Dalton Transactions

Haxton, Katherine J.; Cole-Hamilton, David J.; Morris, Russell E.

doi: 10.1039/b404260cpmid: 15252560

Molecular dynamics modelling has been used to simulate the structures of phopshine-functionalised, silsesquioxane-based dendrimers whose excellent catalytic properties have been previously demonstrated. The effect of changing the chemical composition of the dendrimer branches is simulated. The results indicate that adding a methylene unit to a branch increases the overall size of the dendrimer but replacing a methylene unit with an oxygen atom decreases the size of the dendrimer. The size and shape of the dendrimers have also been simulated on changing the temperature and polarity of the solvent. The distribution of phosphine groups on the exterior has also been modelled and this suggests that all are available for bonding to catalytic metals in all the compounds.

Humphrey, Simon M.; Mole, Richard A.; Rawson, Jeremy M.; Wood, Paul T.

doi: 10.1039/b401887gpmid: 15252561

The hydrothermal reaction of thiosalicylic acid, (CH(COH)(SH)-1,2) with manganese() acetate leads to formation of the coordination solid [Mn((CH(CO)(S)-1,2))(μ-OH)]()a redox reaction, where resulting manganese() centres are coordinated by oxygen donor atoms and S–S disulfide bridge formation is simultaneously observed. Reaction of the same ligand under similar conditions with zinc() chloride yields the layered coordination solid [Zn(CH(CO)(S)-1,2)](). Hydrothermal treatment of manganese() acetate with 2-mercaptonicotinic acid, (NCH(SH)(COH)-2,3) was found to produce the 1-dimensional chain structure [Mn((NCH(S)(CO)-2,3))(OH)]·4HO () which also exhibits disulfide bridge formation and oxygen-only metal interactions. Compound has been studied by thermogravimetric analysis and indicates sequential loss of lattice and coordinated water, prior to more comprehensive ligand fragmentation at elevated temperatures. The magnetic behaviour of and has been investigated and both exhibit antiferromagnetic interactions. The magnetic behaviour of has been modelled as two corner-sharing isosceles triangles whilst has been modelled as a 1-dimensional chain.

Haumann, Marco; Meijboom, Reinout; Moss, John R.; Roodt, Andreas

doi: 10.1039/b403033hpmid: 15252562

The dinuclear complex [Co(CO){P(OPh)}]() has been synthesised and was fully characterised. The solid state structure revealed a diaxial geometry, no bridging carbonyls, and Co–Co and Co–P bond lengths of 2.6722(4) and 2.1224(4)Å, respectively. Catalysed hydroformylation of 1-pentene with was attempted at temperatures in the range 120 to 210 °C and pressures between 34 and 80 bar. High pressure spectroscopy (HP-IR and HP-NMR) was used to detect hydride intermediates. High pressure infrared (HP-IR) studies revealed the formation of [HCo(CO)P(OPh)]() at . 110 °C, but at higher temperatures absorption bands corresponding to [HCo(CO)]() were observed. The hydride intermediate has also been synthesised and characterised. Upon increased ligand concentration, HP-IR studies showed the formation of new carbonyl absorption bands due to a higher substituted cobalt carbonyl complex-[HCo(CO){P(OPh)}](), which is believed to be catalytically less active. Complex has been synthesised independently and was fully characterised. A low temperature crystal structural study of revealed a trigonal bipyramidal structure with a H–Co–CO arrangement and two equatorial phosphite ligands, the Co–P bond lengths being 2.1093(8) and 2.1076(8)Å, respectively.

Ghoshal, Debajyoti; Maji, Tapas Kumar; Mostafa, Golam; Sain, Saugata; Lu, Tian-Huey; Ribas, Joan; Zangrando, Ennio; Ray Chaudhuri, Nirmalendu

doi: 10.1039/b401738bpmid: 15252563

Four succinato-bridged complexes of copper() have been synthesized. Complex , [Cu(μ-OH)L(bpy)(NO)] and , [Cu(μ-OH)L(phen)(NO)](bpy = 2,2′-bipyridine; phen = 1,10-phenanthroline and LH= succinic acid) exhibit 1D coordination polymer structures where both the nitrate ions are directly linked to the copper() producing synthons in a 2D sheet. A novel 2D grid-like network, {[CuL(bpy)(HO)](ClO)(HO)}, is obtained upon changing the nitrate by perchlorate anion in complex , where the channels are occupied by the anions. On changing the nitrate by tetrafluoroborate anion in complex , a novel octanuclear complex, [CuL(phen)](BF)·8HO , is isolated. The coligand bpy and phen in these complexes show face-to-face (in ) or edge-to-face (in )π–π interactions forming the multidimensional supramolecular architectures. Interestingly, the appearance of edge-to-face π–π interactions in complex facilitates the formation of discrete octanuclear entities. Variable-temperature (300–2 K) magnetic measurements of complexes have been done. Complexes and show very weak antiferromagnetic (OOC–CH–CH–COO) and ferromagnetic coupling (μ-HO). Complex also shows antiferromagnetic (μ-OCO), and ferromagnetic coupling (μ-O of the -COO group). Complex with two types ( and ) of binding modes of the carboxylate group shows strong antiferromagnetic interaction.

