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Investigating new reactions for coordinated dinitrogen

University of British Columbia

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.

Thesis/Dissertation

application/pdf

2008-09-23

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/2344

Chemistry

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/