Electrospray mass spectrometry of neutral ¿-hydrocarbon organometallic complexes

Electrospray mass spectrometry (ESMS) provides a convenient new technique for the characterisation of neutral [(Π-hydrocarbon) M(CO)3] species and related eneone and eneimine complexes which have protonatable sites on their hydrocarbon ligands. At low skimmer voltages (20 V) strong [M + H]+ ions are generally observed, even for adducts known to be relatively labile. Progressively higher skimmer voltages cause fragmentation of the parent ions, including sequential loss of the CO ligands. Ferrocene derivatives with protonatable substituents behave similarly. However, ferrocene and [Cp Fe(C5H4Ph)] instead exhibit [M]·+ base peaks in their ESMS, presumably arising from oxidation to the associated ferricenium cations in the ion source. In contrast, ESMS is not generally useful as a technique for characterising neutral binary metal carbonyls and clusters, except for complexes such as [Fe(CO)5 - x(PPh3)x] (x = 1, 2) containing ligands which provide a site for protonation.