Variable Reactivity of a N-Heterocyclic Phosphenium Complex: P-C Bond Activation or "Abnormal" Deprotonation.

The reaction of an N-heterocyclic phosphenium complex of manganese with MeLi/Et3 NHCl under formal addition of CH4 to the Mn=P double bond can be reversed upon UV photolysis, providing a rare example for selective P-C(alkyl) bond activation. Action of LDA on the phosphenium complex does not proceed via attack at phosphorus but rather via C4-deprotonation to yield a unique P-analogue of an "abnormal" carbene. A transmetalation product of the original complex was fully characterized. The C-metalation is also applicable to bis-phosphenium complexes of other metals.

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

The reversible reaction of H2 with a bis-phosphenium complex of chromium provides a rare example of 3d transition metal/phosphenium cooperativity. Photolysis induces the activation of H2 and yields a spectroscopically detectable phosphenium-stabilized (σ-H2)-complex, readily showing exchange with gaseous H2 and D2. Further reaction of this complex affords a phosphine-functionalized metal hydride, representing a unique example of reversible H2 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 H2 upon heating or irradiation. Dihydrogen transfer from the H2-complex to styrene is exploited to demonstrate the first example of promoting hydrogenation with a phosphenium complex.