EHMO Calculations Research Articles

Osmium–azopyrimidine chemistry. Part VII: synthesis, structural characterisation and electrochemistry

Reaction of 2-(arylazo)pyrimidines (RC 6H 4NNC 4H 3N 2, abbreviated aapm; R=H (papm), o-Me ( o-tapm), m-Me ( m-tapm), p-Me ( p-tapm), p-Cl ( p-Clpapm)) with (NH 4) 2[OsCl 6] in 2-methoxyethanol gives two isomers of composition OsCl 2(aapm) 2. They are structurally characterised by 1H NMR spectra and established as the cis– trans– cis ( ctc) and cis– cis– cis ( ccc) isomer. With reference to the coordination pairs of Cl; N(pyrimidine) (N) and N(azo) (N′), the structure of ctc-OsCl 2( p-tapm) 2 is confirmed by an X-ray diffraction study. The complexes exhibit multiple MLCT transitions in the visible to near-IR region. Redox studies show an Os(III)/Os(II) couple at 1.2–1.3 V and Os(IV)/Os(III) couple at ∼2 V versus SCE. EHMO calculations and comparison with analogous ruthenium(II) complexes explain the spectral and redox properties of the complexes.

Reduction and Oxidation of the Arachno Clusters Fe2(CO)6(μ-S)2PtL2: Characterization of Distinct One- and Two-Electron Transfer Sites in Heteropolynuclear Compounds

The reduction and oxidation properties of the arachno-heteropolynuclear metal clusters Fe2(CO)6(μ3-S)2PtL2, where L2 = bipyridine (1), phenanthroline (2), diphenylphosphinoethane (3), diphenylphosphinoferrocene (4), or cyclooctadiene (5), have been examined by electrochemistry, IR spectroscopy, and ESR spectroscopy. An electron-transfer series involving up to five electrons is observed. The common characteristics are a fully reversible one-electron oxidation process to a monocation (in the range 0.13−0.38 V vs ferrocene) and a chemically reversible but electrochemically quasi-reversible two-electron reduction process (range −1.9 to −2.4 V). Complexes 1 and 2 also display a fully reversible one-electron reduction at a potential less negative (ca. −1.8 V) than the subsequent two-electron reduction. The LUMOs of 1 and 2 are predicted by EHMO calculations to be primarily π*-diimine based. Spectral data from the monoanions 1- and 2- are consistent with this orbital assignment: very small shifts of the metal−carbonyl IR frequencies (ca. −13 cm-1) from those of the neutral complexes are observed, and the 195Pt hyperfine splitting in ESR spectra is very small compared to that expected for a metal-localized radical. The two-electron reductions forming, e.g., 13- or 32-, appear to involve the Fe2S2 moiety and most likely are concomitant with breaking and making of an Fe−Fe bond. Carbonyl IR energies are lowered in excess of 100 cm-1 in the two-electron reduction. The oxidation processes appear to be localized on the Fe2(CO)6S2 fragment, with IR shifts of 46−76 cm-1 for 1+−5+ and small 195Pt hyperfine splittings. X-ray crystal structures are reported for 2 and 5.

Five Ternary Zintl Phases in the Systems Alkali-Metal–Indium–Bismuth

Five new compounds of alkali metal, indium, and bismuth were synthesized by direct fusion of the elements. The structures of these compounds, Na3In2Bi3 (I) (refined composition NaIn0.61(1)Bi, orthorhombic, Pnma, a=8.062(2), b=4.8684(8), and c=9.2455(9) Å), Na3InBi2 (II) (monoclinic, P21/c, a=18.841(3), b=9.235(1), and c=12.661(2) Å, β=98.67(2)°), K7In4Bi6 (III) (refined composition K4.71(3)In2.52(2)Bi4, tetragonal, P43, a=9.703(1), and c=17.519(4) Å), K11In6Bi9 (IV) (triclinic, P1, a=12.012(7), b=13.380(4), and c=13.695(4) Å, α=76.70(2), β=64.14(3), and γ=75.68(3)°), and Rb7In4Bi6 (V) (tetragonal, P43, a=9.915(2) and c=17.870(4) Å) are built of indium-centered tetrahedra of bismuth that are connected by corner- or/and edge-sharing and form different types of three-dimensional networks. All five compounds are diamagnetic and, therefore, electronically balanced, salt-like Zintl phases. According to EHMO calculations they are wide band-gap semiconductors.

