Alice Brink

Solid state isostructural behavior and quantified limiting substitution kinetics in Schiff-base bidentate ligand complexes fac-[Re(O,N-Bid)(CO)3(MeOH)](n).

A range of N,O-donor atom salicylidene complexes of the type fac-[M(O,N-Bid)(CO)3(L)](n) (O,N-Bid = anionic N,O-bidentate ligands; L = neutral coordinated ligand) have been studied. The unique feature of the complexes which crystallize in a monoclinic isostructural space group for complexes containing methanol in the sixth position (L = MeOH) is highlighted. The reactivity and stability of the complexes were evaluated by rapid stopped-flow techniques, and the methanol substitution by a range of pyridine type ligands indicates significant activation by the N,O-salicylidene type of bidentate ligands as observed from the variation in the second-order rate constants. In particular, following the introduction of the sterically demanding and electron rich cyclohexyl salicylidene moiety on the bidentate ligand, novel limiting kinetic behavior is displayed by all entering ligands, thus enabling a systematic probe and manipulation of the limiting kinetic constants. Clear evidence of an interchange type of intimate mechanism for the methanol substitution is produced. The equilibrium and rate constants (25 °C) for the two steps in the dissociative interchange mechanism for methanol substitution in fac-[Re(Sal-Cy)(CO)3(MeOH)] (5) by the pyridine type ligands 3-chloropyridine, pyridine, 4-picoline, and DMAP are k3 (s(-1)), 40 ± 4, 13 ± 2, 10.4 ± 0.7, and 2.11 ± 0.09, and K2 (M(-1)), 0.13 ± 0.01, 0.21 ± 0.03, 0.26 ± 0.02, and 1.8 ± 0.1, respectively.

Fast and reversible insertion of carbon dioxide into zirconocene–alkoxide bonds. A mechanistic study

In two consecutive equilibria the compound (Cp*)2Zr(OMe)2 undergoes insertion of CO2 to form the mono- and bis-hemicarbonates. Both equilibria are exothermic but entropically disfavoured. Magnetisation transfer experiments gave kinetic data for the first equilibrium showing that the rate of insertion is overall second order with a rate constant of 3.20 ± 0.12 M(-1) s(-1), which is substantially higher than those reported for other early transition metal alkoxides, which are currently the best homogeneous catalysts for dimethyl carbonate formation from methanol and CO2. Activation parameters for the insertion reaction point to a highly ordered transition state and we interpret that as there being a substantial interaction between the CO2 and the metal during the C-O bond formation. This is supported by DFT calculations showing the lateral attack by CO2 to have the lowest energy transition state.

Crystal structure of benzoato-κO-bis(1,3,5-triaza-7-phosphaadamantane-κP)silver(I) monohydrate C19H31AgN6O3P2

Abstract C19H31AgN6O3P2, monoclinic, P21/c (no. 14), a = 16.5661(8) Å, b = 6.1644(3) Å, c = 23.8822(10) Å, β = 114.553(3)°, V = 2218.32(18) Å3, Z = 4, Rgt(F) = 0.0188, wRref(F2) = 0.0525, T = 100(2) K.

The crystal structure of tetrakis(1,3,5-triaza-7-phosphatricyclo[3.3.1.13,7]decane-κP)silver(I) chloride dihydrate, C24H60AgClN12O6P4

Abstract C24H60AgClN12O6P4, tetragonal, P42/nmc (no. 137), a = 14.1874(3) Å, c = 9.8721(3) Å, V = 1987.08(1) Å3, Z = 2, Rgt(F) = 0.0148, wRref(F2) = 0.0417, T = 100 K.

