David G. Humphrey

Fourier-transform infrared study of short-lived highly reduced dithiolene complexes by potential-modulation spectroelectrochemical techniques

The reduction of [M(mnt)3]3–(M = V, Mo or Re; mnt = maleonitriledithiolate) has been examined by potential-modulation spectroelectrochemical techniques. Despite the highly reducing potentials required to effect the reductions (–1.57 to –2 V) and the highly unstable character of the reduction products the values of ν(CN) have been obtained for [M(mnt)3]4–(M = V, Re or Mo)(2164, 2133 and 2134 cm–1 respectively). The sensitivity of the ν(CN) values to the identity of the metal for [M(mnt)3]4– is greater than that found for the corresponding trianions suggesting an increased metal contribution to the frontier orbitals. The application of potential-modulation techniques to the examination of bulk solution species is described and shown to offer significant advantages for highly reactive electrochemically generated species.

Comparison of the reactivity of [2.2]paracyclophane and p-xylene

The relative abilities of [2.2]paracyclophane (C16H16) and p-xylene (C6H4Me2-1,4) to form arene tricarbonyl complexes from chromium hexacarbonyl has been studied in dioxane using the Strohmeier reflux method, and the rate constants contrasted. The reactions are found to proceed more quickly with [2.2]paracyclophane by ca. 25%. Density functional molecular-orbital calculations have rationalised this observation, and indicate that the enhanced reactivity of the [2.2]paracyclophane system relative to p-xylene is a consequence of repulsive interactions between the two arene decks in the former, which are relieved to some extent by co-ordination of the electron-withdrawing Cr(CO)3 fragment.

Direct Visualization of Au Atoms Bound to TiO2(110) O-Vacancies

Au nanoparticles supported on reducible metal oxide surfaces are known to be active catalysts for a number of reactions including CO oxidation and hydrogen production. The exact choice of a metal oxide support has been shown to have a marked impact on activity, suggesting that interactions between Au and the support play a key role in catalysis. For TiO2, a model substrate for Au catalysis, it had been thought that bridging oxygen vacancies are involved in binding Au atoms to the (110) surface based on indirect evidence. However, a recent scanning transmission electron microscopy study of single Pt atoms on TiO2(110) suggests that subsurface vacancies are more important. To clarify the role of bridging or subsurface vacancies we employ scanning tunneling microscopy to determine the bonding site of single Au atoms on TiO2(110). Using in situ deposition as well as a manipulation method, we provide definitive evidence that the bonding site is atop surface oxygen vacancies.

The use of spectroelectrochemistry to probe the redox-activated ligand-exchange reactions of the complexes trans-[NBu4][RuX4(CNXyl)2] (X = Cl or Br, Xyl = 2,6-dimethylphenyl)

The previously unreported complexes trans-[NBu4][RuX4(CNXyl)2] (X = Cl or Br, Xyl = 2,6-dimethylphenyl) have been prepared by treating [NBu4]2[RuX6] with the isocyanide ligand CNXyl in dichloromethane–ethanol and characterised by IR and UV-Vis spectroscopy, fast-atom-bombardment mass spectrometry, and elemental analysis (C, H, N and X). Their solution redox chemistry has been investigated using electrochemical and in situ spectroelectrochemical techniques. At low temperatures each complex undergoes a one-electron reduction to trans-[RuX4(CNXyl)2]2− (X = Cl or Br). At ambient temperature the same complexes undergo reduction in the presence of acetonitrile to afford mer,trans-[RuX3(CNXyl)2(NCMe)]−, which can be oxidised reversibly to mer,trans-[RuX3(CNXyl)2(NCMe)] (X = Cl or Br). Simulation of the cyclic voltammograms of [NBu4][RuX4(CNR)2] (X = Cl or Br, R = Xyl or But) in acetonitrile has enabled the rate constants for the formation of mer,trans-[RuX3(CNR)2(NCMe)]− to be evaluated. The rate constants were found to vary in the order X = Cl, R = Xyl < X = Br, R = Xyl < X = Cl, R = But < X = Br, R = But. The oxidation of trans-[RuX4(CNXyl)2]− (X = Cl or Br) in acetonitrile is accompanied by the reductive elimination of X˙. The number of product(s) formed is dependent upon the identity of the halide. For X = Cl oxidation ultimately leads to the formation of several species, which include mer,trans-[RuCl3(CNXyl)2(NCMe)] and trans,trans,trans-[RuCl2(CNXyl)2(NCMe)2]+, whereas for X = Br oxidation only produces mer,trans-[RuBr3(CNXyl)2(NCMe)]. All of the redox products have been characterised in situ by IR and UV-Vis spectroscopy in as many oxidation states as possible.