Ligand Tuning in Pyridine-Alkoxide Ligated Cp*Ir III Oxidation Catalysts

Six novel derivatives of pyridine-alkoxide ligated Cp*IrIII complexes, potent precursors for homogeneous water and C–H oxidation catalysts, have been synthesized, characterized, and analyzed spectroscopically and kinetically for ligand effects. Variation of alkoxide and pyridine substituents was found to affect their solution speciation, activation behavior, and oxidation kinetics. Application of these precursors to catalytic C–H oxidation of ethyl benzenesulfonate with aqueous sodium periodate showed that the ligand substitution pattern, solution pH, and solvent all have pronounced influences on initial rates and final conversion values. Correlation with O2 evolution profiles during C–H oxidation catalysis showed these competing reactions to occur sequentially, and demonstrates how it is possible to tune the activity and selectivity of the active species through the N^O ligand structure

Subphthalocyanine-Stoppered [2]Rotaxanes:Synthesis and Size/Energy Threshold of Slippage

Subphthalocyanine (SubPc)-stoppered [2]rotaxanes were synthesized for the first time. The rotaxane bearing unsubstituted SubPc as a stopper exhibited an equilibrium of slipping-on and slipping-off, whereas a perfluorinated SubPc stopper completely blocked slippage of the ring due to its slightly larger size. Kinetic studies revealed the Gibbs free energy of activation for the slipping-on and slipping-off processes. The optical properties of the rotaxanes, including photoinduced electron transfer, were also revealed.</p

New di-n-butyltin(iv)-bis-(1-alkoxy-isoquinoline-4-nitrile thiolate):crystallographic and computational studies

The reaction between di-n-butyltin(iv) chloride with the dinegative dithiolate ligand 2-(cyanobenzo)nitrile-dithiolate in two different alcoholic media viz. methyl alcohol and ethyl alcohol fortuitously yielded di-n-butyltin(iv)-bis-(1-methoxy-isoquinoline-4-nitrile thiolate) (Sn-Me) and di-n-butyltin(iv)-bis-(1-ethoxy-isoquinoline-4-nitrile thiolate) (Sn-Et). Similarly the reaction of di-n-butyltin(iv) chloride with 2-methoxy phenyl acetonitrile dithiolate yielded di-n-butyltin(iv)-2-methoxy phenyl acetonitrile dithiolate (2-MeCN-Sn). These compounds have been characterized by micro analyses, IR, UV-vis, 1H, 13C and 119Sn NMR spectroscopy as well as by single crystal X-ray diffraction technique in case of Sn-Et, Sn-Me. The X-ray analyses revealed that in both Sn-Me and Sn-Et, the Sn(iv) center adopts a skew trapezoidal bipyramidal geometry with Sn at the centre and two sulfur and two ring nitrogen atoms of 1-alkoxy-isoquinoline-4-nitrile thiolates are at the corners of a trapezoid with two n-butyl groups adopting axial positions resembling the cis-trans pathway. Both Sn-Me and Sn-Et display varied types of non-covalent interactions. The nature of these interactions has been addressed with the aid of Hirshfeld surface analysis, density functional theory and quantum theory of atoms-in-molecules (QTAIM) analyses.</p

Ligand Tuning in Pyridine-Alkoxide Ligated Cp*Ir III Oxidation Catalysts

Six novel derivatives of pyridine-alkoxide ligated Cp*IrIII complexes, potent precursors for homogeneous water and C–H oxidation catalysts, have been synthesized, characterized, and analyzed spectroscopically and kinetically for ligand effects. Variation of alkoxide and pyridine substituents was found to affect their solution speciation, activation behavior, and oxidation kinetics. Application of these precursors to catalytic C–H oxidation of ethyl benzenesulfonate with aqueous sodium periodate showed that the ligand substitution pattern, solution pH, and solvent all have pronounced influences on initial rates and final conversion values. Correlation with O2 evolution profiles during C–H oxidation catalysis showed these competing reactions to occur sequentially, and demonstrates how it is possible to tune the activity and selectivity of the active species through the N^O ligand structure

C4-aldehyde of guaiazulene:synthesis and derivatisation

Guaiazulene is an alkyl-substituted azulene available from natural sources and is a much lower cost starting material for the synthesis of azulene derivatives than azulene itself. Here we report an approach for the selective functionalisation of guaiazulene which takes advantage of the acidity of the protons on the guaiazulene C4 methyl group. The aldehyde produced by this approach constitutes a building block for the construction of azulenes substituted on the seven-membered ring. Derivatives of this aldehyde synthesised by alkenylation, reduction and condensation are reported, and the halochromic properties of a subset of these derivatives have been studied.</p

Persistent azulene α-carbocations:synthesis from aldehydes, spectroscopic and crystallographic properties

The non-benzenoid aromatic system azulene is sufficiently nucleophilic at C1 that it can react with a protonated aldehyde to form an α-azulenyl alcohol. This in turn may be protonated and undergo loss of water to give an azulene α-carbocation. We report the isolation of such azulenyl cations as salts with non-coordinating anions. The salts have been characterised by NMR, UV/Vis absorption and (in certain cases) X-ray crystallography. Reduction of representative salts to afford azulenyl(aryl) methylenes has been demonstrated.</p

Sulfido-bridged 1,2-bis(diphenylphosphino)ethane (dppe) appended trinuclear nickel(II) clusters:Crystallographic and computational analyses

