Pentaamine(nitrogen)ruthenium(II) chloride is an inorganic compound with the formula [Ru(NH<sub>3</sub>)<sub>5</sub>(N<sub>2</sub>)]Cl2. It is a nearly white solid, but its solutions are yellow. The cationic complex is of historic significance as the first compound with N2 bound to a metal center.[1] [2] [Ru(NH<sub>3</sub>)<sub>5</sub>(N<sub>2</sub>)]2+ adopts an octahedral structure with C4v symmetry.[3]
Pentaamine(nitrogen)ruthenium(II) chloride is synthesized in an aqueous solution from pentaamminechlororuthenium(III) chloride, sodium azide, and methanesulfonic acid:[4]
[Ru(NH<sub>3</sub>)<sub>5</sub>Cl]Cl2 + NaN3 → [Ru(NH<sub>3</sub>)<sub>5</sub>N<sub>2</sub>]Cl2 + ...If it is to be used in situ, the cation can be made more conveniently from ruthenium(III) chloride and hydrazine hydrate:[4]
RuCl3 + 4 N2H4 → [Ru(NH<sub>3</sub>)<sub>5</sub>N<sub>2</sub>]2+ + ...
This N2 complex is stable in aqueous solution and has a relatively low ligand exchange rate with water. Being a d6 complex, the Ru-N bond is stabilized by the pi backbonding, the donation of metal d-electrons into the N2 π* orbitals.[5] The related metal ammine complex [Os(NH<sub>3</sub>)<sub>5</sub>(N<sub>2</sub>)]2+ is also known.
The dinitrogen ligand is not reduced by aqueous sodium borohydride.[6] 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>]2+ with halide sources:[4]
[Ru(NH<sub>3</sub>)<sub>5</sub>N<sub>2</sub>]2+ + X− → [Ru(NH<sub>3</sub>)<sub>5</sub>X]+ + N2
[Ru(NH<sub>3</sub>)<sub>5</sub>N<sub>2</sub>]2+ forms the symmetrically bridging symmetrical dinitrogen complex [(NH<sub>3</sub>)<sub>5</sub>Ru-NN-Ru(NH<sub>3</sub>)<sub>5</sub>]4+.[7] [8]