Synthesis, Spectroscopic and Electrochemical Studies of Isomeric Dichloro-bis-[ N (1)-Alkyl-2-(Arylazo)Imidazole]-Osmium(II). Single Crystal X-ray Structures of Blue-Violet Dichloro-Bis-[ N (1)-Methyl-2-(Arylazo)Imidazole]-Osmium(II) Species

1-Alkyl-2-(arylazo)imidazoles (p-R-C6H4-N=N-C3H2N2X, abbreviated as RaaiX, R = H(a), CH3(b), Cl(c); X = N(1)-CH3 (1), N(1)-CH2-C6H5 (2)) have been reacted with (NH4)2[OsCl6] and OsCl2(RaaiX)2 species isolated in two isomeric forms, blue-violet (3, 5) and red-violet (4, 6). IR spectra show two x (Os-Cl) modes and support a cis-OsCl2 configuration. X-ray diffraction methods were used to determine structures of blue-violet isomers. In terms of the three coordination pairs around Os(II), Cl, Cl, N, N (N(imidazole), N) and N', N' (N(azo), N') the blue-violet isomers have a cis-trans-cis (ctc) configuration. 1H NMR data for the red-violet complexes (isomers B) and results concerning analogous ruthenium(II) complexes indicate isomer B to have cis-cis-cis (ccc) configuration. Absorption spectra show an intense MLCT band at ca 580 nm along with two weak bands at 800 and 1000 nm. Cyclic voltammetry shows quasi-reversible Os(III)/Os(II) and Os(IV)/Os(III) couples at 0.4-0.6 V and 1.3-1.5 V versus SCE and ill-defined azo reductions. The X-Ray structures show unusually long N=N bond lengths, 1.31-1.32 Å, elongated by some 0.06 Å compared to the free ligand value. Os(II) prefers to bind N(azo) (Os-N(azo), 1.98 Å) rather than N(imidazole) (Os-N(imidazole), 2.03 Å). EHMO calculations of ctc-OsCl2 (MeaaiMe) and comparison with the ruthenium(II) complex account for the MLCT transitions in terms of a metal-dominated HOMO to a ligand-dominated LUMO shift.

Synthesis and Characterization of Cs5In3As4 with a Structure of Two Coexisting “Polymorphic” Forms of Different Dimensionality

The title compound was made by fusion of a stoichiometric mixture of the pure elements at 500 degrees C. The structure (monoclinic, P2(1)/c, Z = 8, a = 17.037(6), b = 12.253(1), c = 18.105(4) A, beta = 117.24(2) degrees) is made of alternating one- and two-dimensional sections with the same composition of Cs(5)In(3)As(4), and can be considered as two coexisting polymorphic forms of the same compound. The chains and layers in these sections are made of repeating semicubane motifs of [In(3)As(4)](5)(-) that are connected to each other by In-As bonds in the chains, and by both In-As and In-In bonds in the layers. According to magnetic measurement and EHMO calculations, Cs(5)In(3)As(4) is a closed-shell compound that fulfills the Zintl concept.

Syntheses and Structures of New Luminescent Cyclometalated Palladium(II) and Platinum(II) Complexes: M(Bab)Cl, M(Br−Bab)Cl (M = Pd(II), Pt(II)), and Pd3Cl4(Tab)2 (Bab = 1,3-bis(7-azaindolyl)phenyl, Br−Bab = 1-Bromo-3,5-bis(7-azaindolyl)phenyl, Tab =1,3,5-tris(7-azaindolyl)phenyl)

The reactions of blue luminescent ligands 1,3-bis(7-azaindolyl)benzene (BabH), 1-bromo-3,5-bis(7-azaindolyl)benzene (Br−BabH), and 1,3,5-tris(7-azaindolyl)benzene (TabH) with K2PdCl4 and K2PtCl4 have been investigated. Five new luminescent cyclometalated palladium(II) and platinum(II) complexes Pd(Bab)Cl (1), Pt(Bab)Cl (2), Pd(Br−Bab)Cl (3), Pt(Br−Bab)Cl (4), and Pd3Cl4(Tab)2 (5) have been synthesized and fully characterized. The molecular structures of 1 and 2, and 3 and 4, are similar. There are however significant variations in the solid-state structures and luminescence of 1 and 2, and 3 and 4. EHMO calculations revealed that it is most likely that the electronic transitions in the Pt(II) complexes are π to π* transitions with significant contributions from dπ lone pairs of the Pt(II) center in the π level, and the electronic transitions in the Pd(II) complexes are either d(z2) to π* charge-transfer transitions or π to π* transitions similar to the Pt(II) complexes.