The cluster compounds are still gaining considerable attention due to their peculiar behaviour and M−M bonding or M···M interactions. In this report, two sufido-bridged, 1,2-bis-(diphenylphosphino)ethane (dppe) appended trinuclear Ni(II) clusters having formula [Ni3S2(dppe)3].2BPh4 (Ni3S2-1) and [Ni3S2(dppe)2(4-pyCH2OH)2].2PF6 (Ni3S2-2) are reported. These clusters are synthesized from the same starting reactants the xanthate ligand 4-PyCH2OCS2Na, Ni(II) and dppe employing two different reaction pathways. The obtained compounds have been characterized by microanalyses, FTIR, UV–Vis, 1H, 13C and 31P NMR spectroscopy as well as by single crystal X-ray diffraction technique. The X-ray analyses revealed that in both compounds three Ni(II) centers are coordinated to two sulfido and dppe ligands. In Ni3S2-1 three dppe and two sulfido ligands are stabilising the trinuclar cluster cation while in Ni3S2-2 along with two sulfido and two dppe ligands, two 4-pyCH2OH are also coordinating with one of the Ni(II) center. Both Ni3S2-1 and Ni3S2-2 display different non-covalent interactions along with the Ni···Ni interactions. The nature of these interactions has been addressed with the aid of Hirshfeld surface analysis, density functional theory and quantum theory of atoms-in-molecules (QTAIM) analyses. The occurrence of such non-covalent intermolecular interactions is also well supported by the non-covalent interactions reduced density gradient (NCI-RDG) approaches. Also, the Wiberg bond index, Mayer bond order and delocalization indices have been calculated to assess the nature of Ni···Ni interactions.</p

Sulfido-bridged 1,2-bis(diphenylphosphino)ethane (dppe) appended trinuclear nickel(II) clusters:Crystallographic and computational analyses

The cluster compounds are still gaining considerable attention due to their peculiar behaviour and M−M bonding or M···M interactions. In this report, two sufido-bridged, 1,2-bis-(diphenylphosphino)ethane (dppe) appended trinuclear Ni(II) clusters having formula [Ni3S2(dppe)3].2BPh4 (Ni3S2-1) and [Ni3S2(dppe)2(4-pyCH2OH)2].2PF6 (Ni3S2-2) are reported. These clusters are synthesized from the same starting reactants the xanthate ligand 4-PyCH2OCS2Na, Ni(II) and dppe employing two different reaction pathways. The obtained compounds have been characterized by microanalyses, FTIR, UV–Vis, 1H, 13C and 31P NMR spectroscopy as well as by single crystal X-ray diffraction technique. The X-ray analyses revealed that in both compounds three Ni(II) centers are coordinated to two sulfido and dppe ligands. In Ni3S2-1 three dppe and two sulfido ligands are stabilising the trinuclar cluster cation while in Ni3S2-2 along with two sulfido and two dppe ligands, two 4-pyCH2OH are also coordinating with one of the Ni(II) center. Both Ni3S2-1 and Ni3S2-2 display different non-covalent interactions along with the Ni···Ni interactions. The nature of these interactions has been addressed with the aid of Hirshfeld surface analysis, density functional theory and quantum theory of atoms-in-molecules (QTAIM) analyses. The occurrence of such non-covalent intermolecular interactions is also well supported by the non-covalent interactions reduced density gradient (NCI-RDG) approaches. Also, the Wiberg bond index, Mayer bond order and delocalization indices have been calculated to assess the nature of Ni···Ni interactions.</p

Persistent azulene α-carbocations:synthesis from aldehydes, spectroscopic and crystallographic properties

The non-benzenoid aromatic system azulene is sufficiently nucleophilic at C1 that it can react with a protonated aldehyde to form an α-azulenyl alcohol. This in turn may be protonated and undergo loss of water to give an azulene α-carbocation. We report the isolation of such azulenyl cations as salts with non-coordinating anions. The salts have been characterised by NMR, UV/Vis absorption and (in certain cases) X-ray crystallography. Reduction of representative salts to afford azulenyl(aryl) methylenes has been demonstrated.</p

Novel rhenium(V) nitride complexes with dithiocarbimate ligands: A synchrotron X-ray and DFT structural investigation

The application of rhenium complexes as therapeutic agents in nuclear medicine has propelled research into the chemistry of these compounds. In our effort to develop and investigate new therapeutic radiopharmaceuticals based on the complexes of rhenium we have investigated the nitride core, [ReN]2+. This work looks at the behavior of sulfonamide based dithiocarbimates towards the rhenium(V) nitride core. The aim here was to prepare anionic complexes with aromatic as well as fluorescent aromatic groups in the sulfonamide substituent located on the dithiocarbimate backbone. We envisaged that the polar sulfonamide and dianionic charge would confer solubility in water. Here we report the reactions of the dithiocarbimate ligands towards the rhenium(V) precursors: [ReNCl2(PPh3)2] and [ReNCl2(PMe2Ph)3]. These reactions proceeded with bis-substitution by the dithiocarbimate ligand, resulting in the formation of a dianionic rhenium(V) complex, of the type [ReN(S-S)2]2-, where (S-S) denotes the sulfonamide-tagged dithiocarbimato unit. Spectroscopic characterization data, as well as the synchrotron X-ray diffraction structure of the metal complex with the phenyl sulfonamide backbone shed light into the structural features of this interesting class of ligands and opens up opportunities for further studies in molecular imaging and therapeutic arenas.</p