassischen Liganden: Hydrogenasen katalysieren die reversible Bildung von Diwasserstoff aus zwei Elektronen und zwei Protonen. Die Reifung des Cofaktors im aktiven Zentrum der [FeFe]-Hydrogenase (bezeichnet als H-Cluster) erfordert drei Genprodukte, HydE, HydF und HydG. Cyanid wurde als eines der Produkte der Tyrosinspaltung durch das S-Adenosylmethionin-abhängige Enzym HydG identifiziert, was seine Rolle in der Biosynthese des H-Clusters erklärt. DOA=Desoxyadenosin. Detailed facts of importance to specialist readers are published as ”Supporting Information”. Such documents are peer-reviewed, but not copy-edited or typeset. They are made available as submitted by the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

Trigonal bipyramidal magnetic molecules based on [MoIII(CN)6]3−

The trigonal bipyramidal molecules [M(tmphen)(2)](3)[Mo(CN)(6)](2).(solvent) (M = Co, Ni; tmphen = 3,4,7,8-tetramethyl-1,10-phenanthroline) based on the [Mo(III)(CN)(6)](3-) unit were prepared by loss of a cyanide ligand from [Mo(III)(CN)(7)](4-) and found to exhibit ferromagnetic interactions between the M(II) and Mo(III) centers.

Design, synthesis, characterisation and chemical reactivity of mixed-ligand platinum(ii) oxadiazoline complexes with potential cytotoxic properties

A series of mixed ligand platinum(II) oxadiazoline complexes bearing 7-nitro-1,3,5-triazaadamantane (7-NO(2)TAA) as a labile and reactive nitrogen ligand has been synthesised from easily accessible starting materials. [2+3] cycloaddition of nitrones R(1)R(2)C-N(+)(Me)O(-) to only one of the nitrile ligands in trans-[PtX(2)(PhCN)(2)] (X = Cl, Br) results in the selective formation of mono-oxadiazoline complexes trans-[PtX(2)(PhCN){N=C(Ph)-O-N(Me)-CR(1)R(2)}] from which the remaining nitrile can be replaced by 7-NO(2)TAA. The resulting complexes trans-[PtX(2)(7-NO(2)TAA) {N=C(Ph)-O-N(Me)-CR(1)R(2)}] and their precursors were characterised by elemental analysis, IR and multinuclear NMR spectroscopy.The suitability of the target complexes as anticancer agents was extrapolated from their general chemical reactivity. They are stable in DMSO, but react with thiols and undergo aquation of a chloro ligand. In the absence of a competing ligand, the coordinated 7-NO(2)TAA ligand slowly hydrolyses in an aqueous medium under release of formaldehyde, and this could induce bioactivity independent of the one typically found with platinum compounds. With nitrogen heterocycles such as pyridine a slow exchange of the 7-NO(2)TAA ligand occurs. A combined DFT/AIM study confirms the reaction observed in the experiment and predicts that other nitrogen heterocycles such as DNA nucleobases should react in the same way. Moreover, the 7-NO(2)TAA should be even more labile in an aqueous medium where protonation of the remaining amines can occur. A PM6 molecular modelling study suggests that the PtCl(oxadiazoline) fragment formed after release of one chloro and the labile 7-NO(2)TAA ligand fits well into the DNA groove and is able to form d(GpG) intrastrand crosslinks similar to the ones observed with cisplatin.

Cyanide Lability and Linkage Isomerism of Hexacyanochromate(III) Induced by the Co(II) Ion

Reactions between the [M(III)(CN)(6)](3-) (M = Fe and Co) anions and the mononuclear complex [Co(II)(dppe)(2)(H(2)O)][BF(4)](2) result in the formation of two isostructural trinuclear clusters {[Co(II)(dppe)(2)](2)[M(III)(CN)(6)]}(BF(4)). Surprisingly, reactions of [Co(dppe)(2)(H(2)O)](BF(4))(2) and [Co(triphos)(CH(3)CN)(2)](BF(4))(2) with [Cr(CN)(6)](3-) yield the mononuclear complexes [Co(dppe)(2)(CN)](BF(4)) and [Co(triphos)(CN)(2)], respectively. In the former case, an unusual pentanuclear intermediate complex {[Co(II)(3)(dppe)(4)(MeCN)][Cr(III)(CN)(6)](2)} was isolated. The reaction was probed by solution IR spectroscopy, which revealed a gradual conversion of the nu(C[triple bond]N) stretches of the starting materials to those of the CN-bridged intermediate and eventually to the single nu(C[triple bond]N) stretch of the final mononuclear product. The loss of carbon-bound CN(-) ligands from [Cr(CN)(6)](3-) occurs on a sufficiently slow time-scale for observation of varying degrees of cyanide linkage isomerism in the trigonal bipyramidal complex {[Co(tmphen)(2)](3)[Cr(CN)(6)](2)}; the study was aided by the use of different Co(II) starting materials. Results obtained by a combination of X-ray crystallography, infrared spectroscopy, and magnetometry provide unequivocal evidence that the presence of certain Lewis acids (e.g., Co(II) in this work and Fe(II) ions and BPh(3) in previously reported studies) promote the process of cyanide linkage isomerism, which, in the case of Co(II) species, leads to facile labilization of cyanide ligands from the [Cr(CN)(6)](3-) anion.

Bis[tris(ethane-1,2-diamine)nickel(II)] octacyanidomolybdate(IV) pentahydrate

In the title compound, [Ni(C2H8N2)3]2[Mo(CN)8]·5H2O, the NiII ion is coordinated by six N atoms from three ethane-1,2-diamine ligands in a distorted octa­hedral geometry, while the MoIV atom is coordianted by eight cyanide ligands. The Ni—N bond distances range from 2.1061 (18) to 2.1425 (18) Å. The Mo—C and C—N distances in the [Mo(CN)8] unit range from 2.154 (2) to 2.174 (2) Å and 1.149 (3) to 1.156 (3) Å, respectively. The complex ions and water mol­ecules are linked by weak N—H⋯N/O and O—H⋯N/O hydrogen bonds into a three-demensional structure.

A kinetic and thermodynamic understanding of O 2 tolerance in [NiFe]-hydrogenases

In biology, rapid oxidation and evolution of H(2) is catalyzed by metalloenzymes known as hydrogenases. These enzymes have unusual active sites, consisting of iron complexed by carbonyl, cyanide, and thiolate ligands, often together with nickel, and are typically inhibited or irreversibly damaged by O(2). The Knallgas bacterium Ralstonia eutropha H16 (Re) uses H(2) as an energy source with O(2) as a terminal electron acceptor, and its membrane-bound uptake [NiFe]-hydrogenase (MBH) is an important example of an "O(2)-tolerant" hydrogenase. The mechanism of O(2) tolerance of Re MBH has been probed by measuring H(2) oxidation activity in the presence of O(2) over a range of potential, pH and temperature, and comparing with the same dependencies for individual processes involved in the attack by O(2) and subsequent reactivation of the active site. Most significantly, O(2) tolerance increases with increasing temperature and decreasing potentials. These trends correlate with the trends observed for reactivation kinetics but not for H(2) affinity or the kinetics of O(2) attack. Clearly, the rate of recovery is a crucial factor. We present a kinetic and thermodynamic model to account for O(2) tolerance in Re MBH that may be more widely applied to other [NiFe]-hydrogenases.