Conor Long

Novel acetylene-linked di-cobalt and tetra-cobalt carbonyl clusters

Abstract {Co2(CO)6} groups were attached to p-diethynylbenzene-based acetylenes giving complexes of general formula [{Co2(CO)6}(μ2-η2:2-RC2C6H4C2R′)] ((4): R=R′=H; (4a): R=SiMe3, R′=H; (4b): R=R′=SiMe3); [{Co2(CO)6}2(μ4-η2:2:2:2-RC2C6H4C2R′)] ((3): R=R′=H; (3a): R=SiMe3, R′=H; (3b): R=R′=SiMe3); [{Co2(CO)6}4(μ8-η2:2:2:2:2:2:2:2-R2C6H4C2C2C6H4C2R)]((5): R=H; (5b):R=SiMe3). The addition of Co4(CO)12 to p-diethynylbenzene and to 4 was also investigated, producing [{Co4(CO)8(μ-CO)2}(μ4-HC2C6H4C2H)] (6) and [{Co2(CO)6}{(Co4(CO)8(μ-CO)2}(μ8-HC2C6H4C2H)] (7). The syntheses of the acetylenic derivatives of C60 [(trimethylsilyl)ethynyl]hydrofullerene[60] (8a) and (phenylethynyl)hydrofullerene[60] (9) and the new ligand [(trimethylsilyl)diethynylbenzene]hydrofullerene[60] (10a) were performed and the resulting acetylenes were reacted with dicobaltoctacarbonyl giving the corresponding complexes [(trimethylsilyl)(dicobalthexacarbonyl)ethynyl]hydrofullerene[60] (11a), (phenylethynyl)(dicobalthexacarbonyl)hydrofullerene[60] (12) and [(trimethylsilyl)bis(dicobalthexacarbonyl)diethynylbenzene] (13a). The reaction of 1-bromo-3,5-diethynylbenzene and 1,3,5-triethynylbenzene with dicobaltoctacarbonyl resulted in the formation of [HC2{Co2(CO)6}]2C6H2Br (16) and [HC2{Co2(CO)6}]2C6H3 (15) as expected. Crystals of 3a, 3b, 4, 4b, 15 and 16 suitable for single-crystal X-ray diffraction were grown and the molecular structures of these compounds are discussed.

Acid-base chemistry of some 1,2,4-triazole and imidazole complexes of ruthenium(II)bis(2,2'-bipyridyl)

Abstract The acid-base chemistry of [Ru(2,2′-bipyridyl) 2 (imidazole) 2 ] 2+ and [Ru(2,2′-bipyridyl) 2 (1,2,4-triazole) 2 ] 2+ has been studied in both the ground and the excited state. From the pH dependence of emission and absorption spectra it was found that both complexes are stronger acids in the excited state compared to the ground state. In sulphuric acid media the 1,2,4-triazole complex is a stronger base in the excited state than in the ground state. pK values for the different proton-equilibria are reported.

GROUP VI METAL PENTACARBONYL COMPLEXES OF 1,2,4-TRIAZOLES

Abstract The synthesis of chromium and tungsten pentacarbonyl complexes with 4-methyl and 4-phenyl-1,2,4-triazole is reported. The nature of the lowest energy absorption in the ultraviolet spectra of these complexes has been examined and shown to be principally a ligand field band. The triazoles are shown to be acting as monodentate ligands by infrared and 1 H nuclear magnetic resonance spectroscopy. The compounds show strong solvent dependence in the 1 H NMR and these effects are explained by solvent—solute interaction. The temperature dependence of the 1 H NMR spectrum of W(CO) 5 (4-phenyl-1,2,4-triazole) has also been examined.

Carbonyl complexes of 1,2,4-triazoles ☆: II. The crystal structure of pentacarbonyl-4-methyl-1,2,4-triazolechromium(0), Cr(CO)5(C3H3H5). Chromium-to-triazole π-bonding

Abstract The crystal structure of pentacarbonyl-4-methyl-1,2,4-triazolechromium [Cr(CO) 5 (C 3 N 3 H 5 )] has been determined by single-crystal X-ray techniques. The compound crystallizes in the space group Pbca with a 10.899(2), b 17.572(2), c 11.877(2) A and Z = 8. The compound consists of monomeric units in which the chromium atom is coordinated octahedrally to five CO groups and one monodentate coordinating 4-methyl-1,2,4-triazole ligand (CrN 2.111(2) A). Full matrix least-squares refinement resulted in a final R = 0.025 ( R w = 0.0324). There appears to be no or little π-interaction between the triazole ligand and the chromium atom.

Photochemistry of (η(6)-arene)Cr(CO)3 (arene = methylbenzoate, naphthalene, or phenanthrene) in n-heptane solution: population of two excited states following 400 nm excitation as detected by picosecond time-resolved infrared spectroscopy.

