Adduct ion formation by metal complexes under methane negative chemical ionization conditions

Negative chemical ionization mass spectrometry is used as a probe to examine reactions between hydrocarbon radicals and metal complexes in the gas phase. The methane negative chemical ionization mass spectra of 27 complexes of cobalt( II ), nickel( II ) and copper( II ) in the presence of O 4 , O 2 N 2 and N 4 donor atom sets are characterized by two dominant series of adduct ions of the form [M + C n H 2 n ] − and [M + C n H 2 n +1 ] − at m / z values above the molecular ion, [M] − . Insertion of the CH radical into the ligand followed by radical/radical recombination and electron capture is proposed as the major mechanism leading to the formation of [M + C n H 2 n ] − adduct ions. A second pathway involves ligand substitution by C n H 2 n +1 radicals concomitant with H elimination and electron capture. Oxidative addition at the metal followed by ionization is suggested as the principal pathway for the formation of [M + C n H 2 n +1 ] − adduct ions.