Ion-molecule reaction chemistry of ionic transition-metal carbonyl cluster fragments. I, Ligand-exchange reactions of Cr2(CO)y+ ions

The ligand-exchange ion-molecule reaction chemistry of Cr2(CO),+ ionic transition metal cluster fragments has been investigated by using a two-section ion cell Fourier transform ion cyclotron resonance mass spectrometer. Simple ligand-exchange reactions involving ligand (L) addition followed by metal-ligand (M- - -CO) bond cleavage (Le., an associative ligand-exchange mechanism) as well as ligand exchange involving metal-metal cleavage (Le., addition of L to Cr2(CO),+ followed by metal-metal bond cleavage) are observed. The branching ratios for reactions involving metal-metal bond cleavage increase as the metal-to-ligand ratio decreases. In addition, the ratio for simple ligand exchange to metal-metal bond cleavage is strongly dependent upon the nature of the reacting ligand (L). These data combined with collision-induced dissociation data for Cr2(CO),+ ionic cluster fragments suggest that the Cr-Cr bond strength decreases as y is increased; Le., the Cr---Cr bond order is strongly dependent upon the ligand environment.