Reversible dihydrogen addition to a tungsten–tungsten triple bond: X-ray crystal structure of {[W(η-C 5 H 4 Pr i )Cl 2 ] 2 }

Reduction of [W(η-C5H4R)Cl4] with sodium amalgam gives {[W(η-C5H4R)Cl2]2}[(1)a; R = Me, b; R = Pri], in which the unsupported tungsten–tungsten triple bond [W–W 2.3678(6)Å] undergoes facile reversible addition of dihydrogen.