Cyanide Ligands Research Articles

Mer-[FeIII(bpca)(CN)3]-: A New Low-Spin Iron(III) Complex to Build Heterometallic Ladder-like Chains

The novel mononuclear complex PPh(4)-mer-[Fe(III)(bpca)(3)(CN)(3)].H(2)O (1) [PPh(4)(+) = tetraphenylphosphonium cation and bpca = bis(2-pyridylcarbonyl)amidate anion] and ladder-like chain compound [[Fe(III)(bpca)(micro-CN)(3)Mn(II)(H(2)O)(3)] [Fe(III)(bpca)(CN)(3)]].3H(2)O (2) have been prepared and characterized by X-ray diffraction analysis. Compound 1 is a low-spin iron(III) compound with three cyanide ligands in mer arrangement and a tridentate N-donor ligand building a distorted octahedral environment around the iron atom. Compound 2 is an ionic salt made up of cationic ladder-like chains [[Fe(III)(bpca)(micro-CN)(3)Mn(II)(H(2)O)(3)]](+) and uncoordinated anions [Fe(III)(bpca)(3)(CN)(3)](-). The magnetic properties of 2 correspond to those of a ferrimagnetic chain with significant intrachain antiferromagnetic coupling between the low-spin iron(III) centers and the high-spin manganese(II) cations. This compound exhibits ferrimagnetic ordering below 2.0 K.

Kinetics, thermodynamics, and effect of BPh3 on competitive C-C and C-H bond activation reactions in the interconversion of allyl cyanide by [Ni(dippe)

Reaction of [(dippe)Ni(micro-H)](2) with allyl cyanide at low temperature quantitatively generates the eta(2)-olefin complex (dippe)Ni(CH(2)=CHCH(2)CN) (1). At ambient temperature or above, the olefin complex is converted to a mixture of C-CN cleavage product (dippe)Ni(eta(3)-allyl)(CN) (3) and the olefin-isomerization products (dippe)Ni(eta(2)-crotonitrile) (cis- and trans-2), which form via C-H activation. The latter are the exclusive products at longer reaction times, indicating that C-CN cleavage is reversible and the crotononitrile complexes 2 are more thermodynamically stable than eta(3)-allyl species 3. The kinetics of this reaction have been followed as a function of temperature, and rate constants have been extracted by modeling of the reaction. The rate constants for C-CN bond formation (the reverse of C-CN cleavage) show a stronger temperature dependence than those for C-CN and C-H activation, making the observed distribution of C-H versus C-CN cleavage products strongly temperature-dependent. The activation parameters for the C-CN formation step are also quite distinct from those of the C-CN and C-H cleavage steps (larger DeltaH(++) and positive DeltaS(++)). Addition of the Lewis acid BPh(3) to 1 at low temperature yields exclusively the C-CN activation product (dippe)Ni(eta(3)-allyl)(CNBPh(3)) (4). Independently prepared (dippe)Ni(crotononitrile-BPh(3)) (cis- and trans-7) does not interconvert with 4, indicating that 4 is the kinetic product of the BPh(3)-mediated reaction. On standing in solution at ambient temperature, 4 decomposes slowly to complex 5, with structure [(dippe)Ni(eta(3)-allyl)(N triple bond C-BPh(3)), while addition of a second equivalent of BPh(3) immediately produces [(dippe)Ni(eta(3)-allyl)](+)[Ph(3)BC triple bond NBPh(3)](-) (6). Comparison of the barriers to pi-sigma allyl interconversion (determined via dynamic (1)H NMR spectroscopy) for all of the eta(3)-allyl complexes reveals that axial cyanide ligands facilitate pi-sigma interconversion by moving into the P(2)Ni square plane when the allyl group is sigma-bound.

Inter-string arrays of bimetallic assemblies with alternative Cu2+-Cl-Cu2+ and Cu-NC-M (M = Co3+, Fe+3, Cr+3) bridges: syntheses, crystal structure, and magnetic properties.