The fluoretic difference in homoleptic mononuclear and dinuclear indium species

Quinolinol derivatives have been since envisaged as promising fluorophores based on their peculiarities since the birth of Alq3 entities as the prototype complex which was discovered by Tang and Van Slyke back in 1987.[1] As a result, that has prompted growth along the science of these M(Ox)3 entities with other triels down the boron group such as gallium (Ga) and indium (In) as potential electroluminescence layer in the edifice of OLED’s devices. There have been structural discrepancies for over two decades posed by the perturbed geometrical conformation of these complexes resorting to isomerism (meridional vs. facial) which potentially significantly impacts on the luminescence properties thereof. It was mainly the aforementioned effect that shaded the trials of varying many substitutions (EDG and EWG’s) on the backbone (to increase the efficiency of this complexes) and potentially set astray the postulated light outcome (unpredictable wavelength shifts).[2] What has been very true and crucial is the ability of this quinolinol framework to give light and form very rigid inorganic complexes with various metal centers and that is directly related to their chelato-aromatic properties, stability and tuneable luminescence properties.

Rhenium reactivity – manipulation by ligand development

Drug development can be approached from numerous angles, i.e. bio-activity, receptor binding, structural analysis combining small molecules with proteins, fragment-based drug design, functionalization of model pharmaceuticals, etc. Our interest is in the coordination of biomolecules and bifunctional chelators to technetium(I) and rhenium(I) for use as diagnostic or therapeutic radiopharmaceutical agents. The synthesis of radiopharmaceuticals can be accomplished by a good understanding of the transition metal chemistry of the specific reagents involved, but the kinetic effects caused by the bound molecules on the metal centre is critical for understanding reactivity, stability and structure. This study focuses on the kinetic and crystallographic properties of the fac-[M(L,L’)(CO)3(S)] (M= Re, Tc) model radiopharmaceutical complexes utilising the {2+1} approach. The significant labilisation caused by the coordinated bidentate ligands and the isostructural behaviour of the crystallised complexes will be highlighted.

Crystal structure of bis(μ2-chlorido)-bis(di-p-tolylhydroxyphosphine-κP)-bis(di-p-tolylphosphite-κP)dipalladium(II), C56H58Cl2O4P4Pd2

Abstract C56H58Cl2O4P4Pd2, monoclinic, P21/c (no. 14), a = 12.736(2) Å, b = 18.187(2) Å, c = 12.335(2) Å, β = 109.053(4)°, V = 2700.63 Å3, Z = 2, Rgt(F) = 0.034, wRref(F2) = 0.0955, T = 100 K.

Crystal structure of hexacarbonyl bis(μ2-2-methoxybenzenethiolato-κ2S)pyridine(triphenylphosphane)dirhenium(I), C43H34NO8PS2Re2

Abstract C43H34NO8PS2Re2, monoclinic, P21/c (no. 14), a = 12.165(8) Å, b = 19.027(11) Å, c = 18.848(14) Å, β = 108.735(2)°, V = 4131(5) Å3, Z = 4, Rgt(F) = 0.0308, wRref(F2) = 0.0683, T = 100(2) K.

Crystal structure of bis(μ2-2-((3-methylphenyl)imino)methylphenolato-κ2N,O:O)hexacarbonyldimanganese(I), C34H24Mn2N2O8

Abstract C34H24Mn2N2O8, triclinic, P1̅ (no. 2) a = 7.737(5) Å, b = 9.483(5) Å, c = 11.309(5) Å, β = 102.514(5)°, V = 766.6(7) Å3, Z = 1, Rgt(F) = 0.0478, wRref(F2) = 0.1297, T = 100(2) K

Crystal structure of (E)-2-(((1,10-phenanthrolin-5-yl)imino)methyl)-5-methylphenol monohydrate, C20H15N3O·H2O

Abstract C20H15N3O·H2O, triclinic, P1̅ (No. 2), a = 7.066(3) Å, b = 9.996(4) Å, c = 12.873(5) Å, α = 86.007(14)°, β = 74.861(14)°, γ = 69.596(13)°, V = 822.4(6) Å3, Z = 2, Rgt(F) = 0.0424, wRref(F2) = 0.1241, T = 100 K.