Bis-phosphonio-isophosphindolide copper complexes

Bis-triphenylphosphonio-isophosphindolide salts 1[X] react with Cu(I)-halid es CuX to give isolable products of composition [(1)Cu2X3]. X-ray crystal s tructure analyses confirmed that for X = Br Cl dinuclear complexes [(mu-1)( mu-X)Cu2X2] with mu(2),eta(1) (P)-bridging cations 1 are Formed, while for X = I a solid phase containing a salt (1)(2) [Cu4I6] and a complex [(1)(2)C u4I6] with a terminal eta(1)(P)-coordinated ligand I was obtained. The bond ing parameters in the two types of complexes suggest that 1 is a hybrid bet ween a phosphenium cation and a phospholide anion whose pi-system is less n ucleophilic than the phosphorus lone-pair. P-31 NMR studies revealed that i n solution in all cases binuclear complexes [(1)Cu2X3] are in dynamic equil ibrium with small amounts of mononuclear species and Free I. The same equil ibria were detected in the system 1[OTf]/CuOTf. NMR studies of ligand excha nge reactions indicated that the stability of complexes [(1)Cu2X3] increase s in the order X = OTf < I < Br, Cl, and titration of [(1)Cu2Br3] with Et4N Br allowed to determine the equilibrium constant of the complex formation r eaction.