Three bimetallic assemblies with alternate homometallic bridges through chloride ligands and heterometallic bridges through cyanide ligands of formula [(323)(2)Cu(2)(Cl)M(CN)(6)](n).2n(H(2)O), where 323 = N,N'-bis(3-aminopropyl)ethylenediamine and M = Co(3+) for 1, Fe(3+) for 2, and Cr(3+) for 3, were synthesized. They have been characterized structurally, analytically, spectroscopically, and magnetically. All three assemblies crystallize in the monoclinic system in the same space group P2(1)/n, with a = 11.642(2) A, b = 10.285(3) A, c = 13.622(2) A, beta = 95.69(3) degrees, V = 1623.1(6) A(3), and Z = 4 for 1; a = 11.681(4) A, b = 10.315(3) A, c = 13.567(5) A, beta = 95.62(3) degrees, V = 1626.8(9) A(3), Z = 4 for 2, and a = 11.782(4) A, b = 10.386(2) A, c = 13.755(4) A, beta = 95.51(3) degrees, V = 1657.4(8) A(3), Z = 4 for 3. Crystal structure analyses reveal that one-dimensional zigzag chains propagate in two different crystallographic directions (a and b) which are held together during the course of their propagation. All three assemblies have a homometallic Cu-Cl-Cu core in common. Assembly 1 exhibits metamagnetic behavior and shows weak antiferromagnetic interactions between Cu(2+) paramagnetic centers, through the chloride bridges. The Neel temperature, T(N), is 3.5 K, and the critical field is 4 T. In the presence of a magnetic field larger than 4 T, the local spin doublets of Cu(2+) in the assembly 1 remain in parallel arrangements. Assemblies 2 and 3 may be described as an alternative repetition of the antiferromagnetically coupled Cu-Cl-Cu fragment and ferromagnetically coupled Cu-CN-Fe(3+)/Cr(3+)fragment. The overall magnetic character of the strings in assemblies 2 and 3 are antiferromagnetic. Ferromagnetic interaction evidenced by the (Cu-CN-Fe(3+)/Cr(3+)) fragment was masked by the antiferromagnetic interaction between the Cu(2+) centers through the chloride bridge. The magnetic properties agree well with those expected for two [323 Cu(2+)] and a [Fe(CN)](3+) unit with spin-orbit coupling effect of the low-spin iron(III) ions for 2 and for two [323 Cu(2+)] and a [Cr(CN)](3+) unit for 3. In aqueous solution, trinuclear [(323)(2)Cu(2)M(CN)(6)](+) and dinuclear [(323)CuM(CN)(6)](-) species were observed.

Discrete Triangle, Square and Hexametallic Alkynyl Cyano‐Bridged Compounds Based on [cis‐Pt(CCR)2(CN)2]2− Building Blocks

Novel mixed bis(alkynyl)bis(cyano)platinate(II) species [cis-Pt(Ctbond;CR)(2)(CN)(2)](2-) (1 a: R = tBu, 1 b: R = Ph) have been prepared and their potential as building blocks in the generation of self-organized systems with a variable molecular architecture has been studied. The reaction of 1 with the ditopic acceptor species [[cis-Pt(C(6)F(5))(2)S](2)(dppa)] (dppa=diphenylphosphinoacetylene) gave the dianionic cyanide/dppa bridged molecular platinotriangles (NBu(4))(2)[(C(6)F(5))(2)Pt(micro-dppa)[(micro-CN)(2)Pt(Ctbond;CR)(2)]Pt(C(6)F(5))(2)] (2). X-ray analysis of 2 a confirmed that the "Pt(2)(C(6)F(5))(4)(micro-dppa)" binuclear moiety is connected to the dianionic "Pt(Ctbond;CR)(2)(CN)(2)" unit by two bridging cyanide ligands. Moreover, treatment of 1 with the solvent cationic species [M(cod)(acetone)(2)](+) afforded heterometallic molecular squares Pt(2)M(2) (M=Rh, Ir) containing cyanide bridges and terminal alkynyl ligands, (NBu(4))(2)[cyclo[[cis-Pt(Ctbond;CR)(2)(micro-CN)(2)][M(cod)]](2)] (3: M=Rh, 4: M = Ir). The solid-state structures of phenyl derivatives have been determined by X-ray crystallography. The terminal alkynyl ligands in these cyanide-bridged molecular squares 3 and 4 have been used in the assembly of higher multimetallic complexes. Thus, very unusual bis(double-alkynide)-cyanide-bridged hexametallic compounds (NBu(4))(2)[[(C(6)F(5))(2)Pt(micro-Ctbond;CPh)(2)(micro-CN)(2)](2)[M(cod)](2)] (5 b: M=Rh, 6 b: M = Ir) were easily formed by simple reactions of 3 b and 4 b with two equivalents of [cis-Pt(C(6)F(5))(2)(thf)(2)]. An X-ray diffraction study on complex 5 b indicated that the derivative was formed by a simultaneous migration of one sigma-alkynyl group from each "Pt(Ctbond;CPh)(2)(micro-CN)(2)" corner of the square to both "Pt(C(6)F(5))(2)" units, resulting in bent sigma,pi-double-alkynyl bridging systems. Finally, the novel supramolecular anionic assemblies (NBu(4))(4)[cyclo[[cis-Pt(Ctbond;CR)(2)(micro-CN)(2)][SnPh(3)]](4)] 7 have been obtained by self-assembly of 1 and [SnPh(3)(acetone)(2)](+).