Synthesis, spectral and electrochemical studies of 2-(arylazo)heterocycle complexes of zinc(II). Single-crystal X-ray structure of [Zn(papm)Cl 2·CH 3OH] (papm=2-(phenylazo)pyrimidine)

2-(Arylazo)pyridines (aap) (RC 6H 4NNC 5H 4N, 1) and 2-(arylazo)pyrimidines (aapm) (R-C 6H 4NNC 4H 3N 2, 2); R=H ( a), o-Me ( b), m-Me ( c), p-Me ( d), p-Cl ( e) are used to synthesise title compounds. The complexes are characterised by elemental analyses, IR, UV–Vis and 1H NMR spectral data. Single-crystal X-ray structure of dichloro-{2-(phenylazo)pyrimidine}zinc(II)·methanol suggests that the complex is a distorted trigonal bipyramidal symmetric around Zn(II), and Cl(1), Cl(2), N(4) (N (azo)) make the trigonal plane. Zn(II) moves downwards by 0.12 Å from the centre of gravity of the plane. Two axial positions are occupied by N(1) (N(pyrimidine)) and methanol-O. Molecular packing shows one-dimensional infinite chain via hydrogen bonding. The EHMO calculation has been carried out to explain the electronic behaviour of the complexes and the results are compared with that of copper(I) complex.

Cyclopalladation versus hydroxylation. A case of pH dependence

1-Alkyl-2-(naphthyl-α-azo)imidazoles (NaiR, 2) (C 10H 7NNC 3H 2N 21R; R=Me ( a), Et ( b), PhCH 2 ( c)) have been reacted with Na 2PdCl 4 in MeOH or MeCN solutions of Pd(MeCN) 2Cl 2 to synthesise Pd(NaiR)Cl 2 ( 3). The reaction of Pd(OAc) 2 in boiling benzene with NaiR followed by the addition of LiCl has resulted in the synthesis of the cyclopalladated complex Pd(NaiRH)Cl ( 4). The ligand, NaiR, acts as a N, N′-bidentate chelator while NaiRH acts as a tridentate N, N′, C-cyclometallating ligand. The infrared spectra of 3 exhibit two PdCl stretches correspond to a cis-PdCl 2 geometry, and a single ν(PdCl) band in 4 suggests one PdCl bond. Cyclopalladation is supported by a single crystal X-ray crystal structural study of Pd(NaiEtH)Cl ( 4b) and the metallation takes place at C(8′)-position. The solution of Pd(NaiR)Cl 2 ( 3) is also irreversibly transformed into Pd(NaiRH)Cl ( 4) when the pH is adjusted to 4.5–6.0 by NaOAc or other bases (NaOMe, NaOH, LiOH, Li 2CO 3 etc.). At higher pH values (8–10) the reaction shows the chelative hydroxylation at the C(2′)-site to synthesise Pd(NaiRO)Cl ( 5). The structure of the hydroxylated blue product is also supported by a single crystal X-ray crystal structure of Pd(NaiEtO)Cl ( 5b). The reaction of Pd(NaiR)Cl 2 in MeCN with dilute sodium hydroxide in air, or aqueous silver nitrate under boiling conditions, or its treatment with Tollen's reagent in MeCN solution under ambient conditions has also yielded the hydroxylated product. All the compounds have been characterised by elemental analyses, IR, UV–vis and 1H-NMR data. The solution spectral behaviour has been interpreted by EHMO calculations.

