A series of diamidophosphine donor sets (NPN, NPN and NPN) was prepared, whereby the arylamido groups have no ortho substituents. This allowed for the BuchwaldHartwig 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 [NPNZr(THF)]2(μ-η 2 :η 2-N2) and [ NPNZr(THF)]2(μ-η 2 :η 2-N2) and of titanium dichloride gave the end-on complex [NPNTi(THF)]2(μ-η 1 :η 1-N2). Compared to previously reported sterically encumbered [NPNZr(THF)]2(μ-η 2 :η 2-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. [NPNZr(PPhMe2)]2(μ-η 2 :η 2-N2), compared to the NPN analogue with an open site at one of the zirconium centres i.e. [NPNZr(PPhMe2)](μ-η 2 :η 2-N2)[ NPNZr]. 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. [NPNTi(Py)2]2(μη 1 :η 1-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 NPN with TaMe3Cl2 gave the trimethyl species NPNTaMe3, but [NPNTaMe4][Li(THF)4] was isolated from NPNTaCl3 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.

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G. J. Leigh

Papers

Vanadium, molybdenum and iron complexes based on a trithiolate ligand