Synthesis and Structure of a Terminal Metal Azide Complex: An Isolated Intermediate in the Formation of Imidometal Complexes from Organic Azides

摘要

Organic azides (RN_3) often undergo reactions in which dinitrogen is extruded, and it is this reactivity that has long caused chemists to use them as convenient sources of "RN:" or nitrene fragments. In organometallic chemistry, azides are commonly used as precursors for nitrene (or, more correctly, terminal imido) complexes (M=NR). In the synthesis of imido species, organoazidometal complexes have been proposed as intermediates formed in the initial interaction of a coordinatively unsaturated metal complex with RN_3. However, there are few examples of reactions of this type that yield observable organoazidometal complexes, presumably due to their rapid loss of N_2. Although there are some examples of RN_3 complexes that are stabilized by insertion of the R-N_3 group into a M-X bond, there do not appear to be any monometallic M-N_3R complexes whose structures have been established by X-ray diffraction. This report describes the synthesis and structure determination of the first fully characterized terminal organoazidometal complex, Cp_2Ta(N_3Ph)(CH_3) (1). We also report preliminary mechanistic experiments that bear on the pathway for conversion of this complex to the corresponding imidometal complex Cp_2Ta(NPh)(CH_3) (2).