Octahedral Niobium Chloride Clusters as Building Blocks of Templated Prussian Blue Framework Analogues.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Is the charge on the nitrile carbon atom a driving force of the nucleophilic addition to coordinated nitriles?

The availability of the electrostatic model for the interpretation of nucleophilic addition to nitriles—free and coordinated to platinum—has been discussed. The analysis of effective atomic charges calculated at the HF/6-31G*, B3LYP/6-31G* and MP2/6-31G* levels of theory using both Mulliken and Natural Bond Orbital (NBO) schemes was performed for the neutral and cationic dinitrile complexes of Pt II and Pt IV trans-[Pt IIL 2(NCCH 3) 2] 2+ and trans-[Pt IVCl 2L 2(NCCH 3) 2] 2+ (L=Cl −, NH 3, PH 3, NCCH 3). The oxidation state of the metal, overall charge of the complex moiety and nature of the ligand L only weakly affect the atomic charge on the C atom of the CN group of the bound nitrile (especially the Mulliken one). Meanwhile, the significant enhancement of the latter charge from the free to the coordinated ligand was found for the NBO method. The activation of the nitriles in the complexes compared to the free ligand towards the nucleophilic addition to the CN bond can be interpreted in terms of charge control, but the enhancement of the reactivity from the complexes of Pt II to those of Pt IV should be explained by other arguments (orbital control and the effect of the transition state). The nature of the chemical bonds was investigated using the AIM and NBO methods and the charge decomposition analysis (CDA). The nitrile ligands do not exhibit noticeable π-acceptor properties in the complexes, and the electrostatic interaction plays an important role in the formation of the coordination bond.

Synthesis and crystal structure of bis(dicyclohexylammonium) Tetracyanonickel(II)

A novel, one-dimensional nickel(II) complex, [(C6H11)2NH2]2[Ni(CN)4], has been synthesized and structurally characterized by X-ray single crystallographic methods. The complex crystallizes in the triclinic, space group P1 with a = 9.237(1), b = 9.576(2), c = 9.689(3) Å, α = 61.51(2), β = 85.69(3), γ = 74.27(2)°, V = 723.6(3) Å3, Z = 1. The square-planar Ni(II) centre of the cyanonickellate anion is four coordinated by cyanide ligands. The dicyclohexylammonium cation occupies a bridging position by hydrogen bonding to the cyanide ligand nitrogen atoms of adjacent anions.

Mixed metal cyanide complexes derived from the CpCo(CN) 3− anion

Reaction of the salt KCpCo(CN) 3 ( 1) with zinc iodide leads to the formation of a highly insoluble Co(III)/Zn(II) polymeric chain. However, pyridine was found to disrupt the aggregate that is formed to yield a crystalline trimetallic complex consisting of two CpCo(CN) 3 anions bridging a Zn(py) 4 dication through the cyanide ligands, [CpCo(CN) 2(μ-CN)] 2Zn(py) 4 ( 2). Along these same lines, reaction of CpCo(CN) 2PPh 3 ( 3) with AlCl 3 or CoCl 2 leads to the formation of a highly crystalline Co(II)/Co(III) diamond, [CpCo(PPh 3)(μ-CN) 2CoCl 2] 2 ( 4). Molecular structures of 1, 2, 3 and 4 were determined by single-crystal X-ray crystallography.