Batinić-Haberle, Ines; Spasojević, Ivan; Stevens, Robert D.; Hambright, Peter; Neta, Pedatsur; Okado-Matsumoto, Ayako; Fridovich, Irwin

doi: 10.1039/b400818apmid: 15252564

Three new Mn() porphyrin catalysts of O˙ dismutation (superoxide dismutase mimics), bearing ether oxygen atoms within their side chains, were synthesized and characterized: Mn() 5,10,15,20-tetrakis[-(2-methoxyethyl)pyridinium-2-yl]porphyrin (MnTMOE-2-PyP), Mn()5,10,15,20-tetrakis[-methyl-′-(2-methoxyethyl)imidazolium-2-yl]porphyrin (MnTM,MOE-2-ImP) and Mn() 5,10,15,20-tetrakis[,′-di(2-methoxyethyl)imidazolium-2-yl]porphyrin (MnTDMOE-2-ImP). Their catalytic rate constants for O˙ dismutation( disproportionation) and the related metal-centered redox potentials . NHE are: log = 8.04 (=+251 mV) for MnTMOE-2-PyP, log = 7.98 (=+356 mV) for MnTM,MOE-2-ImP and log = 7.59 (=+365 mV) for MnTDMOE-2-ImP. The new porphyrins were compared to the previously described SOD mimics Mn() 5,10,15,20-tetrakis(-ethylpyridinium-2-yl)porphyrin (MnTE-2-PyP), Mn() 5,10,15,20-tetrakis(--butylpyridinium-2-yl)porphyrin (MnTnBu-2-PyP) and Mn() 5,10,15,20-tetrakis(,′-diethylimidazolium-2-yl)porphyrin (MnTDE-2-ImP). MnTMOE-2-PyP has side chains of the same length and the same , as MnTnBu-2-PyP(= 7.25, =+ 254 mV), yet it is 6-fold more potent a catalyst of O˙ dismutation, presumably due to the presence of the ether oxygen. The log . relationship for all Mn porphyrin-based SOD mimics thus far studied is discussed. None of the new compounds were toxic to in the concentration range studied (up to 30 μM), and protected SOD-deficient in a concentration-dependent manner. At 3 μM levels, the MnTDMOE-2-ImP, bearing an oxygen atom within each of the eight side chains, was the most effective and offered much higher protection than MnTE-2-PyP, while MnTDE-2-ImP was of very low efficacy.

Inamo, Masahiko; Kumagai, Hideto; Harada, Ushio; Itoh, Sumitaka; Iwatsuki, Satoshi; Ishihara, Koji; Takagi, Hideo D.

doi: 10.1039/b403760jpmid: 15252565

Homogeneous electron transfer reactions of the Cu() complexes of 5,10,15,20-tetraphenylporphyrin (TPP) and 2,3,7,8,12,13,17,18-octaethylporphyrin (OEP) with various oxidizing reagents were spectrophotometrically investigated in acetonitrile. The reaction products were confirmed to be the π-cation radicals of the corresponding Cu()-porphyrin complexes on the basis of the electronic spectra and the redox potentials of the complexes. The rate of the electron transfer reaction between the Cu()-porphyrin complex and solvated Cu was determined as a function of the water concentration under the pseudo first-order conditions where Cu is in large excess over the Cu()-porphyrin complex. The decrease in the pseudo first-order rate constant with increasing the water concentration was attributed to the stepwise displacement of acetonitrile in [Cu(AN)](AN = acetonitrile) by water, and it was concluded that only the Cu species fully solvated by acetonitrile, [Cu(AN)], possesses sufficiently high redox potential for the oxidation of Cu()-OEP and Cu()-TPP. The reactions of the Cu()-porphyrin complexes with other oxidizing reagents such as [Ni(tacn)](tacn = 1,4,7-triazacyclononane) and [Ru(bpy)](bpy = 2,2′-bipyridine) were too fast to be followed by a conventional stopped-flow technique. Marcus cross relation for the outer-sphere electron transfer reaction was used to estimate the rate constants of the electron self-exchange reaction between Cu()-porphyrin and its π-cation radical: log(/M s)= 9.5 ± 0.5 for TPP and log(/M s)= 11.1 ± 0.5 for OEP at 25.0 °C. Such large electron self-exchange rate constants are typical for the porphyrin-centered redox reactions for which very small inner- and outer-sphere reorganization energies are required.