Influence of tetrahedral distortion of CuN 4 complexes on spectroscopic properties. Synthesis, characterization and crystal structures of [Cu( N-(2-methylpyridyl)benzenesulfonylamidate) 2], [Cu( N-(2-methylpyridyl)toluenesulfonylamidate) 2] and [Cu( N-(2-methylpyridyl)naphthalenesulfonylamidate) 2] compounds

A series of new N-sulfonamide ligands and their copper(II) complexes, [Cu( N-(2-methylpyridyl)toluenesulfonylamidate) 2] ( 1), [Cu( N-(2-methylpyridyl)benzenesulfonylamidate) 2] ( 2) and [Cu( N-(2-methylpyridyl)naphthalenesulfonylamidate) 2] ( 3), have been synthesized and characterized. Single crystal X-ray analysis of the three complexes revealed that all of them present a tetracoordinate CuN 4 chromophore. The ligands act as bidentate, coordinating the metal ion through the pyridine and sulfonamido N atoms. The main structural difference among the compounds is the varied degree of distortion of square-planar stereochemistry. Complex 1 exhibits a regular square-planar geometry. In complexes 2 and 3 the tetrahedrality values of 50.2° and 39.0° respectively indicate a strong distortion. EHMO calculations on idealized models show the correlation between the geometrical distortion and the spectroscopic properties.

Extended Hückel calculations on functional and structural models of the FeMo-cofactor of nitrogenase

The possibility of activating N 2 at the molybdenum centre of the FeMo-cofactor of nitrogenase is investigated using EHMO calculations on functional and structural models of the enzyme active site. We consider a diverse range of structurally defined complexes and elicit the EHMO characteristics of these sites. We then compare these with EHMO calculations on model clusters and FeMo-co with N 2 bound at Mo. Our focus is on both the binding of dinitrogen and its activation towards protonation. The latter requires a substantial occupation of the π* molecular orbitals of N 2 which is experimentally achieved in some mononuclear MN 2 complexes. Binding and activation are also theoretically possible at the Mo centre of MoFe 3S 4 clusters provided they have the right oxidation state and geometry. However, structural deformations of the FeMo cofactor cluster core do not appear to provide a favourable situation for N 2-activation at Mo.

Unique structural topologies involving metal–metal and metal–sulfur interactions: salts of [Ni(C3S5)2]x− with cis-anti-cis-dicyclohexyl-18-crown-6 complexed counter ions

Preparation by electrocrystallisation has been carried out for the salts [Rb(anti-dchyl-18c6)]2[Ni(dmit)2] 1, [Rb(anti-dchyl-18c6)][Ni(dmit)2] 2, [Cs(anti-dchyl-18c6)]2[Ni(dmit)2] 3 and [Cs(anti-dchyl-18c6)1.5][Ni(dmit)2]64 (anti-dchyl-18c6 = cis-anti-cis-dicyclohexyl-18-crown-6, dmit = C3S5). Salts 1 and 3 involve the planar dianionic nickel complex sandwiched by two metal–crown units. This leads to short Rb+ ⋯ Ni and Rb+ ⋯ S interactions in 1 and the shortest recorded Cs+ ⋯ Ni distance of 3.47 A in 3, presumably stabilised by the four surrounding S atoms at 3.73–4.44 A. DFT calculations on the dianionic salts 1 and 3 indicate an essentially electrostatic interaction between the [Ni(dmit)2]2− complex and the Rb+ or Cs+ ion and show frontier orbitals qualitatively similar to those previously derived from EHMO calculations on molecular conductors containing [Ni(dmit)2]. Salt 2 consists of non-stacked nickel complexes arranged in chains linked by S ⋯ Rb+ interactions through the terminal sulfurs with the Rb+ ion placed exactly within the plane of the crown oxygens. Magnetic susceptibility measurement indicated weak antiferromagnetic interactions. Salt 4 shows a 2-D sheet of nickel complexes stacked in a herringbone arrangement separated by layers of counter ions complexed by the crowns in a disordered manner with the anion ∶ cation ratio of 6 ∶ 1 uniquely high among [Ni(dmit)2]x− salts. Salt 4 displays semiconductor behaviour with σRT = 10−2 S cm−1.

Unsupported Metal Chain Complex: Synthesis, Characterization, and EHMO Study Involving the Tetraosmium Complex [Os2(CO)5(thd)2]2

Metal carbonyl complex Os3(CO)12 reacts with a hexane solution of (thd)H, thd = 2,2-dimethyl-3,5-heptanedionate, in a sealed autoclave at 190 °C to afford the Os4 metal chain complex [Os2(CO)5(thd)2]2 (1), isolated from repeated recrystallization in air. Treatment of 1 with CO at room temperature gives the Os2 metal complex [Os2(CO)6(thd)2] (2) through reversible cleavage of the central Os−Os bond. EHMO calculation has been carried out to explain the involvement of a short−long−short Os−Os···Os−Os array.

