Versatility of iminophosphoranes and noninnocent behavior of the 1,5-cyclooctadiene ligand in palladium(II) complexes.: Synthesis of σ-allyl derivatives

The treatment of PdCl2(NCPh)(2) with Ph3P=NPh (1) gives the expected complex trans-PdCl2[N(Ph)PPh3](2) (3). However, the reaction of PdCl2(COD) (COD = 1,5-cyclooctadiene) with I or Ph3P=N-1-Np (2) (Np, = naphthyl) occurs through nucleophilic attack of I or 2 on one olefinic bond of the COD ligand followed by proton abstraction on the adjacent methylene group, giving the 77 I-allyl complexes [Ph3P(R)NH center dot center dot center dot Cl2Pd(C8H11)] (R = Ph, 4; Np, 5). The X-ray structure of 4 has been determined and shows two interesting facts: (i) the eta(1)-eta(2)-bonded cyclooctadienyl ligand, containing a eta(1)-allyl fragment, and (ii) the presence of a strong H bond between one of the Cl ligands and the proton of the NH group. This H bond persists in solution, as shown by NMR and molar conductance measurements. The abstraction of a chloride on 4 by reaction with AgClO4 cleaves the H bond and gives a mixture of the salt [Ph3PN(H)Ph](ClO4) (6) and the neutral eta(1)-eta(2)-Cyclooctadienyl complex [Pd(mu-Cl)(C8H11)](2) (7). Complex 7 is an adequate precursor for the synthesis of other stable eta 1-allyl complexes, and no eta(1)-eta(3) allyl interconversion has been observed.