The metalla-Pinner reaction between Pt(iv)-bound nitriles and alkylated oxamic and oximic forms of hydroxamic acids

The nitrile ligands in the platinum(IV) complexes trans-[PtCl4(RCN)2] (R=Me, Et, CH2Ph) and cis/trans-[PtCl4(MeCN)(Me2SO)] are involved in a metalla-Pinner reaction with N-methylbenzohydroxamic acid (N-alkylated form of hydroxamic acid, hydroxamic form; F1), PhC(=O)N(Me)OH, to achieve the imino species [PtCl4[NH=C(R)ON(Me)C(=O)Ph]2 (1-3) and [PtCl4[NH=C(Me)ON(Me)C(=O)Ph](Me2SO)] (7), respectively. Treatment of trans-[PtCl4(RCN)2] (R=Me, Et) and cis/trans-[PtCl4(MeCN)(Me2SO)] with the O-alkylated form of a hydroxamic acid (hydroximic form), i.e. methyl 2,4,6-trimethylbenzohydroximate, 2,4,6-(Me3C6H2)C(OMe)=NOH (F2A), allows the isolation of [PtCl4[NH=C(R)ON=C(OMe)(2,4,6-Me3C6H2)]2] (5, 6) and [PtCl4[NH=C(Me)ON=C(OMe)(2,4,6-Me3C6H2)](Me2SO)] (8), correspondingly. In accord with the latter reaction, the coupling of nitriles in trans-[PtCl4(EtCN)2] with methyl benzohydroximate, PhC(OMe)=NOH (F2B), gives [PtCl4[NH=C(Et)ON=C(OMe)Ph]2] (4). The addition proceeds faster with the hydroximic F2, rather than with the hydroxamic form F1. The complexes 1-8 were characterized by C, H, N elemental analyses, FAB+ mass-spectrometry, IR, 1H and 13C[1H] NMR spectroscopies. The X-ray structure determinations have been performed for both hydroxamic and hydroximic complexes, i.e. 2 and 6, indicating that the imino ligands are mutually trans and they are in the E-configuration.

Preparative and structural studies on iron(II)-thiolate cyanocarbonyls: relevance to the [NiFe]/[Fe]-hydrogenases.

A number of thermally stable iron(II)-thiolate cyanocarbonyl complexes, cis,cis-[Fe(CN)2(CO)2(CS3-S,S)]2-(1), mer-[Fe(CO)2(CN)3(NCCH3)]-(2)mer-[Fe(CO)3(CN)(CS3-S,S)]-(3), cis-[Fe(CO)2(CN)(S(CH2)2S(CH2)2S-S,S,S)]-(4), [Fe(CO)2(CN)3Br]2-(5), mer-[Fe(CO)2(CN)3(m-SC6H4Br)]2-(6) and mer-[Fe(CO)2(CN)3(SPh)]2-(7) were isolated and characterized by IR and X-ray diffraction analysis. The extrusion of one strong sigma-donor CN- ligand instead of CO from the iron(II) center of the thermally stable complexes [FeII(CO)2(CN)3Br]2-(5) containing less electron-donating bromide reflects the electron-rich character of the mononuclear [FeII(CN)2(CO)2(CS3-S,S)]2-(1) when ligated by by the bidentate thiolate, and the combination of one cyanide, two carbonyls and a tridentate thiolate provides the stable complex 4 as a result of the reaction of complex 5 and chelating ligand [S(CH2)2S(CH2)2S]2-. The preference of the sixth ligand coordinated to the unsaturated [FeII(CO)(CN)2(CS3-S,S)]2- Fe(II) center, the iron-site architecture of the bimetallic Ni-Fe active-site of [NiFe] hydrogenases, is a strong pi-acceptor CO group. Scrutiny of the coordination chemistry of iron(II)-thiolate cyanocarbonyl species [FeII(CO)x(CN)y(SR)z]n- reveals that certain combinations of thiolate, cyanide and carbonyl ligands (3 < or = y+z > or = 4) bound to Fe(II) are stable and this could point the way to understand the reasons for Nature's choice of combinations of these ligands in hydrogenases.

On the Reaction Mechanism of “Higher-Order Cuprate”, Alias “Lipshutz Cuprate”

Abstract An organocuprate reagent of the R2Cu(CN)Li composition introduced by Lipshutz has been frequently used in organic synthesis because its reactivity in some reactions is higher than that of the standard Gilman reagent R2CuLi. The higher reactivity of the Lipshutz cuprate was once ascribed to a dianionic tri-coordinated copper(I) (“higher-order”) structure, but numerous structural studies over the last ten years have shown that the Lipshutz cuprate exists as a “cyano-Gilman” (R2CuLi·LiCN) cuprate. This conclusion notwithstanding, our recent theoretical study indicated that a minor and undetectable species such as R(CN)CuLi·LiR may play some roles in the substitution and the addition reactions of the Lipshutz cuprate. The high reactivity of the minor species originates from the anisotropic and multi-coordination capability of the cyanide ligand to metals. Our result accounts for the higher or anomalous reactivity of the Lipsthuz cuprate in some reactions, and further demonstrates the importance of computational study on poly-metallic reaction pathways, where experimental mechanistic information may be difficult to obtain.

