DIASTEREOMERIC SQUARE-PLANAR PLATINUM(II) AND PALLADIUM(II) COMPLEXES DUE TO RESTRICTED ROTATION ABOUT THE CHELATED M-N HETEROARYL BOND

The reaction of 3-bromopyridine, quinoline, or isoquinoline with cis-M(L)(2)(OTf)(2) (M = Pd, Pt; L = triethylphosphine, 1/2 1,3-bis(diphenylphosphino)propane (dppp) or 1/2 (R)-(+)-2,2'-bis(diphenylphosphino)-1,1'-binaphthyl ((R)-(+)-BINAP)) results in the formation of diastereomeric, square-planar, cationic complexes, which exhibit restricted rotation about the metal-nitrogen heteroaryl bond. All complexes were characterized by routine physical and spectroscopic methods, of which P-31(H-1) NMR spectroscopy was most valuable. Only the complexes [Pd(dppp)(isoquinoline)(2)][OTf](2) (14), [Pt(dppp)(isoquinoline)(2)][OTf](2) (15), and [Pd((R)-(+)-BINAP)(isosqinoline)(2)][OTf](2) (22) were found to be dynamic at ambient temperature on the NMR time scale. Variable-temperature studies of the P-31(H-1) NMR spectra of these compounds were performed. The X-ray crystal structure of [Pt(dppp)(quinoline)(2)][OTf](2) (19) in one of its stereoisomeric (syn) forms is reported. [Pd((R)-(+)-BINAP)(isoquinoline)(2)][OTf](2) (22) and [Pt((R)-(+)-BINAP)(isoquinoline)(2)][OTf](2) (23) exhibit three distinct rotamers at -20 degrees C and ambient temperature, respectively. The role of asymmetric induction of the chiral bis-phosphine ligand on the stereoisomeric ratio of the rotamers of 22 and 23 is discussed.