Molecular titanium nitrides: nucleophiles unleashed

In this contribution we present reactivity studies of a rare example of a titanium salt, in the form of [mu K--(2)(OEt2)](2)[(PN)(2)Ti N] (2) (1) (PN (-) =N-(2-(diisopropylphosphino)- 4-methylphenyl)- 2,4,6-trimethylanilide) to produce a series of imide moieties including rare examples such as methylimido, borylimido, phosphonylimido, and a parent imido. For the latter, using various weak acids allowed us to narrow the pK(a) range of the NH group in (PN)(2)Ti NH to be between 26-36. Complex 1 could be produced by a reductively promoted elimination of N-2 from the azide precursor (PN)(2)TiN3, whereas reductive splitting of N-2 could not be achieved using the complex (PN)(2)Ti=N=N=Ti(PN)(2) (2) and a strong reductant. Complete N-atom transfer reactions could also be observed when 1 was treated with ClC(O)Bu-t and OCCPh2 to form (NCBu)-Bu-t and KNCCPh2, respectively, along with the terminal oxo complex (PN)(2)Ti O, which was also characterized. A combination of solid state N-15 NMR (MAS) and theoretical studies allowed us to understand the shielding effect of the counter cation in dimer 1, the monomer [K(18-crown-6)][(PN)(2)Ti N], and the discrete salt [K(2,2,2-Kryptofix)][(PN)(2)Ti N] as well as the origin of the highly downfield N-15 NMR resonance when shifting from dimer to monomer to a terminal nitride (discrete salt). The upfield shift of N-15(nitride) resonance in the N-15 NMR spectrum was found to be linked to the K+ induced electronic structural change of the titanium-nitride functionality by using a combination of MO analysis and quantum chemical analysis of the corresponding shielding tensors.