The photochemistry of (η(6)-methylbenzoate)Cr(CO)(3), (η(6)-naphthalene)Cr(CO)(3), and (η(6)-phenanthrene)Cr(CO)(3) in n-heptane solution was investigated by picosecond time-resolved infrared spectroscopy (TRIR). The observation of two transient IR features in the organic carbonyl region at 1681 and 1724 cm(-1) following 400 nm excitation of (η(6)-methylbenzoate)Cr(CO)(3) confirms formation of two excited states which are classified as metal-to-arene charge transfer (MACT) and metal-to-CO charge transfer (MCCT), respectively. Time-dependent density functional theory calculations have been used to support these assignments. Population of the MCCT excited state results in a slow (150 ps) expulsion of one CO ligand. Excitation of (η(6)-naphthalene)Cr(CO)(3) or (η(6)-phenanthrene)Cr(CO)(3) at either 400 or 345 nm produced two excited states: the MCCT state results in CO loss, while the MACT excited state results in a change to the coordination mode of the polyaromatic ligands before relaxing to the parent complex. A comparison of the infrared absorptions observed following the population of the MACT excited state with those calculated for nonplanar polyaromatic intermediates provides a model for the reduced hapticity species.

The photochemistry of (μ2-RC2H)Co2(CO)6 species (R=H or C6H5), important intermediates in the Pauson–Khand reaction

Abstract The photochemistry of (μ 2 -RC 2 H)Co 2 (CO) 6 (R=H or C 6 H 5 ) has been investigated by both time-resolved and steady-state techniques. Pulsed excitation in cyclohexane solution with λ exc =355 nm causes CoCo bond homolysis while photolysis at λ exc =532 nm results in CO loss. Steady-state photolysis ( λ exc >500 nm) in the presence of suitable trapping ligands (L) produced the monosubstituted complexes (μ 2 -RC 2 H)Co 2 (CO) 5 (L) (L=C 5 H 5 N or PPh 3 ) in high yields.

Visible light driven room temperature Pauson-Khand reaction†

Visible light driven decarbonylation of [(mu(2)-alkyne)Co(2)(CO)(6)] complexes enables the formation of cyclopentenones in good yields at ambient temperatures.

Thermally and photochemically induced co-ordination change in ruthenium(II) bis(2,2′-bipyridine) complexes containing pyridyltriazole ligands

A series of RuII(bipy)2 complexes (bipy = 2,2′-bipyridine) containing monodentate co-ordinated pyridyltriazole ligands has been prepared and characterised. The species are obtained by either thermal or photochemical methods. The co-ordination mode of the products obtained has been investigated using spectroscopic techniques. The molecular structure of one of the products, bis(2,2′-bipyridine)chloro-[3-methyl-1-(pyridin-2-yl)-1,2,4-triazole]ruthenium(II) hexafluorophosphate, has been determined. The compound crystallises in the triclinic space group P with unit-cell parameters a= 8.599(12), b= 13.503(16), c= 16.526(16)A, α= 89.88(9), β= 117.22(8), γ= 111.08(10)° and Z= 2. The pyridyltriazole is co-ordinated via the N4 nitrogen atom. In the compounds containing monodentate 4-methyl-3-(pyridin-2-yl)-1,2,4-triazole the ligand is most likely co-ordinated via the N1 atom. The conversion of the photoproduct acetonitrilebis(2,2′-bipyridine)[4-methyl-3-(pyridin-2-yl)-1,2,4-triazole]ruthenium(II) into the parent complex containing the chelating pyridyltriazole ligand by thermal as well as photochemical methods is reported.

Pentacarbonyl(di-2-pyridyl­amine)tungsten(0)

In the title molecular complex, (I), the W atom is in an octahedral environment with four equatorial carbonyl ligands and a fifth in an axial position trans to the monodentate dipyridylamine ligand. The long dimension of this last bisects the angle between two of the equatorial carbonyl groups and while the non-bonded pyridyl N atom is directed away from the W atom, the bridging amine group is directed towards it. Thus, in addition to the N atom to which it is attached, the amino H has two nearest neighbour C atoms of equatorial carbonyl groups but does not participate in hydrogen bonding in any real or usual sense. The W-C bond distance for the axial carbonyl group is notably less than those of the equatorial groups.

Photoinduced anionic polymerization of cyanoacrylates using substituted pyridine pentacarbonyl complexes of tungsten or chromium

Photoinduced polymerization of cyanoacrylate monomers using a novel class of photoinitiators comprising Group VI metal carbonyl pyridine complexes is reported. Irradiation of a solution containing the monomer and photoinitiator, with visible light (436 nm), leads to a rapid exothermic polymerization reaction which is readily followed by calorimetric techniques. The photoinduced reaction exhibits the features expected of conventional amine initiated polymerization of cyanoacrylates consistent with photo-released pyridine acting as the initiating species.