An Innovative Structural Rearrangement in Imine Palladacycle Metaloligand Chemistry: From Single-Nuclear to Double-Nuclear Pseudo-Pentacoordinated Complexes.

Treatment of the double nuclear complex 1a , di-μ-cloro-bis[N-(4-formylbenzylidene)cyclohexylaminato-C6, N]dipalladium, with Ph 2 PCH 2 CH 2 ) 2 PPh (triphos) and NH 4 PF 6 gave the single nuclear species 2a , 1-N-(cyclohexylamine)-4-N-(formyl)palladium(triphos)(hexafluorophasphate). Reaction of 2a with Ph 2 PCH 2 CH 2 NH 2 in refluxing chloroform via a condensation reaction of the amine and formyl groups to produce the C=N double bond, gave 3a , 1-N-(cyclohexylamine)-4- N-(diphenylphosphinoethylamine)palladium(triphos)(hexafluorophasphate); a potentially bidentate [ N , P ] metaloligand. However, attempts to coordinate a second metal by treatment of 3a with [PdCl 2 (PhCN) 2 ] were to no avail. Notwithstanding, complexes 2a and 3a left to stand in solution spontaneously self-transformed to give in either case the double nuclear complex 10 , 1,4-N,N-terephthalylidene(cyclohexilamine)-3,6-[bispalladium(triphos)]di(hexafluorophosphate), after undergoing further metalation of the phenyl ring, then bearing two mutually trans [Pd(Ph 2 PCH 2 CH 2 ) 2 PPh)- P , P , P ] moieties: an unprecedented and serendipitous result indeed. On the other hand, reaction of the double nuclear complex 1b, di-μ-cloro-bis[N-(3-formylbenzylidene)cyclohexylaminato-C6, N]dipalladium, with Ph 2 PCH 2 CH 2 ) 2 PPh (triphos) and NH 4 PF 6 gave the single nuclear species 2b , 1-N-(cyclohexylamine)-4-N-(formyl)palladium(triphos)(hexafluorophasphate), Treatment of 2b with H 2 O/glacial MeCOOH gave cleavage of the C=N double bond and of the Pd···N interaction, yielding 5b , isophthalaldehyde-6-palladium(triphos)hexafluorophosphate, which then reacted with Ph 2 P(CH 2 ) 3 NH 2 to yield complex 6b , N,N-(isophthalylidene(diphenylphosphinopropylamine)-6-(palladiumtriphos)di(hexafluorophosphate), with two pairs of non-coordinated nitrogen and phosphorus donor atoms. Treatment of 6b with [PdCl 2 (PhCN) 2 ], [PtCl 2 (PhCN) 2 ], or [PtMe 2 (COD)] gave the new double nuclear complexes 7b , 8b and 9b , palladiumdichloro-, platinumdichloro- and platinumdimethyl[N,N-(isophthalylidene(diphenylphosphinopropylamine)-6-(palladiumtriphos)(hexafluorophosphate)-P,P], respectively, showing the behavior of 6b as a palladated bidentate [ P , P ] metaloligand. The complexes were fully characterized by microanalysis, IR, 1 H, and 31 P NMR spectroscopies, as appropriate. The X-ray single-crystal analyses for compounds 10 and 5b have been previously described as the perchlorate salts by JM Vila et al.