Compared Reductive Chemistry of Molybdenocene and Indenyl-Substituted Complexes

Reduction of [IndCpMo(L)Br]Br (L = 1a, CO; 2, NCMe) with Cp2Co in the presence of two equivalents of the ligand L′ gives the ring-slipped neutral complexes [(η3-Ind)CpMoL′2] (L′ = 5, CO; 6, 1/2 dppe; 7, PMe3; 8, P(OMe)3; 9, CNtBu) in good yield. Products 7, 8, and 9, but not [IndCpMoL′], are also formed in the presence of only 1 equivalent of L′ in modest yields. In the case of the reduction of [IndCpMo(L)Br]Br [L = 2, NCMe; 3a, CNtBu; 4, P(OMe)3] mixtures of the complexes, [(η3-Ind)CpMoL2] (8, 9) and [(η5-Ind)CpMoL] [L = 11, P(OMe)3; 12, CNtBu] were obtained. The only product of formal type [(η5-Ind)CpMoL] that could be prepared by these methods was the alkyne complex [(η5-Ind)CpMo(η2-PhC≡CPh)] (10). These results contrast with the well-known reductions of similar bis-cyclopentadienyl cations [Cp2Mo(L)Br]+, which produce [Cp2MoL] complexes under the same conditions. The reduction of the dications [Cp2MoL2][BF4]2 [L = CO; P(OMe)3] with Cp2Co is now reported to afford the neutral complexes [CpMo(η3-C5H5)(CO)2] (13) and [Cp2Mo(P(OMe)3)] (14), respectively, showing that the stability of the ring-slipped complexes is dependent on the other ligands. From DFT and EHMO calculations used to probe the bonding and the energetics of these ring slippage processes it is concluded that weak π acceptor ligands favour η5-Ind η3-Ind slippage and disfavour η5-Cp η3-Cp slippage at the CpMoL2 fragment. Redox-induced ring slippages involve very similar energies for both indenyl and cyclopentadienyl complexes and should be able to produce more examples of the otherwise rare η3-Cp coordination mode.

Roles of π-Alkyne, Hydride–Alkynyl, and Vinylidene Metal Species in the Conversion of Alkynes into Vinylidene: New Theoretical Insights

The transformation of acetylene into vinylidene, as promoted by the metal fragment [(pp3)Co]+ [pp3 = P(CH2CH2PPh2)3], is unimolecular and features the hydride–acetylide species as an intermediate. The paper describes a detailed ab initio study of the reaction, in particular with regard to the step involving 1,3-H shift. The best computational results are obtained by mimicking the pp3 ligand with actual ethylenic chains rather than with single PH3 molecules. The keypoints along the two-step reaction path (π-acetylene, hydride–acetylide, and vinylidene complexes, as well as intermediate transition states) have been optimized for CoI and RhI derivatives at the MP2 level. For the fragment [(pp3)Co]+, the barrier associated with transformation of the hydride–acetylide intermediate to vinylidene (20.6 kcal/mol) is easier to surmount compared to that for reversion to the reactants (28.6 kcal/mol). The situation is reversed for the analogous RhI system, with the initial π-acetylene adduct being slightly more stable. Although higher in energy, the hydride–acetylide species is the experimentally detected product of the reaction of acetylene with the fragment [(pp3)Rh]+. The salient chemical aspects of the 1,3-H shift are discussed in terms of perturbation theory arguments. Parallel EHMO calculations, which have provided a relatively good consistency with the ab initio results, allow the proposal of an orbital rationale for the mode of migration of the hydride ligand along the substantially linear Co–Cα–Cβ grouping.

Cs7In4Bi6: A Zintl Phase Tailored from the PbO-Type Layers of the Parent InBi Compound

The title compound was made by fusion of stoichiometric mixture of the pure elements. The structure (triclinic, P1̄, Z = 4, a = 10.1851(4) Å, b = 10.2318(7) Å, c = 27.617(2) Å, α = 94.457(7)°, β = 91.462(6)°, γ = 90.214(6)°) is based on In-centered tetrahedra of bismuth sharing edges to form folded chains. The latter are linked via In−In bonds in a rather complicated three-dimensional network. The structure can be explained as being carved out from the layered PbO-type structure of the parent group III−V compound of InBi. Cs7In4Bi6is a wide band-gap semiconductor according to EHMO calculations and magnetic measurements.

