COMPARISON OF LASER-DESORPTION AND FAST-ATOM-BOMBARDMENT MASS-SPECTRA OF A SERIES OF RH(PPH3)2(CO)Y COMPLEXES

The mass spectra of a series of involatile Rh(PPh3)2(CO)Y complexes (anion Y− is F−, Cl−, I−, −NCO−, −NCS−, O2CCH3−, ONO2−, O2PF2−, or OSO2CF3−; Rh(PPh3)2(CO) is shortened to RhL2(CO) hereafter) were obtained by using both laser-desorption Fourier-transform ion cyclotron resonance (LDFTICR) and fast-atom-bombardment (FAB) techniques. The FAB positive-ion spectra (sulfolane matrix) showed molecular ions for all complexes except RhL2(CO)OSO2CF3, the species containing the most weakly coordinating anion. These FAB spectra also exhibited fragment ions resulting from loss of CO and PPh3. The sulfolane adduct of RhL2(CO)+ and a derivative were also observed for the series, especially prominent in spectra of complexes of the less tightly bound anions. The LDFTICR positive-ion spectra were less consistent in fragmentation/rearrangement patterns over the range of anions Y− than were their FAB counterparts; peak intensities of the former spectra were also highly variable due to difficulties in preparing consistent probe samples. Although the [M + K]+ pseudomolecular ion was detected for every complex except RhL2(CO)OSO2CF3, only several molecular ions were observed in the series; otherwise, fragmentation patterns similar to those of the FAB experiments were seen. No molecular ions were seen for any RhL2(CO)Y in the LDFTICR negative-ion spectra; however, Rh(CO)Y−, Rh(PPh3)(CO)Y−, and Rh2(CO)2Y2− were characteristically observed, with peak intensities again quite variable. Several tetrarhodium species, Rh4(CO)xY2− (x = 2−4), were detected as well. © 1990, American Chemical Society. All rights reserved.