Controlling the orientation of the emissive dipole has led to a renaissance of organic light-emitting diode (OLED) research, with external quantum efficiencies (EQEs) of >30% being reported for phosphorescent emitters. These highly efficient OLEDs are generally manufactured using evaporative methods and are comprised of small-molecule heteroleptic phosphorescent iridium(III) complexes blended with a host and additional layers to balance charge injection and transport. Large area OLEDs for lighting and display applications would benefit from low-cost solution processing, provided that high EQEs could be achieved. Here, we show that poly(dendrimer)s consisting of a non-conjugated polymer backbone with iridium(III) complexes forming the cores of firstgeneration dendrimer side chains can be co-deposited with a host by solution processing to give highly efficient devices. Simple bilayer devices comprising the emissive layer and an electron transport layer gave an EQE of >20% at luminances of up to ≈300 cd/ m 2 , showing that polymer engineering can enable alignment of the emissive dipole of solution-processed phosphorescent materials.

Oxidation of cyclohexane in TFA using 30% aqueous H 2 O 2 or urea-H 2 O 2 (UHP) gives cyclohexyl trifluoroacetate in good yield, although the reaction is not accelerated by rhodium or ruthenium catalysts casting doubt on earlier claims on the role of transition-metals in oxidations in TFA.The oxidation of unactivated C-H bonds in alkanes is often regarded as one of the Holy Grails of organic chemistry. 1 Whereas in Nature such oxidations are efficiently carried out by enzymes, there exists no single general laboratory or industrial method, despite the undoubted commercial importance of such a process. Nevertheless a number of methods have been developed which do effect the oxidation of unactivated C-H bonds: these include oxidations in superacid media, 2 using peroxide type reagents (including peracids, dioxiranes and oxaziridines), 3 ozone, 4 various cytochrome P450 models, 5 and a range of metal mediated oxidations, 6 including Gif chemistry. 7 Much of the current work in this area focuses on the use of transition-metal catalysed processes, and in view of our own interest in reactions catalysed by dirhodium(II) carboxylates, 8 we were intrigued to see a Chemical Communication in which dirhodium tetraacetate was reported to catalyse the oxidation of cyclohexane by hydrogen peroxide in TFA. 9 As a prelude to investigating the role of dirhodium(II) catalysts in other oxidation reactions, we have reinvestigated this original work, and report our results herein.In their communication, Nomura and Uemura reported that a variety of rhodium salts (0.1-0.3 mol%) catalysed the oxidation of cyclohexane by 30% aqueous hydrogen peroxide in TFA. The yields of cyclohexyl trifluoroacetate were consistently 62-65% irrespective of the rhodium salt used, and the authors suggested a mechanism involving a highly reactive oxorhodium species. 9 The use of strongly acidic media is quite common in metal catalysed oxidations of hydrocarbons since (a) the conjugate base of a strong acid is a poor s-donor and therefore enhances the electrophilicity of the metal ion, and (b) the esterification of the alcohol, the primary product of alkane oxidation, protects it from further oxidation. 10 However, it appears that the authors did not carry out a blank reaction in TFA in the absence of the rhodium salt. 9 This is somewhat surprising since many years earlier Deno and Messer also reported the oxidation of cyclohexane to cyclohexyl trifluoroacetate (73% yield) under more or less identical conditions (30% aqueous H 2 O 2 in TFA) but in the absence of any metal salt. 11 Therefore our initial experiments were designed to investigate this apparent anomaly (Scheme 1). When cyclohexane (5 mmol) was treated with 30% aqueous H 2 O 2 (15 mmol) in TFA (12 ml) in the presence of dirhodium tetraacetate (1 mol%) at room temperature, oxidation to cyclohexyl trifluoroacetate did indeed occur as evidenced by gas chromatographic analysis which clearly showed disappearance of the hydrocarbon and formation of the ester over 12 h (Fig. 1). When the blank experiment ...

A range of dehydro amino acid derivatives has been prepared and subjected to halogenation using either molecular bromine or chlorine, or NBS. Allylic halogenation of the unsaturated amino acid side chains occurs through radical bromination with NBS. The procedure is complementary to treatment with chlorine, which also affords allyl halides. This latter and unusual reaction is shown through a deuterium labelling study to proceed via an ionic mechanism. The choice of NBS or chlorine for allyl halide synthesis is shown to depend on the potential to avoid competing reactions, such as halolactonization of leucine derivatives with chlorine, and hydrogen abstraction and bromine incorporation at multiple sites on treatment of isoleucine derivatives with NBS. The synthetic utility of the allyl halides prepared in this study is indicated through the synthesis of a cyclopropyl amino acid derivative and the extension of the carbon skeleton of an amino acid side chain.

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