Pentaamine(dinitrogen)ruthenium(II) chloride is an inorganic compound with the formula [Ru(NH<sub>3</sub>)<sub>5</sub>(N<sub>2</sub>)]Cl<sub>2</sub>. It is a nearly white solid, but its solutions are yellow. The cationic complex is of historic significance as the first compound with N<sub>2</sub> bound to a metal center. [Ru(NH<sub>3</sub>)<sub>5</sub>(N<sub>2</sub>)]<sup>2+</sup> adopts an octahedral structure with C<sub>4v</sub> symmetry.
Pentaamine(dinitrogen)ruthenium(II) chloride is synthesized in an aqueous solution from pentaamminechlororuthenium(III) chloride, sodium azide, and methanesulfonic acid:
If it is to be used in situ, the cation can be made more conveniently from ruthenium(III) chloride and hydrazine hydrate:
This N<sub>2</sub> complex is stable in aqueous solution and has a relatively low ligand exchange rate with water. Being a d<sup>6</sup> complex, the Ru-N bond is stabilized by the pi backbonding, the donation of metal d-electrons into the N<sub>2</sub> ÃÂ* orbitals. The related metal ammine complex [Os(NH<sub>3</sub>)<sub>5</sub>(N<sub>2</sub>)]<sup>2+</sup> is also known.
The dinitrogen ligand is not reduced by aqueous sodium borohydride. Nearly all known reactions of this compound are displacement reactions. Pentaamine(halogen)ruthenium(II) halides can be synthesized by treating [Ru(NH<sub>3</sub>)<sub>5</sub>N<sub>2</sub>]<sup>2+</sup> with halide sources:
[Ru(NH<sub>3</sub>)<sub>5</sub>N<sub>2</sub>]<sup>2+</sup> forms the symmetrically bridging symmetrical dinitrogen complex [(NH<sub>3</sub>)<sub>5</sub>Ru-NN-Ru(NH<sub>3</sub>)<sub>5</sub>]<sup>4+</sup>.