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Formal coordination of phosphorus(III) by a calix[4]pyrrole Schiff base ligand was achieved through the reaction of this ligand with PCl 3 under basic conditions. The reaction product adopts a Pacman conformation with two PÀ Cl moieties, one in exo and one in endo position. It represents the first non-metal compound of calix[4]pyrrole Schiff base ligands and of Pacman ligands in general. The spatial neighborhood of the two phosphorus atoms enables cooperative reactions. As a first example, the chloride abstraction with AgOTf is presented, yielding a macrocyclic dication with two embedded phosphorus(III) monocations, which both undergo a cooperative, internal activation reaction with an adjacent C=N double bond. This intramolecular redox process affords two pentacoordinated phosphorus(V) centers within the Pacman dication. All reaction products were fully characterized and all results are supported by computations.

The reactivity of the four-membered NP 3 ring system [RN(m-PCl) 2 PR] (R = Mes* = 2,4,6-tri-tert-butylphenyl) towardsL ewis acids, Lewis bases, and reducing agents was investigated. Comparisons with the literature-known, analogous cyclic compounds [ClP(m-NR)] 2 (R = Te r = 2,6-dimesityl-phenyl)a nd [ClP(m-PR)] 2 (R = Mes*) are drawn, to obtain a betters ystematic understanding of the reactivity of cyclic NP species. Apart from experimentalr esults, DFT computations are discussed to furthert he insight into bondinga nd electronic structure of thesec ompounds.Scheme1.Four-membered N 2 P 2 ,N P 3 and P 4 ring systems( R= sterically demanding substituent, X = (pseudo)halogen).[a] Dr.Scheme2.Reactivity of A (R = stericallydemanding substituent, LB = Lewis base;LA= Lewis acid;M= Mg, K; X, Y = Cl, OTf, N 3 ,etc.).Scheme3.Reactivity of C (R = sterically demanding substituent, LB = Lewis base;LA= Lewis acid;X= Cl;Y= C 6 F 5 ,see below).Scheme4.Synthesis of 2 (R = Mes*) starting from Mes*NPCl [37] (a:M es*PH 2 , NEt 3 ;b:nBuLi, PCl 3 , À80 8C; c: THF).Scheme5.Reactionof3 with DMAP (R = Mes*). [33] Scheme6.Reactionof2 with DMAP (R = Mes*).

In solution, the Pacman chlorophosphane (2Cl) shows fast exchange of the endo/exo-orientation of the two P−Cl bonds in the molecule featuring cooperativity. Experimental and quantum mechanical investigations of the inversion on the phosphorus(III) centers reveal a crucial role of chloride ions in the dynamic process. To confirm the results, the homologous Pacman halogen-phosphanes 2X were prepared by halogen exchange reactions (X = F, Br, and I). Besides accelerated dynamic behavior for the heavier analogues, significant differences in the molecular structure are caused by the halogen exchange reactions, including the formation of an endo−endo substituted Pacman fluorophosphane as well as dicationic species by phosphorus halogen bond dissociation. The latter process can be regarded as redox isomerism since two P III atoms in 2X become P V centers in the dications.

We present the extension of Pacman ligands to bidentate phosphane ligands enabling them to bind metals in their sterically protected cavity. The coordination of coinage metals shows the ability of...