Preparation, Characterization, and Luminescence Properties of a 58-Electron Linear Pt(4) Cluster, [Pt(4)(dmb)(4)(PPh(3))(2)](2+) (dmb = 1,8-Diisocyano-p-menthane), and Its Diphosphine Polymers.

The title compounds [Pt(4)(dmb)(4)(PPh(3))(2)]Cl(2) (1) and {[Pt(4)(dmb)(4)(diphos)]Cl(2)}(n)() (diphos = dppb (2), dppp (3), dpph (4)) have been prepared in good yields from the reaction of Pt(2)(dba)(3).CHCl(3) with 2 equiv of dmb and 1 equiv of PPh(3) for 1 (dba = dibenzylideneacetone) and from the reactions of Pt(2)(dba)(3).CHCl(3) with 2 equiv of dmb and 0.5 equiv of diphos for 2-4. The structure for 1 consists of a quasi-linear Pt(4)L(2)(2+) species (L = PPh(3); d(PtPt) = 2.666(2), 2.655(2), 2.641(2) Å), where the dmb ligands bridge the Pt atoms forming a catenate. From Raman spectroscopy, the two nu(PtPt) active modes for 1 are observed at 162 and 84 cm(-)(1) (F(PtPt) = 2.36 mdyn Å(-)(1)). For 2-4, the diphos ligands induce the formation of amorphous polymeric materials (X-ray powder diffraction patterns) with MW ranging from 84 000 to 307 000 according to viscometry. EHMO calculations predict that the HOMO and LUMO are the two dsigma orbitals arising from four interacting Pt atoms via the d(x)()()2(-)(y)()()2, d(z)()()2, s, and p(x)() M atomic orbitals. These are mixed with the ddelta and CNR(pi) MO's. From the examination of the position, absorptivity, and fwhm (full width at half maximum) of the strongly allowed low-energy UV-vis band, a dsigma --> dsigma assignment is made (lambda(max) = 405 nm, epsilon = 35 800 M(-)(1) cm(-)(1); EtOH for 1). The four compounds are luminescent at 77 K in EtOH, where lambda(emi) are 750, 736, 750, and 755 nm and tau(e) are 2.71, 4.78, 5.15, and 5.17 ns for 1-4, respectively. On the basis of the Stokes shifts (10 000-12 000 cm(-)(1)) and the long emission lifetimes, a phosphorescence dsigma --> dsigma assignment is made for the observed emissions. Crystal data for 1: crystal system triclinic; space group P1; a = 12.624(4) Å; b = 14.24(2) Å; c = 27.312(3) Å; alpha = 92.35(3) degrees; beta = 91.655(15) degrees; gamma = 90.28(5) degrees; V = 4903(7) Å(3); Z = 2; D(calc) = 1.528 g cm(-)(3); R(1) = 0.0738; wR(2) = 0.2097; S = 1.018.

Syntheses, structures and electrochemistry of copper(II) salicylaldehyde/tris(3-phenylpyrazolyl)borate complexes as models for the radical copper oxidases

2-Hydroxy-5-methyl-3-methylsulfanylbenzaldehyde (HL2) and 2-hydroxy-5-methyl-3-methylselanylbenzaldehyde (HL3) have been synthesized from 2-hydroxy-5-methylbenzaldehyde (HL1), as have Schiff bases HL4R and HL5R (R = Me or Ph) derived from RNH2 and HL1 or HL2 respectively. The complexes [Cu(L)(TpPh)] ([L]– = [L1]–, 1; [L2]–, 2; [L3]–, 3; [L4Me]–, 4; or [L4Ph]–, 5) have been prepared. Single crystal structure determinations of 1, 2, 4 and 5 show copper(II) centres with square pyramidal [CuN3O2] (1, 2) or [CuN4O] (4, 5) co-ordination spheres; for 4 and 5 the basal plane of the complex is twisted by 20–25° because of the steric properties of the Schiff base Me or Ph substituent. The UV/vis and EPR spectra of 1–5 in CH2Cl2 show the presence of tetragonal copper(II) centres. Cyclic voltammograms of 1–5 and the uncomplexed phenols in CH2Cl2–0.5 M Bun4NPF6 exhibit an irreversible or (for 2) reversible 1-electron oxidation to a phenoxyl radical. The oxidation potentials of HL2 and HL3, and of 2 and 3, are barely distinguishable. However, the irreversibility of this process for 3 compared to that of 2 suggests that a selenoether substituent kinetically stabilises the phenoxyl unpaired spin less efficiently than a thioether one; this is borne out by EHMO calculations on L1˙–L3˙. Spectroelectrochemical characterisation of [2]+, whose UV/vis/NIR spectrum is very similar to that of galactose oxidase, confirms its formulation as the antiferromagnetically coupled species [CuII(L2˙)(TpPh)]+.

