STERIC EFFECTS IN THE OXIDATIVE-ADDITION REACTIONS OF GASEOUS V(CO)5-

Some gas-phase reactions of the 16-electron complex V(CO)5- are reported. The reactions of V(CO)5-, generated by dissociative electron capture from V(CO)6, were performed in a Fourier transform ion cyclotron resonance mass spectrometer. V(CO)5- reacts with V(CO)6 to generate V(CO)6- and V2(CO)9-. V(CO)4-, also generated by dissociative electron capture from V(CO)6, reacts with V(CO)6 to generate V2(CO)7- and V2(CO)8-. These results contrast with condensed-phase photolysis studies of V(CO)6-. The reaction of V(CO)5- with CH3OH generates V(CO)4CH2O-. Labeling studies indicate a 1,2-dehydrogenation with retention of the incoming C‒O group. V(CO)5- is unreactive with larger alcohols (C2‒C4). this difference in reactivity is ascribed to a steric effect in the reaction intermediate. A positive second derivative in a plot of the decay kinetics for V(CO)5- consumed in the V(CO)5-/CH3OH reaction indicates the process is endothermic or there is an energy barrier along the reaction coordinate. These results also indicate internal excitation drives the dehydrogenation reaction. © 1990, American Chemical Society. All rights reserved.