Heteronuclear Transition-Metal Cluster Ions in the Gas Phase. Photodissociation and Reactivity of VFe⁺

The transition-metal cluster ion VFe⁺ was synthesized in the gas phase by reaction of V⁺ with Fe(CO)₅, followed by appropriate collisional activation pulses. Photodissociation of VFe⁺ to generate V⁺ exclusively reveals two peaks at 260 ± 10 and 340 ± 10 nm with a threshold dissociation at 380 ± 10 nm. A cross-section σ(340 nm) = 6±3 × 10^-18 cm² is determined for the photodissociation of VFe⁺. The threshold at 380 ± 10 nm yields D°(V⁺-Fe) = 75 ± 5 kcal/mol, which implies D°(Fe⁺-CH₂) = 101 ± 5 kcal/mol, ΔH_f°(VFe⁺) = 302 ± 5 kcal/mol, and IP(VFe) = 5.4 eV. No reaction is observed between VFe⁺ and linear or cyclic alkanes. VFe⁺ is also unreactive with all linear alkenes through hexene but reacts with C₆ and C₇ cycloalkenes. The primary reaction between VFe⁺ and cyclohexene (or benzene) produces VFe(C₆H₆)⁺, which upon collisional activation readily eliminates C₆H₆. Collisional activation of VFe(C₆H₆)₂⁺, formed by a secondary reaction with cyclohexene, produces loss of Fe to yield V(C₆H₆)₂⁺. VFe⁺ abstracts a carbene from cycloheptatriene, indicating D°(VFe⁺-CH₂) > 70 kcal/mol. The oxide chemistry of VFe⁺ is also modified from that of V⁺ or Fe⁺. VFe⁺ reacts very slowly with 0₂ to yield VO⁺ and Fe⁺ whereas VFe(CO)_x⁺ (x = 2–4) reacts quickly with O₂ to produce VFe0₂⁺, which then abstracts an oxygen from 0₂ to form VFe0₃⁺. VFe⁺ will react sequentially with ethylene oxide to abstract up to three oxygens, producing VFeO⁺, VFeO₂⁺, and VFeO₃⁺. No reaction is observed between VFe⁺ and N₂O, although both V⁺ and Fe⁺ will abstract an oxygen from N₂0.