Investigating new reactions for coordinated dinitrogen

• Main Author: Park, Rosa
• Format: Others
• Language: English
• Published: University of British Columbia 2008
• Subjects: Chemistry; Nitrogen fixation
• Online Access: http://hdl.handle.net/2429/2344

The chemistry of the tantalum dinitrogen complex ([NPN]Ta)₂‚‚(μ-H)₂‚‚(μ-η¹:η²-N₂‚‚)Ta-[NPN], 1, (where [NPN] represents the acyclic tridentate ligand [(PhNSiMe₂‚‚CH₂‚‚)₂‚‚-PPh]²‚‚-), with primary alkenes, group IV and V metallocene complexes, and GaCp* is explored. The reaction of 1 with 1-pentene and 1-hexene occurs via olefin-insertion into the metal-hydride bond to give two new complexes, ([NPN]Ta(CH₂)₄CH₃)₂‚‚(μ-η¹:η¹-N₂‚‚), 10, and ([NPN]Ta(CH₂‚‚)₅CH₃)₂‚‚(μ-η¹:η¹-N₂‚‚), 11, which were characterized using NMR spectroscopy. The solid-state structure of 11 was established and revealed that N₂ has been transformed into a bridging end-on mode. In contrast to its G symmetry in solution, the solid-state structure of 11 is C, symmetric; a VT-NMR study was performed and showed that 11 exists as an equilibrium between two isomers in solution: a C, symmetric isomer 11A,which is the predominant isomer at room temperature, and a C, symmetric isomer 11B,which is the minor isomer. The reactivity of 1 with group IV and V metallocenes was investigated. The reaction of 1 with Cp₂‚‚Hf(PMe₃)(η²-Me₃SiCCSiMe₃) produces [N(μ-P=N)N]Ta(μ-H)₂(μ-N(Hf-Cp₂‚‚))Ta[NPN], 14, in which N₂ is cleaved and new Hf-N and P=N bonds have formed. The reaction of 1 with group V metallocene hydrides Cp₂‚‚MH₃ (M Nb, Ta) was also attempted however these complexes do not react with 1. The reaction of 1 with GaCp* produces a new complex, [NPN]Ta(μ-N(GaCp*))Ta(=NPμ)[NPIA,-N], 18, which was characterized using NMR spectroscopy. Complex 18 decomposes over several days in solution, and one product of decomposition that was isolated was [(PhNH)(NPμ-N)Ta]₂‚‚, 19. The solid-state structure of 19 showed that the [NPN] ligand was cleaved at the N-Si bond, similar to that observed for the reaction of 1 with 9-BBN and HB(C₆H₅)₂‚‚. A mechanism for the formation of complexes 18 and 19 is proposed.