Anderberg, Pia I.; Turner, Jennifer J.; Evans, Krystal J.; Hutchins, Lauren M.; Harding, Margaret M.

doi: 10.1039/b404054fpmid: 15252566

The synthesis of racemic and optically pure ligand , in which two 6,6′-disubstituted bipyridines are connected by methyleneoxy linkers to the molecular cleft dibenzobicyclo[,][3.3.1]nona-5a,6a-diene-6,12-dione, is reported. In the presence of 2 equivalents of zinc() trifluoromethansulfonate (±)- undergoes slow reversible coordination over 24 h to form a pair of enantiomeric [2 + 2] metallomacrocycles, [Zn(+)](OTf) and [Zn(−)](OTf) respectively, that contain either two (+)- ligands or two (−)- ligands. This assignment was confirmed by independent studies with either (+)- or (−)- which formed the same complexes but at a significantly faster rate (3 h), and circular dichroism spectra of [Zn(+)](OTf) and [Zn(−)](OTf) which gave signals of the same intensity with the opposite sign. Treatment of (±)- or optically pure with copper() showed rapid formation of a mixture of oligomers as well as the [2 + 2] metallomacrocycle. The complex Zn(OTf) exhibits slow exchange between two species on the NMR time scale at room temperature. The results are consistent with the formation of a library of metal complexes in which the zinc() binds initially to the most accessible bipyridyl binding sites in (±)-. Equilibration over several hours results in self-recognition of enantiomeric ligands to form a pair of enantiomeric metallomacrocycles, which have been tentatively assigned as having the helical configuration. Slow exchange is attributed to the preference for both metal centres to adopt 6-coordinate geometries involving the linker oxygens, but are limited to exchanging 5-coordinate complexes due to the shape of the cleft and the short linker.

Belova, Natalya V.; Girichev, Georgiy V.; Hinchley, Sarah L.; Kuzmina, Natalya P.; Rankin, David W. H.; Zaitzeva, Irina G.

doi: 10.1039/b401360cpmid: 15252567

Combined gas electron diffraction/mass spectrometry (GED/MS) was used to determine the molecular structure of tris(dipivaloylmethanato)lutetium(), Lu(dpm)(dpm = 2,2,6,6-tetramethyl-heptane-3,5-dionato). Up to about 520–570 K the vapour consisted only of molecules Lu(dpm). The experimental data recorded at 408(5) K indicate that the molecules have symmetry. The bond distances () in the chelate ring are Lu–O 2.197(6)Å, C–O 1.270(4)Å and C–C 1.390(6)Å. Theoretical computations at the HF and DFT levels with basis sets up to 6-311G* afford structures similar to those found experimentally, with a distorted LuO antiprism.

Greatrex, Robert; Workman, Christopher; Johnston, Blair F.; Rankin, David W. H.; Robertson, Heather E.

doi: 10.1039/b402688hpmid: 15252568

The molecular structures of 1-bromo–pentaborane(9) and 2-bromo–pentaborane(9) in the gas phase have been determined by electron diffraction and and DFT computational methods. Computational methods have also been applied to the fluoro and chloro analogues, to 1,2-dibromo-pentaborane(9), and to the parent unsubstituted borane. The electronic effects of halogen substitution on the borane cage are remarkably small, particularly for chlorine and bromine substituents, and steric effects are also minimal, even in the compound with two bromine atoms. The largest effects are (a) lengthening of B–B bonds adjacent to the halogen in the 2-isomers, with an associated shortening of the opposite base–apex bond, (b) shortening of the B–B bond in the 1-fluoro compound, and (c) increase of the B–B–F angle in 1-F–BH, but a decrease in this angle in the 2-bromo compounds.

Chowdhury, Somenath; Schatte, Gabriele; Kraatz, Heinz-Bernhard

doi: 10.1039/b401039fpmid: 15252569

Redox active cyclopeptides Fc[CSA](), Fc[Gly–CSA](), Fc[Ala–CSA](), Fc[Val–CSA]() and Fc[Leu–CSA]()(CSA = cysteamine) which are formed by the reaction of ferrocenedicarboxylic acid with peptide cystamines at high dilutions. These systems exhibit H-bonding involving the amide NH in solution as shown by their temperature dependent NMR spectra. With the exception of , the ferrocene macrocycles display intramolecular N⋯O cross-ring H-bonding in the solid state involving the amino acids proximal to the ferrocene.