Cho Han-Gook, Andrews Lester
Department of Chemistry, University of Incheon, 177 Dohwa-dong, Nam-ku, Incheon, 402-749, South Korea.
J Phys Chem A. 2006 Aug 24;110(33):10063-77. doi: 10.1021/jp0629644.
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.
第5族金属原子与卤代甲烷的反应生成了碳 - 金属单键、双键和三键配合物，这些配合物可通过矩阵红外光谱和密度泛函理论（DFT）计算的振动频率来识别。在甲基氟与激光烧蚀的钒和钽原子的反应中制备了两对不同的配合物。两种钒配合物（CH(3)-VF和CH(2)=VHF）具有持续的光可逆性，并且对CD(2)=VDF的产率表现出动力学同位素效应。CH(2)=TaHF和CH[三键]TaH(2)F(-)以及类似的阴离子铌配合物的鉴定表明，阴离子亚甲基配合物是重第5族金属的一般特性。还进行了铌和钽与CH(3)Cl和CH(3)Br的反应，以了解配体对计算结构和振动特性的影响。随着卤素尺寸的增加，亚甲基配合物变得更加扭曲，而计算出的C = M键长和伸缩频率分别减小和增加。随着卤素尺寸的增加，阴离子亚甲基配合物不太有利。红外光谱显示退火后钽亚甲基的显著增加，表明CH(3)-TaX的形成及其向CH(2)=TaHX的转化基本上不需要活化能。
