Comparison of electrospray mass spectrometry with other soft ionization techniques for the characterisation of cationic π-hydrocarbon organometallic complexes

Abstract

Electrospray (ES) mass spectrometry provides a convenient method for the characterisation of a wide range of π-hydrocarbon complex salts of the general types [FeCp(η-arene)]BF 4, [M(CO) 3(η-C 7H 7)BF 4 (MCr, Mo, W), [Fe(CO) 2L ( η 5-dienyl)]BF 4 L  CO or PPh 3; dienyl  C 6H 7, 2-MeOC 6H 6, or C 7H 9), [CpFe(CO) 3] PF 6 and [CpFe(CO) 2( η-C 2H 4)]BF 4. At low skimmer voltages (20 V), principal (molecular) ions are generally the only observed species. For the arene complexes, [FeCp( η-arene)]BF 4, high skimmer voltages (80–135 V) are required before fragmentation is observed. However, for the carbonyl containing cations, moderate skimmer voltages (40–55 V) also give rise to [MCO] +,[M2CO] + and [M3CO] + ions. Very similar behaviour is observed with phosphonium and imidazolium adducts of the type [Fe(CO) 3(η 4-diene. Nuc)] + ( diene  C 6 H 7 or C 7H 9; Nuc PPh 3 or Im) and [CpFe(CO) 2( η 1-C 2H 4·PPh 3)] +. comparison with fast atom bombardment (FAB) and field desorption (FD) mass spectra for the same complex salts indicates that fragmentation decreases along the series FAB > ES > FD, and that ES mass spectrometry is the most convenient and informative of the three soft ionization techniques.