o-Phenylene bridged diamidophosphine complexes of groups 4 and 5 metals for dinitrogen activation

• Main Author: Hess, Fiona Millicent
• Language: English
• Published: University of British Columbia 2014
• Online Access: http://hdl.handle.net/2429/51247

A series of diamidophosphine donor sets (ipropNPN, tolNPN and phNPN) was prepared, whereby the arylamido groups have no ortho substituents. This allowed for the Buchwald-Hartwig arylamination to be replaced by a directed ortho metalation (DOM) process, sourcing commercial diarylamines. Amido and chloro complexes of Zr, Ti, Hf and Ta with these new diamidophosphine donor sets were prepared. Reduction of the zirconium dichlorides with KC₈ under N₂ gave the side-on dinitrogen complexes [ipropNPNZr(THF)]₂(µ-η²:η²-N₂) and [tolNPNZr(THF)]₂(µ-η²:η²-N₂) and of titanium dichloride gave the end-on complex [tolNPNTi(THF)]₂(µ-η1:η1-N₂). Compared to previously reported sterically encumbered [mesNPNZr(THF)]₂(µ-η²:η²-N₂), the zirconium complexes were more stable, with longer N-N bonds, less labile THF ligands and shorter Zr-O bond lengths. THF adduct displacement thus occurred less readily; for phosphine donors, displacement was at both zirconium centres i.e. [ipropNPNZr(PPhMe₂)]₂(µ-η²:η²-N₂), compared to the mesNPN analogue with an open site at one of the zirconium centres i.e. [mesNPNZr(PPhMe₂)](µ-η²:η²-N₂)[mesNPNZr]. For titanium, four different pyridine adduct species where observed in solution, but only one species was isolated wherein each THF was displaced by two pyridine molecules i.e. [tolNPNTi(Py)₂]₂(µ-η1:η1-N₂). These new dinitrogen complexes were found to be unreactive with H₂; for zirconium, the lack of an open site at one of the metal centres may explain lack of reactivity, and for titanium, the end-on dinitrogen bonding mode is not amenable to hydrogenolysis. The potassium salt of tolNPN with TaMe₃Cl₂ gave the trimethyl species tolNPNTaMe₃, but [tolNPNTaMe₄][Li(THF)₄] was isolated from tolNPNTaCl₃ with MeLi. Tantalum hydrides from trimethyl species and H₂ were unstable and did not form dinitrogen complexes, but mass spectra of tantalum trichlorides with KHBEt₃ and N₂ indicated dinitrogen hydrides [NPNTaH]₂(N₂) and further reaction with BEt₃. Reduction of tantalum trichlorides with KC₈ under N₂ gave mass spectra of dinitrogen complexes [NPNTaCl]₂(N₂), with no crystals isolated. === Science, Faculty of === Chemistry, Department of === Graduate