Oxidation-reduction properties of maize ferredoxin:sulfite oxidoreductase

Oxidation-reduction titrations have been carried out on the wild-type, ferredoxin-dependent sulfite reductase from maize and two site-specific variants of the enzyme. E m values have been determined for the siroheme and [4Fe–4S] cluster prosthetic groups of the enzyme, which titrate as independent, one-electron carriers. Visible-region difference spectra suggest that reduction of the [4Fe–4S] cluster significantly perturbs the spectrum of the reduced siroheme group of the enzyme. The effects of siroheme axial ligation, by either cyanide or phosphate ligands, on the redox properties of sulfite reductase have also been examined. For comparison, the effects of phosphate and cyanide on the redox properties of the ferredoxin-dependent nitrite reductase of spinach chloroplasts, an enzyme with the same prosthetic group arrangement as sulfite reductase, have been examined.

Reactions of diiron mu-aminocarbyne complexes containing nitrile ligands

The acetonitrile ligand in the mu-aminocarbyne complexes [Fe2{mu-CN(Me)R}(mu-CO)(CO)(NCMe)(Cp)2][SO 3CF3] (R = Me, 2a, CH2Ph, 2b, Xyl, 2c) (Xyl = 2,6-Me2C6H3) is readily displaced by halides and cyanide anions affording the corresponding neutral species [Fe2{mu-CN(Me)R}(mu-CO)(CO)(X)(Cp)2 ] (X = Br, I, CN). Complexes 2 undergo deprotonation and rearrangement of the coordinated MeCN upon treatment with organolithium reagents. Trimethylacetonitrile, that does not contain acidic alpha hydrogens has been used in place of MeCN to form the complexes [Fe2{mu-CN(Me)R}(mu-CO)(CO)(NCCMe3 )(Cp)2][SO3CF3] (7a-c). Attempts to replace the nitrile ligand in 3 with carbon nucleophiles (by reaction with RLi) failed, resulting in decomposition products. However the reaction of 7c with LiCºCTol (Tol = C6H4Me), followed by treatment with HSO3CF3, yielded the imino complex [Fe2{mu-CN(Me)Xyl}(mu-CO)(CO) {N(H)C(CºCC6H4Me-4)CMe3}(Cp) 2][SO3CF3 ] (8), obtained via acetilyde addition at the coordinated NCCMe3.

Octahedral niobium chloride clusters as building blocks of templated prussian blue framework analogues.

The preparation, structure, and magnetic properties of the first three-dimensional framework containing octahedral niobium cyanochloride clusters as building units are reported. Reactions of aqueous solutions of (Me(4)N)(2)K(2)[Nb(6)Cl(12)(CN)(6)] (2) with aqueous solutions of MnCl(2) result in the precipitation of the compound (Me(4)N)(2)[MnNb(6)Cl(12)(CN)(6)] (3). The structure of 3 was determined from single-crystal X-ray diffraction study (crystal data: cubic, Fm3macrom(No. 225), a = 15.513(4) A, V = 3733.2(12) A(3), Z = 4). Its 3D framework is based on edge-bridged [Nb(6)Cl(12)](2+) clusters and Mn(2+) ions bridged by cyanide ligands to form a cfc lattice [MnNb(6)Cl(12)(CN)(6)](2)(-) in which all tetrahedral sites are occupied by the cations (Me(4)N)(+) which act as charge compensating template. The structure of 3 can be considered as an expansion of the Prussian blue framework in which [Fe(CN)(6)](4)(-) is replaced by the cluster [Nb(6)Cl(12)(CN)(6)](4)(-). Magnetic susceptibility measurements indicate that Mn(2+) is present in a high spin d(5) configuration. No magnetic ordering is observed.

Cluster-to-metal magnetic coupling: synthesis and characterization of 25-electron [Re6-nOsnSe8(CN)6](5-n)-(n = 1, 2) clusters and (Re6-nOsnSe8[CNCu(Me6tren)]6)9+(n = 0, 1, 2) assemblies.

