Infrared spectra of the CH3-MX, CH2=MHX, and CHMH2X- 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 (CH3-VF and CH2=VHF) are persistently photoreversible and show a kinetic isotope effect on the yield of CD2=VDF. Identification of CH2=TaHF and CH=TH2F-, 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 CH3Cl and CH3Br 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 CdM 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 CH3- TaX and its conversion to CH2=TaHX require essentially no activation energy.