New free-radical halogenations of alkanes, catalysed by N-hydroxyphthalimide. Polar and enthalpic effects on the chemo- and regioselectivity

Reactions of alkanes with different halogenating systems are compared in order to explore the reactivity of phthalimido-N-oxyl radical in hydrogen abstraction; the importance of polar effects is emphasised.     

A tert-butyl/cyano substituted (1,2,3,5-dithiadiazolyl)benzene and η π complexes with CpCr(CO)2

A rational synthesis for 5-tert-butyl-3-cyano-1-(1,2,3,5-dithiadiazolyl)benzene, which was first observed from thermal cleavage of the bis-dithiadiazolyl, has been developed. Voltammetry and electron paramagnetic resonance (EPR) spectra for this radical are reported and its X-ray structure is described. Despite the bulky ^tBu substituent, the cyano supramolecular synthon is still able to maintain links to a single neighbouring sulfur atom of the S₂ unit, as previously observed in cyano-substituted dithiadiazolyls. In the η² complex with CpCr(CO)₂, no such interactions are observed; the nitrile group forms a centrosymmetric dimer through weak contacts with the para H atom on the aryl ring of the partner molecule. This behaviour is contrasted to similar complexes of less bulky dithiadiazolyls, where intermolecular interactions are retained in the crystalline lattice.