The first face-capped octahedral clusters with 25 metal-based valence electrons are shown to provide versatile building units capable of engaging in magnetic exchange coupling. Reactions of [Re(5)OsSe(8)Cl(6)](3-) and [Re(4)Os(2)Se(8)Cl(6)](2-) with NaCN in a melt of NaNO(3) or KCF(3)SO(3) afford the 24-electron clusters [Re(5)OsSe(8)(CN)(6)](3-) and [Re(4)Os(2)Se(8)(CN)(6)](2-). The 13C NMR spectrum of a 13C-labeled version of the latter species indicates a 1:2 mixture of cis and trans isomers. Cyclic voltammograms of the clusters in acetonitrile display reversible [Re(5)OsSe(8)(CN)(6)](3-/4-), cis-[Re(4)Os(2)Se(8)(CN)(6)](2-/3-), and trans-[Re(4)Os(2)Se(8)(CN)(6)](2-/3-) couples at E(1/2) = -1.843, -0.760, and -1.031 V vs FeCp(2)(0/+), respectively, in addition to other redox processes. Accordingly, reduction of [Re(5)OsSe(8)(CN)(6)](3-) with sodium amalgam and [Re(4)Os(2)Se(8)(CN)(6)](2-) with cobaltocene produces the 25-electron clusters [Re(5)OsSe(8)(CN)(6)](4-) and [Re(4)Os(2)Se(8)(CN)(6)](3-). EPR spectra of these S = 1/2 species in frozen DMF solutions exhibit isotropic signals with g = 1.46 for the monoosmium cluster and g = 1.74 and 1.09 for the respective cis and trans isomers of the diosmium cluster. In each case, results from DFT calculations show the unpaired spin to delocalize to some extent into the pi* orbitals of the cyanide ligands, suggesting the possibility of magnetic superexchange. Reaction of [Re(5)OsSe(8)(CN)(6)](3-) with [Ni(H(2)O)(6)](2+) in aqueous solution generates the porous Prussian blue analogue Ni(3)[Re(5)OsSe(8)(CN)(6)](2).32H(2)O; however, the tendency of the 25-electron clusters to oxidize in water prohibits their use in reactions of this type. Instead, a series of cyano-bridged assemblies, [Re(6-n)Os(n)Se(8)[CNCu(Me(6)tren)](6)](9+) (n = 0, 1, 2; Me(6)tren = tris(2-(dimethylamino)ethyl)amine), were synthesized to permit comparison of the exchange coupling abilities of clusters with 23-25 electrons. As expected, the results of magnetic susceptibility measurements show no evidence for exchange coupling in the assemblies containing the 23- and 24-electron clusters, but reveal the presence of weak ferromagnetic coupling in [Re(4)Os(2)Se(8)[CNCu(Me(6)tren)](6)](9+). Assuming all cluster-Cu(II) exchange interactions to be equivalent, the data were fit to give an estimated coupling strength of J = 0.4 cm(-1). To our knowledge, the ability of such clusters to participate in magnetic exchange coupling has never previously been demonstrated.

Ligand discrimination in the reaction of nitrones with [PtCl2(PhCN)2]. Selective formation of mono-oxadiazoline and mixed bis-oxadiazoline complexes under thermal and microwave conditions.

[2+3] Cycloaddition of nitrones to the nitrile ligands in the complexes cis- or trans-[PtCl2(PhCN)2] occurs under ligand differentiation and allows for selective synthesis of complexes of the type cis- or trans-[PtCl2(oxadiazoline)(PhCN)]. Microwave irradiation enhances the reaction rates of the cycloaddition considerably and further favours the selectivity towards the mono-cycloadduct with respect to thermal conditions, because the first cycloaddition is accelerated to a higher extent than the second one. Reaction of the trans-substituted mono-oxadiazoline complexes with a nitrone different from the one used for the first cycloaddition step gives access to mixed bis-oxadiazoline compounds of the composition trans-[PtCl2(oxadiazoline-a)(oxadiazoline-b)]. The corresponding cis-configured complexes, however, do not undergo further cycloaddition. All reactions described occur without isomerisation of the stereochemistry around the platinum center, independently of whether thermal or microwave heating is applied.

