Infrared spectra of the CH3-MX, CH2=MHX, and CH[triple bond]MH2X- complexes formed by reaction of methyl halides with laser-ablated group 5 metal atoms.

Reactions of group 5 metal atoms and methyl halides give carbon-metal single, double, and triple bonded complexes that are identified from matrix IR spectra and vibrational frequencies computed by DFT. Two different pairs of complexes are prepared in reactions of methyl fluoride with laser-ablated vanadium and tantalum atoms. The two vanadium complexes (CH(3)-VF and CH(2)=VHF) are persistently photoreversible and show a kinetic isotope effect on the yield of CD(2)=VDF. Identification of CH(2)=TaHF and CH[triple bond]TaH(2)F(-), along with the similar anionic Nb complex, suggests that the anionic methylidyne complex is a general property of the heavy group 5 metals. Reactions of Nb and Ta with CH(3)Cl and CH(3)Br have also been carried out to understand the ligand effects on the calculated structures and the vibrational characteristics. The methylidene complexes become more distorted with increasing halogen size, while the calculated C=M bond lengths and stretching frequencies decrease and increase, respectively. The anionic methylidyne complexes are less favored with increasing halogen size. Infrared spectra show a dramatic increase of the Ta methylidenes upon annealing, suggesting that the formation of CH(3)-TaX and its conversion to CH(2)=TaHX require essentially no activation energy.