The reaction of an N-heterocyclic phosphenium complex of manganese with MeLi/Et NHCl under formal addition of CH 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.

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...

Reaction of P-chloro-1,3,2-diazaphospholenes with alkynyllithium or Grignard reagents produced N-heterocyclic alkynylphosphanes 3a-c. Terminal alkynylphosphane 3c reacted in the presence of a catalytic amount of CuCl with formation of bis-phosphanylalkyne 4, ethyne and chlorodiazaphospholene 2b, which was converted into the appropriate azide 6 upon addition of LiN 3 . Detailed studies allowed us to explain the formal alkynyl/Cl metathesis and alkynyl scrambling as arising from a combination of Cu-catalysed crosscoupling steps and the reverse processes, which involved Cu-induced P-C bond breaking. The superposition of individual steps allows the formulation of an equilibrium reac-

Die Reaktion eines N-heterocyclischen Phosphenium-Mangan-Komplexes mit MeLi/Et 3 NHCl unter formaler Addition von CH 4 an die Mn-P-Doppelbindung kann durch UV-Bestrahlung rückgängig gemacht werden. Dies liefert ein seltenes Beispiel füre ine selektive Aktivierung einer P-C(Alkyl)-Bindung.D ie Umsetzung des Phosphenium-Komplexes mit LDAv erläuft demgegenüber nicht unter nukleophilem Angriff am Phosphoratom, sondern unter C4-Deprotonierung und liefert das P-Analogon eines "abnormalen" Carbens.Ein Transmetallierungsprodukt des ursprünglichen Komplexes wurde vollständig charakterisiert. Die C4-Metallierung ist auch auf Bisphosphenium-Komplexe anderer Metalle übertragbar.

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