(π-Allyl)palladium Complexes with N,N‘-Diphenylbispidinone Derivatives as a New Type of Chelating Nitrogen Ligand:  Complexation Studies, Spectroscopic Properties, and an X-ray Structure of (3,7-Diphenyl-1,5-dimethylbispidinone)[(1,3-η³-propenyl)- palladium] Trifluoromethanesulfonate^†

A series of 3,7-diazabicyclo[3.3.1]nonane (bispidine) derivatives have been synthesized, and their properties as bidentate nitrogen ligands for (π-allyl)palladium complexes have been investigated. Complexes of these ligands and of N,N‘-diphenylpiperazine (7) and N,N‘-diphenyl-1,5-diazacyclooctane (8) with (1,3-η³-propenyl)palladium are described, in particular their effects on the proton chemical shifts of the π-allyl ligand. Ligand dynamics of the complexes is discussed. The structure of [(3,7-diphenyl-1,5-dimethylbispidinone)(1,3-η³-propenyl)Pd]CF₃SO₃ (15) has been determined by X-ray crystallography. N,N‘-Diphenylbispidine derivatives show an unusually large steric interaction with the π-allyl ligand, indicated by a tilt of the π-allyl plane toward the N−Pd−N plane by 122.8(8)°. Chemical shift changes of the π-allyl protons due to the aromatic ring current are related to the geometry of the complexes. The ligands are tested on the larger 2-methylene-6,6-dimethylbicyclo[3.1.1]hept-2,3,10-η³-enyl ligand, demonstrating their potential as chemical shift reagents.