New side-on bound dinitrogen complexes of zirconium supported by an arene-bridged diamidophosphine ligand and their reactivity with dihydrogen

A new dinitrogen complex, deep blue-green {[NPN]*Zr(THF)}(2)(mu-eta(2):eta(2)-N-2) ([NPN]* = {[N-(2,4,6-Me3C6H2)(2-N-5-MeC6H3)](2)PPh}), was prepared in high yield by the reduction of [NPN]*ZrCl2 with 2.2 equiv of KC8 in THF under N-2. The solid-state molecular structure shows that N-2 is strongly activated (N-N bond length: 1.503(6) angstrom) and bound side-on to two Zr atoms. Coordinated THF can be readily replaced by adding pyncline (py) or PMe2R (R = Me, Ph) to the complex to obtain {[NPN]*Zr(py)}(2)(mu-eta(2):eta(2)-N-2) or {[NPN]*Zr(PMe2R)}(mu-eta(2):eta(2)-N-2){Zr[NPN]*} in high yield. X-ray diffraction experiments show that the N-2 moiety is strongly activated and remains side-on bound to Zr for the py and PMe2Ph adducts; interestingly, only one PMe2Ph coordinates to the Zr2N2 unit. {[NPN]*Zr(PMe2R)}(mu-eta(2):eta(2)-N-2){Zr[NPN]*} reacts slowly with H-2 to provide {[NPN]*Zr(PMe2R)}(mu-H)(mu-eta(2):eta(2)-N2H){Zr[NPN]*}, as determined by isotopic labeling, and multinuclear NMR spectroscopy. The THF adduct does not react with H-2 even after an extended period, whereas the pyridine adduct does undergo a reaction with H-2, but to a mixture of products.