Transition-metal derivatives of arenediazonium ions. Part VII. Fluorine-19 nuclear magnetic resonance and nitrogen-l5 infrared labelling studies on some benzene-, meta-fluorobenzene-, and para-fiuorobenzene-diazo-complexes of iron, molybdenum, platinum, and tungsten

Abstract

¹⁹ F N.m.r. spectra of fifteen different classes of m- and p-fluorobenzenediazo-complexes containing iron, molybdenum, platinum, or tungsten have been measured. The ¹⁹F n.m.r. technique is shown to be a sensitive tool for determination of the degree of M–N₂Ar π-bonding provided all complexes studied are of the same structural type. Direct evidence has been obtained for the view that the cation ArN₂⁺ is a poorer π-acceptor than NO⁺. The ν(NN) stretching frequencies of the ArN₂ complexes (Ar = Ph, m-FC₆H₄, or p-FC₆H₄) have been identified by ¹⁵N¹⁴N labelling. Many of these complexes show an unexpected multiplicity of bands associated with the N₂chromophore.