Crown compounds for anions. Sandwich complexes of cyclic trimeric perfluoro- o-phenylenemercury with hexacyanoferrate(III) and nitroprusside anions

Cyclic trimeric perfluoro- o-phenylenemercury ( o-C 6F 4Hg) 3 ( 1) is able to bind hexacyanoferrate(III) and nitroprusside anions to form complexes {[( o-C 6F 4Hg) 3] 2[Fe(CN) 6]} 3− and {[( o-C 6F 4Hg) 3] 2[Fe(CN) 5NO]} 2−, respectively, which contain one anionic species per two macrocycles. According to X-ray diffraction data, the complexes have unusual sandwich structures wherein the anionic guest is located between the planes of two molecules of 1 and is coordinated to each of these through two types of Fe–C–N–Hg bridges. One type is the simultaneous coordination of a cyanide ligand to all three Hg centres of the cycle. The other type is the coordination of a cyanide group to a single Hg atom of the macrocycle. In both types, the bonding of the anionic guest with the macrocyclic host is accomplished with the participation of π-electrons of the cyanide ligands. The synthesized compounds are the first examples of host–guest complexes of a macrocyclic multidentate Lewis acid with anionic metal complexes.

Structure and Properties of the [Ru(bpy)(CN)4]2- Complex and Its Solvent Environment: X-ray Diffraction and Density Functional Study

The structure of [Ru(bpy)(CN)4]2- and its solvent shell in aqueous solution has been investigated by the X-ray diffraction technique. The characteristic bond lengths of the complex obtained by this method are in good agreement with those determined by a single-crystal X-ray study. The number of solvent molecules of the hydration shell has been determined. Three water molecules are arranged near to each cyanide ligand. The average distance between the nitrogen atoms of the cyanides and the oxygen atoms of these solvent molecules is found to be 3.2 Å. To examine this specific solvent−solute interaction, DFT calculations were performed on the gas phase complex and on its partially hydrated cluster models [Ru(bpy)(CN)4]2-·(H2O)n (n = 4, 8). These calculations confirmed the relatively strong CN···H−OH hydrogen bonds. It has also been demonstrated that the hydrogen bond is notably weaker in the triplet excited state than in the ground state of the complex. The lengthening of the N···H bonds due to the formation of the triplet excited complex is about 0.05 Å, and an appreciable influence on the second hydration shell is also demonstrated by the increase of the related O···H bond, which is at least 0.02 Å longer in the excited state.

Synthesis and Structural Characterization of Potassium Salts of Phosphane‐Substituted (Cyclopentadienyl)iron Dicyanides, and Their Use as Bridging Ligands for Copper(I) Phosphane Derivatives

AbstractPhosphane‐substituted CpFe(CN)2 anions have been synthesized by photochemical decarbonylation of KCpFe(CN)2CO in the presence of various mono‐ and diphosphanes. The synthesis and characterization of uniquely bridged diphosphane derivatives, [KCpFe(CN)2]2‐μ‐(Ph2P)2−(CH2)n (n = 2−4), are particularly noteworthy. These phosphane‐substituted CpFe(CN)2− units have afforded stable mixed‐metal complexes upon reaction with CuI in the presence of tricyclohexylphosphane in acetonitrile solution. X‐ray crystallography shows these derivatives to display two‐dimensional diamond‐shaped structures with copper(I) of the form [Fe(CN)2Cu]2, where the CuI centers exhibit both trigonal and tetrahedral geometries. Infrared data reveal that the withdrawal of electron density from the iron centers in these mixed metal cyanides via the cyanide ligands is enhanced upon replacing CO in CpFe(CN)2CO− with phosphanes. (© Wiley‐VCH Verlag GmbH &amp; Co. KGaA, 69451 Weinheim, Germany, 2003)

Reactivity of [MCl(η3-allyl)(1,10-phenanthroline)(CO)2] (M = Mo, W) Complexes toward Enolate Anions

The reactions of the complexes [MCl(η3-C3H4-R)(CO)2(phen)] (1a−c; M = Mo, W) with KCH2C(O)Ar afford the O-bound enolato complexes [M(η3-C3H4-R){OC(CH2)Ar}(CO)2(phen)] (2a−d). On the other hand, the reactions of molybdenum chloro complexes with KCH2CN yield the complexes [Mo(η3-C3H4-R)(CH2CN)(CO)2(phen)] (3a,b), in which the nitrile enolate ligand is C-bound. In addition to the spectroscopic characterization by means of IR and NMR, the structures of [Mo(η3-C3H5){OC(CH2)(naphthyl}(CO)2(phen)] (2c) and [Mo(η3-C3H4-Me-2)(CH2CN)(CO)2(phen)] (3a) were determined by X-ray diffraction.