Oxidatively induced isomerisation of vinylidene ligands to alkynes: ESR spectra of paramagnetic vinylidene and alkyne arene metal complexes

UV irradiation of [M(CO)3(η-arene)] and Me3SiCCSiMe3 gives [M(CO)2{CC(SiMe3)2}(η-arene)] (M = Cr, arene = C6H2Me4-1,2,3,5 2V, C6H3Me3-1,2,3 3V or C6H6 4V; M = Mo, arene = C6Me6 5V or C6H3Me3-1,3,5 6V). The crystal structure of [Cr(CO)2{CC(SiMe3)2}(η-C6H6)] 4V confirms the presence of the vinylidene ligand; the complex has approximate Cs symmetry with the C(SiMe3)2 plane orthogonal to the arenecentroid–Cr–Cα–Cβ plane. Voltammetry and IR and NMR spectroscopy show that in solution [Mo(CO)2{CC(SiMe3)2}(η-C6H3Me3-1,3,5)] 6V thermally equilibrates with the alkyne isomer [Mo(CO)2(η-Me3SiCCSiMe3)(η-C6H3Me3-1,3,5)] 6A. The vinylidene complexes [M(CO)2{CC(SiMe3)2}(η-arene)] 2V–6V undergo one-electron oxidation to the alkyne cations [M(CO)2(η-Me3SiCCSiMe3)(η-arene)]+ 2A+–6A+via fast, redox-induced vinylidene-to-alkyne isomerisation. These cations are reduced to the neutral alkyne complexes [M(CO)2(η-Me3SiCCSiMe3)(η-arene)] 2A–6A which slowly isomerise thermally to the neutral vinylidene complexes 2V–6V. Paramagnetic vinylidene and alkyne complex cations have been characterised by ESR spectroscopy; unpaired electron density is extensively delocalised from the metal centre to the C2 ligand, in agreement with the results of EHMO calculations.

Synthesis, structure and metal compounds of a novel chromophoric cyanamide ligand

The novel compound 2-cyanaminofluoren-9-one (HL) has been synthesized, and is readily deprotonated to form the corresponding cyanamide anion L–. This has been isolated as the Tl+L– and AsPh4+L– salts. The UV/visible spectra of HL and AsPh4+L– show the same amine to carbonyl charge transfer transition seen in other aminofluorenones, although at longer wavelengths. The compound AsPh4+L– undergoes the reversible one electron reduction typical of fluorenones, whilst HL undergoes an irreversible reduction. The crystal structure of AsPh4+L– was determined and related to the solvatochromic behaviour of the L– anion. Some simple EHMO calculations have been carried out on the L– anion of AsPh4+L–, which show the cyanamide based HOMO and carbonyl based LUMO involved in the aforementioned CT transition. The thallium salt Tl+L– has also been used as a transmetallating agent in reaction with trimethyltin chloride to produce the corresponding tin cyanamide complex [SnMe3L], and in reaction with (triphenylphosphine)gold chloride to produce the first reported gold cyanamide compound [AuL(PPh3)], whose crystal structure has been determined.

The syntheses of pyridine-functionalyzed methylidynetricobalt nona-carbonyl clusters, their X-ray analyses, and its coordination to Pd(II)

Two kinds of methylidynetricobalt nonacarbonyls with a pyridine functional group as an apical substituent have been synthesized from trichloromethylpyridine derivatives. The structures of two new clusters have been determined by single crystal X-ray analysis. EH-MO calculations have shown that the atomic charge on the N atom in NC5H4-3-CCo3(CO)9 is close to that of β-picoline. This cluster can coordinate to Pd(II) and trans-PdCl2{NC5H4-3-CCo3(CO)9}2 with a nanometer dimension has been synthesized as a precursor of molecular dot.