Reversible cooperative dihydrogen binding and transfer with a bis-phosphenium complex of chromium

The reversible reaction of H(2) with a bis-phosphenium complex of chromium provides a rare example of 3d transition metal/phosphenium cooperativity. Photolysis induces the activation of H(2) and yields a spectroscopically detectable phosphenium-stabilized (σ–H(2))-complex, readily showing exchange with gaseous H(2) and D(2). Further reaction of this complex affords a phosphine-functionalized metal hydride, representing a unique example of reversible H(2) cleavage across a 3d M[double bond, length as m-dash]P bond. The same species is also accessible via stepwise H(+)/H(−) transfer to the bis-phosphenium complex, and releases H(2) upon heating or irradiation. Dihydrogen transfer from the H(2)-complex to styrene is exploited to demonstrate the first example of promoting hydrogenation with a phosphenium complex.