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-Me(3)C(6)H(2))(2-N-5-MeC(6)H(3))PPh}), was prepared in high yield by the reduction of [NPN]*ZrCl(2) with 2.2 equiv of KC(8) in THF under N(2). The solid-state molecular structure shows that N(2) is strongly activated (N-N bond length: 1.503(6) A) and bound side-on to two Zr atoms. Coordinated THF can be readily replaced by adding pyridine (py) or PMe(2)R (R = Me, Ph) to the complex to obtain {[NPN]*Zr(py)}(2)(mu-eta(2):eta(2)-N(2)) or {[NPN]Zr(PMe(2)R)}(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 PMe(2)Ph adducts; interestingly, only one PMe(2)Ph coordinates to the Zr(2)N(2) unit. {[NPN]Zr(PMe(2)R)}(mu-eta(2):eta(2)-N(2)){Zr[NPN]} reacts slowly with H(2) to provide {[NPN]Zr(PMe(2)R)}(mu-H)(mu-eta(2):eta(2)-N(2)H){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.