Polynuclear alkoxy-zinc complexes of bowl-shaped macrocycles and their use in the copolymerisation of cyclohexene oxide and CO2
James R. Pankhurst, Shyeni Paul, Yunqing Zhu, Charlotte K. Williams, Jason B. Love
The reactions between alcohols and the tetranuclear ethyl-Zn complexes of an ortho-phenylene-bridged polypyrrole macrocycle, Zn4Et4(L3) 1 and the related anthracenyl-bridged macrocyclic complex, Zn4Et4(THF)4(L4) 2 have been studied. With long-chain alcohols such as n-hexanol, the clean formation of the tetranuclear hexoxide complex Zn4(OC6H13)4(L3) 3 occurs. In contrast, the use of shorter-chain alcohols such as i-propanol results in the trinuclear complex Zn3(μ2-OiPr)2(μ3-OiPr)(HL3) 4 that arises from demetalation; this complex was characterised by X-ray crystallography. The clean formation of these polynuclear zinc clusters allowed a study of their use as catalysts in the ring-opening copolymerisation (ROCOP) reaction between cyclohexene oxide and CO2. In-situ reactions involving the pre-catalyst 1 and n-hexanol formed the desired polymer with the best selectivity for polycarbonate (90 %) at 30 atm CO2, whilst the activity and performance of pre-catalyst 2 was poor in comparison.
Elena Höppener has joined the group as a research intern for 5 months. She graduated with a bachelors degree in chemistry at Utrecht University in the Netherlands and is currently enrolled in the Masters program Nanomaterials Science at Utrecht University working with Prof. Bert Klein Gebbink. She will be working on the synthesis and characterization of new dipyrrin Pacman complexes and their properties in redox chemistry.
Controlled Photocatalytic Hydrocarbon Oxidation by Uranyl Complexes
Polly Arnold, Jamie Purkis, Ryte Rutkauskaite, Daniel Kovacs, Jason Love, Jonathan Austin
Controlled, photocatalytic C−H bond activations are key reactions in the toolkits of the modern synthetic chemist. While it is known that the uranyl(VI) ion, [UVIO2]2+, the environmentally dominant form of uranium, is photoactive, most literature examines its luminescent properties, neglecting its potential synthetic utility for photocatalytic C−H bond cleavage. Here, we synthesise and fully characterise an air‐stable and hydrocarbon‐soluble uranyl phenanthroline complex, [UVIO2(NO3)2(Ph2phen)], UPh2phen, and demonstrate that it can catalytically abstract hydrogen atoms from a variety of organic substrates under visible light irradiation. We show that the commercially available parent complex, uranyl nitrate ([UVIO2(NO3)2(OH2)2]⋅4H2O; UNO3), is also competent, but from electronic spectroscopy we attribute the higher rates and selectivity of UPh2phen to ligand‐mediated electronic effects. Ketones are selectively formed over other oxygenated products (alcohols, etc.), and the catalytic oxidation of substrates containing a benzylic C−H position is particularly improved for UPh2phen. We also show uranyl‐mediated photocatalytic C−C bond cleavage in a model lignin compound for the first time.
Jason is currently enjoying being a guest Professor at the University of Osaka, Japan. He is being hosted by Prof. Konno and his staff Dr’s Yoshinari, Kuramura, and Kojima. He recently took part in the 2nd International Symposium on Coordination Ionic Compounds along with others from Taiwan, Singapore, Korea, Japan, and the UK (Malcolm Halcrow and Michaela Hardie from the University of Leeds).
Geoff Cloke at 65: a pioneer in organometallic chemistry
Professor Geoff Cloke FRS celebrates his 65th birthday in 2018. In a career spanning four decades, his research endeavours have accounted for some of the most innovative synthetic chemistry of the modern era, with his many publications describing truly exceptional compounds and experimental methods that portray a unique chemical imagination. In addition to his scientific accomplishments, Cloke can be particularly proud of his successful mentoring, a level of dedication that propelled many students and post-docs on to become research leaders in their own right. In compiling this collection of some of his research articles, a small cross-section of his friends, colleagues and collaborators, wish to pay tribute to his modesty, compassion and generous personality.
Radical Relatives: Facile Oxidation of Hetero-Diarylmethene Anions to Neutral Radicals
Inorg. Chem., 2018
Massimiliano Curcio, Daniel Henschel, Mareike Hüttenschmidt, Stephen Sproules, Jason B. Love
ABSTRACT. Furan and thiophene diarylmethenes are potential redox-active ligands for metal centers that could be exploited in the development of non-traditional, stoichiometric, and catalytic redox reactions. As such, we describe here the selective meso-deprotonations of the dithiophene, difuran, and diimine-difuran diarylmethanes to form the p-conjugated anions, for which only the diimino-difuryl anion is truly isolable and studied by X-ray crystallography. In all cases, facile one-electron oxidation of these anions occurs which allows the isolation of the neutral dithienyl and diimino-difuryl radicals. UV-visible and TD-DFT studies reveal that the oxidation of the dithienyl anion to its radical is associated with an increase in the H(S)OMO-LUMO gap, evident through a hypsochromic shift of the main absorption band in the electronic spectrum, whereas oxidation of the diimino-difuryl anion causes only minor spectroscopic changes. Electrochemical studies support the stability of the radicals with respect to the anion, showing strongly negative oxidation potentials. The control of the redox activity of these diarylmethene carbanions through variation of the nature of the substituents, donor-atom, and the conjugated p-system and their potential as ligands for redox-inert metal centers makes them intriguing candidates as non-innocent partners for redox reactions.