Nitride Formation by Thermolysis of a Kinetically Stable Niobium Dinitrogen Complex

The reduction of [P2N2]NbCl (where [P2N2] = PhP(CH2SiMe2NSiMe2CH2)2PPh) with KC8 under
a dinitrogen atmosphere generates the paramagnetic dinuclear dinitrogen complex ([P2N2]Nb)2(μ-N2) (2).
Complex 2 has been characterized crystallographically and by EPR spectroscopy. Variable-temperature
magnetic susceptibility measurements indicate that 2 displays antiferromagnetic coupling between two
Nb(IV) (d1) centers. A density functional theory calculation on the model complex [(PH3)2(NH2)2Nb]2(μ-N2)
was performed. Thermolysis of ([P2N2]Nb)2(μ-N2) in toluene generates the paramagnetic bridging nitride
species where one N atom of the dinitrogen ligand inserts into the macrocycle backbone to form [P2N2]Nb(μ-N)Nb[PN3] (3) (where [PN3] = PhPMe(CHSiMe2NSiMe2CH2P(Ph)CH2SiMe2NSiMe2N)). Complex 3
has been characterized in the solid state as well as by variable-temperature magnetic susceptibility
measurements. The reaction of ([P2N2]Nb)2(μ-N2) with phenylacetylene displaces the dinitrogen fragment
to generate a paramagnetic η2-alkyne complex, [P2N2]Nb(η2-HCCPh) (4).