Synthesis, characterization and reactivity of ionic palladium(II) complexes containing bidentate nitrogen ligands in a unidentate coordination mode ,

Abstract

The novel ionic complexes [Pd(Me)( p-An-BIAN)(LL)]SO 3CF 3 (LL= p-An-BIAN (bis(anisylimino)acenaphthene) ( 1a), phen ( 2a), dmphen ( 3a), dppe ( 4a), dppp ( 5a)) have been synthesized via the reaction of [Pd(Me)(NCMe)( p-An-BIAN)]SO 3CF 3 with LL. The X-ray crystal structure of complex 1a has been determined and shows a distorted square planar geometry in which one BIAN ligand is coordinated in a bidentate fashion (PdN(1)=2.037(4) Å; PdN(2)=2.189(4) Å) and, interestingly, the other BIAN ligand in a unidentate fashion (PdN(3)=2.066(4) Å; PdN(4)=2.714(6) Å). Spectroscopic data of the mixed ligand complexes [Pd(Me)( p-An-BIAN)(LL)]SO 3CF 3 (LL=phen ( 2a), dppe ( 4a), dppp ( 5a)) indicate that the LL ligand is coordinated in a bidentate fashion and the p-An-BIAN ligand in a unidentate fashion, which is in agreement with the larger complexation strength of the phen, dppe and dppp ligands, as compared with that of the p-An-BIAN ligand. In contrast, complex 3a (LL=dmphen) contains a bidentate p-An-BIAN ligand and a unidentate dmphen ligand, which can be explained by the sterically demanding methyl groups of the dmphen ligand. Complexes 1a– 4a underwent insertion of carbon monoxide, resulting in the formation of acetylpalladium complexes [Pd(C(O)Me)( p-An-BIAN)(LL)]SO 3CF 3 ( 1b– 4b). Since mass-law retardation by excess p-An-BIAN has been observed for CO insertion for complexes 1a and 4a, it is proposed that the mechanism involves dissociation of the unidentate nitrogen ligand. Complexes 1a– 5a and 1b– 4b show fluxional behavior due to flipping of the unidentate nitrogen ligand. Complexes 1a– 3a and 1b– 3b also show fluxional behavior due to site exchange of the nitrogen atoms of the bidentate nitrogen ligand. A mechanism for this exchange process has been proposed. This mechanism involves (a) substitution of a nitrogen atom of the bidentate nitrogen ligand by the uncoordinated nitrogen atom of the unidentate nitrogen ligand, (b) flipping of the unidentate nitrogen ligand, and (c) a second nitrogen substitution reaction. Reaction of the acetylpalladium complexes 1b– 4b with norbornadiene led to dissociation of the unidentate nitrogen ligand and formation of the known alkylpalladium complexes [Pd(C 7H 8C(O)Me)( p-An-BIAN)]SO 3CF 3 ( 1c), [Pd(C 7H 8C(O)Me)(phen)]SO 3CF 3 ( 2c), 1c, and [Pd(C 7H 8C(O)Me)(dppe)]SO 3CF 3 ( 4c), respectively.